Design and manufacture of improved power devices

Abstract

A device is described herein. The device comprises a unit cell on a SiC substrate. The unit cell comprises a gate insulator film, a trench in a well region, a first sinker region having a second conduction type, and a second sinker region having the second conduction type. The first sinker region has a depth that is equal to or greater than a depth of the well region. Each of the first sinker region and the second sinker region is in contact with a region having a first conduction type to form a p-n junction.

Description

DESIGN AND MANUFACTURE OF IMPROVED POWER DEVICESCROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application is related to U.S. Serial No. 16 / 352,698, filed March 13, 2019, entitled “DESIGN AND MANUFACTURE OF IMPROVED POWER DEVICES”; U.S. Serial No. 16 / 431,655, filed June 04, 2019, entitled “DESIGN AND MANUFACTURE OF SELFALIGNED POWER DEVICES”; U.S. Serial No. 17 / 342,761, filed June 09, 2021, entitled “DESIGN AND MANUFACTURE OF SELF -ALIGNED POWER DEVICES”; U.S. Serial No. 16 / 374,025, filed April 03, 2019, entitled “DESIGN AND MANUFACTURE OF POWER DEVICES HAVING INVERSION CHANNEL”; U.S. Serial No. 16 / 550,249, filed August 25,2019, entitled “DESIGN AND MANUFACTURE OF ROBUST, HIGH-PERFORMANCE DEVICES”; U.S. Serial No. 17 / 231,301, filed April 15, 2021, entitled “DESIGN AND MANUFACTURE OF ROBUST, HIGH-PERFORMANCE DEVICES”; U.S. Serial No. 17 / 242,650, filed April 28, 2021, entitled “DESIGN AND MANUFACTURE OF ROBUST, HIGH-PERFORMANCE DEVICES”; U.S. Serial No. 16 / 777,928, filed January 31, 2020, entitled “IMPROVED PERFORMANCE SIC SCHOTTKY DIODES”; U.S. Serial No. 17 / 099,305, filed November 16, 2020, entitled “IMPROVED PERFORMANCE SIC SCHOTTKY DIODES”; U.S. Serial No. 16 / 670,963, filed October 31, 2019, entitled “SILICON CARBIDE POWER DEVICES”; U.S. Serial No. 16 / 741,800, filed January 14, 2020, entitled “SILICON CARBIDE POWER DEVICES”; U.S. Serial No. 16 / 945,781, filed July 31, 2020, entitled “DESIGN AND MANUFACTURE OF POWER DEVICES HAVING INCREASED CROSS OVER CURRENT”; U.S. Serial No. 17 / 227,897, filed April 12, 2021, entitled “DESIGN AND MANUFACTURE OF POWER DEVICES HAVING INCREASED CROSS OVER CURRENT”; U.S. Serial No. 17 / 227,921, filed April 12, 2021, entitled “DESIGN AND MANUFACTURE OF POWER DEVICES HAVING INCREASED CROSS OVER CURRENT”; U.S. Serial No. 17 / 227,936, filed April 12, 2021, entitled “DESIGN AND MANUFACTURE OF POWER DEVICES HAVING INCREASED CROSS OVER CURRENT”; U.S. Serial No. 17 / 227,951, filed April 12, 2021, entitled “DESIGN AND MANUFACTURE OF POWER DEVICES HAVING INCREASED CROSS OVER CURRENT”; and U.S. Serial No. 17 / 007,014, filed August 31,2020, entitled “INVERSION CHANNEL DEVICES ON MULTIPLE CRYSTAL ORIENTATIONS”. This application claims priority from the provisional application U.S. Serial No. 63 / 072,473, filed August 31, 2020, entitled “POWER DEVICES”; and the above-mentioned applications and the disclosure of the above-mentioned applications are herein incorporated by reference in their entirety.FIELD OF THE INVENTION

[0002] This invention relates to power semiconductor devices using a vertical silicon carbide (SiC) Double-Implantation Metal oxide semiconductor field-effect transistor (DMOSFET). A power metal oxide semiconductor field-effect transistor (MOSFET) is a specific type of MOSFET designed to handle significant power levels.

[0003] Further, this invention relates to 4H-SiC devices, which include diodes and transistors having inter-digitated n-type and P-Type areas such as Junction Barrier Schottky (JBS) diodes, Merged PiN / Schottky (MPS) diodes, Metal oxide semiconductor field effect transistors (MOSFETs) and Junction field effect transistors (JFETs) having inter-digitated N-Type and P- Type areas.BACKGROUND OF INVENTION

[0004] Silicon based power devices have long dominated power electronics and power system applications. On the other hand, SiC is a wider bandgap (Eg) material with Eg = 3.3 eV as compared to silicon (Eg = 1.1 eV); therefore, SiC has a higher blocking voltage than Si. SiC has a higher breakdown electric field (3 x 106V / cm to 5 x 106V / cm) compared to Si (breakdown electric field for Si is 0.3 x 106V / cm) and is a better thermal conductor (3.7 (W / cm-K) for SiC versus 1.6 (W / cm-K) for Si). SiC has been a material of choice for power MOSFETs. However, “[e]ven with the successful introduction of SiC power MOSFETs into the commercial market place, several key reliability issues have not been fully resolved.” [Source: Key Reliability Issues for SiC Power MOSFETs, A. Lelis, D. Habersat, R. Green, and E. Mooro of the U.S. Army Research Laboratory, published in ECS Transactions, 58 (4) 87-93 (2013), DOI: 10.1149 / 05804.0087ecst],

[0005] SiC exists in a kind of polymorphic crystalline building known as a polytype, e.g., 3C-SiC, 4H-SiC, 6H-SiC. Fig. 1A is the prior art SiC DMOSFET structure reported by B.J. Baliga in Advanced High-Voltage Power Device Concepts (Springer Press, 2011). Fig. IB shows the electric field contours simulated for the prior art SiC DMOSFET structure of Fig. 1A. The electric field distribution near the surface of the 5-kV shielded 4H-SiC inversion-mode power MOSFET structure is shown in Fig. IB to allow examination of the electric field in the junction gate fieldeffect transistor (JFET) region and the gate region. The sharp peak of the electric field at the edge of the P+ shielding region can be observed in this prior art device which will result in a high electric field in the gate oxide, thereby resulting in a poor performance of this MOSFET device. Fig. 1C shows the electric field distribution in the shielded 4H-SiC inversion-mode MOSFET. The simulated results in the figure show an electric field as high as 4 MV / cm in the gate oxide for the prior art SiC DMOSFET structure of Fig. 1A.

[0006] A typical SiC MOSFET device structure such as that shown in Fig. 1A results in high electric field concentration at the comer of the p-well region, which results in a high electric field in the gate oxide layer, especially during high drain bias (blocking mode) operation. The high critical electric fields for breakdown in 4H-SiC (~ 3 MV / cm) results in a very high (> 5 MV / cm) electric field in the gate oxide. Fowler-Nordheim tunneling currents are observed at such high electric fields in the gate oxide, which can result in trapped charge in the gate oxide, which leads to poor device reliability.

[0007] The manufacturing processes for Si uses techniques like diffusion of dopants but these conventional manufacturing processes are not possible for making SiC device because the diffusion coefficients in SiC are negligible at temperatures below 1800 °C. SiC devices are manufactured by ion implantation of both source and p-well regions but ion implantation and deep ion implantation is difficult in SiC. Therefore, there is a long-felt need for improved power devices that address the reliability issues for SiC power MOSFETs.

[0008] Further, Due to the limited (10-25 cm2 / Vs) MOS channel mobility achievable on the state- of-the-art SiC planar DMOSFETs, it is necessary to form MOS channels with sub-micron channel lengths so that the overall ON resistance of the power MOSFET is not significantly degraded. “[I]f the p-well regions and N+ source regions were formed using different masks, the misalignment of two masks would result in a different channel length on each side of the cell. To avoid the decrease of threshold voltage (Vth) and degrade the breakdown voltage (Vbr), the N+ mask is in a selfaligned fashion with respect to the P-well.” [source: Design and Fabrication of 1.2kV 4H-SiC DMOSFET by R. Huang et al. published in 2016 13th China International Forum on Solid State Lighting: International Forum on Wide Bandgap Semiconductors China (SSLChina: IFWS)]. The MOSFET channel region is formed as a result of the offset between the p-well and the N+ source regions in a DMOSFET structure. If the p-well and N+ source regions are formed by two separate masking steps, there will inevitably be a certain amount of lithographic misalignment between these levels, resulting in different (or asymmetric) MOS channel lengths on the two sides of the unit cell. The lithographic misalignment between two masking levels using projection lithography techniques typically used in high-volume semiconductor manufacturing can range from + / - 0.05 pm to + / - 0.2 pm or greater, which sets a lower limit on the practically realizable MOS channel lengths without significant asymmetry. For a target channel length of 0.5 pm, a + / - 0.2 pm misalignment between the N+ source and p-well masking steps can result in a MOS channel length of 0.3 pm on one side of the unit cell and a MOS channel length of 0.7 pm on the other side of the unit cell. While the ON resistance of the MOSFET is increased at higher MOS channel lengths, lower than optimal MOS channel lengths can result in undesirable effects such as gate thresholdvoltage (Vth) degradation and other short-channel effects such as drain-induced barrier lowering (DIBL).

[0009] Self-aligned techniques for eliminating the misalignment between p-well and N+ source regions have been proposed in the literature. Self-aligned MOS channel formation with channel length defined by sidewall spacer deposition and etching is one such technique. Fig. 9 is the prior art process flow of self-aligned implantation technique with channel length defined by sidewall spacer deposition and etching as reported by R. Huang et al. in “Design and Fabrication of 1.2 kV 4H-SiC DMOSFET”.

[0010] Further, “[W]hile SiC power MOSFETs share many similarities to silicon MOSFETs, many challenging differences remain. In particular, the wide-bandgap nature of 4H-SiC (EG=3.26 eV) is both a blessing and a curse, bringing a low intrinsic carrier concentration and a high critical electric field, while presenting challenges with inversion-layer mobility and reliability in passivating dielectric layers.” [Source: Challenges in SiC Power MOSFET Design by Kevin Matocha of the GE Global Research Center - Semiconductor Technology Laboratory, Niskayuna, NY USA, published in ISDRS 2007, December 12-14, 2007, College Park, MD, USA]

[0011] In a typical SiC planar MOSFET structure as shown in Fig. 1A the metal oxide semiconductor (MOS) channel is formed on the horizontal or 0001 crystal plane of SiC. The channel mobility or field effect mobility on the 0001 crystal plane of SiC tends to be lower as compared to the vertical side wall or what is called as the 11-20 or 10-10 crystal plane. The channel mobility or field effect mobility on the 0001 crystal plane of SiC is in the range of 15 to 25 cm2 / V-sec as compared to silicon MOSFETs where it can be more than 350 cm2 / V-sec. When one makes a planar SiC DMOSFET, the ON resistance tends to be large and the MOSFET is limited by the field effect channel mobility. Therefore, there is a long-felt need for improved power devices that addresses the low channel mobility and high ON resistance in SiC MOSFET.

[0012] Further, “[threshold voltage of the power MOSFET is an important design parameter from an application stand-point. A minimum threshold voltage must be maintained at above 1 volt for most system applications to provide immunity against turn-on due to voltage spikes arising from noise. At the same time, a high threshold voltage is not desirable because the voltage available for creating the charge in the channel inversion layer is determined by (VG - VT) where VG is the applied gate bias and VT is the threshold voltage.” [source: B.J. Baliga, Silicon Carbide Power Devices, Springer Press (2005), Page 234]

[0013] Fig. 22 [source: B.J. Baliga, Silicon Carbide Power Devices, Springer Press (2005), Page 235] shows the threshold voltage of 4H-SiC planar MOSFETSs for the case of a gate oxide thickness of 0.1 microns. The results obtained for a silicon power MOSFET with the same gate oxide thickness is also provided in the figure for comparison.

[0014] In the race to achieve lower RDS, ON of planar gate SiC MOSFETs with high breakdown voltage ratings, it is a common practice to make the channel lengths (LCH) as short as possible which reduces a great part of the conduction loss that is associated to the channel. The trade-off in doing so is that, as the channel lengths are becoming shorter, the MOSFET devices become susceptible to undesirable phenomena such as the DIBL effect (the Drain Induced Barrier Lowering effect) which is responsible for the poor device performance including but not limited to the roll-off of the threshold voltage (VTH) at high drain bias and the increase of the drain leakage (II) at high drain bias. A conventional approach to mitigate this problem is to uniformly increase the doping concentration in the channel region, but this approach suffers from a higher than optimal gate threshold voltage and on-resistance, which can offset the gains achieved from the channel length reduction.

[0015] Further, there has been a continuous trend toward higher operating frequencies especially in motor control and switch mode power supplies. In power supplies, operation at high frequencies is attractive because of the reduction in size and power losses in the passive components (inductors and capacitors) which leads to a more efficient, compact system design. To accomplish higher frequency operation, it is essential to use power transistors and rectifiers with improved switching performance. SiC’s electronic parameters superiority would enable dramatic improvement in this regard.

[0016] Fig. 27 is the prior art structure of a MPS diode, consisting of interdigitated pin and Schottky diodes connected in parallel as reported in “T. Kimoto and J. A. Cooper, Fundamentals of Silicon Carbide Technology, IEEE Press (2014), page 296]”. The MPS diode as shown in the prior art in Fig. 27 has metal layer on top which forms ohmic contacts to the P+ regions and Schottky contacts to the n- regions, so the overall device consists of interdigitated Schottky and pin diodes connected in parallel. The P+ anode regions are spaced far enough apart that their depletion regions do not touch under zero or forward bias. This leaves a conductive path through the n- drift regions between each Schottky or non-Schottky contact and the N+ substrate. As forward bias is applied the Schottky or non-Schottky regions conduct first since the current density of the Schottky Barrier Diode is orders of magnitude higher than the pin diode at the same forward voltage. The Schottky or non-Schottky regions therefore effectively clamp the voltage drop across the pin regions and the pin regions do not conduct. As a result, virtually all of the forward current is due to electrons injected from the n- drift region through the Schottky or non-Schottky contact into the metal. Since the P+ regions do not inject holes into the drift region, no minority carrier charge is stored and the turn-off transient is fast, minimizing switching loss. With no conductivity modulation, the series resistance of the drift region is determined by its thickness and doping. This relatively high resistance leads to a voltage drop VDR that dominates the total voltage drop at highcurrents. In a Schottky diode, this poses a problem under high surge current events, since the pure Schottky diode can go into thermal runaway, with catastrophic consequences.

[0017] Further, “[A] silicon carbide (SiC) device may include a gate electrode disposed above a SiC semiconductor layer, wherein the SiC semiconductor layer comprises: a drift region having a first conductivity type; a well region disposed adjacent to the drift region, wherein the well region has a second conductivity type; and a source region having the first conductivity type disposed adjacent to the well region, wherein the source region comprises a source contact region and a pinch region, wherein the pinch region is disposed only partially below the gate electrode, wherein a sheet doping density in the pinch region is less than 2.5 x 1014cm-2, and wherein the pinch region is configured to deplete at a current density greater than a nominal current density of the SiC device to increase the resistance of the source region.” [source: Silicon carbide device and method of making thereof, Peter Almem Losee, Ljubisa Dragoljub Stevanovic, Gregory Thomas Dunne, Alexander Viktorovich Bolotnikov, published as US9899512B2 on February 20, 2018],

[0018] US20190013312A1 discloses body regions numbered 3, 5, respectively, that accommodate a first and a second source region numbered 4, 6, of the N type, extending from the upper surface 2 A into the interior of the body regions 3, 5 and states: “A first metallization layer extends over the first surface and forms, in direct contact with the implanted structure and with the JFET region, a JBS diode.” [source: MOSFET device of silicon carbide having an integrated diode and manufacturing process thereof, Mario Giuseppe Saggio, Simone RASCUNA, published at USPTO as US20190013312A1 on January 10, 2019],

[0019] “An n-MOSFET device (11) has an n-type channel (2) between a substrate (1) and a gate structure (7, 8), the channel (2) being formed by a layer of n-doped germanium of a thickness such that the channel (2) is fully-depleted with no applied gate voltage whereby the device (11) is operative in accumulation mode.” [source: Germanium n-mosfet devices and production methods, Daniele Caimi, Athanasios Dimoulas, Jean Fompeyrine, Chiara Marchiori, Christophe P. Rossel, Marilyne Sousa, Axelle M. Tapponnier, David J. Webb, published as W02011013042A1 on February 03, 2011],

[0020] US9318597B2 discloses that a semiconductor device that includes a vertical field-effect- transistor (FET) and a bypass diode. It further states that the vertical FET device includes a substrate, a drift layer formed over the substrate, a gate contact and a plurality of source contacts located on a first surface of the drift layer opposite the substrate, a drain contact located on a surface of the substrate opposite the drift layer, and a plurality of junction implants, each of the plurality of junction implants laterally separated from one another on the surface of the drift layer opposite the substrate and extending downward toward the substrate and that each of the one or more bypass diodes are formed by placing a Schottky metal contact on the first surface of the drift layer, suchthat each Schottky metal contact runs between two of the plurality of junction implants, [source: Layout configurations for integrating schottky contacts into a power transistor device, Vipindas Paia, Edward Robert Van Brunt, Lin Cheng, John Williams Palmour, published as US9318597B2 at USPTO on April 19, 2016],

[0021] US9876104B2 discloses a multi-cell MOSFET device including a MOSFET cell with an integrated Schottky diode wherein the MOSFET includes n-type source regions formed in p-type well regions which are formed in an n-type drift layer, a p-type body contact region is formed on the periphery of the MOSFET, and the source metallization of the device forms a Schottky contact with an n-type semiconductor region adjacent the p-type body contact region of the device, [source: High voltage semiconductor devices and methods of making the devices, Kevin Matocha, Kiran Chatty, Sujit Baneijee, published as US9876104B2 on January 23, 2018],

[0022] US8436367B1 discloses that a SiC Power Semiconductor device of the Field Effect Type (MOSFET, IGBT or the like) with “muted” channel conduction, negative temperature coefficient of channel mobility, in situ “ballasted” source resistors and optimized thermal management of the cells for increased Safe Operating Area is described. Controlling the location of the Zero Temperature Crossover Point (ZTCP) in relationship to the drain current is achieved by the partition between the “active” and “inactive” channels and by adjusting the mobility of the carriers in the channel for the temperature range of interest.” [source: SiC power vertical DMOS with increased safe operating area, Dumitru Sdrulla, Marc Vandenberg, published at USPTO as US8436367B1 on May 07, 2013],

[0023] Considering the knowledge of persons skilled in the art, there is a long-felt need for power devices having increased third quadrant cross over current to overcome performance and reliability issues.

[0024] Further, FIG. 67A shows two implementations of a power MOSFET in the form of a vertical, planar DMOSFET and a vertical trench UMOSFET. The term DMOSFET derives from the silicon device of the same name, where the n+ source and p-base regions are formed by diffusion of n-type and p-type impurities through the same mask opening (hence “double diffused” MOSFET). In SiC, the same structure is formed by double implantation. The term UMOSFET derives from the U-shaped geometry, but the term trench MOSFET is also used. Historically, the first SiC power MOSFETs were UMOSFETs, but they were joined soon by ion implanted DMOSFETs. [SOURCE: T. Kimoto, J. A. Cooper in Fundamentals of Silicon Carbide Technology, IEEE Press (2014), pages 320-324.]

[0025] Because of their trench geometry, UMOSFETs present both opportunities and challenges relative to planar devices such as the DMOSFETs. The UMOSFET can be fabricated in a smaller surface area than the DMOSFET, since the MOS channel is oriented perpendicular to the surface.It is also easier to form a short sub-micron channel since the channel length is determined by epigrowth. However, the MOS channel is formed on an etched non-polar face of the crystal, and the properties of the gate oxide are different from those on the (1000) plane. The channel mobility or field effect mobility on the 0001 crystal plane tends to be lower as compared to the vertical side wall or what is called as the 11-20 or 10-10 crystal plane. The channel mobility can be in the range of 15-25 cm2 / Vs on the 1000 plane whereas it can be as high as 60-80 cm2 / Vs on the 11-20 or 10- 10 crystal planes of SiC. [SOURCE: T. Kimoto, J.A. Cooper in Fundamentals of Silicon Carbide Technology, IEEE Press (2014), pages 320-324.]

[0026] FIG. 67B and 67C show major resistances in the vertical DMOSFET and the UMOSFET respectively and it is apparent that the geometry of the device effectively eliminates the JFET resistance present in the DMOSFET. FIG. 67D illustrates the electric fields in the UMOSFET in the blocking state, the trench corners are significant locations of significant field crowding. Because the oxide field is ~ 2.5X higher than the peak field in the semiconductor (due to Gauss’ law of electrostatics), this is a serious problem inherent to the UMOSFET device design. [SOURCE: T. Kimoto, J.A. Cooper in Fundamentals of Silicon Carbide Technology, IEEE Press (2014), pages 320-324.]

[0027] Therefore, there is a long-felt need to combine the desirable features of the planar DMOSFET and the trench UMOSFET into a single device that can be advantageously and flexibly designed to exploit the specific benefits of each device structure for a given application. Furthermore, there is a long-felt need to incorporate junction barrier Schottky (JBS) or merged PiN Schottky (MPS) rectifier elements into the hybrid DMOSFET / UMOSFET device geometry.SUMMARY OF INVENTION

[0028] One or more aspects of the present invention are disclosed herein.

[0029] In one aspect, a device is described herein. The device comprises a unit cell on a SiC substrate. The unit cell comprises a gate insulator film, a trench in a well region, a first sinker region having a second conduction type, and a second sinker region having the second conduction type. The first sinker region has a depth that is equal to or greater than a depth of the well region. Each of the first sinker region and the second sinker region is in contact with a region having a first conduction type to form a p-n junction.

[0030] In an embodiment, the device comprises a semiconductor metal-insulator-semiconductor transistor component.

[0031] In another embodiment, the well region is next to an insulator-semiconductor interface; and a source region of the first conduction type formed within the well region.

[0032] In yet another embodiment, a depth of the trench is greater than or equal to a thickness of the source region.

[0033] In yet another embodiment, the first sinker region is located below the trench.

[0034] In yet another embodiment, a depth of the second sinker region is less than the depth of the first sinker region.

[0035] In yet another embodiment, a depth of the second sinker region is greater than the depth of the well region.

[0036] In yet another embodiment, the device has an on-resistance of less than 4 milliohm centimeter squared, a gate threshold voltage of greater than 1.5 Volt, a breakdown voltage of greater than 500 Volt, and an electric field of less than 3.5 megavolt per cm in the gate insulator film.

[0037] In another aspect, a device comprising a unit cell on a SiC substrate is described. The unit cell comprises a gate insulator film, a trench in a well region, a first sinker region of a second conduction type, a second sinker region of the second conduction type, and a source region. The source region is in direct contact with the second sinker region.

[0038] In an embodiment, the device comprises a semiconductor metal-insulator-transistor component.

[0039] In another embodiment, the unit cell further comprises a semiconductor body of a first conduction type that comprises a drift zone; the well region of the second conduction type next to an insulator-semiconductor interface; and the source region of the first conduction type formed within the well region.

[0040] In yet another embodiment, a depth of the trench is greater than or equal to a thickness of the source region.

[0041] In yet another embodiment, a depth of the trench is greater than a depth of the source region.

[0042] In yet another embodiment, the device has an avalanche energy of greater than 10 Joule per centimeter squared, calculated by dividing an avalanche energy in Joules by a total die area in centimeter squared.

[0043] In yet another embodiment, an avalanche failure is located within the unit cell.

[0044] In another aspect, a device comprising a unit cell on a SiC substrate is disclosed. The unit cell comprises a gate insulator film, a trench in a well region, a first sinker region of a second conduction type, a second sinker region of the second conduction type, and a source region. The first sinker region has a depth that is greater than a depth of the second sinker region. The second sinker has a width that is greater than that of the first sinker

[0045] In another embodiment, the first sinker region is located below the trench.

[0046] In yet another embodiment, the depth of the second sinker region is less than the depth of the first sinker region.

[0047] In yet another embodiment, the depth of the second sinker region is greater than a depth of the well region.

[0048] In yet another aspect, a device comprising a unit cell on a Silicon Carbide (SiC) substrate is disclosed. The unit cell comprises a first conductivity type first source region; a first conductivity type second source region; a second conductivity type well region; and a silicide layer. The device comprises a vertical Silicon Carbide (SiC) double-implantation metal oxide semiconductor fieldeffect transistor (DMOSFET) comprising a drain terminal on a backside of the SiC substrate and a source terminal on a topside of the SiC substrate. The first conductivity type second source region comprises a thickness lower than a thickness of the first conductivity type first source region. The first conductivity type second source region is interspersed between the second conductivity type well region and the silicide layer. The first conductivity type second source region comprises a sheet of source region located between a recessed SiC trench region and the second conductivity type well region.

[0049] In an embodiment, the sheet of source region comprises a thin sheet of source region.

[0050] In another embodiment, first conductivity type second source region comprises at least one of (a) a target thickness and (b) a target doping concentration.

[0051] In yet another embodiment, the target thickness of the first conductivity type second source region ranges from 1 nm to 1 pm and the target doping concentration ranges from 1015cm'3to 1021-3 cm .

[0052] In yet another embodiment, the first conductivity type second source region comprises a sheet of source region located between the silicide layer and the second conductivity type well region.

[0053] In yet another embodiment, the device is capable of carrying a drain current of less than negative 500 milliamperes at a drain voltage of negative 3 volts.

[0054] In yet another aspect, a device comprising a unit cell on a silicon carbide (SiC) substrate. The unit cell comprises a first conductivity type source region; a second conductivity type well region; and a second conductivity type shield region. The second conductivity type shield region is confined within the second conductivity type well region.

[0055] In an embodiment, the second conductivity type shield region is located within a metal oxide semiconductor field-effect transistor (MOSFET) channel.

[0056] In another embodiment, the second conductivity type shield region is located closer to an edge of the second conductivity type well region.

[0057] In yet another embodiment, a doping concentration inside the second conductivity type well region is non-uniform in a lateral direction.

[0058] In yet another embodiment, a doping concentration inside the second conductivity type shield region is higher than a doping concentration inside the second conductivity type well region.

[0059] In yet another embodiment, the second conductivity type shield region extends beyond a vertical extent of the second conductivity type well region.

[0060] In yet another embodiment, the device further comprises a trench region in the second conductivity type well region. The trench region comprises a depth of one of greater than and equal to a thickness of the first conductivity type source region.

[0061] In yet another embodiment, the device comprises a gate oxide layer in contact with the second conductivity type well region and the first conductivity type source region. The device comprises a double-implantation metal oxide semiconductor field-effect transistor (DMOSFET).

[0062] In yet another embodiment, the device comprises multiple second conductivity type shield regions within a metal oxide semiconductor field-effect transistor (MOSFET) channel.

[0063] In yet another embodiment, the multiple second conductivity type shield regions are located closer to an edge of the second conductivity type well region.

[0064] In yet another embodiment, the multiple second conductivity type shield regions extend beyond a vertical extent of the second conductivity type well region.

[0065] In yet another embodiment, the second conductivity type shield region is buried within the second conductivity type well region.

[0066] In yet another aspect, a device comprising a unit cell on a silicon carbide (SiC) substrate is disclosed. The device comprises a first conductivity type source region; a second conductivity type well region; and a second conductivity type shield region. The second conductivity type shield region is confined within the second conductivity type well region. The second conductivity type shield region shields a metal oxide semiconductor field-effect transistor (MOSFET) channel from a high potential applied to a drain terminal.

[0067] In an embodiment, the device further comprises a trench region in the second conductivity type well region, the trench region comprises a depth of one of greater than and equal to a thickness of the first conductivity type source region.

[0068] In another embodiment, the device comprises a gate threshold voltage of greater than 2.5 volts, a breakdown voltage of greater than 3300 volts at a gate to source voltage of 0 volt, an on- resistance of less than 15 milliohm centimeter squared, and a short-circuit withstand time of greater than 4 microseconds at a drain voltage of 1500 volts.

[0069] In yet another embodiment, the device comprises a gate threshold voltage of greater than 2 volts, a breakdown voltage of greater than 1200 volts at a gate to source voltage bias of 0 volt, anon-resistance of less than 4.5 milliohm centimeter squared, and a short-circuit withstand time of greater than 2.5 microseconds at a drain voltage of 800 volts.

[0070] In yet another embodiment, the device comprises a gate threshold voltage of greater than2.5 volts, a breakdown voltage of greater than 6500 volts at a gate to source voltage of 0 volt, an on-resistance of less than 50 milliohm centimeter squared, and a short-circuit withstand time of greater than 4 microseconds at a drain voltage of 3600 volts.

[0071] In yet another embodiment, the device comprises a gate threshold voltage of greater than2.5 volts, a breakdown voltage of greater than 10000 volts at a gate to source voltage of 0 volt, an on-resistance of less than 100 milliohm centimeter squared, and a short-circuit withstand time of greater than 4 microseconds at a drain voltage of 5000 volts.

[0072] In yet another embodiment, the device comprises a gate threshold voltage of greater than2.5 volts, a breakdown voltage of greater than 13000 volts at a gate to source voltage of 0 volt, an on-resistance of less than 400 milliohm centimeter squared, and a short-circuit withstand time of greater than 4 microseconds at a drain voltage of 10000 volts.

[0073] In yet another embodiment, the second conductivity type shield region shields the metal oxide semiconductor field-effect transistor (MOSFET) channel from the high potential applied to the drain terminal during one of an off-state and a blocking operation.

[0074] In yet another aspect, a method is described herein. The method comprises forming a silicon carbide (SiC) metal oxide semiconductor field-effect transistor (MOSFET); forming a second conductivity type well region; forming a first conductivity type source region within the second conductivity type well region; and forming a second conductivity type shield region. The second conductivity type shield region is located outside the first conductivity type source region.

[0075] In an embodiment, the second conductivity type shield region is located within the second conductivity type well region.

[0076] In another embodiment, the second conductivity type shield region extends beyond the second conductivity type well region.

[0077] In yet another embodiment, the SiC MOSFET is manufactured on SiC epi-wafer comprising a doping ranging from 1014to 1018cm'3and a thickness ranging from 1 micrometers (pm) to 300 micrometers (pm).

[0078] In yet another embodiment, forming the second conductivity type well region comprises: depositing a hard mask comprising at least one of a silicon dioxide layer, a silicon nitride layer, a polysilicon layer, a silicon oxynitride layer, and a metallic layer with a total thickness ranging from 50 nanometers to 5 micrometers; patterning the hard mask; etching the hard mask; and performing one of an ion-implantation and an epitaxial growth using second conductivity type ions. The step of performing the ion-implantation comprises implanting the second conductivity type ions atenergies ranging from 10 keV to 1000 keV, and at implant doses ranging from 1012cm'2to 1015cm'2. The second conductivity type ions comprise one of aluminum and boron.

[0079] In an embodiment, forming the second conductivity type shield region comprises forming the second conductivity type shield region closer to an edge of the second conductivity type well region.

[0080] In another embodiment, forming the second conductivity type shield region comprises forming the second conductivity type shield region confined within the second conductivity type well region.

[0081] In yet another embodiment, the method further comprises forming a metal oxide semiconductor field-effect transistor (MOSFET) channel.

[0082] In yet another embodiment, forming the second conductivity type shield region comprises forming the second conductivity type shield region in contact with the metal oxide semiconductor field-effect transistor (MOSFET) channel.

[0083] In yet another embodiment, forming the second conductivity type shield region comprises forming multiple second conductivity type shield regions in contact with the metal oxide semiconductor field-effect transistor (MOSFET) channel.

[0084] In yet another embodiment, forming the first conductivity type source region comprises forming the first conductivity type source region using one of nitrogen and phosphorus ions.

[0085] In yet another embodiment, the method further comprises forming a gate oxide layer; forming a polysilicon gate layer; forming an interlayer dielectric (ILD) layer; forming a silicide region; and forming an interconnect metal layer.

[0086] In yet another embodiment, forming the gate oxide layer comprises performing either one or a stacked combination of a thermal oxidation and a chemical vapor deposition (CVD) of a dielectric layer of one of a silicon dioxide layer, a silicon nitride layer, and a silicon oxynitride layer. The gate oxide layer is formed with a thickness ranging from 10 nanometers to 100 nanometers.

[0087] In yet another embodiment, forming the polysilicon gate layer comprises depositing a polysilicon layer using one of a plasma-enhanced chemical vapor deposition (PECVD) and a low- pressure chemical vapor deposition (LPCVD) through one of an in-situ doping and a subsequent drive-in doping.

[0088] In yet another embodiment, forming the interlayer dielectric (ILD) layer comprises depositing one of at least one of a silicon dioxide layer, a silicon nitride layer, and a silicon oxynitride layer; and a stacked combination of the silicon dioxide layer, the silicon nitride layer, and the silicon oxynitride layer. The ILD layer comprises a thickness one of greater than and equal to 50 nanometers.

[0089] In yet another embodiment, forming the silicide region comprises forming a nickel silicide region on an exposed SiC surface.

[0090] In yet another embodiment, forming the second conductivity type shield region comprises forming the second conductivity type shield region extending beyond a vertical extent of the second conductivity type well region.

[0091] In yet another aspect, a method is described herein. The method comprises forming a silicon carbide (SiC) metal oxide semiconductor field-effect transistor (MOSFET); forming a second conductivity type well region; forming a first conductivity type source region within the second conductivity type well region; and forming a second conductivity type shield region. The second conductivity type shield region is located outside the first conductivity type source region. A doping concentration in the second conductivity type well region within a metal oxide semiconductor field-effect transistor (MOSFET) channel is non-uniform. At least a portion of the second conductivity type shield region is located within the second conductivity type well region.

[0092] In an embodiment, doping concentration profiles of the second conductivity type shield region at different locations are different.

[0093] In another embodiment, doping concentration profiles of the second conductivity type shield region at different locations are not different.

[0094] In yet another aspect, a semiconductor component is described herein. The semiconductor component comprises a semiconductor body of a first conduction type comprising a voltage blocking layer; and islands of a second conductivity type on a contact surface; and a metal layer on the voltage blocking layer. The metal layer and the voltage blocking layer includes a Schottky contact, and a first conductivity type layer comprising the first conduction type not in contact with the Schottky contact that is interspersed between the islands of the second conductivity type.

[0095] In an embodiment, a vertical extent of the first conductivity type layer is lower than a bottom of the islands of the second conductivity type.

[0096] In another embodiment, a vertical extent of the first conductivity type layer is higher than a bottom of the islands of the second conductivity type.

[0097] In yet another embodiment, a doping concentration within the first conductivity type layer is non-uniform in a direction that is perpendicular to the Schottky contact.

[0098] In yet another embodiment, a vertical extent of the first conductivity type layer is higher or lower than a bottom of the islands of the second conductivity type.

[0099] In yet another embodiment, the first conductivity type layer has a doping concentration that does not vary in any direction along the contact surface.

[0100] In yet another embodiment, the first conductivity type layer has a first doping concentration that is higher than a second doping concentration of a drift region.

[0101] In yet another embodiment, the first conductivity type layer has a first doping concentration that is lower than a second doping concentration of a drift region.

[0102] In yet another embodiment, the Schottky contact comprises a metal comprising Al, Ag, Au, Mo, Ni, Ti, W, TixWy, TixNy, or combinations thereof.

[0103] In yet another aspect, a diode comprising P+ islands interspersed within a N+ region and a N- region contacts with a Schottky layer.

[0104] In an embodiment, a vertical extent of the N+ region is lower than a bottom of the P+ islands.

[0105] In another embodiment, a vertical extent of the N+ region is higher than a bottom of the P+ islands.

[0106] In yet another embodiment, a doping concentration within the N+ region is non-uniform in a direction that is perpendicular to the Schottky layer.

[0107] In yet another embodiment, a vertical extent of the N+ region is higher or lower than a bottom of the P+ islands.

[0108] In yet another aspect, a diode comprising N+ islands interspersed within a P+ region and a P- region contacts with a Schottky layer.

[0109] In an embodiment, a vertical extent of the P+ region is lower than a bottom of the N+ islands.

[0110] In another embodiment, a vertical extent of the P+ region is higher than a bottom of the N+ islands.

[0111] In yet another embodiment, a doping concentration within the P+ region is non-uniform in a direction that is perpendicular to the Schottky layer.

[0112] In yet another embodiment, a vertical extent of the P+ region is higher or lower than a bottom of the N+ islands.

[0113] In an aspect, a metal-insulator-semiconductor field effect transistor is disclosed herein. The metal-insulator-semiconductor field effect transistor comprises a unit cell on a SiC substrate. The unit cell comprises a trench in a well region having a second conduction type, a source region of a first conduction type, a first sinker region having a second conduction type, and a second sinker region having the second conduction type. The first sinker region has a depth that is equal to or greater than a depth of the well region. Each of the first sinker region and the second sinker region is in contact with a region having a first conduction type to form a p-n junction.

[0114] In an embodiment, the first sinker region has a depth that is greater than a depth of the second sinker region. The second sinker has a width that is greater than that of the first sinker.

[0115] In another aspect, a metal-insulator-semiconductor field effect transistor is disclosed herein. The metal-insulator-semiconductor field effect transistor comprises a unit cell on a siliconcarbide (SiC) substrate. The unit cell comprises: a first conductivity type source region; a second conductivity type well region; and a second conductivity type shield region. The second conductivity type shield region is located outside the first conductivity type source region.

[0116] In an embodiment, the second conductivity type shield region extends beyond a vertical extent of the second conductivity type well region.

[0117] In another embodiment, the device further comprises a trench region in the second conductivity type well region. The trench region comprises a depth that is greater than and equal to a thickness of the first conductivity type source region.

[0118] In yet another embodiment, the device further comprises a sinker region of a first conduction type that is located directly below the trench region.

[0119] In yet another aspect, a semiconductor component is disclosed herein. The semiconductor component comprises a semiconductor body of a first conduction type comprising a voltage blocking layer; and islands of a second conductivity type on a contact surface; and a metal layer on the voltage blocking layer. The metal layer and the voltage blocking layer includes a Schottky contact, and a first conductivity type layer comprising the first conduction type not in contact with the Schottky contact that is interspersed between the islands of the second conductivity type.

[0120] In an embodiment, a vertical extent of the first conductivity type layer is lower than a bottom of the islands of the second conductivity type.

[0121] In another embodiment, a doping concentration within the first conductivity type layer is non-uniform in a direction that is perpendicular to the Schottky contact.

[0122] In yet another aspect, a silicon carbide diode is disclosed herein. The silicon carbide diode comprises first conduction type islands interspersed within a second region of a first conduction type and a first region of the first conduction type in contact with a metal layer.BRIEF DESCRIPTION OF THE FIGURES

[0123] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0124] Fig. 1A shows the prior art SiC DMOSFET structure reported by B.J. Baliga in Advanced High-Voltage Power Device Concepts, Springer Press, 2011.

[0125] Fig. IB shows the electric field contours simulated for the prior art SiC DMOSFET structure in Fig. 1A.

[0126] Fig. IC shows the electric field distribution for the prior art SiC DMOSFET structure in Fig. 1A.

[0127] Fig. 2A shows an embodiment of a SiC DMOSFET with the P+ plug region to ground the p-well region with the N+ source contact.

[0128] Fig. 2B shows the breakdown simulation of the SiC DMOSFET structure in Fig. 2A.

[0129] Fig. 3 shows an embodiment of a SiC DMOSFET where the P+ plug region in Fig. 2a is replaced with a deep P-type Sinker# 1 region.

[0130] Fig. 4A to Fig. 4R are cross sectional views showing the process steps for manufacturing the SiC DMOSFET structure in Fig. 3.

[0131] Fig. 5A shows an embodiment of a SiC DMOSFET where a P-type Sinker#2 region under the N+ source region is formed in addition to the deep P-type Sinker#l region.

[0132] Fig. 5B shows the breakdown simulation of the SiC DMOSFET structure designed according to embodiments shown in Fig. 3 and Fig. 5A.

[0133] Fig. 6A to Fig. 6J are cross sectional views showing the process steps for manufacturing the SiC DMOSFET structure in Fig. 5A.

[0134] Fig. 7A shows an embodiment of a SiC DMOSFET where a trench is etched into the N+ source region before implanting the P-type Sinker# 1 region.

[0135] Fig. 7B shows the breakdown simulation of the SiC MOSFET structure in Fig. 7A.

[0136] Fig. 8A to Fig. 8BB are cross sectional views showing the process steps for manufacturing the SiC DMOSFET structure in Fig. 7A.

[0137] Fig. 9 shows the prior art SiC DMOSFET process flow for self-aligned MOS channel formation.

[0138] Fig. 10 shows an embodiment of a SiC DMOSFET structure for removal of a parasitic N+ source region formed in the periphery.

[0139] Fig. 11A to Fig. 11GG are cross sectional views showing the process steps for manufacturing the SiC DMOSFET structure in Fig. 10.

[0140] Fig. 12 shows an embodiment of a SiC DMOSFET with a dedicated process step utilized for masking the implantation of the N+ source region in the device periphery.

[0141] Fig. 13A to Fig. 13GG are cross sectional views showing the process steps for manufacturing the SiC DMOSFET structure in Fig. 12.

[0142] Fig. 14 shows an embodiment of a SiC DMOSFET with a dedicated process step for masking the implantation of the N+ source region in the device periphery as well as the N+ source region in the active region to enable ohmic contact to the p-well region

[0143] Fig. 15A to Fig. 15FF are cross sectional views showing the process steps for manufacturing the SiC DMOSFET structure in Fig. 14.

[0144] Fig. 16 shows an embodiment of a SiC DMOSFET where the polysilicon gate metallization layers are segmented in the peripheral region.

[0145] Fig. 17A to Fig. 17FF are cross sectional views showing the process steps for manufacturing the SiC DMOSFET structure in Fig. 16.

[0146] Fig. 18 shows an embodiment of a SiC DMOSFET with a portion of the MOS channel on (1000) and a second portion on (11-20) or (11-00) crystal planes.

[0147] Fig. 19A to Fig. 19U are cross sectional views showing the process steps for manufacturing the SiC DMOSFET structure in Fig. 18.

[0148] Fig. 20 shows an embodiment of a SiC DMOSFET with a portion of the MOS channel on (1000) and a second portion on (11-20) or (11-00) crystal planes and a deeper p-well trench and formation of a second p-well region under the N+ source region

[0149] Fig. 21A to Fig. 21V are cross sectional views showing the process steps for manufacturing the SiC DMOSFET structure in Fig. 20.

[0150] Fig. 22 is the prior art and shows the plot of threshold voltage versus p-base doping concentration for a 4H-SiC Planar MOSFET.

[0151] Figs. 23A to Fig. 23D shows embodiments of a SiC DMOSFET structure for field shielding within the p-well region.

[0152] Figs. 24A to Fig. 24U are cross sectional views showing the process steps for manufacturing the SiC DMOSFET structure in Fig. 23 A.

[0153] Figs. 25A to Fig. 25D show embodiments of a SiC DMOSFET structure for field shielding formed buried within the p-well structure.

[0154] Figs. 26A to Fig. 26U are cross sectional views showing the process steps for manufacturing the SiC DMOSFET structure in Fig. 25A.

[0155] Fig. 27 is the cross-sectional schematic of a prior-art SiC MPS diode.

[0156] Fig. 28A is an embodiment of MPS diode structure with buried N+ regions.

[0157] Fig. 28B the I-V characteristic for the embodiment described in Fig. 28A.

[0158] Fig. 28C is the comparison of the cross-sections of the devices in Fig. 28A.

[0159] Figs. 29A to Fig. 29L are cross sectional views showing the process steps for manufacturing the SiC MPS diode shown in Fig. 28A.

[0160] Fig. 30 is an embodiment of MPS diode structure where the bottom of the N+ region is higher than the bottom of the P+ region.

[0161] Figs. 31A to Fig. 31L are cross sectional views showing the process steps for manufacturing the SiC MPS diode shown in Fig. 30.

[0162] Fig. 32A to Fig 32F are embodiments of MPS diode structures with multiple N subregions, P sub-regions or both

[0163] Fig. 33AA to Fig. 33AL are cross sectional views showing the process steps for manufacturing the SiC MPS diode shown in Fig. 32A.

[0164] Fig. 33BA to Fig. 33BL are cross sectional views showing the process steps for manufacturing the SiC MPS diode shown in Fig. 32B.

[0165] Fig. 33EA to Fig. 33EL are cross sectional views showing the process steps for manufacturing the SiC MPS diode shown in Fig. 32E.

[0166] Fig. 33FA to Fig. 33FL are cross sectional views showing the process steps for manufacturing the SiC MPS diode shown in Fig. 32F.

[0167] Fig. 34 is an embodiment of MPS diode structure with two different types of P+ wells depending on their depths which are in comparison to the depth of the N+ layer.

[0168] Figs. 35A to Fig. 35P are cross sectional views showing the process steps for manufacturing the SiC MPS diode shown in Fig. 34.

[0169] Fig. 36A is the blocking performances of the devices of this invention with varying ratios ofWl / Dl.

[0170] Fig. 36B is the blocking I-V curves of the devices of this invention with varying ratios of Wl / Dl.

[0171] Fig. 36C is the forward I-V curves of the devices of this invention with varying ratios of Wl / Dl.

[0172] Fig. 36D is the performance of differential specific on-resistances of the devices of this invention with varying ratios ofWl / Dl.

[0173] Fig. 37A shows the device structure of DMOSFET according to an embodiment.

[0174] Fig. 37B shows the device structure of junction field effect transistors (JFET) according to an embodiment.

[0175] Fig. 38 shows an example of the n-type layer formed using ion-implantation according to an embodiment.

[0176] Fig. 39A to 39C shows the N Layer vertical extent with respect to the P+ gate layer in a JFET according to various embodiments.

[0177] Fig. 40A to 40C shows the N Layer vertical extent with respect to the p-well layer in a DMOSFET according to various embodiments.

[0178] Fig. 41A to 41E a cross-sectional schematic of a vertical JFET showing the process steps for the device shown in Fig. 37B.

[0179] Fig. 42A to 42D a cross-sectional schematic of a power MOSFET structure showing the process steps for the device shown in Fig. 37A.

[0180] Fig. 43A and Fig. 43B show the output and breakdown I-V characteristics of 1200 V SiC DMOSFETs fabricated using the teachings of this invention.

[0181] Fig. 44A and Fig. 44B show the transfer (ID v / s VGS) characteristics of 1200 V SiC MOSFETs fabricated using the teachings of this invention.

[0182] Fig. 45 is a single-pulse avalanche energy measured for a 1200 V SiC MOSFET fabricated using the teachings of this invention.

[0183] Fig. 46 is a photograph showing a SiC DMOSFET fabricated using the teachings of these inventions and tested for single-pulse avalanche energy test.

[0184] Fig. 47A and Fig. 47B are output characteristics of two 3.3 kV SiC MOSFETs fabricated using the teachings of these inventions.

[0185] Fig. 47C is the transfer characteristics of two 3.3 kV SiC MOSFETs fabricated using the teachings of these inventions.

[0186] Fig. 47D is a short-circuit test measured for two 3.3 kV SiC MOSFETs fabricated using the teachings of this invention.

[0187] FIG. 48A illustrates an embodiment of a cross sectional structure of a unit cell of a double-implantation metal oxide semiconductor field-effect transistor (DMOSFET) comprising a first conductivity type second source region within a first conductivity type first source region.

[0188] FIG. 48B illustrates an embodiment of a cross sectional structure of one or more unit cells of the DMOSFET, comprising one or more unit cells of an integrated Schottky diode, each DMOSFET unit cell comprising the first conductivity type second source region within the first conductivity type first source region.

[0189] FIG. 48C illustrates an embodiment of a cross sectional structure of one or more unit cells of a trench gate MOSFET, comprising one or more unit cells of the integrated Schottky diode, each MOSFET unit cell comprising the first conductivity type second source region within the first conductivity type first source region.

[0190] FIG. 49A to 49T illustrates an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 48A.

[0191] FIG. 50A illustrates an embodiment of a voltage-current characteristic of a SiC DMOSFET with conventional p-n junction vs the SiC DMOSFET with deactivated p-n junction (i.e., the first conductivity type second source region).

[0192] FIG. 50B is a perspective view that illustrates an embodiment of sides of the DMOSFET in relation to a dice.

[0193] FIG. 50C and 50D illustrate current flow paths through the MOSFET and through an intrinsic anti-parallel diode region in an H-bridge circuit respectively.

[0194] FIG. 51A illustrates an embodiment of a cross sectional structure of a unit cell of a double-implantation metal oxide semiconductor field-effect transistor (DMOSFET) comprising a first conductivity type second source region within a first conductivity type first source region.

[0195] FIG. 51B illustrates an embodiment of a cross sectional structure of one or more unit cells of the DMOSFET, comprising one or more unit cells of an integrated Schottky diode, eachDMOSFET unit cell comprising the first conductivity type second source region within the first conductivity type first source region.

[0196] FIG. 52A to 52T illustrate an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 51 A.

[0197] FIG. 53A illustrates an embodiment of a cross sectional structure of a unit cell of a double-implantation metal oxide semiconductor field effect transistor (DMOSFET) comprising a first metal region in direct contact with a second conductivity type well contact region.

[0198] FIG. 53B illustrates an embodiment of a cross sectional structure of one or more unit cells of the DMOSFET, comprising one or more unit cells of an integrated Schottky diode, each DMOSFET unit cell comprising the first metal region in direct contact with the respective second conductivity type well contact region.

[0199] FIG. 53C illustrates an embodiment of a third quadrant current conduction through an intrinsic p-n junction diode region vs a Schottky diode region connected in parallel to the DMOSFET.

[0200] FIG. 53D illustrates an embodiment of a third quadrant current conduction through the DMOSFET after connecting the one or more Schottky diode regions in series with the one or more body diode regions of the DMOSFET.

[0201] FIG. 54A to 54X illustrate an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 53 A.

[0202] FIG. 55A, 55B & 55C illustrate an embodiment of cross-sectional structures of a unit cell of a double-implantation metal oxide semiconductor field effect transistor (DMOSFET) comprising a second conductivity type well contact region that meanders at three different locations respectively.

[0203] FIG. 55D, 55E & 55F illustrates an embodiment of cross-sectional structures of one or more unit cells of a diode integrated DMOSFET, each DMOSFET unit cell comprising the second conductivity type well contact region that meanders at three different locations respectively.

[0204] FIG. 56A to 56T illustrate an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 55 A.

[0205] FIG. 57A to 57T illustrate an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 55B.

[0206] FIG. 58A to 58T illustrate an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 55C.

[0207] FIG. 59A, 59B & 59C illustrate an embodiment of cross sectional structures of a unit cell of a double-implantation metal oxide semiconductor field effect transistor (DMOSFET) comprising a second conductivity type well contact region that meanders at three differentlocations respectively, allowing a second conductivity type well region to be in contact with a source metal only through the second conductivity type well contact region.

[0208] FIG. 59D, 59E & 59F illustrate an embodiment of cross sectional structures of one or more unit cells of a diode integrated DMOSFET, each DMOSFET unit cell comprising the second conductivity type well contact region that meanders at three different locations respectively, allowing the second conductivity type well region to be in contact with the source metal only through the second conductivity type well contact region.

[0209] FIG. 59G illustrates an embodiment of a cross sectional structure of one or more unit cells of a diode integrated trench gate MOSFET, comprising one or more unit cells of an integrated Schottky diode, each MOSFET unit cell comprising the second conductivity type well contact region at the first location, allowing the second conductivity type well region to be in contact with the source metal only through the second conductivity type well contact region.

[0210] FIG. 60A to 60T illustrate an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 59 A.

[0211] FIG. 61 A to 61T illustrate an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 59B.

[0212] FIG. 62A to 62T illustrate an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 59C.

[0213] FIG. 63 illustrates an embodiment of a cross-sectional structure of one or more unit cells of a power MOSFET, a first unit cell of the one or more unit cells comprising a first metal oxide semiconductor (MOS) interface on a horizontal surface of a semiconductor substrate and a trench sidewall, and a second unit cell of the one or more unit cells comprising a second metal oxide semiconductor (MOS) interface formed solely on the trench sidewall.

[0214] FIG. 64A to 64AB are cross-sectional views illustrating an embodiment of a process of manufacturing the MOSFET structure shown in FIG. 63.

[0215] FIG. 65 illustrates an embodiment of a cross-sectional structure of one or more unit cells of a power MOSFET, a first unit cell of the one or more unit cells comprising a first metal oxide semiconductor (MOS) interface on a horizontal surface of a semiconductor substrate and a trench sidewall, and a second unit cell of the one or more unit cells comprising a metal region formed adjacent to a first conductivity type drift layer of the MOSFET.

[0216] FIG. 66A to 66AA are cross-sectional views illustrating an embodiment of a process of manufacturing the MOSFET structure shown in FIG. 65.

[0217] FIG. 67A shows two implementations of a power MOSFET in the form of a vertical, planar DMOSFET and a vertical trench UMOSFET.

[0218] FIG. 67B and 67C show major resistances in a vertical DMOSFET and a UMOSFET respectively and it is apparent that the geometry of the device effectively eliminates JFET resistance present in the DMOSFET.

[0219] FIG. 67D illustrates electric fields in a UMOSFET in a blocking state, trench corners are significant locations of significant field crowding.

[0220] Other features of the present embodiments will be apparent from the accompanying drawings and from the detailed description that follows.DETAILED DESCRIPTIONDefinitions and General Techniques

[0221] Unless otherwise defined herein, scientific, and technical terms used in connection with the present invention shall have the meanings that are commonly understood by those of ordinary skill in the art. Further, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular. Generally, nomenclatures used in connection with, and techniques of, semiconductor processing described herein are those well-known and commonly used in the art.

[0222] The methods and techniques of the present invention are generally performed according to conventional methods well known in the art and as described in various general and more specific references that are cited and discussed throughout the present specification unless otherwise indicated. The nomenclatures used in connection with, and the procedures and techniques of semiconductor device technology, semiconductor processing, and other related fields described herein are those well-known and commonly used in the art.

[0223] For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the present disclosure. Additionally, elements in the drawing figures are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments of the present disclosure. The same reference numerals in different figures denotes the same elements.

[0224] The terms "first," "second," "third," "fourth," and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "include," and "have," and any variations thereof, areintended to cover a non-exclusive inclusion, such that a process, method, system, article, device, or apparatus that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, system, article, device, or apparatus.

[0225] The terms "left," "right," "front," "back," "top," "bottom," "over," "under," and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the apparatus, methods, and / or articles of manufacture described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.

[0226] No element, act, or instruction used herein should be construed as critical or essential unless explicitly described as such. Also, as used herein, the articles "a" and "an" are intended to include items, and may be used interchangeably with "one or more." Furthermore, as used herein, the term "set" is intended to include items (e.g., related items, unrelated items, a combination of related items, and unrelated items, etc.), and may be used interchangeably with "one or more." Where only one item is intended, the term "one" or similar language is used. Also, as used herein, the terms "has," "have," "having," or the like are intended to be open-ended terms. Further, the phrase "based on" is intended to mean "based, at least in part, on" unless explicitly stated otherwise.

[0227] The following terms and phrases, unless otherwise indicated, shall be understood to have the following meanings.

[0228] The term “unit cell” as used herein refers to a piece of a pattern in a semiconductor which is repeated in the semiconductor.

[0229] The term “SiC” as used herein refers to silicon carbide which is a compound semiconductor and is a mixture of silicon and carbon with the chemical formula SiC. Silicon is covalently bonded with carbon. In 4H-SiC, 4H is written in the Ramsdell classification scheme here the number indicates the layer, and the letter indicates the Bravais lattice. That means in a 4H- SiC structure four hexagonal layers of SiC are present. SiC exists in a kind of polymorphic crystalline building known as a polytype, e.g., 3C-SiC, 4H-SiC, 6H-SiC. Presently 4H-SiC is used in power device manufacturing. [Source: A complete analytical potential based solution for a 4H- SiC MOSFET in nanoscale, M K Yadav, K P Pradhan and P K Sahu Published 24 May 2016 • © 2016 Vietnam Academy of Science & Technology]

[0230] The term “substrate” as used herein refers to the supporting material on or in which the components of an integrated circuit are fabricated or attached.

[0231] The term “JFET” as used herein refers to junction gate field-effect transistor which is a three-terminal semiconductor device that can be used as electronically controlled switches,amplifiers, or voltage-controlled resistors. A FET (field-effect transistor) is a unipolar transistor in which current carriers are injected at a source terminal and pass to a drain terminal through a channel of semiconductor material whose conductivity depends largely on an electric field applied to the semiconductor from a control electrode. There are two main types of FETs, a junction FET, and an insulated-gate FET. In the junction FET, the gate is isolated from the channel by a pn- junction. In an insulated-gate FET, the gate is isolated from the channel by an insulating layer so that the gate and channel form a capacitor with the insulating layer as the capacitor dielectric.

[0232] The term “MOSFET” as used herein refers to a metal oxide semiconductor field-effect transistor, which is a four-terminal device with source(S), gate (G), drain (D) and body (B) terminals. The body of the MOSFET is frequently connected to the source terminal making it a three-terminal device like field effect transistor.

[0233] The term “DMOSFET” as used herein refers to double-implantation metal oxide semiconductor field-effect transistor. A common physical structure of SiC MOSFETs is the planar double-implanted MOSFET in 4H-SiC (SiC-DMOSFET).

[0234] The term “dopant” as used herein refers to an impurity added from an external source to a material by diffusion, coating, or implanting into a substrate, such as changing the properties thereof. In semiconductor technology, an impurity may be added to a semiconductor to modify its electrical properties or to a material to produce a semiconductor having desired electrical properties. N-type (negative) dopants (e.g., such as phosphorus for a group IV semiconductor) typically come from group V of the periodic table. When added to a semiconductor, n-type dopants create a material that contains conduction electrons. P-type (positive) dopants (e.g., such as boron for a group IV semiconductor) typically come from group III and result in conduction holes (i.e., vacancies in the electron shells).

[0235] The term “drain” as used herein refers to the electrode of a field effect transistor which receives charge carriers which pass through the transistor channel from the source electrode.

[0236] The term “source” as used herein refers to the active region / el ectrode to which the source of charge carriers is connected in a field effect transistor,

[0237] The term “gate” as used herein refers to the control electrode or control region that exerts an effect on a semiconductor region directly associated therewith, such that the conductivity characteristic of the semiconductor region is altered in a temporary manner, often resulting in an on-off type switching action. The control electrode or control region of a field effect transistor is located between the source and drain electrodes, and regions thereof.

[0238] The term “impurity” as used herein refers to A foreign material present in a semiconductor crystal, such as boron or arsenic in silicon, which is added to the semiconductor to produce eitherp-type or n-type semiconductor material, or to otherwise result in material whose electrical characteristics depend on the impurity dopant atoms.

[0239] The term “PN junction” as used herein refers to the interface and region of transition between p-type and n-type semiconductors.

[0240] The term “polysilicon” as used herein refers to a polycrystalline form of silicon.

[0241] The term “P-type” as used herein refers to extrinsic semiconductor in which the hole density exceeds the conduction electron density.

[0242] The term “bandgap” as used herein refers to the difference between the energy levels of electrons bound to their nuclei (valence electrons) and the energy levels that allow electrons to migrate freely (conduction electrons). The band gap depends on the particular semiconductor involved.

[0243] The term “breakdown” as used herein refers to a sudden change from high dynamic electrical resistance to a very low dynamic resistance in a reverse biased semiconductor device (e.g., a reverse biased junction between p-type and n-type semiconductor materials) wherein reverse current increases rapidly for a small increase in reverse applied voltage, and the device behaves as if it had negative electrical resistance.

[0244] The term “channel” as used herein refers to a path for conducting current between a source and drain of a field effect transistor.

[0245] The term “chip” as used herein refers to a single crystal substrate of semiconductor material on which one or more active or passive solid-state electronic devices are formed. A chip may contain an integrated circuit. A chip is not normally ready for use until packaged and provided with external connectors.

[0246] The term “contact” as used herein refers to the point or part of a conductor which touches another electrical conductor or electrical component to carry electrical current to or from the conductor or electrical component.

[0247] The term “die” as used herein refers to a tiny piece of semiconductor material, separated from a semiconductor slice, on which one or more active electronic components are formed. Sometimes called a chip. N+ substrate.

[0248] The term “sinker” as used herein refers to deep implanted regions at key locations within the DMOSFET structure

[0249] The term “plug” as used herein refers to the structure used to ground the well and the source contact.

[0250] The term “drift layer” as used herein refers to lightly doped region to support the high voltage in power MOSFET

[0251] The term “well” used herein refers certain to regions in a metal-oxide-semiconductor (MOS) transistor. MOS transistors are always created in a “well” region. A PMOS (positivechannel MOS) transistor is made in an N-doped region, called “n-well” region. Similarly, an NMOS transistor (negative-channel MOS) is made in a “P-type” region called “p-well”. This ensures that the leakage between two transistors, through the bottom side, is low due to the reverse bias between the transistor areas and the well region.

[0252] The term “source interconnect metallization” as used herein refers to interconnection metallization that interconnects thousands of MOSFETs using fine-line metal patterns.

[0253] The term “self-aligned” used herein refers to processing steps in manufacturing of semiconductor devices. It is often necessary to achieve precise alignment between structures fabricated at different lithographic stages of integrated circuit fabrication. Stringent requirements on lithographic alignment tolerance can be relaxed if the structures are “self-aligned” which means one is forced into a specific position relative to the other for a wide range of lithographically defined positions.

[0254] The term “device” as used herein refers to the physical realization of an individual electrical element in a physically independent body which cannot be further divided without destroying its stated function.

[0255] The term “surface” as used herein refers to the outer or exterior boundary of a thing.

[0256] The term “trench” as used herein refers to electrical isolation of electronic components in a monolithic integrated circuit by the use of grooves or other indentations in the surface of the substrate, which may or may not be filled with electrically insulative (i.e., dielectric) material.

[0257] The term “dielectric” as used herein refers to a non-conductor of electricity, otherwise known as an insulator.

[0258] The term “mobility” as used herein refers to the facility with which carriers move through a semiconductor when subjected to an applied electric field. Electrons and holes typically have different mobilities in the same semiconductor.

[0259] The term “RIE” as used herein refers to reactive ion etching which is an etching technology used in microfabrication. RIE is a type of dry etching which has different characteristics than wet etching. RLE uses chemically reactive plasma to remove material deposited on wafers. The plasma is generated under low pressure (vacuum) by an electromagnetic field. High-energy ions from the plasma attack the wafer surface and react with it.

[0260] The term “ILD” as used herein refers to interlayer dielectric, a dielectric material used to electrically separate closely spaced interconnect lines arranged in several levels (multilevel metallization) in an advanced integrated circuit.

[0261] The term “CVD” as used herein refers to chemical vapor deposition is a method used to produce high quality, high-performance, solid materials, typically under vacuum. The process is often used in the semiconductor industry to produce thin films. In typical CVD, the wafer (substrate) is exposed to one or more volatile precursors, which react and / or decompose on the substrate surface to produce the desired deposit. Frequently, volatile by-products are also produced, which are removed by gas flow through the reaction chamber.

[0262] The term “PECVD” as used herein refers to plasma-enhanced chemical vapor deposition process used to deposit thin films from a gas state (vapor) to a solid state on a substrate. Chemical reactions are involved in the process, which occur after creation of a plasma of the reacting gases.

[0263] The term “LPCVD” as used herein refers to low pressure chemical vapor deposition technology that uses heat to initiate a reaction of a precursor gas on the solid substrate. This reaction at the surface is what forms the solid phase material.

[0264] The term “DIBL” as used herein refers to drain induced barrier lowering and is a shortchannel effect in MOSFETs referring originally to a reduction of threshold voltage of the transistor at higher drain voltages. In a classic planar field-effect transistor with a long channel, the bottleneck in channel formation occurs far enough from the drain contact that it is electrostatically shielded from the drain potential by the combination of the substrate and gate, and so classically the threshold voltage was independent of drain voltage. In short-channel devices this is no longer true: The drain potential can gate the channel, and so a high drain voltage can open the bottleneck and turn on the transistor prematurely.

[0265] The term “ICP” as used herein refers to inductively coupled plasma etching technology often used in specialty semiconductor markets for device manufacturing. This technology can combine both chemical reactions and ion-induced etching. The independent control of ion flux enables high process flexibility. ICP etching is based on the use of an inductively coupled plasma source. The ICP source generates a high-density plasma due to inductive coupling between the RF antenna and the plasma. The antenna, located in the plasma generation region, creates an alternating RF magnetic field, and induces RF electric fields, which energize electrons that participate in the ionization of gas molecules and atoms at low pressure. Due to the absence of an electric field near the reactor walls there is virtually no ion bombardment or erosion of the walls.

[0266] The term “p-shield” as used herein refers to a carefully designed p-type doped region strategically located close to or within the MOSFET channel region, with the objective of shielding the MOSFET channel from the high potential applied to the drain terminal during off-state or blocking operation.

[0267] The terms "first conductivity type region" and "second conductivity type region" as used herein, are used to describe n-type and p-type regions respectively for a N type device. For a Ptype device "first conductivity type region" and "second conductivity type region" are used to describe p-type and n-type regions respectively.

[0268] The term “I-V Characteristic Curves” used herein refers to Current- Voltage Characteristic Curves or simply I-V curves of an electrical device or component, refers to a set of graphical curves which are used to define its operation within an electrical circuit.

[0269] The term “MV / cm” as used herein refers to Megavolt per centimeter and refers to unit of electric field.

[0270] The term “avalanche failure” as used herein refers to a phenomenon that can occur in both insulating and semiconducting materials. It is a form of electric current multiplication that can allow very large currents within materials which are otherwise good insulators. It is a type of electron avalanche. The avalanche process occurs when carriers in the transition region are accelerated by the electric field to energies sufficient to create mobile or free electron-hole pairs via collisions with bound electrons. The voltage at which the breakdown occurs is called the breakdown voltage. Avalanche failure can cause structural damage to a semiconductor device.

[0271] The term “avalanche energy” as used herein is defined as the amount of energy the MOSFET can withstand when it is set into avalanche mode or its breakdown voltage is exceeded.

[0272] The term “topside” as used herein refers to the outer side / top of the DMOSFET. The topside of the vertical SiC DMOSFET may comprise a source terminal.

[0273] The term “bottom side” as used herein refers to the underside / base of the DMOSFET. The bottom side of the vertical SiC DMOSFET may comprise a drain terminal.

[0274] The term “front side” as used herein refers to a side of the DMOSFET which is visible in front.

[0275] The term “back side” as used herein refers to the rear side of the DMOSFET. The back side of the vertical SiC DMOSFET may comprise the drain terminal.

[0276] The term “plus” used herein refers to certain regions in a metal-oxide-semiconductor (MOS) transistor where doping concentration is excessive.

[0277] The term “active region” as used herein refers to a region of the DMOSFET where the current conduction happens.

[0278] The term “depletion region” as used herein refers to a region where flow of charged carriers decreases over a given time.

[0279] The term “thermal budget” as used herein refers to the total amount of thermal energy transferred to a wafer during the given elevated temperature operation.

[0280] The term “work function” as used herein refers to minimum quantity of energy required to remove an electron to infinity from the surface of a given metal.

[0281] As defined herein, two or more elements are "integral" if they are comprised of the same piece of material. As defined herein, two or more elements are "non-integral" if each is comprised of a different piece of material.

[0282] The term “trench sidewalls” as used herein refers to walls that form sides of the trench region.

[0283] The term “bottom portion” as used herein refers to the base of the trench region.

[0284] The term “crystal plane” as used herein refers to an imaginary plane inside a crystal of a semiconductor substrate in which large concentrations of atoms are present.

[0285] The term “MOS interface” as used herein refers to a region / path that electrically interconnects two regions.

[0286] The term “horizontal surface” as used herein refers to an unetched surface on topside of the semiconductor substrate.

[0287] The term “RF” as used herein refers to Radio frequency. Radio frequency is an oscillation rate of an alternating electric current or voltage or of a magnetic, electric, or electromagnetic field or mechanical system.

[0288] Embodiments relate to SiC DMOSFET power devices where the p-well regions effectively shield the sensitive gate oxide from the high electric fields present in SiC especially during high drain bias or blocking mode operation.

[0289] An embodiment relates to using a P+-plug to ground the p-well region with the N+ source contact.

[0290] An embodiment relates to making the lateral spacing between the p-well regions narrow enough to suppress the electric field in the gate oxide while ensuring the ON-resistance is not high.

[0291] An embodiment relates to replacing the P+ plug region of the DMOSFET with a deep P- type Sinker# 1 region.

[0292] Embodiments relate to formation of one or more deep implanted sinker regions at certain locations within the MOSFET device structure such as a first P-type sinker region at the center of the MOSFET unit cell whose depth may be equal to or greater than the depth of the p-well region.

[0293] Embodiment relates to forming a second P-type sinker region under the N+ source region, whose depth may be equal to or greater than the p-well region, but less than or equal to the depth of the first P-type sinker region.

[0294] Embodiment relates to boron implantation which may be advantageously used for forming the deep sinker regions since boron has a larger implant range than aluminum that can result in deeper implant profiles

[0295] Embodiment relates to the formation of a first trench with desired shape which may be etched in the N+ source region, prior to the formation of the first P-type sinker region, which mayserve to increase the depth of the first P-type sinker region. The depth of the first trench may range from 0.01 pm up to 2 pm. The depth of the resulting first sinker region may be 0% to 100% larger than the depth of the p-well region. The depth of the first P-type sinker region can be as large as the entire epitaxial layer.

[0296] Embodiment relating to the formation of the first trench in the N+ source region may reduce or eliminate the need for expensive ultra-high energy implantation steps for forming the first P-type sinker region.

[0297] Embodiment relating to the first trench may be advantageously used to remove the N+ source implant from the first P-type sinker region, which may be desirable to prevent compensation of the first P-type sinker region by the N+ source implant. This is especially useful if the N+ source region is self-aligned to the p-well region.

[0298] Embodiment relates to a gradually decreasing implant concentration which may be employed for forming the first and second P-type sinker regions in lieu of a box-shaped implant profile, as this may be advantageous in appropriately shaping the electric field under high drain bias. The doping in the P-type sinker regions may be varied linearly from a maximum value close to the SiC surface to a value equal to or slightly higher than the drift layer doping concentration at the other end of the P-type sinker regions.

[0299] Embodiment of a design of the first and second sinker regions may simplify the design of the p-well region, which can be designed to support metal-oxide-semiconductor (MOS) channel formation and may be advantageously designed for achieving low on-resistance, without compromising other performance metrics, such as reverse leakage current and electric field in gate oxide.

[0300] SiC devices in power electronics feature fast switching times, high blocking voltage capabilities, and the ability to operate at high temperatures. These characteristics, along with recent advancements in manufacturing processes, suggest that SiC has the potential to revolutionize power electronics as a successor to traditional silicon-based (Si) devices. SiC is a wide band gap material (3.3 eV) and has a higher breakdown electric field (3 x 106V / cm to 5 x 106V / cm) compared to Si (Si band gap is 1.1 eV and breakdown electric field for Si is 0.3 x 106V / cm). SiC is a better thermal conductor (3.7 (W / cm-K) for SiC versus 1.6 (W / cm-K) for Si) which enables SiC devices to operate at extremely high-power levels and still dissipate the large amounts of excess heat generated. These material properties of SiC offer multiple advantages of using SiC instead of Si on power devices. In a comparison of SiC and Si semiconductor die with identical structures and dimensions, the SiC die exhibits a lower specific ON resistance and a higher breakdown voltage than the Si die.

[0301] The disclosed embodiments herein provide novel techniques for SiC DMOSFET design and fabrication for shaping of the electric field over the device structure and reducing concentration of electric fields at singular points. The embodiments herein reduce the electric field in the gate oxide region to less than 3.5 MV / cm and improve the device reliability.

[0302] The manufacturing process in Si uses techniques like diffusion of dopants but these conventional manufacturing processes are not possible for making SiC device because the diffusion coefficients in SiC are negligible at temperatures below 1800 °C. SiC devices are manufactured by ion implantation of both source and p-well regions but ion implantation and especially deep ion implantation is difficult in SiC. In the embodiments herein, the ion implantation of source and p-well regions are made deep with novel techniques.

[0303] The increased reliability, higher operating temperature, increased efficiency, higher voltage capabilities of the SiC devices of the embodiments herein as compared to the silicon devices make them highly desirable in the electric vehicle and renewable energy industries. Traction inverters in electric vehicles are subjected to high thermal (> 150°C) and load cycling and renewable energy converters are subjected to extreme environmental conditions. The embodiments described herein for the SiC devices maximize power conversion efficiency to >98% for example while providing high reliability thus making it an ideal candidate for electric vehicles to minimize maintenance and downtime, which is expensive for the operators of the electric vehicles.

[0304] The disclosed embodiments change the way in which SiC power DMOSFET devices can effectively shield the sensitive gate oxide from the high electric fields present in 4H-SiC especially during high drain bias (blocking mode operation).

[0305] In embodiments herein, SiC power DMOSFET devices overcome the trade-off between achieving a low ON resistance and achieving a robust blocking performance, which implies a low electric field in the structure close to a gate oxide.

[0306] Embodiments herein include a unit cell of a SiC power DMOSFET comprising a vertical MOSFET. Certain regions of the SiC power DMOSFET device are a p-well region, which is formed by an implantation, an N+ source region, a N- drift layer, and an N+ substrate. In the embodiment herein, during the ON state the current flows vertically from the drain, through the inversion layer which is formed at the top of the p-well layer, when a gate voltage is applied to this device in through the N+ source region and out through the source metallization. In the OFF state or the blocking state, in the embodiments herein a voltage is supported across the p-well and N- drift layer junction. There is a PN junction which is formed between the p-well and the N drift layer. The voltage applied to the structure is supported across this PN junction in the reverse bias.

[0307] In the embodiments herein, a power MOSFET has several physical dimensions, including: the pitch of the unit cell, which is the repeat unit for the MOSFET; the channel length, which isthe portion of the p-well in which the inversion channels is formed; the distance between two successive p-wells, referred to as the junction gate field-effect transistor (JFET) region or the JFET gap; the thickness of the gate oxide; and an inter-layer dielectric (ILD) layer, which is used to insulate the source interconnect metallization from the poly-silicon gate.

[0308] In the embodiments herein, the advantage of using SiC over Si is that for similar chip sizes, SiC can support much higher power density. The amount of voltage one can support in SiC can be ten times more than in Si, and the current that the SiC chip can carry through the MOSFET can be 10 to 50 times more than in Si. SiC MOSFETs form a convenient switch, because one can achieve much higher power density. The performance advantage relates to the trade-off between voltage and current. Voltage blocking and current conduction capability, is about 200 times better in the case of SiC as compared to Si.

[0309] In the embodiment herein, the P+ plug, which is in the center of the SiC DMOSFET unit cell, is replaced by the PS#1 region. In the embodiment the PS#1 region extends below the p-well region. During the blocking condition, the electric field, or the main region where the breakdown can happen, is at the center of the unit cell of a SiC DMOSFET, which is basically between the PS#1 region and the N- drift layer. SiC structures tend to break down between the p-well and the N- drift layer, and especially at the curvature of the p-well region. In the embodiments herein, the structure will break down between the PS#1 region and the N- drift layer. Here the location of the breakdown has been moved towards the center of the unit cell which results in a lower electric field closer to the gate oxide region. There is a reduced electric field close to the gate oxide region in the embodiment due to PS#1 region, and this should make for a more robust device.

[0310] The embodiments herein have difference in structure, difference in the method of manufacturing, difference in the functionality of the devices, and difference in the results that the devices produce than the prior art SiC devices. Simulation data of the embodiments herein show the differences in performance and results of structures. In addition to the PS#1 region, the devices of the embodiments herein also have a PS#2 region, which is placed under the N+ source region. This improves the electric field profile in the embodiment in a way that during the blocking mode of operation, the voltage is shed across a larger area of the unit cell, which results in even more robust operation. In the embodiments herein, the PS#2 region could be deeper than the p-well region and could be made shallower than the PS#1 region. In the embodiment herein of all the P- type regions in the SiC DMOSFET structure, the deepest of them is the PS#1 region, the intermediate one is the PS#2 region, and the shallower one is the p-well region. The embodiments herein show more appropriate electric field shaping from these PS#1 and PS#2 structures.

[0311] In the embodiments herein, another advantage of including the PS#2 region is that the PS#2 serves as a secondary p-well region. The design of the p-well region needs to satisfy severaldifferent constraints. The electrical dose in the p-well region can be large enough such that the desired breakdown voltage is realized while at the same time, the doping of the p-well region near the gate oxide region where the MOS channel is formed, can be low enough such that a reasonably low threshold voltage is realized.

[0312] In the embodiment the p-well region could now satisfy conflicting requirements. By placing the PS#2 under the N+ source region, it relaxes the design of the p-well region, whose purpose now is solely for channel definition and channel formation. In embodiments herein, the p- well does not have to be designed with the objective of supporting the breakdown voltage. The embodiments herein give a lot more flexibility to the designer to design the p-well region suitably only for MOS channel formation.

[0313] In the embodiment herein, the PS#1 is formed after a trench is etched into the N+ source region which is in the middle of the unit cell of the SiC DMOSFET. The advantage of this trench is that it moves the electric field location farther away from the gate oxide interface and to the middle of the unit cell of the SiC DMOSFET. In the embodiment etching a recess trench into the N+ source region, effectively creates a deeper PS#1 region. The electric field moves even further away from the gate oxide region, which would make for more robust blocking capability. In the embodiments herein, one of the reasons for doing the trench is because ion implantation and particularly deep ion implantation in SiC is difficult. Deep PS#1 sinker region can be made because of source trench. In the embodiments herein etching a trench and then doing the ion implantation, allows to make a deeper PS#1 region, which is effective and achieves the functionality.

[0314] In the embodiments herein since the trench helps in making a deeper PS#1 due to the source trench allows to make a thinner oxide region by reducing the oxide. SiC DMOSFET needs a thicker oxide to prevent them from breaking down in a dielectric field. In the embodiments herein by introducing the P-type sinker regions, one can use thinner oxide.

[0315] In the embodiments herein, the SiC DMOSFET devices are made using a series of masking steps followed by either ion implantation or etching and a deposition step. In the embodiments herein, the unit cell is produced where a series of structures are made using photolithography that is used to mask certain portions of the wafer or certain portion of device, and implementing certain steps, and then removing that mask, and doing the other steps. To minimize the number of steps is of great importance to realize cost-effectiveness. That is, the cost structure is lower if one can somehow reduce the number of steps. Also, certain steps in manufacturing of SiC are expensive, and the embodiments herein minimize the number of those expensive steps. For example, ion implantation is a relatively expensive step in SiC. p-well, P-plug, and N+ source regions are made using ion implantation. Ion implantations are expensive steps, particularly deeper ion implantation is even more expensive. So, minimizing deep ion implantation is of importance.Further, P-type Implantation is 5 to 10 times more expensive than doing N-type Implantation, since P-type implantation needs to be performed at higher temperatures (400-1000°C) in contrast to N- type implants which can be performed at room-temperature. So, minimizing P-type implants is also of importance.

[0316] In the embodiments, herein the wafer goes through a series of ion implantation steps first, which is typically called the front end of the process, then there is a high temperature annealing, which is used to anneal out the implant damage and electrically activate the implants. The back end of the process typically consists of forming the gate oxide, ILD and other metallization steps.

[0317] In the embodiments herein to make the SiC DMOSFET structure, photolithography would be used to mask a certain part of the wafer to create a p-well region, following which, a next masking step could be used to realize an N+ source region, followed by another masking step would be used to realize the P+ plug region. The wafers would need to be annealed to activate the implanted regions. After this, a gate oxide or a gate dielectric can be grown by either thermal oxide or using a deposited oxide. A gate metallization can be formed using a polysilicon or other refractory metals. The gate metallization is then selectively patterned and etched to access the N+ source regions, following which the ILD is deposited and then patterned to realize the window for creating these ohmic contacts for the N+ source regions. The ohmic contact can be realized on the backside of the wafer, which is the drain, for the drain region. At the end of the process, a source interconnect metallization is used to connect the various unit cells.

[0318] SiC MOSFET is typically produced in several masking steps. Some of these masking steps could be for forming implanted regions, while other masking steps are for forming structures such as gate oxide, ILD etc. The embodiments herein are all done in 11 masking steps without increasing a masking step for any additional feature like PS#1, PS#2, source trench formations or other structures in the embodiments.

[0319] In SiC, ion implantation is a method to introduce dopants since diffusion does not work well. So, to realize the PS#1 region to be deeper than the p-well region, requires higher implantation energy. In the embodiments herein typically either aluminum or boron is used for realizing P-type regions in SiC. So, for realizing the PS#1 region and a deep PS#1 region, in the embodiments herein boron implantation is used in lieu of aluminum implantation, since for a given energy, the boron implantation can result in deeper regions as compared to aluminum implantation. Another way to realize a deep PS#1 region is to use a much higher energy and still use aluminum as the P-type dope.

[0320] In an embodiment herein, a p-well region is formed, following which, the N+ source region is formed. While forming the N+ source region, ion implantation is performed to realize the PS#2 region. The same masking step is used for forming the N+ source region and the PS#2 region.In the embodiment herein, this enables one to realize a PS#2 region exactly under the N+ source region.

[0321] In the embodiments herein, the N+ source implant is made self-aligned to the p-well implant, to reduce or even eliminate misalignment which could occur if the two regions are realized in different masking steps.

[0322] In the embodiment herein to realize sub 0.5-micron channel lengths or sub 1-micron channel lengths the first p-well region is formed using a traditional implantation masking step. A dielectric layer of a sufficient thickness is deposited, and then using photolithography, one would selectively pattern this layer, and then perform ion implantation, to realize the p-well region. Once this is done, a second dielectric layer is deposited on top of this patterned first dielectric layer, and then subjected to a blanket etch. This results in a dielectric spacer region which then defines the region which is subjected to the N+ source implant. So, by choosing an appropriate thickness of the second dielectric layer, one can define the MOS channel length.

[0323] In the embodiment herein to realize a channel which is 0.5-micron wide first create a p- well region using conventional photolithography technique, for example one may deposit and pattern silicon dioxide layer, then one may deposit a second silicon dioxide layer of a thickness equal to like 0.5-micron. When one etches this layer down, one would realize a spacer which would be 0.5-micron also. When one performs the N+ source implant, one would have effectively an MOS channel length of 0.5-micron.

[0324] In the embodiment, the channel length is formed not by the limitations of lithography techniques, but by the ability of depositing dielectric layers, for example silicon dioxide, where one has much better control. One can deposit dielectric or silicon dioxide layers with a resolution which is much better than what lithography can allow.

[0325] In one method called the subtractive method, the process first fabricates a N+ source, then deposits a dielectric layer, and then forms the P+ layer through the poly-silicon variation. The embodiments herein do the additive method, where first one does the p-well, and then deposits the dielectric of a controlled thickness, which will define the channel length, and then put the N+ source. So, the order of N+ and p-well is reversed in the embodiments herein when compared to how prior art SiC DMOSFET’s are formed.

[0326] The embodiments herein avoid implanting N+ source region in the gate region. In a SiC MOSFET structure there exists a parasitic NPN transistor, that can get triggered not during normal operation but when you're switching this device from OFF to ON or ON to OFF with extremely high speed.

[0327] In the embodiments herein, the trench into the N+ source region is formed prior to the implantation of the PS#1 region results in a deeper PS#1 region. But another benefit of doing thisis that one can also remove the N+ source regions from the portions of the device that do not want the N+ source region to be implanted. So, that is the secondary benefit of having a trench etched into the N+ source region. The same masking step is used for performing the SiC dry etch, and then implanting the PS#1 region. This is achieved with just one masking step. In an embodiment, the PS#2 region is formed along with the N+ source region with the same masking step. The SiC trench and the PS#1 region are again formed using the same masking step. In this embodiment, four features are made using two masking steps.

[0328] In the embodiments herein, the cost of PS#1 sinker is reduced, because one does not have to employ deep ion implantation. Deep ion implantation, which are high doses, is expensive. And on the periphery, having a deep P+ is also beneficial, to prevent breakdown regions that can be formed. In the embodiments herein, one is avoiding the breakdown region at the periphery because one is using a single step for creating PS#1 and the trench. When one forms the MOS channel in a self-aligned fashion, N+ source region is formed everywhere where one has a p-well region, which extends to even the periphery of the device. In the embodiments herein, one avoids the breakdown at the periphery due to formation of trench and PS#1.

[0329] An embodiment shown in Fig. 2A is the unit cell of a cross-sectional structure of a SiC DMOSFET. The key regions of this device are a p-well region 203, which is formed by ionimplantation or epitaxial re-growth of a p-type species such as aluminum or boron. There is an N+ source region 204, N- drift layer 202, and an N+ substrate 201. In the ON state when a gate voltage is applied to the polysilicon gate 206, the current flows vertically from the drain 201, through the inversion layer which is formed at the top of the p-well layer 203, through the N+ source region 204, and out through the source metallization 208. In the OFF state or the blocking state, a voltage is supported across the p-well 203, N- drift layer 202 junction and there is a PN junction which is formed between the p-well and the N- drift layer. The voltage applied to the structure is supported across this PN junction in the reverse bias. There are several key features in a power MOSFET, which include the pitch of the unit cell, which is the repeat unit for the MOSFET, the channel length, which is the portion of the p-well in which the inversion channel is formed, the distance between two successive p-wells, which is referred to as the JFET region or the JFET gap and the thickness of the gate oxide 205. Another feature is an ILD layer 207 which is used to insulate the source interconnect metallization 208 from the poly-silicon gate 206. At the very center of the unit cell, there is a P+ plug layer 209 which is grounded with the N+ source metallization. The purpose of the P+ plug in SiC DMOSFET is to ground the p-well region with the N+ source contact. Typically, the depth of the P+ plug implant is made shallower than the p-well region as shown in Fig. 2A. The DMOSFET device structure can result in high electric field concentration at the comer of the p-well region 203, which results in a high electric field in the gate oxide layer 205, especiallyduring high drain bias (blocking mode) operation. The high critical electric fields for breakdown in 4H-SiC (~ 3 MV / cm) results in a very high (> 5 MV / cm) electric field in the gate oxide. Fowler- Nordheim tunneling currents are observed at such high electric fields in the gate oxide, which can result in trapped charge in the gate oxide, which leads to poor device reliability. In the embodiment herein, the lateral spacing between p-well regions (JFET region) is made narrow enough to suppress the electric field in the gate oxide while making sure that the MOSFET ON-resistance is low enough.

[0330] Fig. 2B is the breakdown simulation of a SiC MOSFET shown in Fig. 2A. The simulation shows the peak electric field located at the comer of the p-well region, which results in a certain high electric field in the gate oxide layer. The electric field is strongly concentrated at the corner of the p-well region because that is the region of maximum curvature, (this embodiment has limitation)

[0331] An embodiment shown in Fig. 3 is the cross-sectional unit cell of a SiC DMOSFET. The key regions of this device are a p-well region 303, which is formed by ion- implantation or epitaxial re-growth of a p-type species such as aluminum or boron. There is an N+ source region 304, N- drift layer 302, and an N+ substrate 301. In the ON state when a gate voltage is applied to the polysilicon gate 306, the current flows vertically from the drain 301, through the inversion layer which is formed at the top of the p-well layer 303, through the N+ source region 304, and out through the source metallization 308. There are several key features in a power MOSFET, which include the pitch of the unit cell, which is the repeat unit for the MOSFET, the channel length, which is the portion of the p-well in which the inversion channel is formed, the distance between two successive p-wells, which is referred to as the JFET region or the JFET gap and the thickness of the gate oxide 305. Another feature is an ILD layer 307 which is used to insulate the source interconnect metallization 308 from the poly-silicon gate 306. Here the P+ plug region 209 of the SiC DMOSFET from Fig. 2A is replaced with a deep P-type Sinker #1 (PS#1) region 309. The depth of the PS#1 region, is greater than the depth of the p-well region. During the OFF state or the blocking condition, the structure shown in Fig. 2A, will break down between the p-well 203 and the N- drift layer 202 especially at the curvature of the p-well region. But with the PS#1 region 309 being introduced in Fig. 3 the electric field or the main region where the breakdown will happen, is now at the very center of the drawing, which is basically between the PS#1 region 309 and the N- drift layer 302. The presence of the deeper PS#1 region results in moving the peak electric field location from the corner of the p-well region 303 to the PS#1 region 309. The location of the peak electric field in 4H-SiC during high drain bias operation has been moved farther away from the gate oxide 305. The electric field in the gate oxide 305 is now lower than that of Fig. 2A device.

[0332] Fig. 4A to Fig. 4R describes the process of manufacturing the structure shown in Fig. 3. The manufacturing process for a SiC DMOSFET is on a SiC substrate 401 and starts with using a 4H-SiC Si-face epi-wafer with suitable doping (1014- 1018cm'3) and thickness (1 pm to 300 pm) for the epilayer 402 shown in Fig. 4A. A blanket hard mask 403 (comprising a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm) is deposited in Fig. 4B and then patterned using photolithography followed by a dry etch (using a reactive ion-etch for example) as shown in Fig. 4C. A P-type implantation 404 (comprising boron or aluminum, at energies ranging from 10 keV to 800 keV, at implant doses ranging from 1012cm'2to 1015cm'2) in Fig. 4D is performed to create a p-well 405 in Fig. 4E. The mask 403 is removed, and another hard mask layer 406 is deposited (comprising a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm) and patterned in Fig. 4F to define the N+ source region. Notice that the center of the unit cell is masked for source (SRC) implantation. The SRC (N+ source region) 407 is formed by implantation of the n-type (N+) impurity 408 (comprising nitrogen or phosphorus, at energies ranging from 10 keV to 500 keV, at implant doses ranging from 1013cm'2to 1016cm'2) as shown in Fig. 4G. After removing the hard mask 406 another hard mask layer 409 is deposited and patterned in Fig. 4H. The PS#1 region 411 is formed by implantation of the p-type impurity 410 in Fig. 4H. The deep PS#1 region can be formed using ion-implantation of aluminum or boron, which are commonly used p-type dopants in 4H-SiC. Boron can be advantageously used for forming this deep P-type Sinker region, since it has significantly higher implant range as compared to aluminum, and deep implants using boron can be formed with lower ion-implantation energies. In one example, the PS#1 region can be formed with boron implantation with a 20-50% higher depth as compared to the p-well region. The boron implant may comprise of energies ranging from 10 keV to 800 keV, at implant doses ranging from 1012cm'2to 1015cm'2. In a related embodiment of this invention, the doping profile of the PS#1 region can be formed with gradually decreasing doping concentration with a peak value at the SiC surface. This graded doping profile for the PS#1 region can prevent the formation of sharp corners in the 3-Dimensional landscape and is beneficial for spreading the peak electric field during high drain bias operation over a larger area which results in a higher breakdown voltage. In one example, the PS#1 region can be formed with a peak doping in the range of 1019cm'3to IO20cm'3close to the SiC surface, which linearly decreases as a function of depth into the silicon carbide to the background N-drift layer doping (in the range of 1014-1016cm'3). A linearly graded doping profile of the PS#1 region results in a sufficient portion of the drain potential being supported within the PS#1 region and not only the N- drift region. This results in a pseudo charge-balanced structure, which promotes breakdown over a larger SiC region, which results in a lower criticalelectric field at breakdown and consequently a lower electric field in the gate insulator. This is followed by the removal of the hard mask 409 (using either dry or wet etching techniques commonly practiced by those in the field) in Fig. 41. Then the oxide layer 412 which is the gate oxide is either thermally grown or deposited using chemical vapor deposition (CVD) in Fig. 4J. The thickness of the gate oxide could range from 10 nm to 100 nm. Either dry or wet thermal oxidation could be used for oxide growth. Plasma-enhanced CVD (PECVD) or low-pressure CVD (LPCVD) could be used for gate oxide deposition. A polysilicon gate layer is then deposited on the top 413 in Fig. 4K. The polysilicon layer may be deposited using PECVD or LPCVD. The polysilicon layer may be degenerately doped using boron or phosphorus, either in-situ or in a subsequent step. In-situ doping may be performed by the addition of PH3 precursor to the polysilicon deposition chemistry. Post-deposition doping of polysilicon may be performed by depositing a layer of POCh followed by a drive-in step at temperatures ranging from 700-900°C. A hard mask 414 is deposited on top and patterned as shown in Fig. 4L. The polysilicon gate layer 413 is etched by using the patterned mask layer 414 in Fig. 4M. The mask layer 414 is then removed from the top in Fig. 4N. An interlayer dielectric (ILD) layer 415 (comprising 50 nm - 1000 nm thick silicon dioxide, silicon nitride, silicon oxynitride layers or a stacked combination thereof) is deposited on the wafer; a hard mask 416 is deposited and patterned on top to define the ILD opening; the ILD layer is patterned using the hard mask 416 as shown in Fig. 40. Further the gate oxide is etched using the same mask 416 in Fig. 4P. The mask 416 is then removed and a nickel silicide region 417 is formed on the exposed SiC surface in Fig. 4Q. Interconnect metal layers 418 (either Al or Ag or Au) is deposited and patterned on the top and bottom of the chip in Fig. 4R.

[0333] The main problem in the prior art device in Fig. lAas recognized by the authors of this invention is that the p-well regions do not effectively shield the sensitive gate oxide from the high electric fields present in 4H-SiC especially during high drain bias (blocking mode operation). The presence of the deeper PS#1 region results in moving the peak electric field location from the comer of the p-well region to the PS#1 region. In other words, the location of the peak electric field in 4H-SiC during high drain bias operation has been moved farther away from the gate oxide.

[0334] The advantage of this embodiment is that the breakdown location has been moved from the corner of the p-well region to the base of the newly formed PS#1 region, which is both farther away from the gate oxide interface and deeper into the semiconductor. The electric field in the gate oxide for the device structure incorporating the PS#1 region is now significantly lower than the prior art device which is shown using device simulation using SILVACO ATLAS in Fig. 5B.

[0335] An embodiment shown in Fig. 5A is the cross-sectional unit cell of a vertical power DMOSFET. The key regions of this device are a p-well region 503, which is formed by ion-implantation or epitaxial re-growth of a p-type species such as aluminum or boron. There is an N+ source region 504, N- drift layer 502, and an N+ substrate 501. In the ON state when a gate voltage is applied to the polysilicon gate 506, the current flows vertically from the drain 501, through the inversion layer which is formed at the top of the p-well layer 503, through the N+ source region 504, and out through the source metallization 508. There are several key features in a power MOSFET, which include the pitch of the unit cell, which is the repeat unit for the MOSFET, the channel length, which is the portion of the p-well in which the inversion channel is formed, the distance between two successive p-wells, which is referred to as the JFET region or the JFET gap and the thickness of the gate oxide 505. Another feature is an ILD layer 507 which is used to insulate the source interconnect metallization 508 from the poly-silicon gate 506. Here a second P-type Sinker #2 (PS#2) region 510 under the N+ source region 504 is formed in addition to the PS#1 region 509 already described in an embodiment shown in Fig. 3. The PS#2 region is formed deeper than the p-well region 503 but shallower than the PS#1 region 509. For example, the PS#2 region 510 can be made 20% deeper than the p-well region 503, while the PS#1 region 509 can be made 20% deeper than the PS#2 region 510.

[0336] The presence of the PS#2 region results in a sharing of the peak electric field under high drain bias operation between the PS#1 and PS#2 regions. The presence of the PS#2 region alleviates a local maximum of the peak electric field in the device structure under high drain bias conditions. In the prior art SiC MOSFET shown in Fig. 1 A, the design of the p-well region needs to satisfy conflicting requirements. The electrical dose in the p-well region under the N+ source region must be high enough to prevent reach-through breakdown under off-state (high drain bias) operation. But, at the same time, the surface doping of the p-well region must be low enough to maintain a reasonably low gate threshold voltage and device ON resistance. In this context, the PS#2 region introduced in this embodiment can be thought of as a secondary p-well region and can be designed with the main purpose of preventing reach-through breakdown and for appropriately shaping the electric field profile under high drain bias operation. The presence of the PS#2 region frees up the constraint in the design of the primary p-well region, which can be used for ON-state related device metrics such as gate threshold voltage and ON resistance. Since with the introduction of the PS#2 region, p-well region does not have to be designed with the objective of supporting the breakdown voltage it gives a lot more flexibility to the designer to design the p-well region suitably for just MOS channel formation.

[0337] Breakdown simulation Fig. 5B of a SiC DMOSFET designed according to the two embodiments described in Fig. 3 and Fig. 5A shows that the peak electric field location has been moved away from the comer of the p-well region to the center of the unit cell, which results in a lower electric field in the gate oxide layer.

[0338] Fig. 6A to Fig. 6J describes the process of manufacturing the structure shown in Fig. 5a. The manufacturing process for a SiC DMOSFET is on a SiC substrate 601 and starts with using a 4H-SiC Si-face epi-wafer with suitable doping (1014- 1018cm'3) and thickness (1 pm to 300 pm) for the epilayer 602 shown in Fig. 6A. A blanket hard mask 603 (comprising a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm) is deposited in Fig. 6B and then patterned using photolithography followed by a dry etch (using a reactive ion-etch for example) as shown in Fig. 6C. A P-type implantation 604 (comprising Boron or Aluminum, at energies ranging from 10 keV to 800 keV, at implant doses ranging from 1012cm'2to 1015cm'2) is performed in Fig. 6D to create a p-well 605 in Fig. 6E. The mask 603 is removed, and another hard mask layer 606 is deposited (comprising a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm) and patterned in Fig. 6F to define the N+ source region. Notice that the center of the unit cell is masked for source (SRC) implantation. The SRC (N+ source region) 607 is formed by implantation of the n-type (N+) impurity 608 (comprising nitrogen or phosphorus, at energies ranging from 10 keV to 500 keV, at implant doses ranging from 1013cm'2to 1016cm'2) as shown in Fig. 6G. The PS#2 region 609 is formed by implantation of the P type impurity 610 as shown in Fig. 6H. The deep PS#2 region can be formed using ion-implantation of aluminum or boron, which are commonly used p-type dopants in 4H-SiC. Boron can be advantageously used for forming this deep P-type Sinker region, since it has significantly higher implant range as compared to aluminum, and deep implants using boron can be formed with lower ion-implantation energies. If using aluminum, the PS#2 region may comprise implant energies ranging from 100 keV to 1 MeV and implant dose ranging from 1013cm'2to 1016cm'2. If using boron, the PS#2 region may comprise implant energies ranging from 50 keV to 800 keV and implant dose ranging from 1013cm'2to 1016cm'2. The same hard mask 606 utilized for forming the N+ source region is utilized for defining the ion-implanted PS#2 region. In this case, the PS#2 region is self-aligned under the N+ source region. The hard mask 606 is removed and another hard mask layer 612 is deposited and patterned in Fig. 61. The PS#1 region 611 is formed by implantation of the P-type impurity 613 that may comprise aluminum or boron. Boron can be advantageously used for forming the PS#1 region, since it has significantly higher implant range as compared to aluminum, and deep implants using boron can be formed with lower ion-implantation energies. If using aluminum, the PS#1 region may comprise implant energies ranging from 100 keV to 1 MeV and implant dose ranging from 1013cm'2to 1016cm'2. If using boron, the PS#1 region may comprise implant energies ranging from 50 keV to 800 keV and implant dose ranging from 1013cm'2to 1016cm'2. PS#2 region can be formed with a depth higher than that of the p-well region but lower than that of the PS#1 region. As a second example of thisembodiment, the PS#2 region can be made 20% deeper than the p-well region, while the PS#1 region can be made 20% deeper than the PS#2 region. In a related embodiment of this invention, the doping profile of the PS#1 and PS#2 regions can be formed with gradually decreasing doping concentration with a peak value at the SiC surface. This graded doping profile for the PS#1 and PS#2 regions can prevent the formation of sharp corners in the 3-Dimensional landscape and is beneficial for spreading the peak electric field during high drain bias operation over a larger area which results in a higher breakdown voltage. As examples, the PS#1 and PS#2 regions can be formed with a peak doping in the range of 1019cm'3to IO20cm'3close to the SiC surface and close to the N+ Source region, respectively. The doping concentration in the PS#1 and PS#2 regions may linearly decrease as a function of depth into the silicon carbide to the background N-drift layer doping (in the range of 1014- 1016cm'3). A linearly graded doping profile of the PS#1 / PS#2 regions results in a sufficient portion of the drain potential being supported within the PS#1 / PS#2 regions and not only the N- drift region. This results in a pseudo charge-balanced structure, which promotes breakdown over a larger SiC region, which results in a lower critical electric field at breakdown and consequently a lower electric field in the gate insulator. The formation of the PS#1 region is followed by the removal of the hard mask 612 (dry or wet etch) in Fig. 6J. The remaining steps in the process to create the structure shown in Fig. 5A exactly follows the same steps shown in Fig. 4J to Fig. 4R.

[0339] This “staircase” arrangement of the PS#1 and PS#2 regions with certain depths can result in an even lower electric field in the gate oxide under high drain bias operation. Yet another benefit of the PS#2 region is that the p-well region can be made shallower and with a lower implant dose, which can reduce the device ON-resistance while simultaneously increasing the gate threshold voltage, both of which are desirable from an applications standpoint. Thus, a better trade-off between the off-state and on-state performance is enabled by the teachings of this invention.

[0340] An embodiment shown in Fig. 7A is the cross-sectional unit cell of a SiC DMOSFET. The key regions of this device are a p-well region 703, which is formed by ion- implantation or epitaxial re-growth of a p-type species such as aluminum or boron. There is an N+ source region 704, N- drift layer 702, and an N+ substrate 701. In the ON state when a gate voltage is applied to the polysilicon gate 706, the current flows vertically from the drain 701, through the inversion layer which is formed at the top of the p-well layer 703, through the N+ source region 704, and out through the source metallization 708. There are several key features in a power MOSFET, which include the pitch of the unit cell, which is the repeat unit for the MOSFET, the channel length, which is the portion of the p-well in which the inversion channel is formed, the distance between two successive p-wells, which is referred to as the JFET region or the JFET gap and the thickness of the gate oxide 705. Another feature is an inter-layer dielectric (ILD) layer 707 which is used toinsulate the source interconnect metallization 708 from the poly-silicon gate 706. Here a trench 711 is etched into the N+ source region 704 before implanting the PS#1 region 709. Here PS#2 region 710 under the N+ source region 704 is formed in addition to the PS#1 region 709. The PS#2 region is formed deeper than the p-well region 703 but shallower than the PS#1 region 709. It is desirable to move the electric field location as far away from the gate oxide interface for robust blocking capability of the device operation which improves the device reliability. Moving the breakdown location to the middle of the unit cell which is furthest away from the gate oxide 705 is an embodiment and by etching a recess trench 711 into the N+ source region 704, you have effectively created a deeper PS#1 region than what was in Fig. 3 and Fig. 5 A and moved the electric field even further away from the gate oxide region.

[0341] The PS#1 region is designed with the greatest depth among the P-type Sinker regions. While boron implantation is one technique to create such deep P-type regions in SiC technology, when you consider the maximum range of commercial ion-implanters available it becomes clear that ion implantation in SiC is not an easy process and deep ion implantation is particularly difficult. The function of the N+ source region which is also referred to as source trench is that the PS#1 region can be realized with lower ion-implantation energies, which lowers the cost and time of this implantation step, without any compromise in implantation depth. In the embodiment herein, a trench can be dry etched into SiC after the implantation of the N+ source region but before the implantation of the PS#1 region. The same hard mask layer used for the PS#1 implant can be used for etching the source trench into the SiC. In this embodiment herein, the hard mask layer is first patterned, followed by dry etching the trench into SiC, which is immediately followed by ionimplantation of the PS#1 region. The formation of the source trench naturally extends the depth of the PS#1 region. Hence, the PS#1 region can be realized with lower ion-implantation energies, which lowers the cost / time of this implantation step, without any compromise in implant depth. The formation of the source trench also removes the N+ source region and enables a direct connection of the P-well region with the N+ source ohmic contact thereby grounding the p-well and shorting the P-well region with the N+ source region.

[0342] Fig. 7B is the breakdown simulation of a SiC MOSFET designed according to Embodiment shown in Fig. 7A which shows that the peak electric field location has been moved away from the comer of the p-well region to the center of the unit cell, which results in a lower electric field in the gate oxide layer.

[0343] Fig. 8A to Fig. 8BB describes the process of manufacturing the SiC DMOSFET structure shown in Fig. 7A. The manufacturing process for a SiC DMOSFET is on a SiC substrate 801 and starts with using a 4H-SiC Si-face epi-wafer with suitable doping (1014- 1018cm'3) and thickness (1 pm to 300 pm) for the epilayer 802 shown in Fig. 8A. A blanket hard mask 803 (comprising aCVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm) is deposited in Fig. 8B and then patterned using photolithography followed by a dry etch (using a reactive ion-etch for example) as shown in Fig. 8C. A P-type implantation 804 (comprising boron or aluminum, at energies ranging from 10 keV to 800 keV, at implant doses ranging from 1012cm'2to 1015cm'2) in Fig. 8D is performed to create a p-well 805 in Fig. 8E. The mask 803 is removed, and another hard mask layer 806 is deposited (comprising a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm) and patterned in Fig. 8F to define the N+ source region. The N+ source region 807 is formed by implantation of the n-type (N+) impurity 808 (comprising Nitrogen or Phosphorus, at energies ranging from 10 keV to 500 keV, at implant doses ranging from 1013cm'2to 1016cm'2) as shown in Fig. 8G. The PS#2 region 809 is formed by the implantation of the P-type impurity 810 in Fig. 8H. The deep PS#2 region can be formed using ion-implantation of aluminum or boron, which are commonly used p- type dopants in 4H-SiC. Boron can be advantageously used for forming this deep P-type Sinker region, since it has significantly higher implant range as compared to aluminum, and deep implants using boron can be formed with lower ion-implantation energies. The patterned hard mask 806 is removed from the top in Fig. 81. Another hard mask layer 811 is formed on the top in Fig. 8 J and patterned in Fig. 8K. The patterned mask 811 is used to etch 812 into the substrate in Fig. 8L for creating a recessed region. The source trench which is the recessed region 813 is formed in the substrate by penetrating the source region in Fig. 8M. A P-type implant 814 in Fig. 8N is performed for creating the PS#1 region. If using aluminum, the PS#1 region may comprise implant energies ranging from 100 keV to 1 MeV and implant dose ranging from 1013cm'2to 1016cm'2. If using boron, the PS#1 region may comprise implant energies ranging from 50 keV to 800 keV and implant dose ranging from 1013cm'2to 1016cm'2. The PS#1 815 is formed by the self-aligned implantation of the p-type impurity in Fig. 80. As described more completely in the above embodiments, a linearly graded doping profile of the PS#1 / PS#2 regions may be preferable utilized in lieu of a uniform (abrupt) doping profile, which results in a sufficient portion of the drain potential being supported within the PS#1 / PS#2 regions and not only the N- drift region. This results in a pseudo charge-balanced structure, which promotes breakdown over a larger SiC region, which results in a lower critical electric field at breakdown and consequently a lower electric field in the gate insulator.

[0344] PS#1 region is designed with the greatest depth among the P-type Sinker regions using Boron implantation and the formation of the trench naturally extends the depth of the PS#1 region. The same hard mask used for etching the source trench 811 is utilized to define the PS#1 region. As will be apparent to those in the field of this invention, the SiC trench can be formed using dryetching techniques including reactive ion-etching, inductively coupled plasma (ICP)-RIE, etc. While a 90° sidewall slope is shown for this trench region in Fig. 7A, it is advantageous to form the trench regions with lower angle (60-90°) sidewalls, since this will reduce the curvature of the PS#1 region, and therefore improve the blocking performance of the device.

[0345] The patterned hard mask 811 is removed from the top in Fig. 8P. An oxide layer 816 for gate oxide is grown in Fig. 8Q. A polysilicon gate layer is deposited on the top 817 in Fig. 8R. The polysilicon layer may be deposited using PECVD or LPCVD. The polysilicon layer may be degenerately doped using boron or phosphorus, either in-situ or in a subsequent step. In-situ doping may be performed by the addition of PH3 precursor to the polysilicon deposition chemistry. Postdeposition doping of polysilicon may be performed by depositing a layer of POCh followed by a drive-in step at temperatures ranging from 700-900°C. A hard mask 818 is deposited on top and patterned as shown in Fig. 8S. The polysilicon gate layer 817 is etched by using the patterned mask layer 818 in Fig. 8T. The mask layer 818 is then removed from the top in Fig. 8U. An interlayer dielectric (ILD) layer 819 (comprising 50 nm - 1000 nm thick silicon dioxide, silicon nitride, silicon oxynitride layers or a stacked combination thereof) is deposited on the wafer in Fig. 8V. A hard mask 820 is deposited and patterned on top to define the ILD opening in Fig. 8W. The ILD layer is patterned using the hard mask 820 as shown in Fig. 8X. Further the gate oxide 816 is etched using the same mask 820 in Fig. 8Y. The mask 820 is then removed in Fig. 8Z. A nickel silicide region 821 is formed on the exposed SiC surface in Fig. 8AA. Interconnect metal layers 822 (either Al or Ag or Au) are deposited and patterned on the top and bottom of the chip in Fig. 8BB.

[0346] The advantage of the embodiment herein is that by etching the source trench region, prior to the implantation of the PS#1 region, the breakdown location has been moved further into the semiconductor and farther away from the gate oxide layer. Due to the inherent hardness of silicon carbide, the observed range (depth) of ion-implanted dopants is significantly lower than in silicon. For example, forming deep (> 0.3 pm) ion-implanted layers in silicon carbide requires extremely high implantation energies (> 300 keV), which requires doubly or triply ionized implantation species, which drastically reduces the throughput and increase the cost of these ion-implantation steps. Forming the source trench as described in this embodiment obviates the need for doubly / triply ionized implantation steps, and low-cost with high-throughput singly ionized implantation can be utilized for realizing the PS#1 region.

[0347] Embodiments relate to SiC DMOSFET power devices that can be used for fabricating self-aligned power MOSFETs.

[0348] An embodiment relates to increasing MOS channel density.

[0349] An embodiment relates to increasing effective field-effect mobility.

[0350] An embodiment relates to improved device reliability.

[0351] An embodiment relates to reducing ON resistance for a given chip size.

[0352] An embodiment relates to design and manufacturing of self-aligned power devices.

[0353] An embodiment relates to design and manufacturing MOS channels with sub-micron channel lengths.

[0354] An embodiment relates to removal of the parasitic N+ source region inadvertently formed in the periphery of the device.

[0355] An embodiment relates to proper grounding of the p-well region with the source ohmic contact in the active region of the device

[0356] An embodiment relates to removal of the parasitic NPN transistor formed in active and peripheral regions of self-aligned power devices.

[0357] An embodiment relates to a combination of an appropriately located source trench and ion-implanted P+ plug region to enable proper grounding of the p-well region in the main active MOSFET region and removal of a parasitic N+ source region formed in the periphery of the MOSFET

[0358] An embodiment relates to the formation of highly doped P+ plug regions in the periphery of the MOSFET, especially under the gate pad and gate bus regions.

[0359] An embodiment relates to the suppression of false turn-on of the MOSFET during fast switching transitions, at vulnerable locations, due to threshold voltage lowering by the body bias effect.

[0360] An embodiment relates to the improvement of the maximum dV / dt rating of the MOSFET.

[0361] An embodiment relates to the improvement of the maximum avalanche energy rating of the MOSFET.

[0362] An embodiment relates to a dedicated process step being utilized for masking the implantation of the N+ source region in the device periphery. The P+ plug region is formed first in this embodiment, while the source trench is created later on in the process at the ILD etch step.

[0363] An embodiment relates to a dedicated hard mask applied after the sidewall spacer is formed and before the N+ source implantation. This layer prevents the formation of the N+ source region in the device periphery and hence parasitic NPN structures in the device periphery are avoided.

[0364] An embodiment relates to a p-well region (P-Well#2) placed under the N+ source region and electrically connected to the main p-well region. The P-Well#2 provides additional electrical dose under the N+ source implant, to prevent reach-through breakdown, especially after the source trench formation.

[0365] An embodiment relates to a dedicated process step is utilized for masking the implantation of the N+ source region in the device periphery as well as the N+ source region in the middle of the unit cell in the active region to enable ohmic contact to the p-well region.

[0366] An embodiment relates to the formation of the segmented polysilicon gate metallization in the periphery of the device instead of a contiguous gate bus which will decrease the gate-body capacitance of the MOSFET.

[0367] An embodiment relates to the decrease of the gate capacitance of the MOSFET.

[0368] An embodiment relates to the increase of the switching speed of the MOSFET.

[0369] The embodiments described herein show novel techniques for design and manufacture of self-aligned SiC DMOSFET power devices. Due to limited mobility achievable on SiC planar DMOSFET it is necessary to form n-well channels that are submicron length, so that the overall power and ON resistance of the MOSFET are not degraded.

[0370] In a MOSFET, the channel region is formed due to the offset between the p-well and the N+ source region. If the p-well and the N+ source regions are formed by two separate masking steps, there can be lithographic misalignment, which will result in asymmetric MOSFET channel lengths on the two sides of a unit cell. In the embodiments described herein, to minimize this asymmetry in the MOS channel length, the p-well and the N+ source implant are done in a selfaligned fashion. There are several techniques proposed in the literature for achieving self-aligned MOSFET, including ones that use an oxide spacer approach to form a self-aligned p-well and N+ source regions, with the N+ source implant under p-well implant.

[0371] The embodiments herein describe several innovative techniques during self-aligned channel formation that not only allow for the elimination of the misalignment error during manufacturing of SiC MOSFETs, but also allow the possibility of reducing the channel length. The channel lengths can be made smaller with narrow spacers. While the self-aligning process does provide the benefits of making an arbitrarily short channel length as well as eliminating misalignment, it does create some other problems with respect to the structure of the device outside the unit cells, because n+ regions are co-incident with the p-well regions.

[0372] In a conventional MOSFET where the p-well and the N+ source regions are not selfaligned there is a dedicated masking step that will be used for forming the N+ source implant. In the embodiments described herein, in a self-aligned process, there is no dedicated masking step performing the N+ source implant. There is a dedicated masking step performing the p-well implant and followed by depositing the spacer, then etching the spacer followed by implantation for realizing the N+ source region. Everywhere there is a p-well region, there will be N+ source implant as well. It is not desirable to have N+ source implant at the periphery of the device. It is important to terminate the device with just the p-type implant. The various embodiments describedherein introduce techniques in which one can get rid of the N+ source implants in the periphery of the device and replace it with some other regions.

[0373] The active region of the MOSFET is where the current conduction happens while the periphery region of the MOSFET is where the edge termination of the device is provided to block any voltage. The gate pad and gate bus regions are also considered to be part of the peripheral regions of the MOSFET, for the purposes of describing the innovations in this document. In an embodiment described herein, a combination of an appropriately located source trench and ion- implanted P+ plug region enables proper grounding of the p-well region in the main active MOSFET region and removal of a parasitic N+ source region formed in the periphery of the MOSFET.

[0374] In a conventional MOSFET where there is no self-alignment, one can put the source implant wherever needed and then create a region for grounding the p-well. In a self-aligned DMOSFET since the source implant is self-aligned to the p-well, one would have not only the p- well extending all the way to the periphery but also have the N+ source region extends all the way to the periphery.

[0375] A parasitic NPN transistor exists in the active region of the MOSFET unit cell, formed by the N+ source region which acts like the N+ emitter, the p-well region which forms the P-base and the N+ source ohmic contact. In the periphery of the device and also under the gate pad metallization, there is no N+ source ohmic contact, and as a result, the emitter, and base regions of the parasitic NPN transistor are not shorted in this region. The parasitic NPN transistor will not be activated under normal DC or switching operation of the MOSFET, but operating the device under extreme conditions can cause the triggering of the parasitic NPN transistor.

[0376] In the active region, by creating the source trench one has shorted the emitter and the base of this parasitic NPN transistor and ensured that in the active region of the device, this parasitic transistor will not turn ON. In the periphery of the device without a source trench, the parasitic NPN transistor exists even though it is shorted in the active region. It is possible that the parasitic NPN transistor may turn on in the peripheral region and it is not desirable.

[0377] In the embodiment herein, by creating a source trench in the periphery of the device and by providing a p-type implanted plug region, it is ensured that the parasitic NPN transistor is completely removed. Since the emitter of this transistor has been completely removed there is no chance for any kind of parasitic BJT structure. Typically, a separate masking step is carried out for masking the N+ source region from being formed at these locations, but in the embodiment herein, the source trench can be advantageously used for removing the parasitic N+ source regions and replacing them with a P+ plug region, which is self-aligned with the source trench and electrically connected to the p-well region.

[0378] The doping concentration of the P+ plug region to be placed in the device periphery can advantageously be made very high. In doing so, another parasitic device effect described here can be avoided. In a typical power MOSFET device structure, moderately doped P-well regions exist in the device periphery with or without a parasitic N+ Source region, as described above. If the N+ Source region is co-incident with the p-well region in the device periphery (i.e., the n+ source region is not deliberately masked from the peripheral region), this results in a partial compensation of the p-type electrical dose of the p-well region. In either case, the p-well regions in the device periphery can be extremely resistive from an electrical standpoint. During switching of the power MOSFET from off- to on-state or vice-versa, the extremely high rate of change of drain voltage (or dV / dt) can result in capacitive current flow through this resistive peripheral p-well regions, which are only collected by the Source ohmic contact in the active region of the MOSFET. In other words, the capacitive current caused by the high dV / dt during device switching has to traverse an extremely long distance from the device periphery to the Source ohmic contact in the active region. The high resistivity of p-well regions in prior art MOSFETs can result in a significant body bias effect, which has the result of lowering the device threshold voltage in those regions. So, these portions of the device can exhibit a false turn-on, which can result in device failure / destruction. The highly doped P+ plug regions in this embodiment can alleviate the aforementioned effect by reducing the amount of body bias developed in the peripheral regions of the MOSFET, which makes the MOSFET described in this embodiment more resilient to dV / dt induced failure. In other words, the MOSFET structure described in this embodiment will have a higher dV / dt rating than prior art MOSFETs. This reduces the switching losses and increases the circuit efficiency.

[0379] In an embodiment herein, a dedicated process step is utilized for masking the implantation of the N+ source region in the device periphery. The P+ plug region is formed first in this embodiment, while the source trench is created later on in the process at the ILD etch step.

[0380] In the embodiment herein, there is a source trench in the active region of the device but there is no source trench in the periphery of the device. A dedicated masking step is interspersed between the formation of the sidewall spacer after the p-well implant and before the N+ source implant to mask the N+ source implant from the peripheral regions of the MOSFET. The masking layer protects the periphery of the device from the source implanted region. A second deeper p- well region (P-Well#2) is formed using the same masking step used for the N+ source implant. P+ plug regions are formed in a later step in both the active regions of the device as well as the device periphery. A trench is later etched through the N+ source regions at discrete locations in the active region to contact the P+ plug regions, which get shorted to the N+ source region by the ohmic or silicide metallization.

[0381] In an embodiment herein, the source region implantation is masked from the periphery of the device. A dedicated process step is utilized for masking the implantation of the N+ source region in the device periphery as well as the N+ source region in the middle of the unit cell in the active region to enable ohmic contact to the p-well region.

[0382] In an embodiment herein, the polysilicon metallization has been segmented in the periphery of the device and is not one continuous layer as commonly seen. There is a dedicated masking step interspersed between formation of the sidewall spacer, after the p-well implant and before the implementation of the N+ source implant, to mask the N+ source region, from both the peripheral regions of the device as well as the selected areas in the active region.

[0383] In an embodiment herein segmenting the polysilicon metallization reduces the parasitic gate to body or gate to source capacitance which are parasitic capacitances. The islands of polysilicon are not disconnected but are connected at a position orthogonal to the plane of the drawing. Reducing the parasitic capacitance will enable the device to switch faster, which will increase the circuit efficiency by reducing the switching losses.

[0384] An embodiment shown in Fig. 10 is the unit cell and the device periphery of a cross- sectional structure of a SiC DMOSFET. The key regions of this device are a p-well region 203, which is formed by ion- implantation or epitaxial re-growth of a p-type species such as aluminum or boron. There is an N+ source region 204, N- drift layer 202, and an N+ substrate 201. In the ON state when a gate voltage is applied to the polysilicon gate 208 the current flows vertically from the drain 201, through the inversion layer which is formed at the top of the p-well layer 203, through the N+ source region 204, and out through the source metallization 211. In the OFF state or the blocking state, a voltage is supported across the p-well 203, N- drift layer 202 junction and there is a PN junction which is formed between the p-well and the N- drift layer. The voltage applied to the structure is supported across this PN junction in the reverse bias. There are several key features in a power MOSFET, which include the pitch of the unit cell, which is the repeat unit for the MOSFET, the channel length, which is the portion of the p-well in which the inversion channel is formed, the distance between two successive p-wells, which is referred to as the junction gate field-effect transistor (JFET) region or the JFET gap and the thickness of the gate oxide 207. Another feature is an ILD layer 209 which is used to insulate the source interconnect metallization 211 from the polysilicon gate 208.

[0385] Source trench regions 205 are realized by dry etching through the N+ source layer at selected locations of the device, followed by a p-type ion-implantation step to realize P+ plug regions 206 under the source trench. At the very center of the unit cell, there is a P+ plug layer 206 which is grounded with the N+ source metallization. The purpose of the P+ plug in SiC DMOSFET is to ground the p-well region with the N+ source contact.

[0386] The formation of the source trench 205 device structure enables proper grounding of the p-well region in the main active MOSFET region and removal of a parasitic N+ source region 204 formed in the periphery of the MOSFET. When the N+ source region is formed in a self-aligned fashion with the p-well region, the formation of the source trench after the N+ source region formation removes parasitic N+ source regions from the device periphery of the chip and from under the gate pad region.

[0387] In the embodiment herein, combination of the source trench and the ion-implanted P+ plug region provides three important functions. First it provides proper grounding of the p-well region with the source ohmic contact in the active region of the device and second it helps in the removal of the parasitic N+ source region inadvertently formed in the periphery of the device. Third, the highly doped P+ plug region increases the dV / dt rating of the MOSFET. In the embodiment herein both of the above ensures the removal of the parasitic NPN transistor that would be otherwise formed in those regions.

[0388] While a parasitic NPN transistor also exists within the MOSFET unit cell, the N+ emitter (formed by the N+ source region) and the P-base (formed by the p-well region) are shorted by the N+ source ohmic contact. However, in the periphery of the device and also under the gate pad metallization, there is no N+ source ohmic contact, and as a result, the Emitter and Base regions of the parasitic NPN transistor are not shorted in this region. While this parasitic NPN transistor will not be activated under normal DC or switching operation of the MOSFET, operation of the device under extreme conditions like short-circuit or avalanche-mode results in the simultaneous presence of extremely high junction temperatures, high dV / dt and high current densities, which can cause the triggering of the parasitic NPN transistor. Typically, a separate masking step is carried out for masking the N+ source region from being formed at these locations. But in the embodiment herein, the source trench can be advantageously used for removing the parasitic N+ source regions and replacing them with a P+ plug region, which is self-aligned with the source trench and electrically connected to the p-well region.

[0389] Fig. 11 A to Fig. 1 IFF describes the process of manufacturing the structure shown in Fig. 10. The manufacturing process for a SiC DMOSFET is on a SiC substrate 301 and starts with using a 4H-SiC Si-face epi-wafer with suitable doping (1014- 1018cm'3) and thickness (1 pm to 300 pm) for the epilayer 302 shown in Fig. 11 A. A blanket hard mask 303 comprising a chemical vapor deposition (CVD) deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm is deposited in Fig. 1 IB and then patterned using photolithography followed by a dry etch using reactive ion etching (RIE) for example as shown in Fig. 11C. Then p-well region is first formed by ion-implantation or epitaxial growth using aluminum or boron as the p-type impurity. A p-type implantation 304 comprisingboron or aluminum, at energies ranging from 10 keV to 800 keV, at implant doses ranging from 1012cm'2to 1015cm'2in Fig. 1 ID is performed to create a p-well 305 in Fig. 1 IE.

[0390] A second hard mask layer 306 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm in Fig. 1 IF on top of the patterned first hard mask layer 303. This is followed by an anisotropic etching 307 in Fig. 11G to form a sidewall spacer 306 as shown in Fig. 11H.

[0391] A n-type implant 308 is done in Fig. 1 II for creating a N+ source region 309 in Fig. 11 J. A N+ source region is formed by ion-implantation or by epitaxial re-growth by a n-type impurity such as nitrogen or phosphorus. Thus, the source region 309 is formed in a self-aligned fashion with the p-well region 304. The first and second hard mask layers 303 and 306 respectively, are removed in Fig. 1 IK. While the aforementioned sequence of process steps constitutes one method to form a self-aligned p-well and N+ source region, other methods may be employed to achieve the same result. For example, the N+ source region 309 may first be formed after deposition and patterning of a first hard mask layer, followed by further etch back of the first hard mask layer to then form the p-well region 304.

[0392] Another mask layer 310 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top in Fig. 1 IL. The mask layer 310 is patterned in Fig. 1 IM. The patterned mask 310 is used to etch into the substrate 311 in Fig. 1 IN using a dry etch method to create a recessed region within the SIC. The recessed region is the source trench 312 formed in the substrate by penetrating the source region in Fig. 110. The entire N+ source region is removed by dry etching at these selected locations of the device. Using the same hard mask 310, by implantation of a controlled dose of a p-type impurity 313 such as aluminum or boron in Fig. 1 IP a P+ plug layer is formed in Fig. 1 IQ. The depth of the P+ plug layer 314 may preferably exceed the depth of the N+ source implant and may even exceed the depth of the p-well region, in a particular implementation. A p- type implantation comprising boron or aluminum, at energies ranging from 10 keV to 800 keV, at implant doses ranging from 1013cm'2to 1017cm'2in Fig. 11D is performed to create a P+ plug region. The P+ plug region 314 is realized under the source trench 312, which is electrically connected to the p-well region 304. The mask layers are removed in Fig. HR. The wafer is annealed for activating the implanted impurities.

[0393] The oxide layer 315 which is the gate oxide is formed by thermal oxidation or using CVD of a dielectric layer such as silicon dioxide, silicon nitride, silicon oxynitride, etc. in Fig. 1 IS. The thickness of the gate oxide could range from 5 nm to 100 nm. Either dry or wet thermal oxidation could be used for oxide growth. Plasma-enhanced chemical vapor deposition (PECVD) or low- pressure chemical vapor deposition (LPCVD) could be used for gate oxide deposition. Apolysilicon gate layer 316 is then deposited in Fig. 11T. The polysilicon layer may be deposited using PECVD or LPCVD. The polysilicon layer may be degenerately doped using boron or phosphorus, either in-situ or in a subsequent step. In-situ doping may be performed by the addition of PH3 precursor to the polysilicon deposition chemistry. Post-deposition doping of polysilicon may be performed by depositing a layer of POCh followed by a drive-in step at temperatures ranging from 600-900°C. A hard mask 317 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top on top and patterned as shown in Fig. 11U. The polysilicon layer 316 is etched by using the patterned mask layer 317 in Fig. 11V. The mask layer 317 is then removed in Fig. 11W. An ILD layer 318 comprising 50 nm - 1000 nm thick silicon dioxide, silicon nitride, silicon oxynitride layers or a stacked combination thereof is deposited on the wafer in Fig. 11X.

[0394] A hard mask 319 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top and patterned on top to define the ILD opening in Fig. 11 Y. The ILD layer 318 is etched using the hard mask 319 as shown in Fig. 11Z. Further the gate oxide 315 is etched using the same mask 319 in Fig. 11 AA. The mask 319 is then removed in Fig. 1 IBB. A nickel silicide region 320 is formed on the exposed SiC surface in Fig. 11CC. A mask layer 321 is formed by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top and patterned in Fig. 11DD. The ILD layer 318 is etched using mask 321 in Fig. 11EE. The mask layer 321 is removed in Fig. 1 IFF. Interconnect metal layers 322 of either aluminum or silver or gold is deposited and patterned on the top and bottom of the substrate in. Fig. 11GG.

[0395] In the embodiment herein, the same final structure for forming the source trench region and P+ plug region may be alternatively realized using a slightly different approach. As in the above method, the p-well region, and the N+ source region is realized using a self-aligned process. However, in the embodiment herein, the P-plug layer may be formed first using deep boron or aluminum implantation as a buried layer that is placed under the N+ source region. The dry etching for the N+ source trench realization may be performed later on in the process. The N+ source trench may be realized preferably after the high-temperature annealing process in one example implementation.

[0396] An embodiment shown in Fig. 12 is the unit cell and the device periphery of a cross- sectional structure of a SiC DMOSFET. The key regions of this device are a p-well region 403, which is formed by ion- implantation or epitaxial re-growth of a p-type species such as aluminum or boron. There is an N+ source region 404, N- drift layer 402, and an N+ substrate 401. In the ONstate when a gate voltage is applied to the polysilicon gate 407 the current flows vertically from the drain 401, through the inversion layer which is formed at the top of the p-well layer 403, through the N+ source region 404, and out through the source metallization 412. In the OFF state or the blocking state, a voltage is supported across the p-well 403, N- drift layer 402 junction and there is a PN junction which is formed between the p-well and the N- drift layer. The voltage applied to the structure is supported across this PN junction in the reverse bias. There are several key features in a power MOSFET, which include the pitch of the unit cell, which is the repeat unit for the MOSFET, the channel length, which is the portion of the p-well in which the inversion channel is formed, the distance between two successive p-wells, which is referred to as the JFET region or the JFET gap and the thickness of the gate oxide 407. Another feature is an ILD layer 409 which is used to insulate the source interconnect metallization 412 from the polysilicon gate

[0397] A dedicated masking step is interspersed between the formation of the sidewall spacer after the p-well implant and before the N+ source implant to mask the N+ source implant from the peripheral regions of the MOSFET. A second deeper p-well region (P-Well#2) 405 is formed using the same masking step used for the N+ source implant. P+ plug regions 406 are formed in a later step in both the active regions of the device as well as the device periphery. The P+ plug layer 406 is grounded with the N+ source metallization. The purpose of the P+ plug in SiC DMOSFET is to ground the p-well region with the N+ source contact.

[0398] A trench 410 is later etched through the N+ source regions at discrete locations in the active region to contact the P+ plug regions, which get shorted to the N+ source region by the ohmic silicide 411 metallization. The source trench 410 is etched into the SiC at selected regions using the same hard mask used for patterning the interlevel dielectric layer (ILD). In the embodiment herein, the source trench 410 serves two functions. First the source trench reveals the surface of the P+ plug layer that was previously buried under the N+ source region for subsequent contact with the ohmic silicide metal and second the source trench reveals the sidewalls of the N+ source region for subsequent contact with the ohmic silicide metal.

[0399] In the embodiment herein, a dedicated hard mask or photoresist layer is applied after the sidewall spacer is formed and before the N+ source implantation. This layer prevents the formation of the N+ source region in the device periphery and parasitic NPN structures in the device periphery are avoided

[0400] In the embodiment herein, a second p-well region (P-Well#2) 405 is placed under the N+ source region 404 and electrically connected to the main p-well region provides additional electrical dose under the N+ source implant, for preventing reach-through breakdown, especially after the source trench formation. The etching of the source trench may inadvertently etch part ofthe primary p-well region under the N+ source region, thereby locally reducing the p-well dose in this region, resulting in undesirable reach through breakdown at these locations.

[0401] Fig. 13A to Fig. 13GG describes the process of manufacturing the structure shown in Fig. 12. The manufacturing process for a SiC DMOSFET is on a SiC substrate 501 and starts with using a 4H-SiC Si-face epi-wafer with suitable doping (1014- 1018cm'3) and thickness (1 pm to 300 pm) for the epilayer 502 shown in Fig. 13A. A blanket hard mask 503 comprising a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm is deposited in Fig. 13B and then patterned using photolithography followed by a dry etch using RIE for example as shown in Fig. 13C. Then p-well region is first formed by ion-implantation or epitaxial growth using aluminum or boron as the p- type impurity. A p-type implantation 504 comprising boron or aluminum, at energies ranging from 10 keV to 800 keV, at implant doses ranging from 1012cm'2to 1015cm'2in Fig. 13D is performed to create a p-well 505 in Fig. 13E.

[0402] A second hard mask layer 506 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm in Fig. 13F on top of the patterned first hard mask layer 503. This is followed by an anisotropic etching 507 in Fig, 13G to form a sidewall spacer 506 as shown in Fig. 13H. A patterned mask layer 508 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top alongside the patterned mask layer with the sidewall spacer in Fig. 131. The hard mask layer 508 patterned over the peripheral regions of the device.

[0403] A n-type implant 509 is done in Fig. 13 J for creating a N+ source region 510 in Fig. 13 J. A N+ source region is formed by ion-implantation or by epitaxial re-growth by a n-type impurity such as nitrogen or phosphorus. The N+ source region 510 is formed in a self-aligned fashion with the p-well region 504. The source region is formed in a self-aligned fashion with the p-well region, while it is masked from the peripheral regions of the device. A deep second p-well region (P- Well#2) 511 may be formed at the same time as the N+ source region in Fig. 13K. The buried P- well#2 region may be formed using aluminum or boron, and placed under the N+ source region in the active area of the device. The P-Well#2 region may be preferably formed using the p-type species boron which has a higher ion-implantation range as compared to aluminum in SiC. It may not be necessary to mask the p-well region#2 from the peripheral regions of the device.

[0404] The first and second hard mask layers 503 and 506 respectively, are removed in Fig. 13L. Another mask layer 512 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top in Fig. 13M. The mask layer 512 is patterned in Fig. 13N. By implantation with acontrolled dose of a p-type impurity 513 such as aluminum or boron in Fig. 130 a P+ plug region 514 buried under the N+ source region 510 is realized in Fig. 13P. The P+ plug region 514 is electrically connected to the p-well region 504 and the P-well#2 region 511. The P+ plug region may be formed deeper than the p-well and P-Well#2 regions. The mask layer 512 is then removed in Fig. 13Q and the implants are activated by high -temperature annealing.

[0405] The oxide layer 515 which is the gate oxide is formed by thermal oxidation or using CVD of a dielectric layer such as silicon dioxide, silicon nitride, silicon oxynitride, etc. in Fig. 13R. The thickness of the gate oxide could range from 10 nm to 100 nm. Either dry or wet thermal oxidation could be used for oxide growth. PECVD or LPCVD could be used for gate oxide deposition. A polysilicon gate layer 516 is then deposited in Fig. 13S. The polysilicon layer may be deposited using PECVD or LPCVD. The polysilicon layer may be degenerately doped using boron or phosphorus, either in-situ or in a subsequent step. In-situ doping may be performed by the addition of PH3 precursor to the polysilicon deposition chemistry. Post-deposition doping of polysilicon may be performed by depositing a layer of POCh followed by a drive-in step at temperatures ranging from 700-900°C. A hard mask 517 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top on top and patterned as shown in Fig. 13T. The polysilicon layer 516 is etched by using the patterned mask layer 517 in Fig. 13U. The mask layer 517 is then removed in Fig. 13 V. An ILD layer 518 comprising 50 nm - 1000 nm thick silicon dioxide, silicon nitride, silicon oxynitride layers or a stacked combination thereof is deposited on the wafer in Fig. 13W. A hard mask 519 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top and patterned on top to define the ILD opening in Fig. 13X. The ILD layer 518 is etched using the hard mask as shown in Fig. 13Y. Further the gate oxide 515 is etched using the same mask 519 in Fig. 13Z. The hard mask that is used for patterning the ILD layer 519 is used to realize the source trench region 520 by etching completely through the N+ source layer and into the P+ plug layer in Fig 13AA. The mask 519 is then removed in Fig. 13BB. A nickel silicide region 521 is formed on the exposed SiC surface in Fig. 13CC. A mask layer 522 is formed by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top which is then patterned in Fig. 13DD. The ILD layer 518 is etched in Fig. 13EE. The mask layer 522 is removed in Fig. 13FF. Interconnect metal layers 523 of either aluminum or silver or gold is deposited and patterned on the top and bottom of the substrate in. Fig. 13GG. The ohmic contact to the N+ source regions are made through the etched sidewalls of the source trench regions in this embodiment, as opposed to the horizontal surfaces of the N+ source regions in conventional MOSFETs.

[0406] An embodiment shown in Fig. 14 is the unit cell and the device periphery of a cross- sectional structure of a SiC DMOSFET. The key regions of this device are a p-well region 603, which is formed by ion- implantation or epitaxial re-growth of a p-type species such as aluminum or boron. There is an N+ source region 604, N- drift layer 602, and an N+ substrate 601. In the ON state when a gate voltage is applied to the polysilicon gate 607 the current flows vertically from the drain 601, through the inversion layer which is formed at the top of the p-well layer 603, through the N+ source region 604, and out through the source metallization 610. In the OFF state or the blocking state, a voltage is supported across the p-well 603, N- drift layer 602 junction and there is a PN junction which is formed between the p-well and the N- drift layer. The voltage applied to the structure is supported across this PN junction in the reverse bias. There are several key features in a power MOSFET, which include the pitch of the unit cell, which is the repeat unit for the MOSFET, the channel length, which is the portion of the p-well in which the inversion channel is formed, the distance between two successive p-wells, which is referred to as the JFET region or the JFET gap and the thickness of the gate oxide 606. Another feature is an ILD layer 608 which is used to insulate the source interconnect metallization 610 from the polysilicon gate 607. At the very center of the unit cell, there is a P+ plug layer 605 which is grounded with the N+ source metallization. The purpose of the P+ plug in SiC DMOSFET is to ground the p-well region with the N+ source contact.

[0407] In an embodiment herein, a dedicated masking step is interspersed between the formation of the sidewall spacer after the p-well implant and before the N+ source implant to mask the N+ source implant from the peripheral regions of the MOSFET. This also masks the N+ source implant from selected regions in the active area of the device, which enables ohmic contact to the p-well or P+ plug region. This embodiment obviates the need for a source trench that is present in earlier embodiments.

[0408] In the embodiment herein, a dedicated hard mask or photoresist layer is applied after the sidewall spacer is formed and before the N+ source implantation which prevents the formation of the N+ source region in the device periphery and parasitic NPN structures in the device periphery are avoided. The implantation of the N+ source region is avoided in selected areas in the active region, and this enables ohmic contact to the p-well or P+ plug regions without an intervening N+ source region.

[0409] Fig. 15A to Fig. 15FF describes the process of manufacturing the structure shown in Fig. 14. The manufacturing process for a SiC DMOSFET is on a SiC substrate 701 and starts with using a 4H-SiC Si-face epi-wafer with suitable doping (1014- 1018cm'3) and thickness (1 pm to 300 pm) for the epilayer 702 shown in Fig. 15 A. A blanket hard mask 703 comprising a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, withthickness ranging from 50 nm to 5 gm is deposited in Fig. 15B and then patterned using photolithography followed by a dry etch using RIE for example as shown in Fig. 15C. Then p-well region is first formed by ion-implantation or epitaxial growth using aluminum or boron as the p- type impurity. A p-type implantation 704 comprising boron or aluminum, at energies ranging from 10 keV to 800 keV, at implant doses ranging from 1012cm'2to 1015cm'2in Fig. 15D is performed to create a p-well 705 in Fig. 15E.

[0410] A second hard mask layer 706 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm in Fig. 15F on top of the patterned first hard mask layer 703. This is followed by an anisotropic etching 707 in Fig. 15Gto form a sidewall spacer 706 as shown in Fig. 15H. A hard mask layer 708 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm and patterned in Fig. 151. The patterned mask layer is formed on the top alongside the patterned mask layer with the sidewall spacer 706. A n-type implant 709 is done in Fig. 15J for creating a N+ source region 710 in Fig. 15K. A N+ source region is formed by ion-implantation or by epitaxial re-growth by a n-type impurity such as nitrogen or phosphorus. Thus, the source region 710 is formed in a self-aligned fashion with the p-well region 705 while it is masked from the peripheral regions of the device, as well as selected areas of the active region of the device, to enable contact with the source ohmic metallization. The first and second hard mask layers 703 and 708 respectively, are removed in Fig. 15L. Another mask layer 711 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top in Fig. 15M. The mask layer 711 is patterned in Fig. 15N.

[0411] Using the hard mask 711, by implantation of a controlled dose of a p-type impurity 712 such as aluminum or boron in Fig. 150 a P+ plug region is realized in Fig. 15P. The depth of the P+ plug layer 713 may preferably exceed the depth of the N+ source implant and may even exceed the depth of the p-well region, in a particular implementation. The mask layer 711 is removed in Fig. 15Q. The wafer is annealed for activating the implanted impurities.

[0412] The oxide layer 714 which is the gate oxide is formed by thermal oxidation or using CVD of a dielectric layer such as silicon dioxide, silicon nitride, silicon oxynitride, etc. in Fig. 15R. The thickness of the gate oxide could range from 10 nm to 100 nm. Either dry or wet thermal oxidation could be used for oxide growth. PECVD or LPCVD could be used for gate oxide deposition. A polysilicon gate layer 715 is then deposited in Fig. 15S. The polysilicon layer may be deposited using PECVD or LPCVD. The polysilicon layer may be degenerately doped using boron or phosphorus, either in-situ or in a subsequent step. In-situ doping may be performed by the additionof PH3 precursor to the polysilicon deposition chemistry. Post-deposition doping of polysilicon may be performed by depositing a layer of POOL followed by a drive-in step at temperatures ranging from 700-900°C. A hard mask 716 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top on top and patterned as shown in Fig. 15T. The polysilicon layer 715 is etched by using the patterned mask layer 716 in Fig. 15U. The mask layer 716 is then removed in Fig. 15V. An ILD layer 717 comprising 50 nm - 1000 nm thick silicon dioxide, silicon nitride, silicon oxynitride layers or a stacked combination thereof is deposited on the wafer in Fig. 15W.

[0413] A hard mask 718 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top and patterned on top to define the ILD opening in Fig. 15X. The ILD layer 717 is etched using the hard mask as shown in Fig. 15Y. Further the gate oxide 714 is etched using the same mask 718 in Fig. 15Z. The mask 718 is then removed in Fig. 15AA. A nickel silicide region 719 is formed on the exposed SiC surface in Fig. 15BB. A mask layer 720 is formed by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top which is then patterned in Fig. 15CC. The ILD layer 717 is etched in Fig. 15DD. The mask layer 720 is removed in Fig. 15EE. Interconnect metal layers 721 of either aluminum or silver or gold is deposited and patterned on the top and bottom of the substrate in Fig. 15FF.

[0414] An embodiment shown in Fig. 8 is the unit cell and the device periphery of a cross- sectional structure of a SiC DMOSFET. The key regions of this device are a p-well region 803, which is formed by ion- implantation or epitaxial re-growth of a p-type species such as aluminum or boron. There is an N+ source region 804, N- drift layer 802, and an N+ substrate 801. In the ON state when a gate voltage is applied to the polysilicon gate 807 the current flows vertically from the drain 801, through the inversion layer which is formed at the top of the p-well layer 803, through the N+ source region 804, and out through the source metallization 810. In the OFF state or the blocking state, a voltage is supported across the p-well 803, N- drift layer 802 junction and there is a PN junction which is formed between the p-well and the N- drift layer. The voltage applied to the structure is supported across this PN junction in the reverse bias. There are several key features in a power MOSFET, which include the pitch of the unit cell, which is the repeat unit for the MOSFET, the channel length, which is the portion of the p-well in which the inversion channel is formed, the distance between two successive p-wells, which is referred to as the JFET region or the JFET gap and the thickness of the gate oxide 806. Another feature is an ILD layer 808 which is used to insulate the source interconnect metallization 810 from the polysilicon gate807. At the very center of the unit cell, there is a P+ plug layer 805 which is grounded with the N+ source metallization. The purpose of the P+ plug in SiC DMOSFET is to ground the p-well region with the N+ source contact.

[0415] In an embodiment herein, a dedicated masking step is interspersed between the formation of the sidewall spacer after the p-well implant and before the N+ source implant to mask the N+ source implant from the peripheral regions of the MOSFET. This also masks the N+ source implant from selected regions in the active area of the device, which enables ohmic contact to the p-well or P+ plug region. This embodiment obviates the need for a source trench that is present in some earlier embodiments.

[0416] In the embodiment herein, a dedicated hard mask or photoresist layer is applied after the sidewall spacer is formed and before the N+ source implantation which prevents the formation of the N+ source region in the device periphery and parasitic NPN structures in the device periphery are avoided. The implantation of the N+ source region is avoided in selected areas in the active region, and this enables ohmic contact to the p-well or P+ plug regions without an intervening N+ source region.

[0417] In the embodiment herein, the polysilicon metallization in the peripheral regions of the device 807 are segmented and not a contiguous layer. In the embodiment herein, the formation of the segmented gate metallization in the periphery of the device instead of a contiguous gate bus could significantly decrease the gate-body capacitance of the MOSFET. This could result in a significant increase of the switching speed of the MOSFET.

[0418] Fig. 17A to Fig. 17FF describes the process of manufacturing the structure shown in Fig. 8. The manufacturing process for a SiC DMOSFET is on a SiC substrate 901 and starts with using a 4H-SiC Si-face epi-wafer with suitable doping (1014- 1018cm'3) and thickness (1 pm to 300 pm) for the epilayer 902 shown in Fig. 17 A. A blanket hard mask 903 comprising a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm is deposited in Fig. 17B and then patterned using photolithography followed by a dry etch using RIE for example as shown in Fig. 17C. Then p-well region is first formed by ion-implantation or epitaxial growth using aluminum or boron as the p- type impurity. A p-type implantation 904 comprising boron or aluminum, at energies ranging from 10 keV to 800 keV, at implant doses ranging from 1012cm'2to 1015cm'2in Fig. 17D is performed to create a p-well 905 in Fig. 17E.

[0419] A second hard mask layer 906 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm in Fig. 17F on top of the patterned first hard mask layer 903. This is followed by an anisotropic etching 907 in Fig. 17Gto form a sidewall spacer 906 as shown in Fig. 17H. A hardmask layer 908 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm and patterned in Fig. 171. The patterned mask layer 908 is formed on the top alongside the patterned mask layer with the sidewall spacer. A n-type implant 909 is done in Fig. 17J for creating a N+ source region 910 in Fig. 17K. A N+ source region is formed by ion-implantation or by epitaxial re-growth by a n-type impurity such as nitrogen or phosphorus. Thus, the source region 910 is formed in a self-aligned fashion with the p-well region 905 while it is masked from the peripheral regions of the device, as well as selected areas of the active region of the device, to enable contact with the source ohmic metallization. The first and second hard mask layers 903 and 908 respectively, are removed in Fig. 17L. Another mask layer 911 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top in Fig. 17M. The mask layer 911 is patterned in Fig. 17N.

[0420] Using the hard mask 911 and by implantation of a controlled dose of a p-type impurity 912 like aluminum or boron in Fig. 170 a P+ plug region 913 is realized in Fig. 17P. The mask layer 911 is removed in Fig. 17Q. The wafer is annealed for activating the implanted impurities.

[0421] The oxide layer 914 which is the gate oxide is formed by thermal oxidation or using CVD of a dielectric layer such as silicon dioxide, silicon nitride, silicon oxynitride, etc. in Fig. 17R. The thickness of the gate oxide could range from 10 nm to 100 nm. Either dry or wet thermal oxidation could be used for oxide growth. PECVD or LPCVD could be used for gate oxide deposition. A polysilicon gate layer 915 is then deposited in Fig. 17S. The polysilicon layer may be deposited using PECVD or LPCVD. The polysilicon layer may be degenerately doped using boron or phosphorus, either in-situ or in a subsequent step. In-situ doping may be performed by the addition of PH3 precursor to the polysilicon deposition chemistry. Post-deposition doping of polysilicon may be performed by depositing a layer of POCh followed by a drive-in step at temperatures ranging from 700-900°C. A hard mask 916 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top on top and patterned as shown in Fig. 17T. The polysilicon layer 915 is etched by using the patterned mask layer 916 in Fig. 17U. In the embodiment described herein, the masking step used to pattern the polysilicon gate metal, results in a partially segmented polysilicon pattern. While not apparent in the cross-sectional schematic, the disjointed gate fingers would be connected at a position orthogonal to the plane of the drawing. The gate insulator 914 is etched in Fig. 17V using the patterned mask 916. The mask layer 916 is then removed in Fig. 17W. An ILD layer 917 comprising 50 nm - 1000 nm thick silicon dioxide, silicon nitride, silicon oxynitride layers or a stacked combination thereof is deposited on the wafer in Fig. 17X.

[0422] A hard mask 918 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top and patterned on top to define the ILD opening in Fig. 17Y. The ILD layer 917 is etched using the hard mask as shown in Fig. 17Z. The mask 918 is then removed in Fig. 17AA. A nickel silicide region 919 is formed on the exposed SiC surface in Fig. 17BB. A mask layer 920 is formed by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top which is then patterned in Fig. 17CC. The ILD layer 917 is etched in Fig. 17DD. The mask layer 920 is removed in Fig. 17EE. Interconnect metal layers 921 of either aluminum or silver or gold is deposited and patterned on the top and bottom of the substrate in. Fig. 17FF.

[0423] Embodiments relate to SiC DMOSFET power devices where the p-well regions effectively shield the sensitive gate oxide from the high electric fields present in SiC especially during high drain bias or blocking mode operation.

[0424] An embodiment relates to using a P+-plug to ground the p-well region with the N+ source contact.

[0425] An embodiment relates to a p-well trench formed by dry etching into the p-well implanted region immediately preceding the source region formation, resulting in a portion of the MOS channel that is formed on the (0001) or horizontal face and another portion of the MOS channel that is formed on the (11-20 / 10-10) or vertical crystal plane of SiC which has the benefit of increasing the MOS channel mobility.

[0426] An embodiment relates to a much deeper vertical MOS channel formed by etching all the way through the p-well region. Subsequently, after the formation of the N+ Source region, a second p-well region (PW#2) is ion-implanted under and around the N+ source region in order to suppress reach-through breakdown.

[0427] An embodiment relates to the formation of the p-well trench which offers the flexibility to the device designer to either increase the effective channel length for a given ON resistance target, or reduce the ON resistance for a given chip size

[0428] SiC devices in power electronics feature fast switching times, high blocking voltage capabilities, and the ability to operate at high temperatures. These characteristics, along with recent advancements in manufacturing processes, suggest that SiC has the potential to revolutionize power electronics as a successor to traditional silicon-based (Si) devices. SiC is a wide band gap material (3.3 eV) and has a higher breakdown electric field (3 x 106V / cm to 5 x 106V / cm) compared to Si (Si band gap is 1.1 eV and breakdown electric field for Si is 0.3 x 106V / cm). SiC is a better thermal conductor (3.7 (W / cm-K) for SiC versus 1.6 (W / cm-K) for Si) which enables SiC devices to operate at extremely high-power levels and still dissipate the large amounts ofexcess heat generated. These material properties of SiC offer multiple advantages of using SiC instead of Si on power devices. In a comparison of SiC and Si semiconductor die with identical structures and dimensions, the SiC die exhibits a lower specific ON resistance and a higher breakdown voltage than the Si die.

[0429] The disclosed embodiments herein provide novel techniques for SiC DMOSFET design and fabrication to have a higher channel density, which can be advantageous for reducing the ON resistance of the device.

[0430] In a typical SiC planar MOSFET structure also known as the DMOSFET, the MOS channel is formed on the horizontal or 0001 crystal plane of SiC. The channel mobility or field effect mobility on the 0001 crystal plane of SiC tends to be lower as compared to the vertical side wall or what is called as the 11-20 or 10-10 crystal plane. When one makes a planar SiC DMOSFET, the ON resistance tends to be large and the DMOSFET is limited by the field effect channel mobility.

[0431] The channel mobility or field effect mobility on the 0001 crystal plane of SiC is in the range of 15 to 25 cm2 / V-sec as compared to silicon MOSFETs where it can be more than 350 cm2 / V-sec. One way to design lower resistance SiC MOSFETs is to find ways in which you can create very small channel lengths, so that this inversion layer mobility is active only in a smaller region of the current conduction path of this device, but this can lead to problems of short channel effects. Hence, reducing the channel alone does not solve the low channel mobility in the 0001 crystal plane because it introduces short channel effects, which results in poor reliability and poor robustness characteristics for this device. In an embodiment herein one way to combat this problem is by introducing trench MOSFETs in SiC. In a trench MOSFET, instead of forming the MOS channel on a horizontal or a 0001 crystal plane, the channels are now formed on the vertical side wall or on the so called A plane or M plane or also called as 10-10 or the 11-20 planes. Both of these planes have significantly higher channel mobility close to five times higher as compared to the horizontal plane resulting in 110 to 120 cm2 / V-sec for vertical channels.

[0432] A trench MOSFET can provide a higher channel density as compared to a planar MOSFET so one can increase the packing density. Since channel mobility is higher, it enables devices with small ON resistance. Even though a traditional trench MOSFET has an advantage over DMOSFET, the problem with a traditional trench MOSFET structure in SiC is that at the base of the trench there are high electric fields and a portion of a gate oxide in the trench suffers from high electric fields in the blocking mode of operation. This will become a failure point of a typical trench MOSFET structure and to overcome this issue it is necessary to shield the gate oxide at the base of the trench. P-type implantations used to shield gate oxide and approaches like a W-trench MOSFET are used to shield the gate oxide.

[0433] However, creating these shielding regions increases the ON resistance. While the trench MOSFET as compared to the DMOSFET enables higher channel mobilities hence reducing the ON resistance it creates high electric fields at the trench corners. To combat this, shielding regions are introduced, but this increases the ON resistance. Some benefits gained by reduced ON resistance from the trench MOSFET, are now lost due to shielding which is a trade off in designing traditional trench MOSFET.

[0434] In the embodiments herein, the device is neither pure DMOSFET nor is it a pure trench MOSFET. In this device the MOS channel is formed on both the 0001 plane as well as the vertical side wall or 11-20 (or 10-10) plane so it is a hybrid between a DMOSFET and a trench MOSFET.

[0435] In the embodiment herein, the device has a shorter overall channel length as compared to a pure DMOSFET but with the same effective channel mobility. By increasing the channel length in this way enables you to overcome some of the robustness and reliability problems associated with making short channel DMOSFETs. In the embodiments herein, the device has the trench which is completely surrounded or encompassed in a p-type implanted region. This provides a natural shielding to the high electric fields. Since the trench is completely formed inside a p-well there is no region where the trench is exposed to n-type epilayer which mitigates the issue of high electric fields at the trench comers.

[0436] In the embodiments herein, the structure of this device is distinguished by a trench which is etched into the p-well region and this trench is referred to as the p-well trench. In the embodiment first, the p-well region is formed and then the trench is etched into the p-well region, so all sides of this trench are encompassed in this p-well region. This trench also immediately precedes the formation of the N+ source region. With this process as described in this embodiment the device has a portion of the MOS channel which is formed on the 0001 phase and another portion of the channel is formed on the 11-20 or 10-10 plane.

[0437] The main steps to form a device described in the embodiment is forming the p-well region, by either ion implantation or epitaxial growth with aluminum or boron as the p-type impurity. Then the p-well trench is formed by controlled etching into the p-well region by using either reactive ion etching (RIE), or higher power inductively coupled plasma (ICP) source with an appropriate hard mask layer for forming this trench.

[0438] In the embodiment herein, this trench maybe formed with a sidewall angle between 70° and 90°. That is the approximate angle with which the trench is formed. The depth of this trench as an example may range between 0.1 pm to 0.5 pm. The depth of the p-well trench maybe adjusted to be smaller than the depth of the p-well region where the bottom of the p-well trench is completely enclosed within the p-well region.

[0439] In the embodiment herein, after forming the p-well trench, a N+ source region is formed by ion implantation or by epitaxial re-growth by using an impurity such as nitrogen or phosphorus. The N+ source is fully contained within the p-well region and N+ source does not extend beyond the p-well region. In the embodiments herein, one option is that the p-well trench region maybe formed using the same masking step as what may be used for forming the N+ source region even though it is not required. Next a P+ plug layer for grounding the p-well is formed by implantation of either aluminum or boron. The depth of the P+ plug layer may exceed the depth of the source implant layer such that it can both short the source implant with the ohmic layer that is put on top and also provides the grounding for the p-well region. The remainder of the process constitutes heat treatment of the wafers for electrical activation, the electric formation, gate metal formation, interlayer dielectric (ILD), patterning ILD, ohmic metallization, putting down a thick pad metallization.

[0440] In the embodiments herein, for forming the gate insulator either thermal oxidation or chemical vapor deposition (CVD) of a dielectric layer such as silicon dioxide, silicon nitride or oxynitride is used. In SiC, the oxidation rates are different for the 0001 plane as compared to the 11-20 or 10-10 plane which means oxidation rates are different for the horizontal side wall and the vertical side wall. This can lead to thicker gate oxide on the vertical side wall as compared to the horizontal side wall. In the embodiments herein, you can deposit a CVD silicon dioxide, and make sure that the thickness is the same on the horizontal and vertical side

[0441] The p-well trench is formed preceding the source region formation and after the p-well region formation in an embodiment with SiC DMOSFETs described herein. A portion of the MOS channel in the device is now formed parallel to the 0001 plane and another portion is formed parallel to the 11-20 plane. A MOSFET which is fabricated according to this embodiment as compared to a planar device for the same lateral footprint will have a higher channel density, hence enabling for a tighter packing. In addition to geometrically increasing the channel density the embodiment herein can also take advantage of the higher channel mobility of the vertical side wall.

[0442] In the embodiments herein devices have higher channel density and higher channel mobility and lower ON resistance. For a given ON resistance target you can increase the effective channel length. While comparing the device described in an embodiment to a typical planar DMOSFET, for the same ON resistance target, you can have a higher channel length for the device in the embodiment. Short channel effects can degrade the reliability and robustness characteristics and the longer channel length can alleviate short channel effects. Another way to use the device in this embodiment is for the same channel length as in a planar DMOSFET you can realize a smaller chip which means a lower cost device.

[0443] The device in this embodiment can have the same channel length as the planar DMOSFET but because of the higher channel mobility of 11-20 and 10-10 direction one can afford a longer channel in the vertical side wall and still have a shorter, horizontal channel. Due to higher channel mobility, the device in the embodiment will have a lower ON resistance. It allows you to then have a smaller chip size for the same ON resistance and design a device as in the embodiment which has a longer channel in the vertical and shorter on the horizontal, allowing to make a lower ON resistance MOSFET.

[0444] The embodiments described herein, can be distinguished from a prior art disclosed by Tega et al from Hitachi in a US patent application: US 2018 / 0331174 Al, published in November of 2018. The prior art structure described by Tega et al from Hitachi in the US patent describes a SiC MOSFET structure in which the MOS channel is formed on both the horizontal and vertical p-well surfaces and the p-well trench which creates this MOS channel on the vertical and horizontal side walls is not formed contiguously. The p-well trench is only formed at orthogonal locations in the 3D landscape. If it were formed contiguously a cross section anywhere in the device will show the same structure. But in the case of the prior art the cross section through those kinds of trenches shows a different cross section at each location since there are many regions in the device where there is no p-well trench. The p-well trench in the devices described in the embodiments herein are however contiguous in nature which is thus different from the prior art structure described by Tega et al from Hitachi.

[0445] The second difference is that the construction of the MOS channel in the prior art structure described by Tega et al from Hitachi is completely different when compared to what is described in the embodiments here. The MOS channel in the prior art is formed between an N+ source region and a separate N+ accumulation region. In the device in the embodiments described herein the p- well region is formed first followed by a trench into the p-well region, and then the source implant. However, in the prior art structure described by Tega et al from Hitachi the p-well region is formed followed by the source implant, an accumulation region, the heat treatment and then a p-well trench. The difference lies in how and when the MOS channel is formed during the process.

[0446] The third difference is that the process of trench creation for realizing MOS channel on the vertical SiC crystal planes is conducted after all implantation steps are completed in the prior art described by Tega et al from Hitachi. As a result, the N+ Source region is elevated as compared to the MOS channel formed on the vertical sidewall. In the device described in the embodiments herein the p-well trench is etched immediately following the p-well implantation and prior to the N+ source implantation which is formed on the recessed region created by the etching of the p- well trench.

[0447] In the structure proposed by Tega et all, along with a P+ plug region, N+ source region, and p-well region has N+ accumulation region and a P+ shielding region.

[0448] An embodiment described herein enables you to form an extremely long channel on the vertical side wall. The p-well trench can be formed significantly deeper so that the bottom of the p-well trench can extend beyond the p-well region.

[0449] In an embodiment herein, p-well region is formed followed by a deep p-well trench and source implantation. After the source implantation a second p-well region is formed. The second p-well region extends below the source region and has a cover around the corner to prevent any reliability issues of having a sharp edge.

[0450] In the embodiment herein, tilted implantation is used to extend the p-well region beyond the lateral extent of the p-well region and shield the gate oxide from any drain induced electric field. The structure in the embodiment provides a natural way to shield the drain potential from the channel region by extending the second p-well region beyond the source region

[0451] The process to form the device described in the embodiment includes forming a p-well region by ion implantation or epitaxial growth using aluminum or boron. This is followed by a p- well trench that is formed by control etching into the p-well region by RIE or ICP based etching. The p-well trench may be formed with a sidewall angle between 75° and 90°. The depth of the p- well trench region may range anywhere from 0.1 pm to 2 pm. A N+ Source region is then formed by ion-implantation or by epitaxial re-growth by a n-type impurity such as nitrogen or phosphorus. In the embodiment herein, since the bottom of the p-well trench may not be completely enclosed within the p-well region, a second p-well region is formed. The second p-well is formed with a sufficient depth under the N+ source region while making sure that the lateral extent of the p-well region is then now larger than the original p-well region.

[0452] There are two methods to form the second p-well as described in the embodiments here. In one case a dedicated hard mask layer may be deposited and patterned with a slightly larger extent than the original p-well region, and then the ion-implantation for PW#2 may be performed. In the second case tilted ion-implantation may be advantageously used for realizing PW#2. In an embodiment described here, the same hard mask may be used for creating the p-well trench, N+ source region and then the PW#2 region, whose lateral extent is made larger than the original PW region using tilted ion-implantation of a p-type impurity. The remainder of the process constitutes heat treatment of the wafers for electrical activation of the implanted impurities, gate insulator formation, gate electrode formation, inter-level dielectric formation, Source / Drain Ohmic metallization and finally the formation of pad or interconnect metals compatible with die probing and packaging. The gate insulator is formed either by thermal oxidation of the silicon carbide or by CVD of a dielectric layer such as silicon dioxide, silicon nitride, silicon oxynitride, etc.

[0453] The device described in the embodiment allows more freedom in the ON resistance versus robustness trade off that is often encountered in case of SiC power MOSFET. While longer channels allow you to have good short circuit performance and the ON resistance is high because of the lower channel mobility, an intrinsic property of SiC.

[0454] An embodiment shown in Fig. 18 is the unit cell of a cross-sectional structure of a SiC DMOSFET. The key regions of this device are a p-well region 203, which is formed by ionimplantation or epitaxial re-growth of a p-type species such as aluminum or boron. There is an N+ source region 204, N- drift layer 202, and an N+ substrate 201. In the ON state when a gate voltage is applied to the polysilicon gate 206, the current flows vertically from the drain 201, through the inversion layer which is formed at the top of the p-well layer 203, through the N+ source region 204, and out through the source metallization 208. In the OFF state or the blocking state, a voltage is supported across the p-well 203, N- drift layer 202 junction and there is a PN junction which is formed between the p-well and the N- drift layer. The voltage applied to the structure is supported across this PN junction in the reverse bias. There are several key features in a power MOSFET, which include the pitch of the unit cell, which is the repeat unit for the MOSFET, the channel length, which is the portion of the p-well in which the inversion channel is formed, the distance between two successive p-wells, which is referred to as the JFET region or the JFET gap and the thickness of the gate oxide 205. Another feature is an ILD layer 207 which is used to insulate the source interconnect metallization 208 from the poly-silicon gate 206. At the very center of the unit cell, there is a P+ plug layer 209 which is grounded with the N+ source metallization. The purpose of the P+ plug in SiC DMOSFET is to ground the p-well region with the N+ source contact.

[0455] The p-well region 203 is first formed by ion-implantation or epitaxial growth using aluminum or boron as the p-type impurity. Then, a p-well trench 210 is formed by controlled etching into the p-well region 203 by either RIE or ICP etching using an appropriately patterned hard mask layer. The p-well trench may be formed with a sidewall angle between 70° and 90°. The depth of the p-well trench region 210 may range from 0.1 pm to 0.5 pm. The depth of the p-well trench can be adjusted to be shallower than the depth of the p-well region. The bottom of the p- well trench may be enclosed within the p-well region. A N+ source region is then formed by ionimplantation or by epitaxial re-growth by a n-type impurity such as nitrogen or phosphorus. The p-well trench region may be preferably formed using the same masking step used for performing the ion-implantation necessary for forming the N+ source region 204. A P+ plug layer 209 may be formed by implantation of a controlled dose of a p-type impurity such as aluminum or boron. The depth of the P+ plug layer may exceed the depth of the N+ source implant and may even exceed the depth of the p-well region, in a particular implementation. The remainder of the process constitutes heat treatment of the wafers for electrical activation of the implanted impurities, gateinsulator formation, gate electrode formation, inter-level dielectric formation, source / drain ohmic metallization and finally the formation of pad or interconnect metals compatible with die probing and packaging. The gate insulator 205 is formed by thermal oxidation or using CVD of a dielectric layer such as silicon dioxide, silicon nitride, silicon oxynitride, etc.

[0456] In the embodiment herein, the trench is formed into the p-well region immediately preceding the formation of the N+ source region A portion of the MOS channel is formed parallel to the (0001) crystal plane, while another portion of the MOS channel is formed parallel to the (11- 20) or (1-100) crystal plane of SiC. The DMOSFET fabricated according to this embodiment will have a higher channel density, which can be advantageous for reducing the ON resistance of the device. It is well-known to those in the field of the invention that MOS channels formed on vertical sidewalls, parallel to (11-20) or (10-10) crystal planes of 4H-SiC, can achieve much high fieldeffect mobility as compared to the MOS channels formed on the flat (0001) crystal planes. In an embodiment described here, in addition to increasing the channel density, the effective channel mobility for a DMOSFET fabricated according to this embodiment is expected to be higher than for a DMOSFET fabricated with its MOS channel always parallel to the (0001) crystal plane of 4H-SiC. This desirable feature can be exploited for increasing the effective channel length for a given ON resistance target or reducing the ON resistance for a given chip size, whichever may be of interest to the device designer.

[0457] The embodiment described in this application can be distinguished from the device disclosed by Tega et al. in US patent application: US 2018 / 0331174 Al [henceforth referred to as Ref 1], even though that application describes a SiC MOSFET structure in which the MOS channel is formed on vertical and horizontal p-well surfaces:

[0458] (1) In Ref.1 the MOS channel on the vertical SiC crystal planes is not formed contiguously but only formed at discrete orthogonal locations in the active area. So, there are cross-sections through the Ref. 1 MOSFET that do not contain any MOS channel formation on the vertical SiC sidewall.

[0459] (2) The MOS channel construction in Ref.l is completely different compared to that described in the embodiments herein. In Ref.1, the MOS channel is formed between an N+ source region and a separate N+ accumulation region, which connects the MOS channel to the JFET region

[0460] (3) In Ref. 1, the process of trench creation for realizing MOS channel on the vertical SiC crystal planes is conducted after all implantation steps are completed. As a result, the N+ source region is elevated as compared to the MOS channel formed on the vertical sidewall. In the embodiment described herein, the p-well trench is etched immediately following the p-wellimplantation and prior to the N+ source Implantation which is formed on the recessed region created by the etching of the p-well trench.

[0461] Fig. 19A to Fig. 19U describes the process of manufacturing the structure shown in Fig. 18. The manufacturing process for a SiC DMOSFET is on a SiC substrate 301 and starts with using a 4H-SiC Si-face epi-wafer with suitable doping (1014- 1018cm'3) and thickness (1 pm to 300 pm) for the epilayer 302 shown in Fig. 19 A. A blanket hard mask 303 comprising a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm is deposited in Fig. 19B and then patterned using photolithography followed by a dry etch using RIE for example as shown in Fig. 19C. Then p-well region is first formed by ion-implantation or epitaxial growth using aluminum or boron as the p- type impurity. A p-type implantation 304 comprising of boron or aluminum, at energies ranging from 10 keV to 800 keV, at implant doses ranging from 1012cm'2to 1015cm'2in Fig. 19D is performed to create a p-well 305 in Fig. 19E. The mask 303 is removed, and another hard mask layer 306 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm and then patterned as in Fig. 19F. A p-well trench 308 is formed by controlled etching process 307 into the p-well region by RIE or ICP etching using the appropriately patterned hard mask layer 306 in Fig. 19G. The p-well trench 308 is formed with a sidewall angle between 70° and 90°. The depth of the p-well trench region ranges from 0.1 pm to 0.5 pm. The depth of the p-well trench may be adjusted to be shallower than the depth of the p-well region 305. The bottom of the p-well trench 308 may be enclosed within the p-well region 305. A n-type implant 309 is done for creating a N+ source region 310 in Fig. 19H. AN+ source region is formed by ion-implantation or by epitaxial re-growth by a n-type impurity such as nitrogen or phosphorus. The same hard mask layer 306 used for etching the p-well trench may be advantageously used for patterning the N+ source implant so the source implant is perfectly aligned under the p-well trench. The masking layer 306 is removed in Fig. 191. Another hard mask layer 311 is deposited in Fig. 19J. The hard mask layer 311 is patterned in Fig. 19K. A P+ plug layer may be formed by implantation of a controlled dose of a p-type impurity 312 such as aluminum or boron in Fig. 19L. The depth of the P+ plug layer 313 may preferably exceed the depth of the N+ source implant and may even exceed the depth of the p-well region, in a particular implementation in Fig. 19M. This is followed by the removal of the hard mask 311 using either dry or wet etching techniques commonly practiced by those in the field in Fig. 19N. Then the oxide layer 314 which is the gate oxide is formed by thermal oxidation or using CVD of a dielectric layer such as silicon dioxide, silicon nitride, silicon oxynitride, etc. in Fig. 190. The thickness of the gate oxide could range from 10 nm to 100 nm. Either dry or wet thermal oxidation could be used for oxide growth. Plasma-enhanced chemical vapor deposition (PECVD)or low-pressure chemical vapor deposition (LPCVD) could be used for gate oxide deposition. A polysilicon gate layer 315 is then deposited in Fig. 19P. The polysilicon layer may be deposited using PECVD or LPCVD. The polysilicon layer may be degenerately doped using boron or phosphorus, either in-situ or in a subsequent step. In-situ doping may be performed by the addition of PH3 precursor to the polysilicon deposition chemistry. Post-deposition doping of polysilicon may be performed by depositing a layer of POCh followed by a drive-in step at temperatures ranging from 700-900°C. A hard mask 316 is deposited on top and patterned as shown in Fig. 19Q. The polysilicon gate layer 315 is etched by using the patterned mask layer 316. The mask layer 316 is then removed in Fig. 19R. An ILD layer 317 comprising of 50 nm - 1000 nm thick silicon dioxide, silicon nitride, silicon oxynitride layers or a stacked combination thereof is deposited on the wafer; a hard mask is deposited and patterned on top to define the ILD opening; the ILD layer 317 is patterned using the hard mask as shown in Fig. 19S. Further the gate oxide 314 is etched using the same mask. The mask is then removed and a nickel silicide region 318 is formed on the exposed SiC surface in Fig. 19T. Interconnect metal layers 319 of either aluminum or silver or gold is deposited and patterned on the top and bottom of the chip in Fig. 19U

[0462] An embodiment shown in Fig. 20 is the unit cell of a cross-sectional structure of a SiC DMOSFET. The key regions of this device are a p-well region 403, which is formed by ionimplantation or epitaxial re-growth of a p-type species such as aluminum or boron. There is an N+ source region 404, N- drift layer 402, and an N+ substrate 401. In the ON state when a gate voltage is applied to the polysilicon gate 406, the current flows vertically from the drain 401, through the inversion layer which is formed at the top of the p-well layer 403, through the N+ source region 404, and out through the source metallization 408. In the OFF state or the blocking state, a voltage is supported across the p-well 403, N- drift layer 402 junction and there is a PN junction which is formed between the p-well and the N- drift layer. The voltage applied to the structure is supported across this PN junction in the reverse bias. There are several key features in a power MOSFET, which include the pitch of the unit cell, which is the repeat unit for the MOSFET, the channel length, which is the portion of the p-well in which the inversion channel is formed, the distance between two successive p-wells, which is referred to as the JFET region or the JFET gap and the thickness of the gate oxide 405. Another feature is an ILD layer 407 which is used to insulate the source interconnect metallization 408 from the poly-silicon gate 406. At the very center of the unit cell, there is a P+ plug layer 409 which is grounded with the N+ source metallization. The purpose of the P+ plug in SiC DMOSFET is to ground the p-well region with the N+ source contact.

[0463] A p-well trench 410 is formed by dry etching into the p-well implanted region immediately preceding the source region 404 formation, resulting in a portion of the MOS channel that is formed on the (0001) or horizontal face and another portion of the MOS channel that isformed on the (11-20 / 10-10) or vertical crystal plane of SiC. However, in the embodiment shown in Fig. 20, a much deeper vertical MOS channel is formed by etching all the way through the p- well region. Subsequently, after the formation of the N+ source region, a second p-well region indicated as PW#2411 is ion-implanted under and around the N+ source region in order to suppress reach-through breakdown.

[0464] The p-well region 403 is first formed by ion-implantation or epitaxial growth using aluminum or boron as the p-type impurity. Then, a p-well trench 410 is formed by controlled etching into the p-well region by RIE or ICP etching using an appropriately patterned hard mask layer. The p-well trench 410 may be formed with a sidewall angle between 75° and 90°. The depth of the p-well trench region may range from 0.5 pm to 2 pm. Compared to the device shown in Fig. 18 the device in Fig. 20 has the depth of the p-well trench which may be adjusted to be of the same depth or even slightly deeper than the p-well region. The bottom of the p-well trench in the embodiment shown in Fig. 20 may not be completely enclosed within the p-well region. A N+ source region is then formed by ion-implantation or by epitaxial re-growth by a n-type impurity such as nitrogen or phosphorus. A second p-well region (PW#2) 411 is then formed to a sufficient depth under the N+ source region, such that the lateral extent of the PW#2 region is larger than that of the original p-well region. Two methods for forming the PW#2 411 regions are identified. (1) A dedicated hard mask layer may be deposited and patterned with a slightly larger extent than the original p-well region, and then the ion-implantation for PW#2 may be performed. (2) Tilted ion-implantation may be advantageously used for realizing PW#2. In the embodiment here, the same hard mask may be used for creating the trench, N+ source region and then the PW#2 region, whose lateral extent is made larger than the original p-well region 403 using tilted ion-implantation of a p-type impurity. The remainder of the process constitutes heat treatment of the wafers for electrical activation of the implanted impurities, gate insulator formation, gate electrode formation, inter-level dielectric formation, source / drain ohmic metallization and finally the formation of pad or interconnect metals compatible with die probing and packaging. The gate insulator 405 is formed either by thermal oxidation of the silicon carbide or by CVD of a dielectric layer such as silicon dioxide, silicon nitride, silicon oxynitride, etc.

[0465] The device described in this embodiment in Fig. 20 is an enhancement to the device described in the embodiment in Fig. 18 and has several additional functions and advantages. The vertical portion of the MOS channel of the embodiment in Fig. 20 can be made much larger than the device shown in Fig. 18, due to a deeper p-well trench 410 for the MOSFET in Fig. 20. A larger percentage of the MOS channel can be realized on the higher channel mobility capable vertical sidewall as compared to the horizontal surface. For example, for a total channel length of 1 pm, 0.25 pm of the MOS channel can be realized on the horizontal surface and 0.75 pm of the MOSchannel can be realized on the vertical sidewall. Thus, the effective channel mobility of the device described in embodiment shown in Fig. 20 can be larger than the device described in embodiment shown in Fig. 18, for the same MOS channel length. Hence for the same effective channel mobility, a longer channel MOSFET can be fabricated using embodiment in Fig. 20 as compared to the MOSFET fabricated using embodiment in Fig. 18. A longer channel MOSFET offers higher device robustness, including lower drain saturation current, higher short-circuit robustness, lower Vth roll-off with drain voltage, immunity from drain induced barrier lowering (DIBL) effects.

[0466] In the embodiment in Fig. 20 a larger extent for the PW#2 411 as compared to the original p-well 403 is necessary and beneficial for reducing the channel length of the horizontal portion of the MOS channel. By forming a PW#2 with a larger lateral extent than the original p-well, the drain potential during the high-voltage blocking condition is effectively shielded from the original p-well region by the PW#2 region. This enables a significantly reduced lateral extent (electrical dose) for the original p-well region that extends beyond the p-well trench, without risk of reach- through breakdown. A reduced lateral extent for the p-well region beyond the p-well trench leads to a smaller portion of the MOSFET channel formed on the horizontal surface.

[0467] Fig. 21A to Fig. 21V describes the process of manufacturing the structure shown in Fig. 20. The manufacturing process for a SiC DMOSFET is on a SiC substrate 501 and starts with using a 4H-SiC Si-face epi-wafer with suitable doping (1014- 1018cm'3) and thickness (1 pm to 300 pm) for the epilayer 502 shown in Fig. 21 A. A blanket hard mask 503 comprising a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm is deposited in Fig. 2 IB and then patterned using photolithography followed by a dry etch using a RIE for example as shown in Fig. 21C. Then p- well region is first formed by ion-implantation or epitaxial growth using aluminum or boron as the p-type impurity. A p-type implantation 504 comprising of boron or aluminum, at energies ranging from 10 keV to 800 keV, at implant doses ranging from 1012cm'2to 1015cm'2in Fig. 21D is performed to create a p-well 505 in Fig. 2 IE. The mask 503 is removed, and another hard mask layer 506 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm and then patterned as in Fig. 21F. A deep p-well trench 508 is formed by controlled etching process 507 into the p-well region by RLE or ICP etching using the appropriately patterned hard mask layer 506 in Fig. 21G. The p-well trench 508 may be formed with a sidewall angle between 75° and 90°. The depth of the p-well trench region for example may range from 0.5 pm to 2 pm. The depth of the p- well trench 508 may be adjusted to be of the same depth or even slightly deeper than the p-well region. The bottom of the p-well trench may not be completed enclosed within the p-well region.

[0468] A N-type implant 509 is done for creating a N+ source region 510 in Fig. 21H. A N+ source region is formed by ion-implantation or by epitaxial re-growth by a n-type impurity such as nitrogen or phosphorus. A second p-well region (PW#2) 511 is then formed to a sufficient depth under the N+ source region, such that the lateral extent of the PW#2 region is larger than that of the original p-well region in Fig. 211. Two methods for forming the PW#2 region 511 are identified. (1) A dedicated hard mask layer may be deposited and patterned with a slightly larger extent than the original p-well region, and then the ion-implantation for PW#2 may be performed. (2) Tilted ion-implantation may be advantageously used for realizing PW#2. In this implementation, the same hard mask 506 may be used for creating the p-well trench 508, N+ source region 510 and then the PW#2 region 511, whose lateral extent is made larger than the original p-well region using tilted ion-implantation of a p-type impurity.

[0469] The masking layer 506 is removed in Fig. 21 J. Another hard mask layer 512 is deposited in Fig. 2 IK. The hard mask layer 512 is patterned in Fig. 2 IL. A P+ plug layer may be formed by implantation of a controlled dose of a p-type impurity 513 such as aluminum or boron in Fig. 2 IM. The depth of the P+ plug layer 514 may preferably exceed the depth of the N+ source implant and may even exceed the depth of the p-well region, in a particular implementation in Fig. 2 IN. This is followed by the removal of the hard mask 512 using either dry or wet etching techniques commonly practiced by those in the field in Fig. 210. Then the oxide layer 515 which is the gate oxide is formed by thermal oxidation or using CVD of a dielectric layer such as silicon dioxide, silicon nitride, silicon oxynitride, etc. in Fig. 2 IP. The thickness of the gate oxide could range from 10 nm to 100 nm. Either dry or wet thermal oxidation could be used for oxide growth. PECVD or LPCVD could be used for gate oxide deposition. A polysilicon gate layer 516 is then deposited in Fig. 2 IQ. The polysilicon layer may be deposited using PECVD or LPCVD. The polysilicon layer may be degenerately doped using boron or phosphorus, either in-situ or in a subsequent step. In- situ doping may be performed by the addition of PH3 precursor to the polysilicon deposition chemistry. Post-deposition doping of polysilicon may be performed by depositing a layer of POCL followed by a drive-in step at temperatures ranging from 700-900°C. A hard mask 517 is deposited and patterned as shown in Fig. 21R. The polysilicon gate layer 516 is etched by using the patterned mask layer 517. The mask layer 517 is then removed in Fig. 21 S. An ILD layer 518 comprising of 50 nm - 1000 nm thick silicon dioxide, silicon nitride, silicon oxynitride layers or a stacked combination thereof is deposited on the wafer; a hard mask is deposited and patterned on top to define the ILD opening; the ILD layer 518 is patterned using the hard mask as shown in Fig. 2 IT. Further the gate oxide 515 is etched using the same mask. The mask is then removed and a nickel silicide region 519 is formed on the exposed SiC surface in Fig. 21U. Interconnect metal layers520 of either aluminum, silver or gold is deposited and patterned on the top and bottom of the chip in Fig. 21V.

[0470] An embodiment described herein relates to design and manufacturing of a short-channel SiC MOSFET.

[0471] An embodiment described herein relates to minimizing the DIBL effect of the high voltage, short-channel SiC MOSFETs.

[0472] An embodiment described herein relates to design and manufacturing MOS channels with sub-micron channel lengths.

[0473] The embodiments described herein achieve a device with both low enough ON resistance as well as high enough short circuit withstand time.

[0474] The embodiments described herein relate to increasing the doping concentration of the channel locally in certain regions of the channel. The non-uniformly doped channels for SiC MOSFET provide better tradeoff between ON resistance, threshold voltage and short circuit withstand time.

[0475] In the embodiments described herein relate to increasing the doping concentration in the channel locally such that they do not increase the threshold voltage too much, but at the same time reduce the DIBL effect to achieve a better trade off.

[0476] In an embodiment described herein a p-type shielding layer called the p-shield is formed within the p-well region. The p-shield always originates within the p-well region, but it can extend beyond the vertical extent of the p-well region.

[0477] In an embodiment described herein the bottom of the p-shield region can extend beneath the p-well.

[0478] In an embodiment described herein there can be multiple p-shield regions. The doping concentrations in the different p-shield region can be different from each other.

[0479] The embodiment described herein relates to a device where a p-shield region is formed buried within the p-well structure. The p-shield region always originates within the p-well region, but can extend beyond the vertical extent of the p-well region.

[0480] In an embodiment herein, device structures can have multiple p-shield regions. In these cases, their doping concentration profiles of the different p-shield regions do not necessarily have to be the same and can be different from each other.

[0481] In the race to achieve a lower ON stage resistance in planar gate SiC MOSFET, especially with high breakdown voltage ratings, it's a common practice to make the channel lengths as short as possible because this reduces a great part of the conduction loss that is associated with SiC channels. The MOS mobility in SiC MOS structures is significantly smaller as compared to thosefound in silicon MOSFETS and as a result to achieve a low enough ON resistance, one needs to make the channel lengths quite short and sometimes in the sub-micron range.

[0482] As the channel lengths become shorter, short channel effects become a problem in a SiC power MOSFET causing the drain induced barrier lowering effect, also called the DIBL effect which is responsible for a lot of reliability issues in SiC MOSFETs.

[0483] One associated problem is a roll off of the threshold voltage at high drain bias where the designed device achieves a certain desired threshold voltage only at very low drain bias. But, as the drain bias approaches it's blocking value, the threshold voltage gets reduced substantially which is undesirable since the channel could inadvertently turn on.

[0484] Also, a device suffering the DIBL effect has extremely large saturation currents under high drain bias, which results in excessive power dissipation under short circuit load conditions. This results in a low short circuit withstand time. While limited MOS channel mobility of SiC MOSFETS can be overcome with short channel lengths, it is associated with problems due to DIBL effects.

[0485] One approach to mitigating this problem is to increase the doping concentration in the channel region which uniformly increases the threshold voltage of the device. While this approach can reduce the saturation drain current, this also increases the ON resistance of the device.

[0486] The embodiments described herein can help achieve a device with both low enough ON resistance as well as high enough short circuit withstand time. While the conventional approach is to just uniformly increase the doping concentration in the channel region, the embodiments described herein do not increase the doping concentration of the other channel uniformly but increases it locally in certain regions of the channel. The non-uniformly doped channels for SiC MOSFET provide better tradeoff between ON resistance, threshold voltage and short circuit withstand time.

[0487] In the embodiments herein the doping concentration is increased such that they do not increase the threshold voltage too much, but at the same time reduce the DIBL effect and hence achieving a better trade off.

[0488] In an embodiment herein a p-type shielding layer called the p-shield is formed within the p-well region. The p-shield always originates within the p-well region, but in certain examples of this embodiment, it can extend beyond the vertical extent of the p-well region.

[0489] In an embodiment herein the bottom of the p-shield region can be extended further down and can reach beneath the p-well. In an embodiment herein there can be multiple p-shield regions. The doping concentrations in the different p-shield region can be different from each other.

[0490] In an embodiment herein a p-type shielding layer called the p-shield is formed buried within the p-well region. The p-shield always originates within the p-well region, but in certain examples of this embodiment, it can extend beyond the vertical extent of the p-well region.

[0491] In an embodiment herein the bottom of the p-shield region can be extended further down and can reach beneath the p-well. In an embodiment herein there can be multiple p-shield regions buried in the p-well region. The doping concentrations in the different p-shield region can be different from each other.

[0492] A p-shield region is formed buried within the p-well structure re-enforces” the doping of the p-well region locally and provides better shielding of the MOSFET channel at the surface, while minimizing the DIBL effect. In the embodiment described herein since the p-shield is not directly connected to the channel, the p-shield does not change the VTH.

[0493] An embodiment shown in Fig. 23 A is the half unit cell of a cross-sectional structure of a SiC DMOSFET. The key regions of this device are a p-well region 203, which is formed by ionimplantation or epitaxial re-growth of a p-type species such as aluminum or boron. There is an N+ source region 205, N- drift layer 202, and an N+ substrate 201. In the ON state when a gate voltage is applied to the polysilicon gate 207 the current flows vertically from the drain 201, through the inversion layer which is formed at the top of the p-well layer 203, through the N+ source region 205, and out through the source metallization 210. In the OFF state or the blocking state, a voltage is supported across the p-well 203, N- drift layer 202 junction and there is a PN junction which is formed between the p-well and the N- drift layer. The voltage applied to the structure is supported across this PN junction in the reverse bias. There are several key features in a power MOSFET, which include the pitch of the unit cell, which is the repeat unit for the MOSFET, the channel length, which is the portion of the p-well in which the inversion channel is formed, the distance between two successive p-wells, which is referred to as the junction gate field-effect transistor (JFET) region or the JFET gap and the thickness of the gate oxide 206. Another feature is an ILD layer 208 which is used to insulate the source interconnect metallization 210 from the polysilicon gate 207.

[0494] In the embodiments herein a p-type shielding layer which is called p-shield 204a is formed within the p-well region. The p-shield can be located inside the p-well such that its lateral location of the point whose doping concentration is the highest as compared to the average background doping concentration of the p-well is positioned within the boundary of the p-well. The p-shield region always originates within the p-well region. Points A and B are given as the reference points for describing how the doping profile of the implanted p-shield region looks like.

[0495] The embodiment shown in Fig. 23B is similar to that of Fig. 23 A except that the bottom of the p-shield region is extended further down into the p-well and can reach outside the p-well region.

[0496] In an embodiment shown in Fig. 23C and Fig. 23D the devices are similar to Fig. 23 A. The devices in Fig. 23C and Fig. 23D exemplify the case where there are multiple p-shield regions. In these cases, their doping concentration profiles of the different p-shield regions do not necessarily have to be the same and can be different from each other.

[0497] In case of biasing the drain with high voltage, the p-shield that is formed in the middle of the channel can help in mitigating the expansion of the drain bias-induced depletion region, which eliminates the DIBL effect. In addition to the mitigation of the DIBL effect, the p-shield region also provides a simple way for controlling the VTH of the MOSFET, which enables improving the short circuit time (tsc). The p-shield enables a local increase of the doping concentration of the p- well at critical locations in the device structure, as opposed to an uniform increase of the p-well doping concentration. A better trade-off with respect to lower Vth, ON resistance and better immunity to short-channel effects is obtained by methods described in the embodiment. In the case, where the depth of the p-shield region is greater than the p-well region, i.e., the p-shield extends beyond the p-well region in the vertical direction, the p-shield can also provide better shielding of the electric field to the channel region which further mitigates the DIBL effect in the channel. The device structure with multiple p-shield regions can be designed with different doping concentrations in the different p-shield regions. In an embodiment described herein, a higher doping concentration can be applied to the p-shield region / s close to the edge of the p-well (POINT A), while the p-shield regions closer to POINT B can be made with lower doping concentrations. This structure will have the benefit of a lower gate threshold voltage as well as excellent immunity to short-channel effects, for a given channel length.

[0498] Fig. 24A to Fig. 24U describes the process of manufacturing the structure shown in Fig. 23 A. The manufacturing process for a SiC DMOSFET is on a SiC substrate 301 and starts with using a 4H-SiC Si-face epi-wafer with suitable doping (1014- 1018cm'3) and thickness (1 pm to 300 pm) for the epilayer 302 shown in Fig. 24A. A blanket hard mask 303 comprising a chemical vapor deposition (CVD) deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm is deposited in Fig. 24B and then patterned using photolithography followed by a dry etch using reactive ion etching (RIE) for example as shown in Fig. 24C. The p-well region is first formed by ion-implantation or epitaxial growth using aluminum or boron as the p-type impurity. A p-type implantation 304 comprising boron or aluminum, at energies ranging from 10 keV to 1000 keV, at implant doses ranging from1012cm'2to 1015cm'2is performed to create a p-well 305 in Fig. 24D. The patterned mask layer 303 is removed in Fig. 24E.

[0499] A hard mask layer 306 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm in Fig. 24F. The mask layer 306 is patterned using photolithography followed by a dry etch using RTE for example in Fig. 24G.

[0500] A p-type implant 307 is done as shown in Fig. 24H for creating a p-type region inside the p-well called p-shield 308. The p-shield region 308 can be formed using aluminum or boron as the p-type impurity. The doping concentration in the p-shield region may be in the range of 1E16 cm- 3 to 1E21 cm-3. The patterned mask layer 306 is removed in Fig. 241.

[0501] A blanket hard mask 309 comprising a chemical vapor deposition (CVD) deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm is deposited in Fig. 24J and then patterned using photolithography followed by a dry etch using RIE for example as shown in Fig. 24K.

[0502] A N+ source region 311 is formed by ion-implantation or by epitaxial re-growth by a n- type impurity such as nitrogen or phosphorus 310 in Fig. 24L. The patterned mask layer 309 is removed in Fig. 24M.

[0503] The oxide layer 312 which is the gate oxide is formed by thermal oxidation or using CVD of a dielectric layer such as silicon dioxide, silicon nitride, silicon oxynitride, etc. in Fig. 24N. The thickness of the gate oxide could range from 10 nm to 100 nm. Either dry or wet thermal oxidation could be used for oxide growth. Plasma-enhanced chemical vapor deposition (PECVD) or low- pressure chemical vapor deposition (LPCVD) could be used for gate oxide deposition. A polysilicon gate layer 313 is then deposited in Fig. 240. The polysilicon layer may be deposited using PECVD or LPCVD. The polysilicon layer may be degenerately doped using boron or phosphorus, either in-situ or in a subsequent step. In-situ doping may be performed by the addition of PH3 precursor to the polysilicon deposition chemistry. Post-deposition doping of polysilicon may be performed by depositing a layer of POCh followed by a drive-in step at temperatures ranging from 700-900°C. The polysilicon layer 313 is patterned in Fig. 24P. An ILD layer 314 comprising 50 nm - 1000 nm thick silicon dioxide, silicon nitride, silicon oxynitride layers or a stacked combination thereof is deposited on the wafer in Fig. 24Q. The ILD layer 314 is patterned in Fig. 24R. The gate oxide 312 is patterned in Fig. 24S.

[0504] Nickel silicide regions 315 are formed on the exposed SiC surface in Fig. 24T. Interconnect metal layers 316 of either aluminum or silver or gold is deposited and patterned on the top and bottom of the substrate in. Fig. 24U.

[0505] An embodiment shown in Fig. 25A is the half unit cell of a cross-sectional structure of a SiC DMOSFET. The key regions of this device are a p-well region 403, which is formed by ionimplantation or epitaxial re-growth of a p-type species such as aluminum or boron. There is an N+ source region 405, N- drift layer 402, and an N+ substrate 401. In the ON state when a gate voltage is applied to the polysilicon gate 407 the current flows vertically from the drain 401, through the inversion layer which is formed at the top of the p-well layer 403, through the N+ source region 405, and out through the source metallization 410. In the OFF state or the blocking state, a voltage is supported across the p-well 403, N- drift layer 402 junction and there is a PN junction which is formed between the p-well and the N- drift layer. The voltage applied to the structure is supported across this PN junction in the reverse bias. There are several key features in a power MOSFET, which include the pitch of the unit cell, which is the repeat unit for the MOSFET, the channel length, which is the portion of the p-well in which the inversion channel is formed, the distance between two successive p-wells, which is referred to as the junction gate field-effect transistor region (JFET region) or the JFET gap and the thickness of the gate oxide 406. Another feature is an ILD layer 408 which is used to insulate the source interconnect metallization 410 from the polysilicon gate 407.

[0506] A p-shield region 404a is formed buried within the p-well structure. In other words, the p-shield is formed beneath the SiC surface, where the MOSFET channel is located. The p-shield region always originates within the p-well region as seen in Fig. 25 A, but may in certain examples of this embodiment extend beyond the vertical extent of the p-well region as shown in Fig. 25B.

[0507] The embodiment shown in Fig. 25B is similar to that of Fig. 25 A except that the bottom of the p-shield region is extended further down into the p-well and can reach outside the p-well region.

[0508] Device structures shown in Fig. 25C and Fig. 25D are also similar to the device in Fig. 25A, but they exemplify the case where there are multiple p-shield regions. In these cases, their doping concentration profiles of the different p-shield regions do not necessarily have to be the same and can be different from each other. Points A and B in each of these figures are given as the reference points for describing how the doping profile of the implanted p-shield region looks like.

[0509] The p-shield in Fig. 25 A to Fig. 25D “re-enforces” the doping of the p-well region locally and provides better shielding of the MOSFET channel at the surface, while minimizing the DIBL effect. Since the p-shield is not directly connected to the channel, the p-shield in this case does not change the threshold voltage. The device shown in Fig. 25A provides the same kind of field shielding for mitigating the DIBL but does not require the change of the threshold voltage value where it is inevitable for the device of Fig. 23 A.

[0510] Fig. 26A to Fig. 26U describes the process of manufacturing the structure shown in Fig. 25A. The manufacturing process for a SiC DMOSFET is on a SiC substrate 501 and starts with using a 4H-SiC Si-face epi-wafer with suitable doping (1014- 1018cm'3) and thickness (1 pm to 300 pm) for the epilayer 502 shown in Fig. 26A. A blanket hard mask 503 comprising a chemical vapor deposition (CVD) deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm is deposited in Fig. 26B and then patterned using photolithography followed by a dry etch using reactive ion etching (RIE) for example as shown in Fig. 26C. Then p-well region is first formed by ion-implantation or epitaxial growth using aluminum or boron as the p-type impurity. A p-type implantation 504 comprising boron or aluminum, at energies ranging from 10 keV to 1000 keV, at implant doses ranging from 1012cm'2to 1015cm'2is performed to create a p-well 505 in Fig. 26D. The patterned mask layer 503 is removed in Fig. 26E.

[0511] A hard mask layer 506 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm in Fig. 26F. The mask layer 506 is patterned using photolithography followed by a dry etch using RIE for example in Fig. 26G.

[0512] A p-type implant 507 is done in Fig. 26H for creating a p-type region inside the p-well called p-shield 508. The p-shield region 508 can be formed using aluminum or boron as the p-type impurity. A p-shield region is formed buried within the p-well structure. In other words, the p- shield is formed beneath the SiC surface, where the MOSFET channel is located. The p-shield region always originates within the p-well region. The location of the p-shield region, which is controlled by careful adjustment of the implant energies used for realizing the p-shield region.

[0513] The p-shield region may be created by a p-type ion-implantation step comprising boron or aluminum, at energies ranging from 25 keV to 800 keV, at implant doses ranging from 1012cm'2to 1015cm'2. The patterned mask layer 506 is removed in Fig. 261.

[0514] A blanket hard mask 509 comprising a chemical vapor deposition (CVD) deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm is deposited in Fig. 261 and then patterned using photolithography followed by a dry etch using RIE for example as shown in Fig. 26K.

[0515] A N+ source region 511 is formed by ion-implantation or by epitaxial re-growth by a n- type impurity such as nitrogen or phosphorus 510 in Fig. 26L. The patterned mask layer 509 is removed in Fig. 26M.

[0516] The oxide layer 512 which is the gate oxide is formed by thermal oxidation or using CVD of a dielectric layer such as silicon dioxide, silicon nitride, silicon oxynitride, etc. in Fig. 26N. The thickness of the gate oxide could range from 10 nm to 100 nm. Either dry or wet thermal oxidationcould be used for oxide growth. Plasma-enhanced chemical vapor deposition (PECVD) or low- pressure chemical vapor deposition (LPCVD) could be used for gate oxide deposition. A polysilicon gate layer 513 is then deposited in Fig. 260. The polysilicon layer may be deposited using PECVD or LPCVD. The polysilicon layer may be degenerately doped using boron or phosphorus, either in-situ or in a subsequent step. In-situ doping may be performed by the addition of PH3 precursor to the polysilicon deposition chemistry. Post-deposition doping of polysilicon may be performed by depositing a layer of POOL followed by a drive-in step at temperatures ranging from 700-900°C. The polysilicon layer 513 is patterned in Fig. 26P. An ILD layer 514 comprising 50 nm - 1000 nm thick silicon dioxide, silicon nitride, silicon oxynitride layers or a stacked combination thereof is deposited on the wafer in Fig. 26Q. The ILD layer 514 is patterned in Fig. 26R. The gate oxide 512 is patterned in Fig. 26S.

[0517] Nickel silicide regions 515 are formed on the exposed SiC surface in Fig. 26T. Interconnect metal layers 516 of either aluminum or silver or gold is deposited and patterned on the top and bottom of the substrate in. Fig. 26U.

[0518] The embodiments described herein relate to SiC transistors

[0519] The device described in an embodiment herein has a buried N+ region, which is located in between that P+ islands. The buried N+ region is formed in a way that it is physically separated from the wafer surface because it does not contact the Schottky layer. There is a portion of the N- drift layer in contact with the Schottky surface. The physical separation of the N+ region from the wafer surface is a critical feature of this embodiment since SiC devices at the Schottky metal have the N- doping concentration, not the N+ doping concentration. The silicon carbide surfaces in contact with a Schottky metal has the N- doping concentration which is critical for reducing the strength of the electric field at the Schottky metal interface with the SiC. In an embodiment described herein, the vertical extent of the buried N+ region is lower than the bottom of the P+ region and covers the bottom of the P+ region. The spacing between the P+ islands are narrower and the depth of the P+ islands is deeper when compared to prior art MPS diodes. The presence of the N+ region allows the spacing between the P+ islands to be narrower. The P+ islands shield the electric field that develops during the high voltage operation from the Schottky interface. In the embodiments herein the P+ regions interspersed with the N+ regions are designed such as to achieve a certain level of charge balance between the P+ islands and N+ regions which provides the benefit of further reducing the ON resistance of this device and also keeping a low electric field.

[0520] In an embodiment herein, the bottom of the N+ region is higher than the bottom of the P+ region. The bottom of the P+ region is in contact with the N- drift layer which is a trade off as this will enable lower leakage currents but higher ON resistance. Better ON resistance can be achievedin an embodiment of the device where the N+ region located in between the P+ islands is buried while lower leakage currents can be achieved in an embodiment of the device where the N+ region does not enclose the bottom of the P+ islands completely. In an embodiment described herein, both buried N+ region located in between the P+ islands and N+ region that do not enclose the bottom of the P+ islands completely can exist on the same device.

[0521] In an embodiment described herein the N+ region is formed of several sub N regions while the P+ is formed of many sub P regions such that the doping concentration in each of these different layers or slices could be different. In an embodiment herein either the final slice of the N+ region is underneath the P+ islands and covers around the P+ islands completely or the bottom of the N+ slice is higher than the bottom of the P+ region. The doping concentration of N+ types sub regions farther away from the silicon carbide surface could be progressively higher which may have a benefit of lower conduction losses. In another implementation the doping concentration of the p- type sub regions farther away from the SiC surface could be made progressively lower which may enable better blocking characteristics. The varying doping concentration described in the embodiments herein allows freedom to appropriately tune the device design towards a lower leakage currents, better conduction losses, lowered resistance etc. Better trade off can be achieved with layered and differently doped N+ and P+ regions as opposed to just having one P+ layer and one N+ layer and this can be achieved by using multiple ion implantation steps or multiple epi growth.

[0522] In an embodiment herein the N+ region which is interspersed between a set of multiple P+ wells are formed in such a way that it is physically separated from the wafer surface and extends all the way into the N- drift region. The physical separation of the N+ region from a SiC wafer surface in the embodiments herein distinguishes it from other similar inventions.

[0523] In an embodiment herein, a part of the SiC wafer which is in contact with a Schottky metal (METAL 1) and is an n-type semiconductor has the same doping concentration of the N- drift since the doping concentration of the n-type SiC semiconductor which is in direct contact with the Schottky metal (METAL 1) is critical for reducing the strength of the electric field at the wafer surface, during the high-voltage blocking mode of operation of the SiC MPS diode.

[0524] The device of embodiment shown in Fig. 28A is the cross-sectional schematic of the SiC MPS diode. The key regions of this device are an N+ substrate 201 at the bottom which gives mechanical support of the wafer and is -350 pm-thick. An N- drift region 202 which is usually an epi layer and is on top of the N+ substrate. There are multiple P+ wells 204 that are formed as linear stripes or more complex circular or hexagonal patterns. The device has a first metal layer 205 denoted as METAL 1, which is the Schottky metal to an n-type SiC semiconductor region and forms Schottky contact to its underlying n-type regions. The device has a second metal layer 206denoted as METAL 2 on the front side of the wafer which is in contact with the METAL 1. METAL 2 is often called “power metal” and is usually in Aluminum. There is a silicide layer 207 under the bottom of the N+ substrate. There is a third metal layer 208 denoted as METAL 3 under the back side of the wafer which is in contact with the silicide layer.

[0525] The device shown in Fig. 28A has a N+ region 203 which is interspersed between a set of multiple P+ wells 204. The N+ region 203 is formed in such a way that it is physically separated from the wafer surface and extends all the way into the N- drift region 202. The physical separation of the N+ region from a SiC wafer surface is a critical feature of the embodiment described herein and distinguishes it from other similar inventions. A part of the SiC wafer which is in contact with a Schottky metal 205 denoted as METAL 1 and is an n-type semiconductor has the same doping concentration of the N- drift 202. In the embodiment described herein, the doping concentration of the n-type SiC semiconductor which is in direct contact with the Schottky metal 205 labeled METAL 1 is critical for reducing the strength of the electric field at the wafer surface, during the high-voltage blocking mode of operation of the SiC MPS diode. The vertical extent of the N+ region 203 is lower than the bottom of the P+ region 204. The buried N+ region completely surrounds the P+ region which provides Schottky-injected majority carriers a more conductive travel path and reduces the total forward conduction loss.

[0526] The embodiment described in the device herein, uses a different kind of Schottky metal for the METAL 1 layer when compared to the METAL 1 of the prior art. The choice of METAL 1 205 of the device described in Fig. 28A is made so that the barrier height of its Schottky contact is lower than that of the prior art. Due to the smaller Schottky barrier height, the injection of the majority carrier over the Schottky barrier becomes more efficient and this reflects as a lower Knee Voltage (VKnee) in the forward I-V characteristics as shown in Fig. 28B. The new devices with lower VKnee (marked as #2 and #3) have lower forward conduction loss than their counterpart (marked as #1). The lower Schottky barrier height, leads to higher reverse leakage current as shown in the reverse I-V curves - marked as #2 and #3. The amount of the leakage current can be kept under control in the embodiment described here by fine tuning the barrier height which is dependent on various design elements including but not limited to the annealing temperature of the Schottky contact, the pitch of the device, depth and doping of the P+ region, the doping and depth of the N+ region, and the doping of the N- drift region.

[0527] Another distinct feature of the embodiment described here is that the N+ substrate of the new device is thinner (which is usually 100 ~ 200 pm) than its counterpart (which is usually - 350 pm). The thinned N+ substrate directly impacts on the forward I-V characteristics that the linear region of the forward I-V curves where VF > VKnee becomes steeper because the thinned substrate contributes less series resistance to the total amount of the forward conduction loss. As shown inFig. 28B, the diode with the lower VKnee and thinned substrate (marked #3) must have less conduction loss than another diode with the exact lower VKnee and thick substrate (marked #2). In the embodiment here the Differential On-Resistance (RON, Diff) which is the inverse of the slope of the linear segment of the forward I-V curve is significantly reduced by thinning the N+ substrate. The lower VKnee and RON, Diff of the diode in the embodiment herein enables significant reduction of the forward conduction loss while maintaining the reverse leakage low enough for suitable needs in the market.

[0528] Fig. 29A to Fig. 29L describes the process of manufacturing the structure shown in Fig. 28A. The manufacturing process of the device includes preparing a SiC wafer in Fig. 29A which consists of a highly conductive N+ substrate 301 and an N- drift region 302, where the N- drift region is typically epi-grown. The N- drift region 302 is designed in such a way that the doping concentration and thickness of the N- drift region are primarily selected based on the required blocking performance. When the SiC wafer is prepared, an ion implantation step with an n-type species 303 such as nitrogen and / or phosphorus is performed onto the active region of the device in Fig. 29B forming an N+ region within the N- drift region. The edge termination which is not shown needs to be masked during the n-type ion implantation step. It is important to note that the n-type ion implantation step 303 needs to be performed in such a fashion that the N+ region 304 is completely buried inside the N- drift region in Fig. 29C. The ion implantation step should form the N+ region 304 where the top of the N+ region is physically off from the wafer surface.

[0529] A patterned mask 305, which is preferably a hard mask made of such as an oxide, a nitride, a polysilicon layer, or a combination of these, is formed on the wafer surface in Fig. 29D. The patterned mask must be thick enough to completely block any high energy impurities during the subsequent ion implant step. A p-type ion implantation step with a p-type impurity 306 such as aluminum and / or boron is performed in Fig. 29E to form a set of multiple P+ wells 307 in Fig. 29F. The bottoms of the set of multiple P+ wells 307 are formed such that they are above the bottom of the N+ region 304. In the embodiments herein, the depth of the set of multiple P+ wells are less than the depth of the N+ region. The set of multiple P+ wells leads to a P+ region as a whole in Fig. 29F. The edge termination region which is not shown may be formed by the p-type ion implantation step. The patterned mask 305 is removed by dry or wet etching process in Fig. 29G. This is followed by a process step to electrically activate all the implanted impurity species by coating the wafer with a suitable coating material such as a carbon cap and annealing at high temperature such as 1700°C. The active region is then defined by forming a field oxide layer on the entire wafer surface and clearing out a part of the field oxide where the conduction current needs to flow for on-state operation of the device.

[0530] The Schottky contact is formed on the wafer surface by depositing a Schottky metal 308 marked as METAL 1 directly on the wafer surface in Fig. 29H. The deposited Schottky metal layer is then patterned by using dry etching, wet etching, or lift-off process and annealed at a certain temperature for a certain amount of time by using a furnace or RTA (Rapid Thermal Anneal). The thermal budget of the annealing step after the Schottky metal deposition needs to be carefully designed and controlled because it directly affects the barrier height of the Schottky contact. A first pad metal 309 marked as METAL 2 is then deposited on top of the wafer in Fig. 291 and patterned by dry etching, wet etching, or lift-off. The first pad metal can be of Aluminum / Aluminum-based alloy. The wafer is then thinned from its back side until its thickness reaches to a target thickness of 100 ~ 200 pm in Fig. 29J. The thickness may be further reduced in the future when the wafer thinning technology improves and provides the target thickness less than the aforementioned 100 ~ 200 pm. The wafer thinning can be accomplished by Chemical Mechanical Polishing (CMP), wet etching, dry etching, or a combination of the aforementioned grinding techniques with a proper protective coating at the front side of the wafer.

[0531] A silicide region 310 on the back side of the wafer is then formed in Fig. 29K. The silicide region is required to form a good ohmic contact on the back side of the wafer. The silicide region is formed by depositing ohmic metal stack and annealing the wafer by using a laser annealing technique as an example. A second pad metal 311 marked as METAL 3 is formed on the back side of the wafer in Fig. 29L. The second pad metal can be of Aluminum or Aluminum-based alloy. After the second pad metal step is finished, a protective coating process step may be followed on top of the wafer to form a moisture barrier.

[0532] Another method to fabricate this embodiment is to use a SiC wafer with multiple n-type epi-grown layers to start with. In this case, the SiC wafer consists of three n-type epi-grown layers in Fig. 29C with different doping concentrations and thicknesses and the N+ substrate at the bottom of the SiC wafer. The three n-type epi-grown layers should be formed in such a way that an N- layer 302 is meeting a device side of the wafer and an N+ layer 304 is positioned right underneath the N- layer, where the N+ layer is on top of a second N- layer also labeled 302 which serves as a drift region and the second N- layer is positioned on top of the N+ substrate 301.

[0533] When the SiC wafer with the aforementioned epi structure is prepared, a patterned mask 305, which is preferably a hard mask made of such as an oxide, a nitride, a polysilicon layer, or a combination of these, is formed on the wafer surface in Fig. 29D. The patterned mask must be thick enough to completely block any high energy impurities during the subsequent ion implant step. A p-type ion implantation step with a p-type impurity 306 such as aluminum and / or boron is performed in Fig. 29E to form a set of multiple P+ wells 307 in Fig. 29F. The bottoms of the set of multiple P+ wells 307 are formed such that they are above the bottom of the N+ region 304. Inthe embodiments herein, the depth of the set of multiple P+ wells are less than the depth of the N+ region. The set of multiple P+ wells lead to a P+ region as a whole in Fig. 29F. The edge termination region which is not shown may be formed by the p-type ion implantation step. The patterned mask 305 is removed by dry or wet etching process in Fig. 29G. This is followed by a process step to electrically activate all the implanted impurity species by coating the wafer with a suitable coating material such as a carbon cap and annealing at high temperature such as 1700°C. The active region is then defined by forming a field oxide layer on the entire wafer surface and clearing out a part of the field oxide where the conduction current needs to flow for on-state operation of the device.

[0534] The Schottky contact is formed on the wafer surface by depositing a Schottky metal 308 marked as METAL 1 directly on the wafer surface in Fig. 29H. The deposited Schottky metal layer is then patterned by using dry etching, wet etching, or lift-off process and annealed at a certain temperature for a certain amount of time by using a furnace or RTA. The thermal budget of the annealing step after the Schottky metal deposition needs to be carefully designed and controlled because it directly affects the barrier height of the Schottky contact. A first pad metal 309 marked as METAL 2 is then deposited on top of the wafer in Fig. 291 and patterned by dry etching, wet etching, or lift-off. The first pad metal can be of Aluminum / Aluminum-based alloy. The wafer is then thinned from its back side until its thickness reaches to a target thickness of 100 ~ 200 pm in Fig. 29J. The thickness may be further reduced in the future when the wafer thinning technology improves and provides the target thickness less than the aforementioned 100 ~ 200 pm. The wafer thinning can be accomplished by CMP, wet etching, dry etching, or a combination of the aforementioned grinding techniques with a proper protective coating at the front side of the wafer.

[0535] A silicide region 310 on the back side of the wafer is then formed in Fig. 29K. The silicide region is required to form a good ohmic contact on the back side of the wafer. The silicide region is formed by depositing ohmic metal stack and annealing the wafer by using a laser annealing technique as an example. A second pad metal 311 marked as METAL 3 is formed on the back side of the wafer in Fig. 29L. The second pad metal can be of Aluminum or Aluminum-based alloy. After the second pad metal step is finished, a protective coating process step may be followed on top of the wafer to form a moisture barrier.

[0536] As seen in the embodiment shown in Fig. 28A the P+ region 204 of the SiC MPS diode of this invention is formed in such a way that the set of multiple P+ wells are spaced narrower in lateral direction and extend vertically deeper into the N- drift region 202 when compared to the case of the prior art. The P+ region of this invention, in conjunction with the aforementioned N+ region, is designed to provide a robust shielding to the Schottky barrier formed on the wafer surface. In contrast, the device of the prior art is vulnerable to the high stress of the electric fieldat its Schottky contact which easily results in temporary / permanent degradation of the Schottky contact leading to the high leakage current and / or irreversible destruction of the device. The device in the prior art has the N- drift region as the sole conduction path only, and it is clear that the majority carriers flowing through the JFET-like region between the P+ wells near the wafer surface will suffer in the carrier transport and increase the total forward conduction loss.

[0537] Fig. 28C compares key dimensions of the device structure of this invention. Regardless of the types of the devices, the lateral spacing between two adjacent P+ wells are defined to be W1 and the vertical depth of the P+ wells measured from the surface of the SiC wafer is defined to be DI. It should be noted that the ratio of W1 over DI (or Wl / Dl) for the device of this invention is less than 3.0 (or Wl / Dl < 3.0).

[0538] The device of embodiment shown in Fig. 30 is the cross-sectional schematic of the SiC MPS diode. The key regions of this device are an N+ substrate 401 at the bottom which gives mechanical support of the wafer and is -350 pm-thick. An N- drift region 402 which is usually an epi layer and is on top of the N+ substrate. There are multiple P+ wells 404 that are formed as linear stripes or more complex circular or hexagonal patterns. The device has a first metal layer 405 denoted as METAL 1, which is the Schottky metal to an n-type SiC semiconductor region and forms Schottky contact to its underlying n-type regions. The device has a second metal layer 406 denoted as METAL 2 on the front side of the wafer which is in contact with the METAL 1. METAL 2 is often called “power metal” and is usually in Aluminum. There is a silicide layer 407 under the bottom of the N+ substrate. There is a third metal layer 408 denoted as METAL 3 under the back side of the wafer which is in contact with the silicide layer.

[0539] The device shown in Fig. 30 has a N+ region 403 which is interspersed between a set of multiple P+ wells 404. The N+ region 403 is formed in such a way to extend near the vicinity of the P+ region 404 but not completely cover the bottom of the P+ region. The physical separation of the N+ region from a SiC wafer surface is a critical feature of the embodiment described herein and distinguishes it from other similar inventions. A part of the SiC wafer which is in contact with a Schottky metal 405 denoted as METAL 1 and is an n-type semiconductor has the same doping concentration of the N- drift 402. In the embodiment described herein, the doping concentration of the n-type SiC semiconductor which is in direct contact with the Schottky metal 405 labeled METAL 1 is critical for reducing the strength of the electric field at the wafer surface, during the high-voltage blocking mode of operation of the SiC MPS diode. The vertical extent of the N+ region 403 is above the bottom of the P+ region 404. The buried N+ region does not completely cover the bottom of the P+ region.

[0540] Fig. 31A to Fig. 3 IL describes the process of manufacturing the structure shown in Fig. 30. The manufacturing process of the device includes preparing a SiC wafer in Fig. 31A whichconsists of a highly conductive N+ substrate 501 and an N- drift region 502, where the N- drift region is typically epi-grown. The N- drift region 502 is designed in such a way that the doping concentration and thickness of the N- drift region are primarily selected based on the required blocking performance. When the SiC wafer is prepared, an ion implantation step with an n-type species 503 such as nitrogen and / or phosphorus is performed onto the active region of the device in Fig. 3 IB forming an N+ region within the N- drift region. The edge termination which is not shown needs to be masked during the n-type ion implantation step. It is important to note that the n-type ion implantation step 503 needs to be performed in such a fashion that the N+ region 504 is completely buried inside the N- drift region in Fig. 31C. The ion implantation step should form the N+ region 504 where the top of the N+ region is physically off from the wafer surface.

[0541] A patterned mask 505, which is preferably a hard mask made of such as an oxide, a nitride, a polysilicon layer, or a combination of these, is formed on the wafer surface in Fig. 3 ID. The patterned mask must be thick enough to completely block any high energy impurities during the subsequent ion implant step. A p-type ion implantation step with a p-type impurity 506 such as aluminum and / or boron is performed in Fig. 3 IE to form a set of multiple P+ wells 507 in Fig. 3 IF. The bottoms of the set of multiple P+ wells 507 are formed such that they are below the bottom of the N+ region 504. In the embodiments herein, the depth of the set of multiple P+ wells are greater than the depth of the N+ region. The set of multiple P+ wells lead to a P+ region as a whole in Fig. 3 IF. The edge termination region which is not shown may be formed by the p-type ion implantation step. The patterned mask 505 is removed by dry or wet etching process in Fig. 31G. This is followed by a process step to electrically activate all the implanted impurity species by coating the wafer with a suitable coating material such as a carbon cap and annealing at high temperature such as 1700°C. The active region is then defined by forming a field oxide layer on the entire wafer surface and clearing out a part of the field oxide where the conduction current needs to flow for on-state operation of the device.

[0542] The Schottky contact is formed on the wafer surface by depositing a Schottky metal 508 marked as METAL 1 directly on the wafer surface in Fig. 31H. The deposited Schottky metal layer is then patterned by using dry etching, wet etching, or lift-off process and annealed at a certain temperature for a certain amount of time by using a furnace or RTA. The thermal budget of the annealing step after the Schottky metal deposition needs to be carefully designed and controlled because it directly affects the barrier height of the Schottky contact. A first pad metal 509 marked as METAL 2 is then deposited on top of the wafer in Fig. 311 and patterned by dry etching, wet etching, or lift-off. The first pad metal can be of Aluminum / Aluminum-based alloy. The wafer is then thinned from its back side until its thickness reaches to a target thickness of 100 ~ 200 pm in Fig. 31 J. The thickness may be further reduced in the future when the wafer thinning technologyimproves and provides the target thickness less than the aforementioned 100 ~ 200 pm. The wafer thinning can be accomplished by CMP, wet etching, dry etching, or a combination of the aforementioned grinding techniques with a proper protective coating at the front side of the wafer.

[0543] A silicide region 510 on the back side of the wafer is then formed in Fig. 3 IK. The silicide region is required to form a good ohmic contact on the back side of the wafer. The silicide region is formed by depositing ohmic metal stack and annealing the wafer by using a laser annealing technique as an example. A second pad metal 511 marked as METAL 3 is formed on the back side of the wafer in Fig. 3 IL. The second pad metal can be of Aluminum or Aluminum-based alloy. After the second pad metal step is finished, a protective coating process step may be followed on top of the wafer to form a moisture barrier.

[0544] Another method to fabricate this embodiment is to use a SiC wafer with multiple n-type epi-grown layers to start with. In this case, the SiC wafer consists of three n-type epi-grown layers in Fig. 31C with different doping concentrations and thicknesses and the N+ substrate at the bottom of the SiC wafer. The three n-type epi-grown layers should be formed in such a way that an N- layer 502 is meeting a device side of the wafer and an N+ layer 504 is positioned right underneath the N- layer, where the N+ layer is on top of a second N- layer also labeled 502 which serves as a drift region and the second N- layer is positioned on top of the N+ substrate 501.

[0545] When the SiC wafer with the aforementioned epi structure is prepared, a patterned mask 505, which is preferably a hard mask made of such as an oxide, a nitride, a polysilicon layer, or a combination of these, is formed on the wafer surface in Fig. 3 ID. The patterned mask must be thick enough to completely block any high energy impurities during the subsequent ion implant step. A p-type ion implantation step with a p-type impurity 506 such as aluminum and / or boron is performed in Fig. 3 IE to form a set of multiple P+ wells 507 in Fig. 3 IF. The bottoms of the set of multiple P+ wells 507 are formed such that they are below the bottom of the N+ region 504. In the embodiments herein, the depth of the set of multiple P+ wells are greater than the depth of the N+ region. The set of multiple P+ wells lead to a P+ region as a whole in Fig. 3 IF. The edge termination region which is not shown may be formed by the p-type ion implantation step. The patterned mask 505 is removed by dry or wet etching process in Fig. 31G. This is followed by a process step to electrically activate all the implanted impurity species by coating the wafer with a suitable coating material such as a carbon cap and annealing at high temperature such as 1700°C. The active region is then defined by forming a field oxide layer on the entire wafer surface and clearing out a part of the field oxide where the conduction current needs to flow for on-state operation of the device.

[0546] The Schottky contact is formed on the wafer surface by depositing a Schottky metal 508 marked as METAL 1 directly on the wafer surface in Fig. 31H. The deposited Schottky metal layeris then patterned by using dry etching, wet etching, or lift-off process and annealed at a certain temperature for a certain amount of time by using a furnace or RTA. The thermal budget of the annealing step after the Schottky metal deposition needs to be carefully designed and controlled because it directly affects the barrier height of the Schottky contact. A first pad metal 509 marked as METAL 2 is then deposited on top of the wafer in Fig. 311 and patterned by dry etching, wet etching, or lift-off. The first pad metal can be of Aluminum / Aluminum-based alloy. The wafer is then thinned from its back side until its thickness reaches to a target thickness of 100 ~ 200 pm in Fig. 31 J. The thickness may be further reduced in the future when the wafer thinning technology improves and provides the target thickness less than the aforementioned 100 ~ 200 pm. The wafer thinning can be accomplished by CMP, wet etching, dry etching, or a combination of the aforementioned grinding techniques with a proper protective coating at the front side of the wafer.

[0547] A silicide region 510 on the back side of the wafer is then formed in Fig. 3 IK. The silicide region is required to form a good ohmic contact on the back side of the wafer. The silicide region is formed by depositing ohmic metal stack and annealing the wafer by using a laser annealing technique as an example. A second pad metal 511 marked as METAL 3 is formed on the back side of the wafer in Fig. 3 IL. The second pad metal can be of Aluminum or Aluminum-based alloy. After the second pad metal step is finished, a protective coating process step may be followed on top of the wafer to form a moisture barrier.

[0548] The embodiment shown in Fig. 30 affords lower leakage current and better blocking performance than embodiment shown in Fig. 28A, by further reducing the electrical field at the Schottky metal interface, but may trade-off a higher on-state voltage drop as compared to the embodiment shown in Fig. 28A.

[0549] The devices of embodiments shown in Fig. 32A to Fig. 32F are the cross-sectional schematic of the SiC MPS diode. The key regions of these devices are an N+ substrate 601 at the bottom which gives mechanical support of the wafer and is -350 pm-thick. An N- drift region 602 which is usually an epi layer and is on top of the N+ substrate. The device has a first metal layer 605 denoted as METAL 1, which is the Schottky metal to an n-type SiC semiconductor region and forms Schottky contact to its underlying n-type regions. The device has a second metal layer 606 denoted as METAL 2 on the front side of the wafer which is in contact with the METAL 1. METAL 2 is often called “power metal” and is usually in Aluminum. There is a silicide layer 607 under the bottom of the N+ substrate. There is a third metal layer 608 denoted as METAL 3 under the back side of the wafer which is in contact with the silicide layer. The devices of embodiments in Fig. 32A to Fig. 32F differs from the ones shown in embodiments Fig. 28A and Fig. 30 because the N+ region in the previous embodiments is replaced by a set of multiple N sub-regions 603 arranged in layers. The thickness and doping concentration in each of these sub-regions may be different.Similarly, the P+ region of devices in embodiments of Fig. 28A and Fig. 30 is replaced by a set of multiple layered P sub-regions. The doping concentration in each slice may be preferably designed.

[0550] The devices in embodiments shown in Fig. 32A to Fig. 32F have the N+ region 603 which is interspersed between a set of multiple P+ wells 604. There are several potential examples of the embodiment shown in Fig. 32A to Fig. 32F including a device with a set of multiple n-type sublayers with different thicknesses and doping concentrations but a set of multiple p-type wells which are of the same kind as in Fig. 32A and Fig. 32B, a device with a set of multiple p-type sub-layers with different thicknesses and doping concentrations but a single n-type layer serving as the N+ region as in Fig. 32C and Fig. 32D, a device with a set of multiple n-type sub-layers and a set of multiple p-type sub-layers with different thicknesses and doping concentrations as in Fig. 32E and Fig. 32F. Devices in Fig. 32A, Fig. 32C and Fig. 32E have the N+ region 603 surrounding and under the P+ wells 604, and devices in Fig. 32B, Fig. 32D and Fig. 32F have the N+ region 603 placed in between the P+ wells but not surrounding the P+ wells 604. The physical separation of the N+ region from a SiC wafer surface is a critical feature of the embodiment described herein and distinguishes it from other similar inventions. A part of the SiC wafer which is in contact with a Schottky metal 605 denoted as METAL 1 and is an n-type semiconductor has the same doping concentration of the N- drift 602. In the embodiment described herein, the doping concentration of the n-type SiC semiconductor which is in direct contact with the Schottky metal 605 labeled METAL 1 is critical for reducing the strength of the electric field at the wafer surface, during the high-voltage blocking mode of operation of the SiC MPS diode.

[0551] Fig. 33AA to Fig. 33AL describes the process of manufacturing the structure shown in Fig. 32A. The manufacturing process of the device includes preparing a SiC wafer in Fig. 33AA which consists of a highly conductive N+ substrate 701a and an N- drift region 702a, where the N- drift region is typically epi-grown. The N- drift region 702a is designed in such a way that the doping concentration and thickness of the N- drift region are primarily selected based on the required blocking performance. When the SiC wafer is prepared, a set of multiple ion implantation steps with an n-type species 703a such as nitrogen and / or phosphorus is performed onto the active region of the device in Fig. 33 AB. The set of multiple ion implantation steps with the n-type species forms a set of sub n-type regions 704a in Fig. 33 AC where each sub region is defined by the dotted line in the schematic for indicating the top and bottom of the sub region and all sub regions are interconnected. The interconnected sub regions consist of the N+ region as a whole. The edge termination which is not shown needs to be masked during the set of n-type ion implantation steps. It is important to note that the n-type ion implantation steps 703a needs to be performed in such a fashion that the N+ region 704a is completely buried inside the N- drift region in Fig. 33AC. Theion implantation steps should form the N+ region 704a where the top of the N+ region is physically off from the wafer surface.

[0552] A patterned mask 705a, which is preferably a hard mask made of such as an oxide, a nitride, a polysilicon layer, or a combination of these, is formed on the wafer surface in Fig. 33 AD. The patterned mask must be thick enough to completely block any high energy impurities during the subsequent ion implant step. A p-type ion implantation step with a p-type impurity 706a such as aluminum and / or boron is performed in Fig. 33AE to form a set of multiple P+ wells 707a in Fig. 33AF. The bottoms of the set of multiple P+ wells 707a are formed such that they are above the bottom of the N+ region 704a. In the embodiments herein, the depth of the set of multiple P+ wells are less than the depth of the N+ region. The set of multiple P+ wells lead to a P+ region as a whole in Fig. 33AF. The edge termination region which is not shown may be formed by the p- type ion implantation step. The patterned mask 705a is removed by dry or wet etching process in Fig. 33AG. This is followed by a process step to electrically activate all the implanted impurity species by coating the wafer with a suitable coating material such as a carbon cap and annealing at high temperature such as 1700°C. The active region is then defined by forming a field oxide layer on the entire wafer surface and clearing out a part of the field oxide where the conduction current needs to flow for on-state operation of the device.

[0553] The Schottky contact is formed on the wafer surface by depositing a Schottky metal 708a marked as METAL 1 directly on the wafer surface in Fig. 33AH. The deposited Schottky metal layer is then patterned by using dry etching, wet etching, or lift-off process and annealed at a certain temperature for a certain amount of time by using a furnace or RTA. The thermal budget of the annealing step after the Schottky metal deposition needs to be carefully designed and controlled because it directly affects the barrier height of the Schottky contact. A first pad metal 709a marked as METAL 2 is then deposited on top of the wafer in Fig. 33AI and patterned by dry etching, wet etching, or lift-off. The first pad metal can be of Aluminum / Aluminum-based alloy. The wafer is then thinned from its back side until its thickness reaches to a target thickness of 100 ~ 200 pm in Fig. 33 AJ. The thickness may be further reduced in the future when the wafer thinning technology improves and provides the target thickness less than the aforementioned 100 ~ 200 pm. The wafer thinning can be accomplished by CMP, wet etching, dry etching, or a combination of the aforementioned grinding techniques with a proper protective coating at the front side of the wafer.

[0554] A silicide region 710a on the back side of the wafer is then formed in Fig. 33AK. The silicide region is required to form a good ohmic contact on the back side of the wafer. The silicide region is formed by depositing ohmic metal stack and annealing the wafer by using a laser annealing technique as an example. A second pad metal 711a marked as METAL 3 is formed on the back side of the wafer in Fig. 33AL. The second pad metal can be of Aluminum or Aluminum-based alloy. After the second pad metal step is finished, a protective coating process step may be followed on top of the wafer to form a moisture barrier.

[0555] Another method to fabricate this embodiment is to use a SiC wafer with multiple n-type epi-grown layers to start with. In this case, the SiC wafer consists of multiple n-type epi-grown layers in Fig. 33AC with different doping concentrations and thicknesses and the N+ substrate at the bottom of the SiC wafer. On top of the N+ substrate 701a, an N- drift layer 702a can be epi- grown for serving as a drift / blocking layer. On top of the N- drift layer, a number of n-type epilayers can be grown to form an N+ region 704a as a whole which consists of a set of sub n-type regions where each sub region is defined by different doping concentration and thickness and all sub regions are interconnected. On top of the buried N+ region, an N- layer can be formed which reaches to the surface of the SIC wafer 702a.

[0556] When the SiC wafer with the aforementioned epi structure is prepared, a patterned mask 705a, which is preferably a hard mask made of such as an oxide, a nitride, a polysilicon layer, or a combination of these, is formed on the wafer surface in Fig. 33AD. The patterned mask must be thick enough to completely block any high energy impurities during the subsequent ion implant step. A p-type ion implantation step with a p-type impurity 706a such as aluminum and / or boron is performed in Fig. 33AE to form a set of multiple P+ wells 707a in Fig. 33AF. The bottoms of the set of multiple P+ wells 707a are formed such that they are above the bottom of the N+ region 704a. In the embodiments herein, the depth of the set of multiple P+ wells are less than the depth of the N+ region. The set of multiple P+ wells lead to a P+ region as a whole in Fig. 33AF. The edge termination region which is not shown may be formed by the p-type ion implantation step. The patterned mask 705a is removed by dry or wet etching process in Fig. 33 AG. This is followed by a process step to electrically activate all the implanted impurity species by coating the wafer with a suitable coating material such as a carbon cap and annealing at high temperature such as 1700°C. The active region is then defined by forming a field oxide layer on the entire wafer surface and clearing out a part of the field oxide where the conduction current needs to flow for on-state operation of the device.

[0557] The Schottky contact is formed on the wafer surface by depositing a Schottky metal 708a marked as METAL 1 directly on the wafer surface in Fig. 33AH. The deposited Schottky metal layer is then patterned by using dry etching, wet etching, or lift-off process and annealed at a certain temperature for a certain amount of time by using a furnace or RTA. The thermal budget of the annealing step after the Schottky metal deposition needs to be carefully designed and controlled because it directly affects the barrier height of the Schottky contact. A first pad metal 709a marked as METAL 2 is then deposited on top of the wafer in Fig. 33AI and patterned by dry etching, wet etching, or lift-off. The first pad metal can be of Aluminum / Aluminum-based alloy. The wafer isthen thinned from its back side until its thickness reaches to a target thickness of 100 ~ 200 gm in Fig. 33 AJ. The thickness may be further reduced in the future when the wafer thinning technology improves and provides the target thickness less than the aforementioned 100 ~ 200 pm. The wafer thinning can be accomplished by CMP, wet etching, dry etching, or a combination of the aforementioned grinding techniques with a proper protective coating at the front side of the wafer.

[0558] A silicide region 710a on the back side of the wafer is then formed in Fig. 33AK. The silicide region is required to form a good ohmic contact on the back side of the wafer. The silicide region is formed by depositing ohmic metal stack and annealing the wafer by using a laser annealing technique as an example. A second pad metal 711a marked as METAL 3 is formed on the back side of the wafer in Fig. 33 AL. The second pad metal can be of Aluminum or Aluminum- based alloy. After the second pad metal step is finished, a protective coating process step may be followed on top of the wafer to form a moisture barrier.

[0559] Fig. 33BA to Fig. 33BL describes the process of manufacturing the structure shown in Fig. 32B. The manufacturing process of the device includes preparing a SiC wafer in Fig. 33BA which consists of a highly conductive N+ substrate 701b and an N- drift region 702b, where the N- drift region is typically epi-grown. The N- drift region 702b is designed in such a way that the doping concentration and thickness of the N- drift region are primarily selected based on the required blocking performance. When the SiC wafer is prepared, a set of multiple ion implantation steps with an n-type species 703b such as nitrogen and / or phosphorus is performed onto the active region of the device in Fig. 33BB. The set of multiple ion implantation steps with the n-type species forms a set of sub n-type regions 704b in Fig. 33BC where each sub region is defined by the dotted line in the schematic for indicating the top and bottom of the sub region and all sub regions are interconnected. The interconnected sub regions consist of the N+ region as a whole. The edge termination which is not shown needs to be masked during the set of n-type ion implantation steps. It is important to note that the n-type ion implantation steps 703b needs to be performed in such a fashion that the N+ region 704b is completely buried inside the N- drift region in Fig. 33BC. The ion implantation steps should form the N+ region 704b where the top of the N+ region is physically off from the wafer surface.

[0560] A patterned mask 705b, which is preferably a hard mask made of such as an oxide, a nitride, a polysilicon layer, or a combination of these, is formed on the wafer surface in Fig. 33BD. The patterned mask must be thick enough to completely block any high energy impurities during the subsequent ion implant step. A p-type ion implantation step with a p-type impurity 706b such as aluminum and / or boron is performed in Fig. 33BE to form a set of multiple P+ wells 707b in Fig. 33BF. The bottoms of the set of multiple P+ wells 707b are formed such that they are below the bottom of the N+ region 704b. In the embodiments herein, the depth of the set of multiple P+wells are greater than the depth of the N+ region. The set of multiple P+ wells lead to a P+ region as a whole in Fig. 33BF. The edge termination region which is not shown may be formed by the p-type ion implantation step. The patterned mask 705b is removed by dry or wet etching process in Fig. 33BG. This is followed by a process step to electrically activate all the implanted impurity species by coating the wafer with a suitable coating material such as a carbon cap and annealing at high temperature such as 1700°C. The active region is then defined by forming a field oxide layer on the entire wafer surface and clearing out a part of the field oxide where the conduction current needs to flow for on-state operation of the device.

[0561] The Schottky contact is formed on the wafer surface by depositing a Schottky metal 708b marked as METAL 1 directly on the wafer surface in Fig. 33BH. The deposited Schottky metal layer is then patterned by using dry etching, wet etching, or lift-off process and annealed at a certain temperature for a certain amount of time by using a furnace or RTA. The thermal budget of the annealing step after the Schottky metal deposition needs to be carefully designed and controlled because it directly affects the barrier height of the Schottky contact. A first pad metal 709b marked as METAL 2 is then deposited on top of the wafer in Fig. 33BI and patterned by dry etching, wet etching, or lift-off. The first pad metal can be of Aluminum / Aluminum-based alloy. The wafer is then thinned from its back side until its thickness reaches to a target thickness of 100 ~ 200 pm in Fig. 33BJ. The thickness may be further reduced in the future when the wafer thinning technology improves and provides the target thickness less than the aforementioned 100 ~ 200 pm. The wafer thinning can be accomplished by CMP, wet etching, dry etching, or a combination of the aforementioned grinding techniques with a proper protective coating at the front side of the wafer.

[0562] A silicide region 710b on the back side of the wafer is then formed in Fig. 33BK. The silicide region is required to form a good ohmic contact on the back side of the wafer. The silicide region is formed by depositing ohmic metal stack and annealing the wafer by using a laser annealing technique as an example. A second pad metal 711b marked as METAL 3 is formed on the back side of the wafer in Fig. 33BL. The second pad metal can be of Aluminum or Aluminum- based alloy. After the second pad metal step is finished, a protective coating process step may be followed on top of the wafer to form a moisture barrier.

[0563] Another method to fabricate this embodiment is to use a SiC wafer with multiple n-type epi-grown layers to start with. In this case, the SiC wafer consists of multiple n-type epi-grown layers in Fig. 33BC with different doping concentrations and thicknesses and the N+ substrate at the bottom of the SiC wafer. On top of the N+ substrate 701b, an N- drift layer 702b can be epi- grown for serving as a drift / blocking layer. On top of the N- drift layer, a number of n-type epilayers can be grown to form an N+ region 704b as a whole which consists of a set of sub n-type regions where each sub region is defined by different doping concentration and thickness and allsub regions are interconnected. On top of the buried N+ region, an N- layer can be formed which reaches to the surface of the SIC wafer 702b.

[0564] When the SiC wafer with the aforementioned epi structure is prepared, a patterned mask 705b, which is preferably a hard mask made of such as an oxide, a nitride, a polysilicon layer, or a combination of these, is formed on the wafer surface in Fig. 33BD. The patterned mask must be thick enough to completely block any high energy impurities during the subsequent ion implant step. A p-type ion implantation step with a p-type impurity 706b such as aluminum and / or boron is performed in Fig. 33BE to form a set of multiple P+ wells 707b in Fig. 33BF. The bottoms of the set of multiple P+ wells 707b are formed such that they are below the bottom of the N+ region 704b. In the embodiments herein, the depth of the set of multiple P+ wells are greater than the depth of the N+ region. The set of multiple P+ wells lead to a P+ region as a whole in Fig. 33BF. The edge termination region which is not shown may be formed by the p-type ion implantation step. The patterned mask 705b is removed by dry or wet etching process in Fig. 33BG. This is followed by a process step to electrically activate all the implanted impurity species by coating the wafer with a suitable coating material such as a carbon cap and annealing at high temperature such as 1700°C. The active region is then defined by forming a field oxide layer on the entire wafer surface and clearing out a part of the field oxide where the conduction current needs to flow for on-state operation of the device.

[0565] The Schottky contact is formed on the wafer surface by depositing a Schottky metal 708b marked as METAL 1 directly on the wafer surface in Fig. 33BH. The deposited Schottky metal layer is then patterned by using dry etching, wet etching, or lift-off process and annealed at a certain temperature for a certain amount of time by using a furnace or RTA. The thermal budget of the annealing step after the Schottky metal deposition needs to be carefully designed and controlled because it directly affects the barrier height of the Schottky contact. A first pad metal 709b marked as METAL 2 is then deposited on top of the wafer in Fig. 33BI and patterned by dry etching, wet etching, or lift-off. The first pad metal can be of Aluminum / Aluminum-based alloy. The wafer is then thinned from its back side until its thickness reaches to a target thickness of 100 ~ 200 pm in Fig. 33BJ. The thickness may be further reduced in the future when the wafer thinning technology improves and provides the target thickness less than the aforementioned 100 ~ 200 pm. The wafer thinning can be accomplished by CMP, wet etching, dry etching, or a combination of the aforementioned grinding techniques with a proper protective coating at the front side of the wafer.

[0566] A silicide region 710b on the back side of the wafer is then formed in Fig. 33BK. The silicide region is required to form a good ohmic contact on the back side of the wafer. The silicide region is formed by depositing ohmic metal stack and annealing the wafer by using a laser annealing technique as an example. A second pad metal 711b marked as METAL 3 is formed onthe back side of the wafer in Fig. 33BL. The second pad metal can be of Aluminum or Aluminum- based alloy. After the second pad metal step is finished, a protective coating process step may be followed on top of the wafer to form a moisture barrier.

[0567] Fig. 33EA to Fig. 33EL describes the process of manufacturing the structure shown in Fig. 32E. The manufacturing process of the device includes preparing a SiC wafer in Fig. 33EA which consists of a highly conductive N+ substrate 701e and an N- drift region 702e, where the N- drift region is typically epi-grown. The N- drift region 702e is designed in such a way that the doping concentration and thickness of the N- drift region are primarily selected based on the required blocking performance. When the SiC wafer is prepared, a set of multiple ion implantation steps with an n-type species 703e such as nitrogen and / or phosphorus is performed onto the active region of the device in Fig. 33EB. The set of multiple ion implantation steps with the n-type species forms a set of sub n-type regions 704e in Fig. 33EC where each sub region is defined by the dotted line in the schematic for indicating the top and bottom of the sub region and all sub regions are interconnected. The interconnected sub regions consist of the N+ region as a whole. The edge termination which is not shown needs to be masked during the set of n-type ion implantation steps. It is important to note that the n-type ion implantation steps 703e needs to be performed in such a fashion that the N+ region 704e is completely buried inside the N- drift region in Fig. 33EC. The ion implantation steps should form the N+ region 704e where the top of the N+ region is physically off from the wafer surface.

[0568] A patterned mask 705e, which is preferably a hard mask made of such as an oxide, a nitride, a polysilicon layer, or a combination of these, is formed on the wafer surface in Fig. 33ED. The patterned mask must be thick enough ...

Claims

WHAT IS CLAIMED IS:

1. A device comprising a unit cell on a SiC substrate, the unit cell comprising: a gate insulator film, a trench in a well region, a first sinker region having a second conduction type, wherein the first sinker region has a depth that is equal to or greater than a depth of the well region, and a second sinker region having the second conduction type; and wherein each of the first sinker region and the second sinker region is in contact with a region having a first conduction type to form a p-n junction.

2. The device of claim 1, wherein the device comprises a semiconductor metal-insulator- semiconductor transistor component.

3. The device of claim 1, wherein the well region is next to an insulator-semiconductor interface; and a source region of the first conduction type formed within the well region.

4. The device of claim 3, wherein a depth of the trench is greater than or equal to a thickness of the source region.

5. The device of claim 1, wherein the first sinker region is located below the trench.

6. The device of claim 1, wherein a depth of the second sinker region is less than the depth of the first sinker region.

7. The device of claim 1, wherein a depth of the second sinker region is greater than the depth of the well region.

8. The device of claim 1, wherein the device has an on-resistance of less than 4 milliohm centimeter squared, a gate threshold voltage of greater than 1.5 Volt, a breakdown voltage of greater than 500 Volt, and an electric field of less than 3.5 megavolt per cm in the gate insulator film.

9. A device comprising a unit cell on a SiC substrate, the unit cell comprising: a gate insulator film, a trench in a well region, a first sinker region of a second conduction type,a second sinker region of the second conduction type, and a source region; and wherein the source region is in direct contact with the second sinker region.

10. The device of claim 9, wherein the device comprises a semiconductor metal -insulator-transistor component.

11. The device of claim 9, wherein the unit cell further comprises a semiconductor body of a first conduction type that comprises a drift zone; the well region of the second conduction type next to an insulator-semiconductor interface; and the source region of the first conduction type formed within the well region.

12. The device of claim 11, wherein a depth of the trench is greater than or equal to a thickness of the source region.

13. The device of claim 9, wherein a depth of the trench is greater than a depth of the source region.

14. The device of claim 9, wherein the device has an avalanche energy of greater than 10 Joule per centimeter squared, calculated by dividing an avalanche energy in Joules by a total die area in centimeter squared.

15. The device of claim 9, wherein an avalanche failure is located within the unit cell.

16. A device comprising a unit cell on a SiC substrate, the unit cell comprising: a gate insulator film, a trench in a well region, a first sinker region of a second conduction type, a second sinker region of the second conduction type, and a source region; wherein the first sinker region has a depth that is greater than a depth of the second sinker region; and wherein the second sinker has a width that is greater than that of the first sinker.

17. The device of claim 16, wherein the first sinker region is located below the trench.

18. The device of claim 16, wherein the depth of the second sinker region is less than the depth of the first sinker region.

19. The device of claim 16, wherein the depth of the second sinker region is greater than a depth of the well region.

20. A device comprising a unit cell on a Silicon Carbide (SiC) substrate, the unit cell comprising: a first conductivity type first source region; a first conductivity type second source region; a second conductivity type well region; and a silicide layer, wherein the device comprises a vertical Silicon Carbide (SiC) double-implantation metal oxide semiconductor field-effect transistor (DMOSFET) comprising a drain terminal on a backside of the SiC substrate and a source terminal on a topside of the SiC substrate, wherein the first conductivity type second source region comprises a thickness lower than a thickness of the first conductivity type first source region, and wherein the first conductivity type second source region is interspersed between the second conductivity type well region and the silicide layer; and wherein the first conductivity type second source region comprises a sheet of source region located between a recessed SiC trench region and the second conductivity type well region.

21. The device of claim 20, wherein the sheet of source region comprises a thin sheet of source region.

22. The device of claim 20, wherein the first conductivity type second source region comprises at least one of (a) a target thickness and (b) a target doping concentration.

23. The device of claim 22, wherein the target thickness of the first conductivity type second source region ranges from 1 nm to 1 pm and the target doping concentration ranges from 1015cm'3to 1021-3 cm .

24. The device of claim 20, wherein the first conductivity type second source region comprises a sheet of source region located between the silicide layer and the second conductivity type well region.16525. The device of claim 20, capable of carrying a drain current of less than negative 500 milliamperes at a drain voltage of negative 3 volts.

26. A device comprising a unit cell on a silicon carbide (SiC) substrate, the unit cell comprising: a first conductivity type source region; a second conductivity type well region; and a second conductivity type shield region, wherein the second conductivity type shield region is confined within the second conductivity type well region.

27. The device of claim 26, wherein the second conductivity type shield region is located within a metal oxide semiconductor field-effect transistor (MOSFET) channel.

28. The device of claim 27, wherein the second conductivity type shield region is located closer to an edge of the second conductivity type well region.

29. The device of claim 26, wherein a doping concentration inside the second conductivity type well region is non-uniform in a lateral direction.

30. The device of claim 26, wherein a doping concentration inside the second conductivity type shield region is higher than a doping concentration inside the second conductivity type well region.

31. The device of claim 26, wherein the second conductivity type shield region extends beyond a vertical extent of the second conductivity type well region.

32. The device of claim 26, wherein the device further comprises a trench region in the second conductivity type well region, the trench region comprises a depth of one of greater than and equal to a thickness of the first conductivity type source region.

33. The device of claim 26, wherein the device comprises a gate oxide layer in contact with the second conductivity type well region and the first conductivity type source region, the device comprises a double-implantation metal oxide semiconductor field-effect transistor (DMOSFET).16634. The device of claim 26, wherein the device comprises multiple second conductivity type shield regions within a metal oxide semiconductor field-effect transistor (MOSFET) channel.

35. The device of claim 34, wherein the multiple second conductivity type shield regions located closer to an edge of the second conductivity type well region.

36. The device of claim 34, wherein the multiple second conductivity type shield regions extend beyond a vertical extent of the second conductivity type well region.

37. The device of claim 27, wherein the second conductivity type shield region is buried within the second conductivity type well region.

38. A device comprising a unit cell on a silicon carbide (SiC) substrate, the unit cell comprising: a first conductivity type source region; a second conductivity type well region; and a second conductivity type shield region, wherein the second conductivity type shield region is confined within the second conductivity type well region, and wherein the second conductivity type shield region shields a metal oxide semiconductor fieldeffect transistor (MOSFET) channel from a high potential applied to a drain terminal.

39. The device of claim 38, wherein the device further comprises a trench region in the second conductivity type well region, the trench region comprises a depth of one of greater than and equal to a thickness of the first conductivity type source region.

40. The device of claim 39, wherein the device comprises a gate threshold voltage of greater than 2.5 volts, a breakdown voltage of greater than 3300 volts at a gate to source voltage of 0 volt, an on-resistance of less than 15 milliohm centimeter squared, and a short-circuit withstand time of greater than 4 microseconds at a drain voltage of 1500 volts.

41. The device of claim 39, wherein the device comprises a gate threshold voltage of greater than 2 volts, a breakdown voltage of greater than 1200 volts at a gate to source voltage bias of 0 volt, an on-resistance of less than 4.5 milliohm centimeter squared, and a short-circuit withstand time of greater than 2.5 microseconds at a drain voltage of 800 volts.16742. The device of claim 39, wherein the device comprises a gate threshold voltage of greater than2.5 volts, a breakdown voltage of greater than 6500 volts at a gate to source voltage of 0 volt, an on-resistance of less than 50 milliohm centimeter squared, and a short-circuit withstand time of greater than 4 microseconds at a drain voltage of 3600 volts.

43. The device of claim 39, wherein the device comprises a gate threshold voltage of greater than2.5 volts, a breakdown voltage of greater than 10000 volts at a gate to source voltage of 0 volt, an on-resistance of less than 100 milliohm centimeter squared, and a short-circuit withstand time of greater than 4 microseconds at a drain voltage of 5000 volts.

44. The device of claim 39, wherein the device comprises a gate threshold voltage of greater than2.5 volts, a breakdown voltage of greater than 13000 volts at a gate to source voltage of 0 volt, an on-resistance of less than 400 milliohm centimeter squared, and a short-circuit withstand time of greater than 4 microseconds at a drain voltage of 10000 volts.

45. The device of claim 38, wherein the second conductivity type shield region shields the metal oxide semiconductor field-effect transistor (MOSFET) channel from the high potential applied to the drain terminal during one of an off-state and a blocking operation.

46. A method comprising: forming a silicon carbide (SiC) metal oxide semiconductor field-effect transistor (MOSFET); forming a second conductivity type well region; forming a first conductivity type source region within the second conductivity type well region; and forming a second conductivity type shield region, wherein the second conductivity type shield region is located outside the first conductivity type source region.

47. The method of claim 46, wherein the second conductivity type shield region is located within the second conductivity type well region.

48. The method of claim 46, wherein the second conductivity type shield region extends beyond the second conductivity type well region.

49. The method of claim 46, wherein the SiC MOSFET is manufactured on SiC epi-wafer comprising a doping ranging from 1014to 1018cm'3and a thickness ranging from 1 micrometers (pm) to 300 micrometers (pm).

50. The method of claim 46, wherein forming the second conductivity type well region comprises: depositing a hard mask comprising at least one of a silicon dioxide layer, a silicon nitride layer, a polysilicon layer, a silicon oxynitride layer, and a metallic layer with a total thickness ranging from 50 nanometers to 5 micrometers; patterning the hard mask; etching the hard mask; and performing one of an ion-implantation and an epitaxial growth using second conductivity type ions, wherein performing the ion-implantation comprises implanting the second conductivity type ions at energies ranging from 10 keV to 1000 keV, and at implant doses ranging from 1012cm'2to 1015cm'2, and wherein the second conductivity type ions comprise one of aluminum and boron.

51. The method of claim 46, wherein forming the second conductivity type shield region comprises forming the second conductivity type shield region closer to an edge of the second conductivity type well region.

52. The method of claim 46, wherein forming the second conductivity type shield region comprises forming the second conductivity type shield region confined within the second conductivity type well region.

53. The method of claim 46, further comprising forming a metal oxide semiconductor field-effect transistor (MOSFET) channel.

54. The method of claim 53, wherein forming the second conductivity type shield region comprises forming the second conductivity type shield region in contact with the metal oxide semiconductor field-effect transistor (MOSFET) channel.

55. The method of claim 53, wherein forming the second conductivity type shield region comprises forming multiple second conductivity type shield regions in contact with the metal oxide semiconductor field-effect transistor (MOSFET) channel.

56. The method of claim 46, wherein forming the first conductivity type source region comprises forming the first conductivity type source region using one of nitrogen and phosphorus ions.

57. The method of claim 46, further comprising:forming a gate oxide layer; forming a polysilicon gate layer; forming an interlayer dielectric (ILD) layer; forming a silicide region; and forming an interconnect metal layer.

58. The method of claim 57, wherein forming the gate oxide layer comprises performing either one or a stacked combination of a thermal oxidation and a chemical vapor deposition (CVD) of a dielectric layer of one of a silicon dioxide layer, a silicon nitride layer, and a silicon oxynitride layer, wherein the gate oxide layer is formed with a thickness ranging from 10 nanometers to 100 nanometers.

59. The method of claim 57, wherein forming the polysilicon gate layer comprises depositing a polysilicon layer using one of a plasma-enhanced chemical vapor deposition (PECVD) and a low- pressure chemical vapor deposition (LPCVD) through one of an in-situ doping and a subsequent drive-in doping.

60. The method of claim 57, wherein forming the interlayer dielectric (ILD) layer comprises depositing one of at least one of a silicon dioxide layer, a silicon nitride layer, and a silicon oxynitride layer; and a stacked combination of the silicon dioxide layer, the silicon nitride layer, and the silicon oxynitride layer, the ILD layer comprises a thickness one of greater than and equal to 50 nanometers.

61. The method of claim 57, wherein forming the silicide region comprises forming a nickel silicide region on exposed SiC surface.

62. The method of claim 46, wherein forming the second conductivity type shield region comprises forming the second conductivity type shield region extending beyond a vertical extent of the second conductivity type well region.

63. A method comprising: forming a silicon carbide (SiC) metal oxide semiconductor field-effect transistor (MOSFET); forming a second conductivity type well region; forming a first conductivity type source region within the second conductivity type well region; and forming a second conductivity type shield region, wherein the second conductivity type shield region is locatedoutside the first conductivity type source region, wherein a doping concentration in the second conductivity type well region within a metal oxide semiconductor field-effect transistor (MOSFET) channel is non-uniform, and wherein at least a portion of the second conductivity type shield region is located within the second conductivity type well region.

64. The method of claim 63, wherein doping concentration profiles of the second conductivity type shield region at different locations are different.

65. The method of claim 63, wherein doping concentration profiles of the second conductivity type shield region at different locations are not different.

66. A semiconductor component, comprising a semiconductor body of a first conduction type comprising a voltage blocking layer; and islands of a second conductivity type on a contact surface; and a metal layer on the voltage blocking layer, wherein the metal layer and the voltage blocking layer includes a Schottky contact, and a first conductivity type layer comprising the first conduction type not in contact with the Schottky contact that is interspersed between the islands of the second conductivity type.

67. The semiconductor component of claim 66, wherein a vertical extent of the first conductivity type layer is lower than a bottom of the islands of the second conductivity type.

68. The semiconductor component of claim 66, wherein a vertical extent of the first conductivity type layer is higher than a bottom of the islands of the second conductivity type.

69. The semiconductor component of claim 66, wherein a doping concentration within the first conductivity type layer is non-uniform in a direction that is perpendicular to the Schottky contact.

70. The semiconductor component of claim 66, wherein a vertical extent of the first conductivity type layer is higher or lower than a bottom of the islands of the second conductivity type.

71. The semiconductor component of claim 66, wherein the first conductivity type layer has a doping concentration that does not vary in any direction along the contact surface.

72. The semiconductor component of claim 66, wherein the first conductivity type layer has a first doping concentration that is higher than a second doping concentration of a drift region.17173. The semiconductor component of claim 66, wherein the first conductivity type layer has a first doping concentration that is lower than a second doping concentration of a drift region.

74. The semiconductor component of claim 66, wherein the Schottky contact comprises a metal comprising Al, Ag, Au, Mo, Ni, Ti, W, TixWy, TixNy, or combinations thereof.

75. A diode comprising P+ islands interspersed within a N+ region and a N- region contacts with a Schottky layer.

76. The diode of claim 75, wherein a vertical extent of the N+ region is lower than a bottom of the P+ islands.

77. The diode of claim 75, wherein a vertical extent of the N+ region is higher than a bottom of the P+ islands.

78. The diode of claim 75, wherein a doping concentration within the N+ region is non-uniform in a direction that is perpendicular to the Schottky layer.

79. The diode of claim 75, wherein a vertical extent of the N+ region is higher or lower than a bottom of the P+ islands.

80. A diode comprising N+ islands interspersed within a P+ region and a P- region contacts with a Schottky layer.

81. The diode of claim 80, wherein a vertical extent of the P+ region is lower than a bottom of the N+ islands.

82. The diode of claim 80, wherein a vertical extent of the P+ region is higher than a bottom of the N+ islands.

83. The diode of claim 80, wherein a doping concentration within the P+ region is non-uniform in a direction that is perpendicular to the Schottky layer.

84. The diode of claim 80, wherein a vertical extent of the P+ region is higher or lower than a bottom of the N+ islands.172

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