Silicon Carbide Devices with SCHOTTKY Contacts

Abstract

A silicon carbide device with SCHOTTKY contact. A silicon carbide device (500) includes a silicon carbide body (100), the silicon carbide body (100) including a source region (110) of a first conductivity type, a cathode region (160) of a first conductivity type, and a separation region (140) of a second conductivity type. A strip-shaped gate structure (150) extends along a first direction (291) and directly adjoins the source region (110) and the separation region (140). The silicon carbide device (500) further includes a first load electrode (310). Along the first direction (291), the cathode region (160) is located between two separation regions in the separation region (140), and at least one separation region in the separation region (140) is located between the cathode region (160) and the source region (110). The source region (110) and the first load electrode (310) form an ohmic contact (OC), and the first load electrode (310) and the cathode region (160) form a Schottky contact (SC).

Description

Technical Field

[0001] The present disclosure relates to a silicon carbide device, and in particular, to a silicon carbide device having a transistor cell and a Schottky contact. Background Art

[0002] Power semiconductor devices are typically used as switches and rectifiers in circuits for converting electrical energy, such as DC / AC converters, AC / AC converters, or AC / DC converters, and in circuits for driving heavy inductive loads, such as motor drive circuits. The dielectric breakdown field strength of silicon carbide (SiC) is higher than that of silicon. Therefore, SiC devices can be significantly thinner than equivalent silicon devices with the same nominal blocking voltage. On the other hand, the electrical parameters of silicon carbide devices tend to deteriorate at a higher rate than is typical for equivalent silicon devices.

[0003] There is a need for improving the long-term stability of silicon carbide device parameters. Summary of the invention

[0004] Embodiments of the present disclosure relate to a silicon carbide device including a silicon carbide body. The silicon carbide body includes a source region of a first conductivity type, a cathode region of the first conductivity type, and a separation region of a second conductivity type. A strip-shaped gate structure extends along a first direction and directly adjoins the source region and the separation region. Along the first direction, the cathode region is located between two of the separation regions and at least one of the separation regions is located between the cathode region and the source region. A first load electrode forms an ohmic contact with the source region. The first load electrode forms a Schottky contact with the cathode region. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The accompanying drawings are included to provide a further understanding of the embodiments and are incorporated into and constitute a part of this specification. The accompanying drawings illustrate embodiments of silicon carbide devices and together with the description serve to explain the principles of the embodiments. Additional embodiments are described in the following detailed description and claims.

[0006] Figure 1A-1B Schematic plan and vertical cross-sectional views of a portion of a silicon carbide device with a Schottky contact between two transistor cells according to an embodiment are shown.

[0007] Figure 2A-2B Schematic plan and vertical cross-sectional views of a portion of a silicon carbide device according to an embodiment having a planar gate structure are shown.

[0008] Figure 3A-3B Schematic plan and vertical cross-sectional views of a portion of a silicon carbide device according to an embodiment having a trench gate structure and a shallow separation region are shown.

[0009] Figures 4A-4E Schematic plan and vertical cross-sectional views of a portion of a silicon carbide device according to an embodiment with deep shielding and separation regions are shown.

[0010] Figure 5A-5B Schematic plan and vertical cross-sectional views of a portion of a silicon carbide device according to another embodiment having deep shielding and separation regions are shown.

[0011] Figure 6A-6B Schematic plan and vertical cross-sectional views of a portion of a silicon carbide device according to an embodiment having deep shielding regions and shallow separation regions are shown.

[0012] Figure 7A-7B Schematic plan and vertical cross-sectional views of a portion of a silicon carbide device according to an embodiment having a cathode region with upper and lower cathode portions are shown.

[0013] Figures 8A-8B Schematic plan and vertical cross-sectional views of a portion of a silicon carbide device according to an embodiment involving a dividing region between lateral cathode portions are shown.

[0014] Figures 9A-9E Schematic plan and vertical cross-sectional views of a portion of a silicon carbide device according to an embodiment with a cathode region and a spacing region between one of the gate structures are shown.

[0015] Figures 10A-10E Schematic plan and vertical cross-sectional views of a portion of a silicon carbide device according to an embodiment with a cathode region and a spacer region between two adjacent gate structures are shown.

[0016] Figures 11A-11E Schematic plan and vertical cross-sectional views of a portion of a silicon carbide device with a Schottky contact according to an embodiment with a wide lower cathode portion are shown.

[0017] Figures 12A-12E Schematic plan and vertical cross-sectional views of a portion of a silicon carbide device according to an embodiment involving a symmetrical transistor cell are shown.

[0018] Figures 13A-13B Shown is a schematic plan view of a portion of a silicon carbide device according to an embodiment having a cathode region adjoining two adjacent gate structures.

[0019] Figures 14A-14B A schematic plan view of a portion of a silicon carbide device according to an embodiment having a cathode region in contact with one of two adjacent gate structures is shown.

[0020] Figures 15A-15B A schematic plan view of a portion of a silicon carbide device according to an embodiment having a cathode region separated from two adjacent trench gate structures is shown. DETAILED DESCRIPTION

[0021] In the following detailed description, reference is made to the accompanying drawings, which form a part of the detailed description and in which specific embodiments in which silicon carbide devices can be practiced are illustrated by way of illustration. It should be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure. For example, features shown or described for one embodiment may be used on other embodiments or in combination with other embodiments to produce yet another embodiment. The present disclosure is intended to include such modifications and variations. Examples are described using specific language and should not be interpreted as limiting the scope of the appended claims. The drawings are not to scale and are for illustrative purposes only. If not otherwise specified, corresponding elements are represented by the same reference numerals in different figures.

[0022] The terms "having", "containing", "including", "comprising" and the like are open ended, and the terms indicate the presence of stated structures, elements or features, but do not exclude the presence of additional elements or features. The articles "a", "an" and "the" are intended to include the plural as well as the singular, unless the context clearly indicates otherwise.

[0023] The term "electrically connected" describes a permanent low resistance connection between electrically connected elements, such as direct contact between the associated elements or a low resistance connection via metal and / or heavily doped semiconductor materials. The term "electrically coupled" includes that one or more intermediate elements suitable for signal and / or power transmission may be connected between the electrically coupled elements, for example, elements controllable to temporarily provide a low resistance connection in a first state and temporarily provide a high resistance electrolytic coupling in a second state.

[0024] An ohmic contact is a non-rectifying electrical junction with a linear or nearly linear current-voltage characteristic. A Schottky contact is a metal-semiconductor junction with rectifying properties, in which the work function of the metal and the dopant concentration in the semiconductor material are selected so that a depletion region is formed in the semiconductor material along the metal-semiconductor junction in the absence of an externally applied electric field. In the context of a Schottky contact, the term "metal-semiconductor junction" may also refer to a junction between a metal-like semiconductor and a semiconductor, wherein the junction has the same properties as a metal-semiconductor junction. For example, it may be possible to form a Schottky contact between polysilicon and silicon carbide. If two components (e.g., two regions) form an ohmic contact or a Schottky contact, respectively, this may mean that there is an ohmic contact or a Schottky contact between the two components. In both cases, it may be possible for the two regions to be directly adjacent to each other. However, it may also be possible for another component to be located between the two components.

[0025] The safe operating area (SOA) defines the voltage and current conditions under which a semiconductor device can be expected to operate without self-destruction. The SOA is given by the published maximum values ​​of device parameters such as maximum continuous load current, maximum gate voltage, and others.

[0026] The accompanying drawings illustrate relative doping concentrations by indicating "-" or "+" next to the doping type "n" or "p". For example, "n-" means a doping concentration that is lower than the doping concentration of an "n" doping region, while an "n+" doping region has a higher doping concentration than an "n" doping region. Doping regions of the same relative doping concentration do not necessarily have the same absolute doping concentration. For example, two different "n" doping regions can have the same or different absolute doping concentrations.

[0027] Two adjacent doped regions of the same conductivity type and having different dopant concentrations form a unipolar junction, such as an n / n+ or p / p+ junction, along the boundary surface between the two doped regions. At the unipolar junction, the dopant concentration profile orthogonal to the unipolar junction may show a step or turning point where the dopant concentration profile changes from concave to convex, or vice versa.

[0028] The ranges given for physical dimensions are inclusive. For example, the range of parameter y from a to b is given by , the same applies to ranges with one boundary value such as "at most" and "at least".

[0029] The main constituents of a layer or structure from a chemical compound or alloy are elements whose atoms form the compound or alloy. For example, nickel and silicon are the main constituents of a nickel silicide layer, and copper and aluminum are the main constituents of a copper-aluminum alloy.

[0030] According to an embodiment, a silicon carbide device may include a silicon carbide body having a source region of a first conductivity type, a cathode region of the first conductivity type, and a separation region of a second complementary conductivity type. The strip-shaped gate structure may extend along a first direction and may directly adjoin the source region and the separation region. The first direction may be a lateral direction of the silicon carbide body.

[0031] Along the lateral first direction, the cathode region is located between two of the separation regions. In some embodiments, exactly one cathode region may be located between two of the separation regions. At least one of the separation regions (e.g., exactly one) is located between the cathode region and the source region. Each separation region may separate the cathode region from the source region. The first load electrode forms an ohmic contact with the source region. The first load electrode forms a Schottky contact with the cathode region. In at least one embodiment, the first load electrode may also form an ohmic contact with the separation region. In addition, it may be possible for the first load electrode to form an ohmic contact with the source region and / or the body region and / or the shielding region.

[0032] The source region may form part of a transistor cell such that along the first direction a Schottky contact may be formed between two transistor cells.

[0033] In at least one operating mode of the semiconductor device, the at least one operating mode is, for example, a reverse conducting mode, a bipolar current of holes and electrons flows through the silicon carbide body, wherein the bipolar current passes through at least the pn junction of the transistor unit. In particular, near the pn junction, and further, if applicable, near the unipolar junction, holes and electrons can recombine at a rate that is not negligible. The recombination can set free energy (e.g., thermal energy) and / or momentum, which can promote bipolar degradation. Bipolar degradation indicates the growth of pre-existing crystal defects. For example, a BPD (basal plane dislocation) between adjacent lattice planes can be transformed into an SSF (Shockley stalking fault), which grows along the lattice plane in the main transversal direction of the vertical load current flowing through the silicon carbide body, so that the lattice defects can increasingly hinder the vertical load current flowing through the silicon carbide body.

[0034] The forward voltage drop across the Schottky contact in silicon carbide is typically lower than the forward voltage drop across the pn junction in silicon carbide, so that the reverse current through the silicon carbide body flows primarily through the Schottky contact. In silicon carbide devices with a high nominal blocking voltage of at least 3.3 kV, the resistance of the drift region typically dominates the total on-state resistance, while the channel resistance contributes only slightly to the total on-state resistance. In such devices, the area loss due to the Schottky contact increases the on-state resistance only to a relatively low degree. The reduced total channel width can also contribute to improved short-circuit ruggedness.

[0035] For example, the ratio between the Schottky contact area of ​​the Schottky contact and the transistor area of ​​the transistor cell can be adjusted by adjusting the ratio between the length of the source region and the length of the cathode region along the first direction. The cathode region can be defined by masking an implant of the transistor cell, for example, by masking an implant of a source region, a body region and / or a shielding region of the transistor cell.

[0036] At least one of the separation regions may isolate and / or shield the cathode region relative to the source region. The separation regions may be shaped and arranged to improve shielding of the transistor channel to reduce DIBL (Drain Induced Barrier Lowering) and to shield the Schottky contact from electric fields to reduce leakage current through the Schottky contact.

[0037] According to an embodiment, the gate structure includes a gate electrode formed on a first surface of the silicon carbide body. In other words, the gate electrode may be a so-called planar gate electrode. By implementing a cathode region and a separation region, established designs for silicon carbide transistors may be modified for increased long-term reliability, reduced DIBL and / or improved short-circuit durability.

[0038] According to another embodiment, the gate structure may extend from the first surface of the silicon carbide body into the silicon carbide body, for example, along a vertical direction running perpendicular to the first direction. In other words, the gate structure may be a trench gate structure. The trench gate structure promotes a vertical transistor channel, which may allow for a higher area efficiency. Therefore, the cathode region and the separation region may be implemented with a small structure size and / or with a high area efficiency. For example, it may be possible to provide a cathode region and a separation region while still maintaining a high channel density of a MOSFET channel.

[0039] According to an embodiment, the silicon carbide body includes a drift structure and a body region of a second conductivity type. The body region and the drift structure form a first pn junction. Alone or in combination, the body region may directly adjoin the drift structure. The first load electrode and the body region form an ohmic contact. The forward voltage drop across the Schottky contact that is lower than the forward voltage across the first pn junction can suppress or at least significantly reduce the bipolar current across the first pn junction, and bipolar degradation can be avoided or at least significantly reduced.

[0040] According to an embodiment, a first vertical extension of the separation region (e.g., each of the separation regions) is equal to or less than the maximum vertical distance between the first pn junction and the first surface. That is, along the vertical direction, the body region may extend into the silicon carbide body at least as deep as or even deeper than each of the separation regions. A relatively shallow separation region with a vertical extension not greater than the maximum vertical distance between the first pn junction and the first surface may promote lateral current diffusion just below the separation region and in this way may contribute to a reduction in the ohmic resistance of a JFET (junction field effect transistor) structure, wherein the separation region and / or a further p-doped region may be formed around a Schottky contact, for example below the body region.

[0041] The maximum vertical distance between the first pn junction and the first surface may correspond to the maximum vertical extension of the body region. For example, the body region may include a heavily doped body contact region directly adjacent to the first load electrode, and the first vertical extension of the separation region may be equal to the vertical extension of the body contact portion. The maximum dopant concentration in the body contact portion may be equal to the maximum dopant concentration in the separation region. It is possible to form the separation region in the same process step as the body contact portion, for example by modifying an implant mask for defining the body contact portion, without an additional implant process.

[0042] According to another embodiment, the first vertical extension of the separation region may be greater than the maximum vertical distance between the first pn junction and the first surface. That is, along the vertical direction, the separation region may extend deeper into the silicon carbide body than the body region. The relatively large vertical extension of the separation region may facilitate shielding of the transistor channel with respect to more than two lateral sides and may also improve shielding of the Schottky contact against high electric field strengths. In particular, the cathode region and the adjacent separation region may form an MPS (merged-pin Schottky) diode structure.

[0043] The silicon carbide device may include a shielding region of the second conductivity type. The shielding region may form a pn junction with the drift structure and / or may directly adjoin the drift structure. The shielding region and the first load electrode may form an ohmic contact. For example, the first vertical extension may be equal to the maximum vertical distance between the first surface and the pn junction between the shielding region and the drift structure. The vertical extension of the shielding region may be greater than the vertical extension of the trench gate structure.

[0044] According to an embodiment, the drift structure may include a drift region of the first conductivity type. The drift region may be lightly doped, i.e., may have a lower doping concentration than the source region and / or the cathode region. The cathode region and the drift structure may form a unipolar junction. The maximum dopant concentration in the cathode region may be at least twice as high as the maximum dopant concentration in the drift region, for example at least ten times as high. The higher dopant concentration in the cathode region may reduce the ohmic resistance between the Schottky contact and the drift region, and may define an appropriate forward voltage drop at the Schottky contact.

[0045] The formation of the cathode region can be combined with the formation of the current diffusion region between the drift region and the body region. For example, by, for example, modifying the implant shielding for the current diffusion region, at least a portion of the cathode region can be formed using the same implant that defines the current diffusion region and without additional process steps. The current diffusion region can be a region that prevents the generation of a space-charge region via a current-driven voltage drop. For example, the current diffusion region can have a higher doping concentration than the adjacent drift region.

[0046] According to an embodiment, the silicon carbide device may include at least one segmentation region of the second conductivity type, wherein the at least one segmentation region may separate the cathode region into at least two cathode portions along the first direction. The at least one segmentation region may have the same vertical extension as the separation region, the same maximum dopant concentration as the separation region, and / or the same vertical dopant distribution as the separation region. The segmentation region may further fine-tune the shielding properties of the Schottky contact.

[0047] According to an embodiment, a plurality of cathode regions and a plurality of source regions may be arranged along a first direction. Each of the cathode regions may be located between two of the separation regions. At least one (e.g., exactly one) of the separation regions is located between at least one (e.g., exactly one) of the cathode regions and at least one (e.g., exactly one) of the source regions. Along the first direction, the source regions may alternate with the cathode regions, wherein the separation regions may separate each cathode region from two adjacent source regions along the first direction.

[0048] By selecting the total length of the cathode region along the first direction, the desired ratio of the Schottky contact area to the transistor area can be adjusted. The transistor current and the Schottky current can be evenly distributed across the lateral cross-sectional area of ​​the silicon carbide body. The vertical extension of the separation region and the length of the cathode region along the first direction can adjust the shielding characteristics of the Schottky contact and the transistor channel.

[0049] According to an embodiment, the source region directly adjoins the first gate sidewall of the gate structure. The shielding region of the second conductivity type may adjoin (e.g., directly adjoin) the second gate sidewall of the gate structure. The second gate sidewall may be opposite to the first gate sidewall. Both the first and second gate sidewalls may extend along the first direction (i.e., may be longitudinal sidewalls of the gate structure). The source region may be directly positioned relative to the shielding region with respect to the gate structure. Therefore, the transistor cell may be an asymmetric transistor cell having a transistor channel formed along only one of the two longitudinal sidewalls of the gate structure. The formation of the separation region may be combined with an implantation process that defines the shielding region. For example, the separation region may be formed without additional process steps by modifying one or more implantation shields used for the formation of the shielding region.

[0050] According to another embodiment, the silicon carbide device includes a first source region and a second source region. The first source region directly adjoins a first gate sidewall of the gate structure. Directly opposite the first source region, the second source region may directly adjoin a second gate sidewall of the gate structure, the second gate sidewall being opposite to the first gate sidewall. In other words, the transistor cell may be a symmetrical transistor cell having a transistor channel formed along two longitudinal sidewalls of the gate structure. Providing transistor channels at both sides of the gate structure may increase the overall channel width without increasing the chip area.

[0051] According to an embodiment, a silicon carbide device includes a plurality of parallel gate structures, and a cathode region can extend from one gate structure to an adjacent gate structure. The full width of a SiC mesa between two adjacent gate structures can be used as a Schottky contact, making the area efficiency high.

[0052] According to another embodiment, the silicon carbide device includes a plurality of parallel gate structures. A spacer region of the second conductivity type may be formed between one of the gate structures and the cathode region. The spacer region may improve the shielding of the Schottky contact. In addition to the shielding structure, the spacer region may also improve the shielding of the bottom of the trench gate structure. For example, the spacer region may extend at least as deep into the silicon carbide body as the trench gate structure or even deeper (e.g., slightly deeper) than the trench gate structure.

[0053] According to further embodiments, the silicon carbide device includes a plurality of parallel gate structures, and a spacer region of the second conductivity type may be formed between the cathode region and two of the gate structures.The spacer region may allow Schottky contacting of shielding on all lateral sides.

[0054] According to an embodiment, the cathode region may include a lower cathode portion and an upper cathode portion between the lower cathode portion and the first surface. A maximum first width of the upper cathode portion orthogonal to the first direction (and orthogonal to the vertical direction) is smaller than a maximum second width of the lower cathode portion orthogonal to the first direction (and orthogonal to the vertical direction). The resulting JFET structure having a widened portion at a certain distance from the first surface may further improve shielding of the Schottky contact.

[0055] In an alternative embodiment, shielding may be improved by means of a narrowed lower cathode portion. In such an embodiment, a maximum first width of the upper cathode portion orthogonal to the first direction (and orthogonal to the vertical direction) is greater than a maximum second width of the lower cathode portion orthogonal to the first direction (and orthogonal to the vertical direction).

[0056] According to an embodiment, a plurality of cathode regions and a plurality of source regions are arranged between gate structures, in particular between two adjacent gate structures. The cathode regions may be arranged along a first direction and / or may extend along the first direction, and the source regions may be arranged along a second direction orthogonal to the first direction (and orthogonal to the vertical direction) and / or may extend along a second direction orthogonal to the first direction (and orthogonal to the vertical direction). In this way, the cathode regions and the separation regions may be formed by relatively simple modifications to the implant shielding.

[0057] According to another embodiment, cathode regions and source regions may alternate along the second direction (ie, along a line extending orthogonal to the first direction).

[0058] Thus, the Schottky contacts and transistor cells may be arranged in a checkered fashion, with the transistor cells corresponding to the “white fields” and the Schottky contacts corresponding to the “black fields” of the checkerboard. Both unipolar Schottky currents and bipolar transistor currents may thus be more evenly distributed across the lateral cross-sectional area of ​​the silicon carbide body.

[0059] Figure 1A and 1BA portion of a semiconductor device 500 is shown having a silicon carbide body 100. By way of example, the semiconductor device 500 may be or may include an IGFET (Insulated Gate Field Effect Transistor), such as a MOSFET (Metal Oxide Semiconductor FET), an MCD (MOS Controlled Diode) or an IGBT (Insulated Gate Bipolar Transistor).

[0060] The silicon carbide body 100 may include or consist of single-crystal silicon carbide, for example, a silicon carbide crystal including main components silicon and carbon. The silicon carbide crystal may include unwanted impurities, such as hydrogen and / or oxygen and / or expected impurities, such as dopant atoms. The polytype of the silicon carbide crystal may be 15R or may be a hexagonal polytype, such as 2H, 6H or 4H. The silicon carbide body 100 may include or consist of a silicon carbide layer grown by epitaxy.

[0061] The silicon carbide semiconductor body may have an offdirection, for example, in a <11-20> or <1-100> direction. The first surface 101 at the front side of the silicon carbide body 100 may be planar or ripped. A surface normal 104 orthogonal to the planar first surface 101 or to the mean plane of the ripped first surface 101 defines a vertical direction. Directions orthogonal to the surface normal 104 are lateral directions (e.g., first and second directions). The surface normal 104 may coincide with the main lattice direction, or may be tilted at an off-axis angle to the main lattice direction, wherein the off-axis angle may be in a range from 2° to 8°, in particular 4°. On the back side of the silicon carbide body 100, the second surface 102 may extend parallel to the planar first surface 101 or parallel to the mean plane of the ripped first surface 101.

[0062] At least two transistor cells TC and Schottky contacts SC are formed at the front side of the silicon carbide body 100 , wherein each Schottky contact SC is formed between two transistor cells TC along a lateral first direction 291 . The drift structure 130 extends laterally through the silicon carbide body 100 between the transistor cells TC and the second surface 102 .

[0063] The drift structure 130 comprises a drift region 131 of a first conductivity type. The drift region 131 forms a voltage sustaining structure, wherein the vertical extension and the dopant concentration in the drift region 131 may be selected such that the semiconductor device 500 provides a nominal blocking voltage capability in an off state of the semiconductor device 500. The drift region 131 may be formed in a layer grown by epitaxy. The average net dopant concentration in the drift region 131 may be, for example, arrive within the range.

[0064] A heavily doped contact portion 139 may be formed between the drift structure 130 and a second load electrode 320 directly adjacent to the second surface 102, wherein the heavily doped contact portion 139 forms a low resistance ohmic contact with the second load electrode 320. The contact portion 139 may have the same conductivity type as the drift region 131, an opposite conductivity type, or may include regions of both conductivity types.

[0065] Each transistor cell TC includes a source region 110 and a body region 120, wherein the body region 120 and the drift structure 130 form a first pn junction pn1, and wherein the body region 120 and the source region 110 form a second pn junction pn2. The gate structure 150 extends along the first direction 291 and contacts the source region 110 and the body region 120 of the transistor cell TC.

[0066] The cathode region 160 is located between the source regions 110 along the lateral first direction 291. The cathode region 160 and the drift structure 130 may form a unipolar junction. The length l0 of the cathode region 160 along the first direction 291 may be in the range from a few 100 nm up to almost the entire length of the trench gate structure along the longitudinal extent of the trench gate structure. For example, the length of the cathode region 160 is at least 0.5 μm, such as at least 1 μm or at least 2 μm, and / or at most 5 μm, such as at most 2 μm.

[0067] The separation region 140 of the second conductivity type separates the source region 110 and the cathode region 160 along the first direction 291. The first vertical extension v1 of the separation region 140 can be in the range of tens of nanometers, in particular at least 100 nm, to several micrometers. The first vertical extension v1 can be equal to the maximum vertical distance v2 between the first pn junction pn1 and the first surface 101, less than the maximum vertical distance v2 or greater than the maximum vertical distance v2.

[0068] The source region 110 and the body region 120 of the transistor cell TC may be electrically connected or coupled to a first load electrode 310 , which may form or may be electrically connected or coupled to the first load terminal L1 . The cathode region 160 and the first load electrode 310 form a Schottky contact SC.

[0069] The second load electrode 320 may form or may be electrically connected or coupled to the second load terminal L2. The gate electrode 155 of the transistor cell TC may be electrically connected or coupled to the gate terminal G. The first load terminal L1 may be an anode terminal of the MCD, a source terminal of the IGFET, or an emitter terminal of the IGBT. For example, the second load terminal L2 may be a cathode terminal of the MCD, a drain terminal of the IGFET, or a collector terminal of the IGBT.

[0070] The transistor cell TC may be an n-channel FET cell having a p-doped body region 120, an n-doped source region 110 and an n-doped drift region 131. Alternatively, the transistor cell TC is a p-channel FET cell having an n-doped body region 120, a p-doped source region 110 and a p-doped drift region 130. Merely by way of example, the following description relates to an n-channel FET cell.

[0071] Figure 2A and 2B A planar gate structure 150 is shown including a conductive gate electrode 155 formed on the first surface 101. A gate dielectric 159 separates the gate electrode 150 from the silicon carbide body 100. The transistor cells TC may be arranged in pairs, wherein each pair of transistor cells TC may be arranged with respect to the silicon carbide body 100. Figure 2A and 2B The cross section is formed in a mirror-inverted manner orthogonal to the vertical symmetry plane.

[0072] An interlayer dielectric 210 may separate the gate electrode 155 and the first load electrode 310. The interlayer dielectric 210 may also separate the first load electrode 310 and a drain portion 132 of the drift structure 130, wherein the drain portion 132 is formed between the drift region 131 and the first surface 101. In an on-state of the transistor cell TC, an inversion channel is formed in the silicon carbide body 100 along the first surface 101 opposite the gate electrode 155 between the source region 110 and the drain portion 132. Between adjacent pairs of source regions 110 of the transistor cell TC, the body region 120 may include a heavily doped body contact portion 125 directly adjoining the first surface.

[0073] The separation region 140 may be formed as a lateral extension of the body region 120 along the first direction 291. The separation region 140 may include a heavily doped separation contact portion 141, which may be formed as a lateral extension of the body contact portion 125.

[0074] Figure 3A and 3B A trench gate structure 150 is shown extending from the first surface 101 into the silicon carbide body 100 . The source region 110 and the body region 120 are in contact with a first gate sidewall 151 of the trench gate structure 150 .

[0075] The shielding region 170 may be in contact with the opposing second gate sidewall 152 of the trench gate structure 150 and may also be formed along a portion of the bottom surface of the trench gate structure 150. In the shielding region 170, the maximum dopant concentration may be higher than in the body region 120. The dopant concentration in the shielding region 170 may be sufficiently high so that no inversion layer is formed along the second trench sidewall 152 at least as long as the semiconductor device 500 operates within the SOA. The shielding region 170 is separated from the first trench sidewall 151. For example, the source region 110 and the body region 120 may be located between the first trench sidewall 151 of the gate structure 150 and the shielding region 170. The shielding region 170 may include a heavily doped shielding contact portion 171 along the first surface 101, wherein the first load electrode 310 and the heavily doped shielding contact portion 171 may form an ohmic contact. The vertical extension v1 of the separation region 140 may be equal to the vertical extension v3 of the shielding contact portion 171.

[0076] exist Figures 4A-4E , each shielding region 170 includes a shielding contact portion 171, a shielding connection portion 172, and a shielding bottom portion 173. The shielding bottom portion 173 may directly adjoin the drift structure 130, and the maximum dopant concentration in the shielding bottom portion 173 may have a greater distance from the bottom of the trench gate structure 150 to the first surface 101. The shielding connection portion 172 connects the shielding bottom portion 173 with the heavily doped shielding contact portion 171.

[0077] The maximum dopant concentration in the shield connection portion 172 is at least ten times higher than the average dopant concentration in the body region 120 . The interlayer dielectric 210 separates the gate electrode 155 and the first load electrode 310 in the trench gate structure 150 .

[0078] The drift structure 130 includes a current diffusion region 137 between the body region 120 and the drift region 131. The current diffusion region 137 may separate the body region 120 and the drift region 131. The current diffusion region 137 and the drift region 131 may form one or more first unipolar junctions jn1. The current diffusion region 137 may also be formed between the cathode region 160 and the drift region 131. The maximum dopant concentration in the current diffusion region 137 is at least twice as high as the maximum dopant concentration in the drift region 131, for example, at least ten times as high. The maximum dopant concentration in the cathode region 160 may be equal to, higher than, or lower than the maximum dopant concentration in the current diffusion region 137.

[0079] The separation region 140 may be formed from the same implant defining the shield contact portion 171, the shield connection portion 172, and the shield bottom 173 of the shield region 170. For example, the separation region 140 includes a separation bottom 143 having the same vertical extension, the same distance to the first surface 101, and / or the same dopant concentration as the shield bottom 173 of the shield region 170. The separation connection portion 142 may have the same vertical extension, the same distance to the first surface 101, and / or the same dopant concentration as the shield connection portion 172 of the shield region 170.

[0080] Additionally or alternatively, the separation contact portion 141 may have the same vertical extension and / or the same dopant concentration as the shield contact portion 171 of the shield region 170 .

[0081] The separation region or at least a portion of the separation region 140 may form a lateral extension of the shielding region 170 .

[0082] The shielding region 170 and the separation region 140 may all originate from the same implant. Alternatively, the separation region 140 and the shielding region 170 may differ in at least one implant.

[0083] For example, in Figure 5A and 5B In the embodiment, the separation region 140 does not include a portion corresponding to the shield bottom 173. Instead, the separation region 140 includes only a separation contact portion 141 corresponding to the shield contact portion 171 and a separation connection portion 142 corresponding to the shield connection portion 172.

[0084] exist Fig. 6A and 6B , the separation region 140 includes a separation contact portion 141 which may correspond to the shield contact portion 171 and another portion formed by a lateral extension of the body region 120 .

[0085] exist Fig. 7A and 7B , cathode region 160 includes a lower cathode portion 162 and an upper cathode portion 161 between the lower cathode portion 162 and the first surface 101. A maximum first length l1 in the upper cathode portion 161 along the first direction 291 may be greater than a maximum second length l2 of the lower cathode portion 162. The lower cathode portion 162 may be formed simultaneously with the current diffusion region 137 by using the same implantation process and / or may have the same vertical dopant distribution as the current diffusion region 137. The maximum dopant concentration in the upper cathode portion 161 may be equal to or greater than the maximum dopant concentration in the lower cathode portion 162.

[0086] exist Fig. 8A and 8B, a conductive type partitioning region 180 of the separation region 140 laterally partitions the cathode region 160 into two lateral cathode portions 165 along a first direction 291. The partitioning region 180 may have the same vertical configuration as the separation region 140 and / or the shielding region 170 or a different configuration.

[0087] For example, the segmentation region 180 can be formed from the same implants that define the separation contact portion 141, the separation connection portion 142, and the separation bottom 143 of the separation region 140. For example, the segmentation region 180 includes a segmentation bottom 183 having the same vertical extension, the same distance to the first surface 101, and / or the same dopant concentration as the separation bottom 143. The segmentation connection portion 182 can have the same vertical extension, the same distance to the first surface 101, and / or the same dopant concentration as the separation connection portion 142. Additionally or alternatively, the segmentation contact portion 181 can have the same vertical extension and / or the same dopant concentration as the separation contact portion 141. Alternatively, the segmentation region 180 can be offset from the separation region 140 in at least one implant.

[0088] Fig. 8A and 8B Only one single segmentation region 180 per cathode region 160 is shown. Other embodiments may provide two or more segmentation regions 180 separating the cathode region 160 into three or more lateral cathode portions 163.

[0089] exist Figures 9A-9E In the embodiment shown in FIG. 2 , the cathode region 160 contacts one gate structure 150 and the spacer 145 separates the cathode region 160 from a second adjacent gate structure 150. The cathode region 160 may have the same width as the source region 110 orthogonal to the first direction 291.

[0090] like Fig.9A and 9E As shown in , spacer region 145 may be a lateral extension of shield region 170 and may include sub-portions corresponding to shield contact portion 171, shield connection portion 172, and shield bottom 173. Alternatively, spacer region 145 may differ from shield region 170 by at least one implant.

[0091] exist Figures 10A-10E In the embodiment of the present invention, the spacer region 145 separates the cathode region 160 from two adjacent gate structures 150. As shown in the figure, the spacer region 145 and the separation region 140 can be formed as a lateral extension of the shielding region 170.

[0092] The cathode region 160 may include a lower cathode portion 162 and an upper cathode portion 161 between the lower cathode portion 162 and the first surface 101. A maximum first width w1 in the upper cathode portion 161 orthogonal to the first direction 291 may be less than a maximum second width w2 of the lower cathode portion 162. The lower cathode portion 162 may be formed simultaneously with the current diffusion region 137 using the same implantation process and / or may have the same vertical dopant profile as the current diffusion region 137. The maximum dopant concentration in the upper cathode portion 161 may be equal to or greater than the maximum dopant concentration in the lower cathode portion 162. The position of the edge between the spacer 145 and the upper cathode portion 161 is decoupled from the position of the edge between the spacer 145 and the lower cathode portion 162 and the tradeoff between conductivity and shielding may be fine-tuned. The additional shallow n-type implant in the upper cathode portion 161 may also overcompensate for the implant p+ tail that reaches the first surface 101.

[0093] Figures 11A-11E A further silicon carbide device 500 is shown having a silicon carbide body 100. A transistor cell TC having a gate structure 150 extending in a lateral first direction 291 is formed along a first surface 101 of the silicon carbide body 100. A drift structure having a lightly doped drift region 131 is formed between the transistor cell TC and a second surface 102 of the silicon carbide body 100. The silicon carbide body 100 further comprises a shielding region 170 and a cathode region 160 as described above, and the semiconductor device 500 further comprises a first load electrode 310 on the back side of the silicon carbide body and a second load electrode 320 on the back side of the silicon carbide body as described above.

[0094] Each cathode region 160 may extend from the first surface 101 into the silicon carbide body 100. The cathode region 160 and the drift region 131 have the same conductivity type. The average dopant concentration in the cathode region 160 may be the same as or may be higher than the average dopant concentration in the drift region 131. For example, the average dopant concentration in the cathode region 160 may be at least twice as high as the average dopant concentration in the drift region 131. The cathode region 160 and the drift structure, such as the drift region 131 or a barrier layer of the conductivity type of the drift region 131, may form a unipolar junction. The length of the cathode region 160 along the first direction 291 may be at least 100 nm. For example, the length of the cathode region 160 may be at least 500 nm, such as at least 1 μm, or at least 2 μm and / or at most 5 μm, such as at most 2 μm.

[0095] The cathode region 160 and the first load electrode 310 form a Schottky contact SC. Along the lateral first direction 291 , each Schottky contact SC is formed between two adjacent transistor cells TC.

[0096] Each shielding area 170 includes a shielding connection portion 172 and a shielding bottom 173. The shielding connection portion 172 is between the first surface 101 and the shielding bottom 173. The shielding connection portion 172 may also include a shielding contact portion formed along the first surface 101 as described above.

[0097] The shielding region 170 includes lateral spacer portions 174 . Each spacer portion 174 contacts an active sidewall of the gate structure 150 between adjacent source regions 110 . The shielding region 170 completely laterally surrounds each cathode region 160 . Each cathode region 160 may be spaced apart from two adjacent gate structures 150 .

[0098] Each cathode region 160 includes a lower cathode portion 162 and an upper cathode portion 161 between the first surface 101 and the lower cathode portion 162. The average dopant concentration in the lower cathode portion 162 and the average dopant concentration in the upper cathode portion 161 may be equal or may be different. The upper cathode portion 161 has a first average width wm1 along the first direction 291. The lower cathode portion 162 has a second average width wm2 along the first direction 291. The second average width wm2 is at least 120%, for example at least 150% or at least 200% of the first average width wm1. The vertical extension v4 of the lower cathode portion 162 may be at least 50nm, for example at least 100nm.

[0099] The upper cathode portion 161 is laterally opposite to the shield connection portion 172. The upper cathode portion 161 and the shield connection portion 172 can form a vertical or almost vertical pn junction. The lower cathode portion 162 is laterally opposite to the shield bottom 173. The lower cathode portion 162 and the shield bottom 173 can form a vertical or almost vertical pn junction. A high unipolar reverse current can flow through the cathode region 160 without the body diode becoming active.

[0100] Figures 12A-12E A silicon carbide device 500 with a symmetrical transistor cell is shown. The first source region 111 directly adjoins the first gate sidewall 151 of each trench gate structure 150, and the second source region 112 directly adjoins the second gate sidewall 152, wherein the first and second source regions 111, 112 are formed directly opposite to each other. In the center of the SiC mesa 190 between the first and second source regions 111, 112, a shielding region 170 may extend from the first surface 101 into the silicon carbide body 100.

[0101] Figures 13A-15BA plan view of a semiconductor device 500 having stripe-shaped trench gate structures 150 running along a first direction 291 is shown. SiC mesas 190 between adjacent trench gate structures 150 include semiconducting portions of transistor cells TC and Schottky contacts SC to source regions 110, cathode regions 160, and separation regions 140 separating adjacent cathode regions 160 from source regions 110.

[0102] Fig.13A and 13B Cathode region 160 is shown extending across the entire width of semiconductor mesa 190 .

[0103] exist Fig.13A , the cathode regions 160 of adjacent SiC mesas 190 extend along a lateral second direction 292 that is orthogonal to the first direction 291. The cathode regions 160 may thus extend along a line extending along the second direction 292.

[0104] exist Fig. 13B , the only cathode regions 160 in each second SiC mesa 190 are arranged along the same line along the second direction 292. In other words, along the second direction 292, the cathode regions 160 alternate with the source regions 110.

[0105] Fig.14A and 14B The embodiment shown in Fig.13A and 13B The arrangement of the Schottky contact SC and the transistor cell TC shown in FIG. 1 is combined with a layout of the Schottky contact SC having a spacer region 145 separating the cathode region 160 from one of the adjacent gate structures 150 .

[0106] Fig.15A and 15B The embodiment shown in Fig.13A and 13B The arrangement of the Schottky contact SC and the transistor cell TC shown in FIG. 1 is combined with a layout of the Schottky contact with a spacer region 145 separating the cathode region 160 from two adjacent gate structures 150 .

Claims

1. A silicon carbide device (500), comprising: A silicon carbide body (100) comprising a source region (110) of a first conductivity type, a cathode region (160) of a first conductivity type, and a separation region (140) of a second conductivity type, A strip-shaped gate structure (150) extending along a first direction (291) and directly adjacent to the source region (110) and the separation region (140), and a first load electrode (310), wherein, along the first direction (291), the cathode region (160) is located between two of the separation regions (140), and at least one of the separation regions (140) is located between the cathode region (160) and the source region (110), and The source region (110) and the first load electrode (310) form an ohmic contact (OC), and the first load electrode (310) and the cathode region (160) form a Schottky contact (SC).

2. A silicon carbide device according to the preceding claim, wherein The gate structure (150) includes a gate electrode (155) formed on a first surface (101) of a silicon carbide body (100).

3. The silicon carbide device according to claim 1, wherein The gate structure (150) extends from a first surface (101) of the silicon carbide body (100) into the silicon carbide body (100).

4. The silicon carbide device according to claim 1, wherein The silicon carbide body (100) comprises a body region (120) of a second conductivity type and a drift structure (130), wherein the body region (120) and the drift structure (130) form a first pn junction (pn1), and wherein a first load electrode (310) and the body region (120) form an ohmic contact (OC).

5. The silicon carbide device according to claim 4, wherein The first vertical extension (v1) of the separation region (140) is equal to or smaller than the maximum vertical distance (v2) between the first pn junction (pn1) and the first surface (101).

6. The silicon carbide device according to claim 4, wherein The first vertical extension (v1) of the separation region (140) is greater than the maximum vertical distance (v2) between the first pn junction (pn1) and the first surface (101).

7. The silicon carbide device according to any one of claims 4 to 6, wherein The drift structure (130) comprises a drift region (131) of a first conductivity type, a cathode region (160) and the drift region (131) forming a unipolar junction (jn), and a maximum dopant concentration in the cathode region (160) being at least twice as high as a maximum dopant concentration in the drift region (131).

8. The silicon carbide device according to claim 1, further comprising: At least one segmentation region (180) of the second conductivity type, wherein the at least one segmentation region (180) separates the cathode region (160) into at least two cathode portions (165) along the first direction (291).

9. The silicon carbide device according to claim 1, wherein A plurality of cathode regions (160) and a plurality of source regions (110) are arranged along a first direction (291), wherein each of the cathode regions (160) is located between two of the separation regions (140), and At least one of the separation regions (140) is located between at least one of the cathode regions (140) and at least one of the source regions (110).

10. The silicon carbide device according to claim 3, wherein The source region (110) is directly adjacent to a first gate sidewall (151) of the gate structure (150), and wherein directly opposite to the source region (110), a shielding region (170) of a second conductivity type is adjacent to a second gate sidewall (152) of the gate structure (150) opposite to the first gate sidewall (151).

11. The silicon carbide device according to claim 3, wherein The silicon carbide device comprises a first source region (111) and a second source region (112), in, The first source region (111) is directly adjacent to the first gate sidewall (151) of the gate structure (150) and is directly opposite to the first source region (111), and the second source region (112) is directly adjacent to the second gate sidewall (152) opposite to the first sidewall (151).

12. The silicon carbide device according to claim 1, comprising: A plurality of parallel gate structures (150) are provided, wherein a cathode region (160) extends from one gate structure (150) to an adjacent gate structure (150).

13. The silicon carbide device according to claim 1, comprising: A plurality of parallel gate structures (150) are provided, wherein a spacer region (145) of a second conductivity type is formed between one of the gate structures (150) and the cathode region (160).

14. The silicon carbide device according to claim 1, comprising: A plurality of parallel gate structures (150) are provided, wherein a spacer region (145) of a second conductivity type is formed between a cathode region (160) and two gate structures (150).

15. The silicon carbide device according to claim 14, wherein The cathode region (160) includes a lower cathode portion (162) and an upper cathode portion (161) between the lower cathode portion (162) and the first surface (101), wherein a maximum first width (w1) of the upper cathode portion (161) orthogonal to the first direction (291) is smaller than a maximum second width (w2) of the lower cathode portion (162) orthogonal to the first direction (291).

16. The silicon carbide device according to any one of claims 12 to 15, wherein A plurality of cathode regions (160) and a plurality of source regions (110) are arranged between the gate structures (150), in, The cathode region (160) is arranged along a first direction (291), and the source region (110) is arranged along a second direction (292) orthogonal to the first direction (291).

17. The silicon carbide device according to any one of claims 12 to 15, wherein A plurality of cathode regions (160) and a plurality of source regions (110) are arranged between the gate structures (150), in, The cathode regions (160) and the source regions (110) are alternated along a second direction (292) orthogonal to the first direction (291).

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