Schottky rectifier with surge current stability and method for manufacturing the same

Abstract

SiC Schottky rectifiers with surge current stability are described that can be configured to provide multiple types of surge current protection. Different current magnitudes and characteristics may be associated with different types of surge current events. The described Schottky rectifier structure provides surge current protection in multiple types of surge current scenarios while minimizing or reducing situations where a solution in one environment undesirably mitigates the effect of a solution in another environment.

Description

Technical Field

[0001] The present application relates to a Schottky rectifier semiconductor device. Background Art

[0002] Silicon Carbide (SiC) devices, especially SiC high-power devices, offer advantages such as high switching speed and low power loss. Examples of high-efficiency SiC power devices include (but are not limited to) rectifiers, field-effect transistors (FETs), and bipolar junction transistors (BJTs).

[0003] Schottky rectifiers are a type of diode with a metal-semiconductor junction. As is known, Schottky rectifiers have low forward voltage drop and fast switching speed. Therefore, SiC Schottky rectifiers offer the advantages of general SiC devices, as well as the advantages of traditional (e.g., silicon-based) Schottky rectifiers.

[0004] Schottky rectifiers, including SiC Schottky rectifiers, are often used, for example, in power conversion systems. In these and other settings, high current surges can be problematic. For example, in a power conversion system, a load short circuit condition can result in a high surge current. The rectifier current cannot be interrupted during the surge current event, so the rectifier should be able to withstand the surge current event without failure. Therefore, Schottky rectifiers are often subject to various reliability or stability requirements related to immunity to forward current surges.

[0005] Existing techniques are used to improve the surge current reliability and stability of Schottky rectifiers. For example, they may include a merged pn diode with a Schottky rectifier (which may be referred to as a "MPS" or Junction-Blocked (JBS) rectifier). Such MPS / JBS devices can be further improved in terms of withstanding surge current events, for example, by adding a relatively wide p-body that increases the forward voltage drop of the Schottky rectifier at certain locations of the rectifier during surge current events. However, these existing methods either fail to achieve the desired surge current reliability or stability levels, or have other disadvantages, such as consuming excessive device area. Summary of the invention

[0006] In the following disclosure, example implementations of Schottky rectifiers are described that provide surge current protection for multiple types of surge current events. For example, one type of surge current event may be relatively short, while a second type may be relatively long (where the length of the surge current event may be defined, for example, in terms of time units or units of associated line cycles). Different current magnitudes and characteristics may be associated with different types of surge current events. The described Schottky rectifier structures provide surge current protection in multiple types of surge current scenarios while minimizing or reducing situations where a solution in one environment undesirably mitigates the effect of a solution in another environment.

[0007] According to one general aspect, a Schottky rectifier device includes a silicon carbide (SiC) layer, a channel region of a first conductivity type formed on the SiC layer, and a metal contact formed on the channel region. The Schottky rectifier device also includes a multilayer body of a second conductivity type, the multilayer body of the second conductivity type is formed in the channel region and extends from the metal contact in the direction of the SiC layer, the multilayer body includes a first layer adjacent to the metal contact and having a first doping concentration, a second layer adjacent to the first layer and having a second doping concentration less than the first doping concentration, and a third layer adjacent to the second layer and having a third doping concentration less than the second doping concentration.

[0008] According to another general aspect, a method for manufacturing a Schottky rectifier device includes forming a silicon carbide (SiC) substrate, forming an epitaxial layer of a first conductivity type on the SiC substrate. The method includes forming a mask layer on the epitaxial layer, performing ion implantation of a second conductivity type donor through the mask layer to form a portion of a charge balancing body, and removing the mask layer. The method also includes repeating the formation of the epitaxial layer and the mask ion implantation until the charge balancing body reaches a specified thickness; forming an injection layer on the charge balancing body, the injection layer having a doping concentration of a second conductivity type, the doping concentration of the second conductivity type being higher than the doping concentration of the charge balancing body; forming a contact layer on the injection layer; and forming a metal contact on the contact layer and the epitaxial layer.

[0009] According to another general aspect, a Schottky rectifier device includes a silicon carbide (SiC) layer, a channel region of a first conductivity type formed on the SiC layer, and a metal contact formed on the channel region. The Schottky rectifier device includes a multilayer body of a second conductivity type, the multilayer body of the second conductivity type is formed in the channel region and extends from the metal contact in the direction of the SiC layer, the multilayer body includes a tunnel contact layer adjacent to the metal contact, an injection layer adjacent to the first layer, and a deep layer adjacent to the second layer, wherein the multilayer body extends at least 30% of the distance between the metal contact and the SiC layer.

[0010] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a schematic cross-sectional view of a SiC Schottky rectifier with surge current stability.

[0012] Figure 2A yes Figure 1 Schematic cross-sectional view of an example implementation of a SiC Schottky rectifier.

[0013] Figure 2B yes Figure 2A A first top view of an example implementation of FIG.

[0014] Figure 2C yes Figure 2A A second top view of an example implementation of FIG.

[0015] Figure 3 It is shown Figure 1 and FIG. 2A to FIG. 2C FIG. 1 is a diagram of the first current-voltage curve of a Schottky rectifier.

[0016] Figure 4 It is shown Figure 1 and FIG. 2A to FIG. 2C FIG. 1 is a diagram of a second current-voltage curve of a Schottky rectifier.

[0017] Figure 5 It is along Figure 1 and FIG. 2A to FIG. 2C Figure 2. Electron concentration profile of a vertical device cross section of a Schottky rectifier.

[0018] Figure 6 yes Figure 1 The rectifier unit cell is in Figure 1 Cross-sectional view of the case of a multilayer p-body with dedicated ohmic contacts.

[0019] 7A to 7J Shown is the method for forming Figures 1 to 2C operation of one or more of the Schottky rectifier devices.

[0020] Figure 8 is a schematic diagram showing a room temperature secondary ion mass spectrometry (SIMS) chart for Al channeling implantation into SiC.

[0021] Fig. 9 is used for Figure 1 and Figure 2ASchematic diagram of a diagram of donor-doped channelized phosphorus in the drift region and a diagram of random implantation. DETAILED DESCRIPTION

[0022] Figure 1 is a schematic cross-sectional view of a SiC Schottky rectifier 100 with surge current stability. As described above, the Schottky rectifier 100 can be configured to provide various types of surge current protection. For example, referring to the following description, the maximum surge current I FM A typical time of about 10 μs is, for example, possible, and a similar measurement time can be used to test I FM (Usually the standard is 10 μs.) Another surge current stability requirement is to maintain a single pulse maximum surge current I for, for example, half a line cycle. FSM The half-cycle of the line cycle can be about 10ms for a typical power application. As described herein, the SiC Schottky rectifier 100 is I FM and I FSM Inrush current events provide inrush current stability.

[0023] exist Figure 1 , a SiC Schottky rectifier 100 is shown as including an n-type channel region 102 parallel to a multilayer p-body 110, Figure 1 In an example of the present invention, the multilayer p-body 110 includes layer 111, layer 112, and layer 113. As described in more detail below, during a surge current event, the multilayer p-body 110 provides surge current stability with respect to the n-type channel 102. For example, the multilayer p-body 110 may include an injection layer 112 that is constructed and doped to provide high injection efficiency. The multilayer p-body 110 may include a deep p-body 113 that extends parallel to the n-type channel and, in some embodiments, extends completely along the remaining length of the n-type channel 102 to contact the substrate 101 of the Schottky rectifier.

[0024] During relatively long surge current events (e.g., I FSM ), the multilayer p-body 110 can provide surge current protection by, for example, allowing electron current to flow along the n-type Schottky channel 102, which generates a voltage drop high enough to turn on the pn diode formed by the multilayer p-body 110 and the n-type channel 102. More specifically, the structure of the multilayer p-body 110 reduces the voltage required to turn on minority carrier injection at the pn diode compared to conventional MPS / JBS Schottky rectifiers.

[0025] For example, in a conventional MPS / JBS Schottky rectifier, a 10ms surge current event may require a surge current of up to 4X to 10X of the rated current of the MPS / JBS Schottky rectifier. However, during the transition from normal current levels to surge current levels, a short circuit of the pn diode may occur across the vertical Schottky rectifier channel due to the relatively low turn-on voltage of the Schottky rectifier (approximately 1V) compared to the turn-on voltage of the adjacent pn diode (approximately 3V). This short circuit effect prevents the pn diode from turning on the injection mode at relatively low forward bias and reduces the surge current stability of such conventional MPS / JBS Schottky rectifier.

[0026] In contrast, the multilayer p-body 110 includes many features and characteristics that are superior to conventional MPS / JBS Schottky rectifiers. For example, the injection layer 112 is constructed to provide high injection efficiency, and together with the relative length of the deep p-body 113, the multilayer p-body 110 provides a superjunction effect for charge balancing of the n-channel 102, wherein such charge balancing occurs during reverse bias conditions. During forward bias surge current events, such as relatively long surge current events (e.g., I FSM ), the forward voltage drop of the pn diode 110 / 102 is reduced relative to the conduction voltage of the Schottky rectifier 100, which mitigates or eliminates the undesirable shorting effect of the vertical Schottky channel 102 on the pn diode 110 / 102.

[0027] Furthermore, the multi-layer p-body 110 may include, for example, a tunnel contact layer 111 in contact with an injection layer 112. Thus, the injection layer 112 connects the tunnel contact layer 111 and the deep p-body layer 113 as shown.

[0028] During relatively short surge current events (for example, I FM ), the tunnel contact layer 111 provides a reduced voltage drop during the period of the transient. In other words, the tunnel contact layer 111 provides surge current stability for scenarios with short current pulses of high current density.

[0029] In embodiments where the injection layer 112 connects the tunnel contact layer 111 and the deep p-body layer 113, the injection layer 112 may be doped and otherwise configured to prevent electrons from recombination at the tunnel contact layer 111 as described below. FSM ), if this recombination is not prevented, it may reduce or be detrimental to the stability of the surge current.

[0030] Charge balancing can occur in Figure 1The region 109 in FIG. 1 schematically shows the charge balance region. In the region above or below the region 109 , charge balance is usually not achieved because the acceptor or donor concentration outside the region 109 is very high.

[0031] exist Figure 1 In the present invention, Schottky rectifier 100 is formed using n-doped epitaxial layers that form drift region 102 on top of n+ substrate 101. Multilayer p-body (represented by multilayer p-body 110) penetrates Lpbody in depth, which is between about 30% and 100% of the drift region thickness Ldrift, for example. As shown, the width of multilayer p-body 110 is Wp. The period of the unit cell is Wcell, which should preferably be less than the drift region length, i.e., Wcell. <Ldrift。

[0032] Figure 1 The unit cell in the embodiment of the present invention may be provided with a metal layer 150 which forms a Schottky contact with the n- region 102 having a desired barrier height. An ohmic contact 160 is provided at the bottom of the n+ substrate 101 .

[0033] Regarding doping, in some example embodiments, the tunnel contact layer 111 may be provided with degenerate acceptor doping to, for example, 10 20 cm -3 In other words, as described above, the heavily doped p-body portion (tunnel contact layer) 111 provides a tunnel contact to the top metal 150, which prevents excessive voltage drop at the interface of metal 150 to layer 111 at very high current densities, which corresponds to the mode of IFM testing. 20 cm -3 The near-surface acceptor concentration of 150 is used to ensure a low forward voltage drop of the multilayer p-body 110 at the metal contact 150 to the tunnel contact layer 111 .

[0034] In a more detailed example, under conditions corresponding to the IFM test, the average current density through the active area of ​​a 650V Schottky rectifier might be close to 40kA / cm 2 During a 10 microsecond surge current event, the local current density through the multilayer p-body 110 may be, for example, twice the average value, for example 80,000 A / cm 2 High-quality ohmic contacts to p-type SiC have a -5 Up to 3x10 -5 Ohm cm 2 The specific resistance is used to optimize the metallization scheme. At a current density of about 100 kA / cm 2When the contact resistance is 10V, the parasitic voltage drop in the p-type body 110 can be much greater than 1V. However, in many cases, the ohmic contact process is simplified for manufacturing considerations, and the specific resistance of such a simplified contact can be 10 -4 Ohm cm 2 or higher. Higher than 1x10 20 / cm 3 A high near-surface acceptor concentration will facilitate direct tunneling at the contact-semiconductor interface 150 / 111 and will prevent an excessively high voltage drop from forming at this interface.

[0035] In an exemplary embodiment, the injection layer 112 is provided with a surface area greater than about 2×10 14 cm -2 The acceptor dose is less than about 2x10 19 cm -3 As described below, in an example embodiment, approximately 1x10 18 cm- 3 to a lower level to ensure acceptable injection efficiency levels.

[0036] In an example embodiment, the multilayer p-body 110 penetrates at least 30% of the drift region 102 toward the substrate 101. In an example embodiment, the ratio of Lpbody to Ldrift may be between 0.7 and 0.9. The acceptor doping of the deep p-body 113 may be about 2x10 16 cm -3 Up to 1x10 18 cm -3 In some example embodiments, the acceptor dose in the deep p-body 113 is selected to provide for its depletion to at least 50% of its length under reverse bias before the avalanche breakdown point.

[0037] As described above, in example embodiments, the injection layer 112 may be designed and configured to provide high injection efficiency. Specifically, the injection layer 112 may be designed to have a high effective Gummel number.

[0038] In this regard, the canonical Gummel number can be understood to represent the integral of the doping concentration over the layer thickness (e.g., carrier path length). The Gummel number indicates the injection efficiency of the doped layer and can in some cases, particularly for relatively low doping levels, provide a sufficient approximation of this injection efficiency.

[0039] However, as doping levels increase, the effect indicated by the Gummel number decreases from what would be expected based on actual dose concentrations. Specifically, various physical effects contribute to this reduction as doping levels increase at a given path length, in particular, bandgap narrowing, which is known to occur in heavily doped regions due to multi-body quantum effects, can promote minority carrier injection into the heavily doped material while inhibiting carrier injection from the heavily doped material.

[0040] For a p-type layer with a box-shaped acceptor profile, the effective Gummel number "NGeff" is obtained as NG eff =Q a *exp(-dEg / kT), where Q a is the ionized acceptor dose, dEg is the band gap reduction due to heavy doping, k is the Boltzmann constant, and T is the Kelvin temperature. Considering this band gap narrowing, in an example embodiment, the upper limit of the doping of the injection layer 112 may be set to about 2×10 19 cm -3 In example embodiments, lower doping may be preferred to optimize injection efficiency, since it is known that from about 2-3x10 18 cm -3 Significant bandgap narrowing begins to occur at lower doping concentrations.

[0041] Therefore, the doping concentration of the connecting layer 112 can be understood to have a value associated with a peak injection efficiency rating (e.g., 2×10 18 Up to 2x10 19 cm -3 ), below which the concentration is insufficient, and above which the bandgap narrowing becomes increasingly detrimental. Thus, the effective Gummel number of the connecting layer 112 may be maintained at, for example, 2×10 14 or higher level.

[0042] Meanwhile, as mentioned above, the preferred doping concentration of the tunnel contact layer 111 is generally higher than the peak injection efficiency value of the injection layer 112, for example, at 1×10 20 cm -3 Thus, it can be observed that attempting to combine regions 111 and 112 may be undesirable in some embodiments, for example, where a high surge current is required for a charge-balanced Schottky rectifier.

[0043] In addition, the high (effective) Gummel number of the injection layer 112 prevents electron recombination at the top contact 150. As described above, such recombination can mitigate the short-term I FM Effect of the tunnel contact layer 111 during a surge current event.

[0044] As also described above, the Schottky rectifier 100 is configured with charge balance between acceptors in the deep p-body 113 and donors in the n-channel 102. This charge balance actually means that the total charges of uncompensated acceptors and donors in the corresponding p-type and n-type materials are present in substantially similar numbers within the region 109. Otherwise, too large a charge difference in the region may deteriorate the reverse blocking performance.

[0045] More specifically, in example embodiments, the average lateral donor charge Qd of the uncompensated donors in the charge balancing channel 102 may be defined as the total number of uncompensated donors in the region 109 divided by the active device area. The acceptor charge Qa may be defined as the total number of uncompensated acceptors within the charge balancing region 109 divided by the active device area. In some embodiments, the donor charge Qd and the acceptor charge Qa may have a value of approximately 1×10 13 cm -2 or less deviation (e.g., charge imbalance). In some embodiments, the rectifier 100 has a value greater than 1x10 13 cm -2 The charge imbalance may lead to premature avalanche breakdown (eg, avalanche breakdown below the desired blocking voltage).

[0046] Figure 2A yes Figure 1 A schematic cross-sectional view of an example embodiment of a SiC Schottky rectifier. As described above, and with reference to FIG. 2A to FIG. 2C Said, Figure 1 The Schottky rectifier 100 in FIG. 1 may be defined as a unit cell of a larger circuit, such as a multi-rectifier circuit, and the unit cells may be sized and spaced relative to each other and other circuit elements in a manner that provides additional surge current protection as well as other features and advantages.

[0047] More specifically, regarding Figure 2A , Figure 1 The SiC charge-balanced Schottky rectifier 100 may benefit from additional design requirements related to the lateral component of the electric field. For example, the lateral electric field may increase with the n-channel (e.g., Figure 1 The increase in the width of the n-channel 102 and / or the donor concentration in the N-channel 102 may undesirably increase, which may lead to premature breakdown.

[0048] To avoid such early breakdown, the rectifier device 200 includes an active region 270 surrounded by the pn diode edge 215 and a termination region 280. The termination region 280 prevents excessive electric fields and early breakdown at the periphery of the diode.

[0049] The active region 270 is composed of Figure 1The unit cell array shown is formed. In Figure 2, the corresponding unit cell includes a multilayer p-body, which includes a degenerate doped region providing a tunnel contact layer 211, an implanted p-body 212 and a deep p-body 213, and an adjacent n-channel 202. The array forming the active area can be one-dimensional (a linear array of p-type and n-type strips), or a two-dimensional array with a mesh structure.

[0050] The diode edge 215 is formed by a continuous p-body surrounding the unit cell array. The top portion of the pn diode edge 215 is preferably provided with heavy doping, and the doping profile may include a top region having the same doping and thickness as regions 212 and 213. An array of deep p-bodies 223a, 223b, 223c is also formed, which may have similar sizes and doping as the deep p-body 213. The deep p-bodies 223a, 223b, 223c are preferably distributed on the diode edge with the same period as the p-body 213 in the active region to maintain charge balance. This design can provide an avalanche breakdown voltage in the edge region, which is preferably equal to or greater than the avalanche breakdown voltage of the active region. Although three deep p-bodies 223a, 223b, 223c are shown in FIG. 2, example embodiments may use a greater number of such deep p-bodies, depending on the desired width of the p-type edge 215.

[0051] The metal contact 250 covers the unit cell array and at least the inner portion of the pn diode edge 215. An ohmic contact 260 is provided on the back side of the substrate.

[0052] A junction termination (JT) region 280 is provided outside the pn diode edge 215 to prevent or mitigate the electric field accumulation at the periphery of the device. Different strategies can be applied to achieve this goal. In an example embodiment, for example Figure 2A , an array of deep p-bodies 233a-233e can be provided around the pn diode edge 215. Figure 2A Five deep p-bodies 233a to 233e are shown in FIG, but the total number of such p-bodies may be greater. A passivation dielectric may be disposed on top of the SiC in the junction termination region 280, which may be silicon dioxide, silicon nitride, polyimide, or a combination thereof.

[0053] The average acceptor dose per unit area in the deep p-bodies 233a-233e may be approximately equal to the acceptor dose of the pn diode edge region 215 of the inner portion of the junction termination region 280. The average acceptor dose in the junction termination region 280 may be defined in a similar manner to the active cell, for example, as the total amount of acceptors in the deep p-bodies 233a-233e divided by the area of ​​the unit cell. More specifically, the average acceptor dose near the p-body 233d may be defined by selecting a dummy unit cell 239d that extends laterally halfway toward the centroid of the adjacent p-body. The average donor / acceptor dose near the p-body 233d may then be defined as the total amount of the relevant dopant contained in 239d divided by the area of ​​the element 239d. The same definition will apply to elements 233a, 233b, and 233c. The width of the outermost cell of the junction termination may be the same as its nearest neighbor.

[0054] The average acceptor dose may gradually decrease with increasing distance from the pn diode edge 215. For example, Figure 2A As shown, the width of each deep p-body 233a-233e can be reduced. A characteristic length Ljt can be defined to characterize the change in the average acceptor dose. Therefore, Ljt can be defined as the distance at which the average acceptor dose drops to 1 / 3 of its peak value. The characteristic length Ljt should preferably be at least 3 times the total thickness of the drift region.

[0055] In one aspect, the junction termination region 280 can be provided with an interconnected, continuous, shallow, low-doped acceptor junction termination body 235 interconnecting all of the p-bodies 233a-233e and the pn diode edge 215. Such a continuous low-doped JT p-body 235 can be provided to minimize the voltage drop between adjacent p-bodies during switching transients of the rectifier device.

[0056] The acceptor dose in region 235 may be, for example, between about 20% and 70% of the characteristic dose Qchar, where Qchar=ε*E cr / q, where E cr is the critical field of SiC for the required breakdown voltage, ε is the absolute dielectric constant of SiC, and q is the electron charge. The characteristic charge Qchar is the electric field E generated. cr The required charge, E cr is the avalanche breakdown field in SiC at the electrode of the one-dimensional rectifier diode. Therefore, the acceptor dose in the interconnect body 235 should ensure that this region is fully depleted before the avalanche breakdown voltage is reached. cr Example values ​​of are between 2 MV / cm and 3 MV / cm, depending on the voltage rating of the diode.

[0057] In an example embodiment, the interconnect junction termination p-body 235 can be extended laterally beyond the position of the last deep p-body 223c by a certain distance. The extension distance should preferably exceed the drift layer thickness. In this way, extending the p-body 235 will further reduce the electric field concentration at the deep b-body.

[0058] In example embodiments, the unit cell deep p-body 213 may extend the entire or nearly the entire depth of the drift region so that Lpbody is approximately equal to Ldrift. Figure 3 , these conditions are suitable for achieving the minimum on-voltage for injection.

[0059] Figure 2B yes Figure 2A A first top view of an example implementation of FIG. Figure 2B 2 shows a top view of the pn diode edge region 215. Region 215 shows a continuous p-body of the junction termination region 280, while region 235 is a continuous low-doped p-body. The outer edge of the metal contact 250 completely overlaps at least a portion of the active region and the pn diode edge 935.

[0060] Figure 2C yes Figure 2A More specifically, Figure 2C A top view configuration of the deep charge balancing p-bodies 213 relative to other device regions is shown, with the footprint of the p-bodies 213 shown with cross-hatching. In this embodiment, the charge balancing p-bodies 213 of the active region form a linear array.

[0061] The p-bodies 223x below the pn diode edge may form a concentric linear array. The inner and outer edges of the pn diode edge are shown by lines 215i and 215o, respectively. A concentric linear array 233x of deep p-bodies is also formed in the junction termination region 280, with the outer edge represented by line 235o. Figure 2A As described above, the average charge of the deep p-body 233 x in the termination region 280 gradually decreases with increasing distance from the pn diode edge 215 .

[0062] Figure 2C Only one of many possible configurations for deep p-bodies is shown. For example, deep p-body 213 can form the same type of concentric pattern as p-bodies 223x and 233x. The p-body can also be a two-dimensional mesh array of p-type islands, which can represent a two-dimensional hexagonal lattice.

[0063] Figure 3 It is shown Figure 1 and FIG. 2A to FIG. 2CA first current-voltage curve of a Schottky diode rectifier is shown in FIG. More specifically, Figure 3 shows a 5x10 16 cm -3 Example results 302 of a TCAD simulation of a deep p-body doped 650V Schottky rectifier, where the deep p-body extends to the substrate.

[0064] For comparison, a simulation of a reference Schottky rectifier without a deep P-body was also performed, as shown in IV curve 304. As can be seen by the kink or inflection in each of curves 302, 304, both rectifiers undergo injection where the injection begins to be seen as a kink in the IV curve.

[0065] It can be observed that the Schottky rectifier represented by curve 302 goes into injection at a much lower voltage than the reference rectifier device that does not include the deep p-body 113 / 213. This is a significant advantage from a device reliability perspective because such a rectifier has a lower forward voltage drop and can withstand higher surge currents without being destroyed. A temperature of 250C was used for the simulation because surge events can cause severe overheating of the diode, which is typically above the standard operating junction temperature.

[0066] Figure 4 It is shown Figure 1 and FIG. 2A to FIG. 2C A second current-voltage curve of a Schottky diode rectifier is shown in FIG. Figure 4 In the figure, the forward current IF versus the forward voltage VF is shown for Figure 1 The Schottky rectifier curve 402, in Figure 1 In the embodiment, the multilayer p-body 110 propagates down to about half way to the n-type substrate 101. The deep p-body 113 has a 8x10 16 The net acceptor doping of Figure 3 Same, Figure 4 A reference curve 404 for a Schottky rectifier without a multilayer p-body is shown in FIG.

[0067] Compare Figure 4 In comparison with the conventional MPS / JBS device with shallow p-body, it can be observed that the curves 402 and 404 plotted in FIG. Figure 1 The obvious reliability / stability advantage of the Schottky rectifier. Figure 5 This effect is illustrated and explained in more detail in Figure 5 The electron distribution along the center of the n-channel (502) and the electron distribution through the center of the p-body (504) are shown. Figure 5 From a sparse perspective, strong electron injection occurs in both the n-channel and the P-body, where electrons are the minority carriers.

[0068] Figure 6 yes Figure 1 6, which has a dedicated ohmic contact 640 to the multilayer p-body 611 / 612 / 613. More specifically, Figure 6 The surge capable rectifier device with deep p-bodies 611 / 612 / 613 is provided with dedicated ohmic contacts 640 to the degenerately doped sub-contact p-type regions forming the tunnel contact layer 611 .

[0069] Meanwhile, an ohmic contact 610 to the n-type substrate 601 is illustrated as region 660, and a solder metal stack is represented as region 670. The solder metal stack 670 may be, for example, Ti / Ni / Ag commonly used in power devices. The back contact 610 may be thermally annealed or laser annealed Ni. In an example embodiment, the back contact 610 may be formed by laser induced silicidation of the Ni / Ti stack. The upper side ohmic contact 640 may be, for example, a nickel silicide layer, wherein the silicide is formed by sintering Ni into SiC at a temperature between about 700C and 950C.

[0070] Typical resistivity values ​​for NiSi ohmic contacts to SiC are around 0.1mOhm*cm 2 , which is usually too high to withstand, for example, about 20 kA / cm through the p-body 611 / 612 / 613 2 -100 kA / cm 2 However, due to the tunneling effect mentioned previously, when the degenerate doping level in the region 611 is maintained, the voltage drop at the 640 to 611 interface will be a relatively low value, such as a few tenths of a volt.

[0071] 7A to 7J A method for forming a Figures 1 to 2C The first to tenth operation of the Schottky rectifier device. 7A to 7J In this process, sequential cycles of ion implantation and epitaxial regrowth are used to form a structure with a deep p-body. Figures 1 to 2C In some embodiments, the donors for the n-channel layer may be provided by doping during epitaxial layer growth, while in other embodiments, implantation doping may be used, particularly where relatively higher doping accuracy is desired.

[0072] In Figure 7a, fabrication can start from a 4H SiC substrate 701. In Figure 7b, an n-type epitaxial layer 702a with the desired doping is provided. Figure 7CIn the embodiment, epitaxial layer 702a is blanket implanted with donor ions 7020, which may be, for example, nitrogen, phosphorus, As, or Sb. Implantation of donor 7020 forms the lower portion of drift region channel 702 (e.g., similar to Figure 1 and Figure 2A channels 102 and 202 in it).

[0073] exist Fig.7D In the embodiment, a mask layer 7131 is deposited from a photoresist or other suitable mask material, such as silicon dioxide, silicon nitride, or tungsten. The mask layer 7131 is patterned, and acceptor ions 7130 are implanted. In an example embodiment, the acceptor dopant may be Al. However, the deep p-body 113 / 213 / 713 may also be Ga or B, or a combination thereof with Al.

[0074] exist Fig. 7E After removing the mask, the crystal is regrown using the additional epitaxial layer 7021a, as shown in FIG. Figure 7F The implantation stages 7C to 7F may be repeated to gradually increase the thickness of the charge balance regions 702 and 713, as shown. Figure 7G and 7H shown.

[0075] It should be understood that the deep p-body (e.g., Figure 2A The deep p-body regions (regions 223a-223c) in the active region unit 213 and the deep p-body regions (regions 233a-233c) in the terminal region can be connected to the deep p-body regions (corresponding to the deep p-body regions) of the active region unit 213. Figure 7D-7H The formation of 713) in the 7A to 7J These areas are omitted in 7A to 7J Only the formation of active structures is shown. However, their manufacturing processes may use the same or similar stages. Similarly, alignment marks may be formed in areas outside of the device locations on the wafer so that the marks are not 7A to 7J Clearly shown in.

[0076] like Fig.7I As shown, regions 711 and 712 may be implanted with doping levels corresponding to similar regions 111 / 211 and 112 / 212, respectively. Device fabrication may continue with implantation of junction termination region 235, at 7A to 7J As shown, fabrication may further include high temperature annealing to activate the implanted dopants, and forming metal contacts 750 and 770 on the top and bottom of the wafer, respectively.

[0077] In additional or alternative embodiments, the surge-capable Schottky rectifier device with deep p-body 113 / 213 / 713 described herein can be formed using ion implantation and subsequent acceptor dopant annealing. The deep p-body 113 / 213 / 713 can be formed by acceptor ion implantation using a high energy ion implanter at an accelerating voltage of, for example, about 1 MV to 5 MV. The ion implantation annealing can be performed at a temperature of about 1500C to 1800C in argon.

[0078] In some embodiments, a carbon coating may be provided on the upper surface of the SiC wafer before high temperature annealing to avoid roughening of the SiC surface. The carbon coating may be removed after high temperature annealing using oxygen plasma, by annealing in an oxygen environment, or a combination of both.

[0079] In yet another example embodiment, channeling room temperature Al ion implantation of the deep p-body 113 / 213 may be utilized. For example, the channeling implantation may be performed along the

[0001] SiC crystal direction, which is perpendicular to the substrate (0001) SiC crystal plane. The surface of the epitaxial SiC crystal is typically offset by about a few degrees from the substrate (0001) crystal plane, which means that the ion beam must be tilted at an equal angle to align with the

[0001] crystal direction.

[0080] Alignment of the Al beam to the

[0001] crystal direction can be performed with high precision, e.g., to within better than 0.5 degrees, or to within 0.01 to 0.2 degrees. The channeling Al implant penetrates deeper into the SiC than so-called random implants, which is a general name for ion implants that deviate more than about 1.5 to 2 degrees from a low index crystal direction.

[0081] Figure 8 It is along the

[0001] 4H SiC crystal direction with a 1x10 13 cm -3 Schematic diagram of room temperature secondary ion mass spectrometry (SIMS) graph 802 for channeling Al implanted into SiC at a dose of 450 keV. In contrast, for random implants, achieving the same ion penetration may disadvantageously require acceleration energies of several MeV. However, using the methods described above and with respect to Figure 8 The deeper channeling implants shown can minimize the number of implant and regrowth cycles while avoiding the need for implanter tools capable of MeV ion acceleration. Room temperature conditions are preferred for the channeling implants because implant depth decreases with increasing crystal temperature.

[0082] In example embodiments, hot implantation may be used to form regions 111 and 112. Attempting to implant the tunnel contact layer 111 / 211 / 711 at room temperature may result in amorphization of the SiC material. Furthermore, unlike silicon, completely amorphized SiC cannot fully recover its structure after annealing. Therefore, amorphization during ion implantation may be avoided by, for example, using an elevated substrate temperature during implantation, for example, between about 200°C and 700°C.

[0083] In another embodiment, a channeling room temperature implant of the lowly doped, deep p-body 113 / 213 is performed in a first stage, and a hot high-dose implant of regions 112 / 212 and 111 / 211 is performed after the room temperature channeling implant. Attempting to perform a channeling implant of region 113 after a high-dose implant of either region 111 or 112 may result in severely suppressed channeling, so that the channeling implant is much shallower than would otherwise be possible for a given implant ion energy. High-dose implants like those used for regions 112 and 111 produce significant ion damage, even at elevated temperatures. For example, if a channeling implant follows a high-dose implant of either region 111 or 112, such damage may adversely suppress ion channeling.

[0084] In additional or alternative embodiments, Fig. 9 As shown, donor doping of the drift region 102 / 202 / 702 can be performed using a channeling implant of phosphorus. For example, a channeling P implant can be established along the

[0001] crystal orientation of 4H SiC, which provides the property of being more than 3 times deeper than a random implant. Such properties are generally unexpected because more common donors, such as nitrogen, do not exhibit such strong channeling effects in SiC. For example, nitrogen typically increases its ion range by only about 40% when changing the beam direction from 4 degrees off-axis (called "random") to channeling conditions. The SIMS graph 902 of the channeled phosphorus is plotted together with the graph 904 of the random implant at Fig. 9 In , the available Pearson IV approximation is used for that calculated from earlier experimental data.

[0085] In some example embodiments of the Schottky rectifier device, the implant layer has at least 2x10 14 cm -2An effective Gummel number, and / or a multilayer body extending from a metal contact to the entire distance of a SiC substrate, wherein an epitaxial layer of a first conductivity type is formed on the SiC substrate. The metal contact may extend over an active region of a Schottky rectifier device, the active region comprising a channel region and a multilayer body, the Schottky rectifier device may further comprise a pn diode edge surrounding the active region with a continuous body of a second conductivity type and an array of deep edge bodies of the second conductivity type parallel to the multilayer body. An embodiment of the Schottky rectifier device may include a junction termination region outside the pn diode edge, and the junction termination region may include a junction termination body surrounding the pn diode edge and connected to a plurality of deep JT bodies extending parallel to the multilayer body and the deep edge body. An embodiment of the Schottky rectifier device may include a silicide ohmic contact between the tunnel contact layer and the metal contact.

[0086] It should be understood that in the foregoing description, when an element such as a layer, region, substrate, or component is referred to as being "located on top of ...," "connected to," "electrically connected to," "coupled to," or "electrically coupled to" another element, it may be "directly located on ...," "directly connected to," or "directly coupled to" another element, or one or more intermediate elements may be present. In contrast, when an element is referred to as being "directly located on ...," "directly connected to," or "directly coupled to" another element or layer, there are no intermediate elements or layers. Although the terms "directly located on ...," "directly connected to," or "directly coupled to" may not be used throughout the detailed description, an element shown as "directly located on ...," "directly connected to," or "directly coupled to" may be referred to as such. If any, the claims of the present application may be modified to list the exemplary relationships described in the specification or shown in the accompanying drawings.

[0087] As used in the specification and claims, the singular may include the plural unless the context clearly indicates a particular situation. Spatially relative terms (e.g., "on," "above," "above," "below," "below," "below," "below," etc.) are intended to include different orientations of the device in use or operation in addition to the orientation shown in the figure. In some embodiments, the relative terms above and below may include vertically above and vertically below, respectively. In some embodiments, the term adjacent may include laterally adjacent or horizontally adjacent.

[0088] Some embodiments may be implemented using various semiconductor processes and / or packaging techniques. Some embodiments may be implemented using various types of semiconductor processing techniques associated with semiconductor substrates including, but not limited to, for example, silicon (Si), gallium arsenide (GaAs), gallium nitride (GaN), silicon carbide (SiC), and / or the like.

[0089] Although certain features of the embodiments have been shown as described herein, many modifications, substitutions, changes and equivalents will occur to those skilled in the art. Therefore, it should be understood that the appended claims are intended to cover all such modifications and changes that fall within the scope of the embodiments. It should be understood that they are presented only as examples and not in a limiting manner, and various changes may be made in form and detail. In addition to mutually exclusive combinations, any part of the apparatus and / or method described herein may be combined in any combination. The embodiments described herein may include various combinations and / or sub-combinations of the functions, components and / or features of the different embodiments described.

[0090] While certain features of the described embodiments have been illustrated as described herein, many modifications, substitutions, changes and equivalents will occur to those skilled in the art. It is therefore to be understood that the appended claims are intended to cover all such modifications and changes that fall within the scope of the embodiments.

Claims

1. A Schottky rectifier device, characterized in that: The Schottky rectifier device comprises: Silicon carbide SiC layer; a channel region of a first conductivity type formed on the SiC layer; an active region, the active region including the channel region and a unit cell array of a plurality of multi-layer bodies formed in the channel region; a metal contact formed on the channel region and extending over the active region, wherein each multilayer body has a second conductivity type and is formed in the channel region and extends from the metal contact in the direction of the SiC layer, each multilayer body includes a first layer adjacent to the metal contact and having a first doping concentration, a second layer adjacent to the first layer and having a second doping concentration less than the first doping concentration, and a third layer adjacent to the second layer and having a third doping concentration less than the second doping concentration; and A pn diode edge of the active area is surrounded by a continuous body of the second conductivity type, and a deep edge body array of the second conductivity type is parallel to the multiple multilayer bodies and distributed with the same period as the multiple multilayer bodies, and the deep edge body array is formed on the side of the pn diode edge close to the SiC layer.

2. The Schottky rectifier device according to claim 1, wherein the second layer has at least 2x10 14 cm -2 The effective Gummel number of .

3. The Schottky rectifier device according to claim 1, wherein the second layer has a 18 cm -3 Up to 1x10 19 cm -3 between the doping concentrations.

4. The Schottky rectifier device of claim 1, wherein the first layer is degenerately doped and provides a tunnel contact between the metal contact and the second layer. 5 . The Schottky rectifier device of claim 1 , wherein the multilayer body extends at least 30% of the distance between the metal contact and the SiC layer.

6. A method for manufacturing a Schottky rectifier device, characterized in that: The method comprises: forming a silicon carbide SiC substrate; forming an epitaxial layer of a first conductivity type on the SiC substrate; forming a mask layer on the epitaxial layer; performing ion implantation of a second conductivity type donor through the mask layer to form a portion of a charge balancing body, the charge balancing body comprising a deep body array in the active region and a deep edge body array parallel to the multilayer body and having the same period as the multilayer body; removing the mask layer; Repeating the formation of the epitaxial layer and the masked ion implantation until the charge balance body reaches a specified thickness; forming an injection layer on the charge balancing body, the injection layer having a doping concentration of a second conductivity type, the doping concentration of the second conductivity type being higher than the doping concentration of the charge balancing body; forming a pn diode edge, the pn diode edge surrounding the active area with a continuous body formed on the deep edge body array, the pn diode edge being located on a side of the deep edge body array away from the SiC substrate; forming a contact layer on the injection layer; and A metal contact is formed on the contact layer and the epitaxial layer. 7 . The method of claim 6 , wherein the contact layer, the injection layer and the charge balancing body extend at least 30% of the distance from the metal contact to the SiC substrate. The method according to claim 6 , wherein the contact layer has a doping concentration higher than a doping concentration of the injection layer.

9. A Schottky rectifier device, characterized in that: The Schottky rectifier device comprises: Silicon carbide SiC layer; a channel region of a first conductivity type formed on the SiC layer; an active region, the active region including the channel region and a unit cell array of a plurality of multi-layer bodies formed in the channel region; forming a metal contact on the channel region, wherein each multilayer body has a second conductivity type and is formed in the channel region and extends from the metal contact in the direction of the SiC layer, the multilayer body comprising a tunnel contact layer adjacent to the metal contact, an injection layer adjacent to the tunnel contact layer, and a deep layer adjacent to the injection layer, wherein the multilayer body extends at least 30% of the distance between the metal contact and the SiC layer; and A pn diode edge of the active area is surrounded by a continuous body of the second conductivity type, and a deep edge body array of the second conductivity type is parallel to the multiple multilayer bodies and distributed with the same period as the multiple multilayer bodies, and the deep edge body array is formed on the side of the pn diode edge close to the SiC layer.

Images