Silicon carbide composite substrate and its preparation method and application

Abstract

The present invention provides a silicon carbide composite substrate and its preparation method and application. The preparation method comprises the following steps: (1) performing a peeling layer implantation treatment on a donor substrate to form a peeling layer; (2) performing masking treatment on a bottom substrate and a donor substrate respectively, and then performing ion implantation treatment to form floating junctions on the bottom substrate and the donor substrate respectively, thereby obtaining a modified bottom substrate and a modified donor substrate; (3) performing debonding treatment on the modified bottom substrate and the modified donor substrate respectively, bonding the ion implanted surfaces of the two, and performing heat treatment to remove the peeling layer to obtain a semi-finished composite substrate; (4) performing masking treatment on the semi-finished composite substrate, and then performing ion implantation, debonding, and annealing to obtain the silicon carbide composite substrate. The silicon carbide composite substrate of the present invention does not require multiple epitaxy processes, and can form a deeper floating junction without high-energy implantation during the preparation process, thereby significantly reducing the preparation cost, required dose, and implantation time.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor materials and relates to a silicon carbide composite substrate and a preparation method and application thereof. Background Art

[0002] Since unipolar devices do not have minority carriers in their structure to modulate conductivity, their switching frequency is much higher than that of bipolar devices, so they are widely used in high-switching frequency circuits. SBD (Schottky barrier diode) is a typical representative. Due to its low switching power loss, it has very important applications in high-frequency circuits and microwave fields.

[0003] Compared to silicon-based materials, silicon carbide has a wider bandgap (approximately three times that of silicon), a stronger critical breakdown electric field (approximately 10 times that of silicon), and higher thermal conductivity (approximately three times that of Si). This wider bandgap allows silicon carbide devices to have a shorter drift region at the same withstand voltage, significantly reducing their on-resistance. This higher thermal conductivity also improves device heat dissipation, eliminating the need for additional heat sinks even in high-temperature environments, significantly reducing system size and cost. These superior properties of silicon carbide enable silicon carbide SBDs to offer higher withstand voltages and operate at higher temperatures, offsetting the shortcomings of silicon SBDs.

[0004] Although silicon carbide boasts many superior properties, its slow crystal growth rate, low yield, and difficulty in expanding its diameter result in low production capacity and high cost. Furthermore, achieving higher withstand voltages for silicon carbide SBD devices requires growing thick silicon carbide epitaxial layers. However, due to technical limitations, the epitaxial growth process often contains numerous defects, which severely impacts device performance.

[0005] CN118156319A discloses a silicon carbide SBD device with a uniformly distributed epitaxial layer and a manufacturing method thereof, which comprises: depositing the N-type SiC epitaxial layer on the upper surface of the 4H-SiC substrate layer, and depositing a P-type SiC epitaxial layer on one side of the surface of the N-type SiC epitaxial layer; the P-type SiC epitaxial layer comprises: a SiO2 protective layer, a plurality of P-type trapezoidal islands of the same length and equal spacing, the SiO2 protective layer is connected to the first P-type trapezoidal island close to the SiO2 protective layer, and the plurality of P-type trapezoidal islands are connected end to end; an anode is deposited on the other side of the surface of the N-type SiC epitaxial layer, and the last P-type trapezoidal island away from the SiO2 protective layer is connected to the anode, and a cathode is deposited on the lower surface of the 4H-SiC substrate layer.

[0006] CN117995880A discloses a method for preparing a silicon carbide SBD structure, comprising: S1: cleaning a SiC material substrate, wherein the SiC material substrate is an n+SiC substrate; S2: growing an n-type epitaxial layer; S3: forming a p-type buried layer region; S4: forming an n+ region; S5: forming a p-type surface region; S6: forming a Schottky contact electrode; S7: thinning the n+SiC substrate; and S8: forming an ohmic contact electrode.

[0007] The above scheme forms a floating junction (FJ) through multiple epitaxy processes. Multiple epitaxy processes may cause defects during the epitaxy process, which in turn affects device performance. Alternatively, the floating junction is formed through high-energy ion implantation. This method requires extremely large equipment energy and is very expensive. The deep implantation and multiple epitaxy processes involved in the above scheme are difficult to achieve commercially. Summary of the Invention

[0008] The purpose of the present invention is to provide a silicon carbide composite substrate, a preparation method and application thereof. The silicon carbide composite substrate described in the present invention does not require multiple epitaxy, thereby reducing defects caused by multiple epitaxy. In addition, a deeper floating junction can be formed without high-energy injection during the preparation process, thereby greatly reducing the preparation cost. Compared with high-energy injection, the required dose and injection time of low-energy injection are also reduced simultaneously, thereby improving production efficiency.

[0009] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a method for preparing a silicon carbide composite substrate, the method comprising the following steps:

[0011] (1) providing two silicon carbide substrates as a bottom substrate and a donor substrate, respectively, performing a peeling layer implantation process on the donor substrate, and forming a peeling layer on one surface of the donor substrate;

[0012] (2) performing a first mask treatment on one side surface of the underlying substrate and the other side of the peeling layer of the donor substrate, respectively, and then performing a first ion implantation treatment to form floating junctions on one side surface of the underlying substrate and the other side of the peeling layer of the donor substrate, respectively, to obtain a modified underlying substrate and a modified donor substrate;

[0013] (3) After performing a first debonding treatment on the modified base substrate and the modified donor substrate, the ion implanted surfaces of the modified base substrate and the modified donor substrate are bonded, and then the peeling layer is removed by heat treatment to obtain a semi-finished composite substrate;

[0014] (4) performing a second masking treatment on the surface of the peeled side of the semi-finished composite substrate and then performing a second ion implantation treatment to obtain a modified semi-finished composite substrate, performing a second debonding treatment on the modified semi-finished composite substrate, and then annealing to obtain the silicon carbide composite substrate;

[0015] The ion implantation energy of the lift-off layer implantation process is less than or equal to the ion implantation energy of the first ion implantation process plus the ion implantation energy of the second ion implantation process.

[0016] The first masking process and the second masking process of the present invention are identical in position and width, thereby ensuring that the floating junctions formed by the first ion implantation process and the second ion implantation process are identical in position. During bonding, alignment using mark points allows for perfect alignment between the two. The ion implantation surface is the side of the substrate that has undergone the ion implantation process, and the surface of the semi-finished composite substrate that has been peeled off is the surface after the peeling layer has been removed.

[0017] During the preparation of conventional floating junction Schottky barrier diode (FJ-SBD) or hybrid power diode (FJ-MPS) substrates, a floating junction (FJ) needs to be formed through multiple epitaxy or high-energy ion implantation. However, multiple epitaxy may produce defects during the epitaxy process, affecting the performance of the substrate, and the cost of high-energy ion implantation is extremely high. The method described in the present invention pre-implants ions into the underlying substrate and the donor substrate to form a floating junction. The two are then bonded together and then heat-treated to remove the donor substrate to form a semi-finished composite silicon carbide substrate. The semi-finished composite silicon carbide substrate is then ion-implanted again to form a floating junction. The composite silicon carbide substrate is then annealed to obtain the composite silicon carbide substrate. The composite silicon carbide substrate produced by the method described in the present invention not only does not require multiple epitaxy, but can be produced according to normal epitaxy, but also does not require the use of high-energy ion implantation. A deeper FJ can be achieved using medium or low energy. At the same time, FJs of a certain depth range can be produced according to requirements. The use of the composite silicon carbide substrate can also reduce material costs.

[0018] Preferably, the bottom substrate and the donor substrate are cleaned before the peeling layer injection process in step (1).

[0019] The cleaning process of the present invention can clean impurities such as particles, metals, organic matter, etc. on the surface of the silicon carbide substrate to ensure a clean surface.

[0020] Preferably, the ion species injected in the stripping layer implantation treatment in step (1) include hydrogen and / or helium.

[0021] Preferably, the ion implantation energy of the stripping layer implantation treatment in step (1) is 1 keV to 400 keV, for example, 1 keV, 15 keV, 50 keV, 100 keV or 400 keV, etc., and is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0022] Preferably, the ion implantation energy of the stripping layer implantation treatment in step (1) is 45 keV to 350 keV, for example, 45 keV, 80 keV, 100 keV, 200 keV or 350 keV, etc., and is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0023] Preferably, the ion implantation dose of the peeling layer implantation treatment in step (1) is 1×10 16 ions / cm²~1×10 18 ions / cm², for example: 1×10 16 ions / cm²、5×10 16 ions / cm²、1×10 17 ions / cm²、3×10 17 ions / cm² or 1×10 18 ions / cm², is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0024] Preferably, the inclination angle of the stripping layer injection treatment in step (1) is 0°~10°, for example: 0°, 5°, 7°, 8° or 10°, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0025] Preferably, the torsion angle of the peeling layer injection treatment in step (1) is 0°~45°, for example: 0°, 11°, 22°, 23°, 45°, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0026] Preferably, the temperature of the stripping layer injection treatment in step (1) is 20°C to 600°C, for example, 20°C, 100°C, 300°C, 500°C or 600°C, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0027] Preferably, the thickness of the peeling layer in step (1) is 0.1 μm to 3 μm, for example, 0.1 μm, 0.5 μm, 1 μm, 2 μm or 3 μm, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0028] Preferably, the first mask processing in step (2) includes coating, exposure and development.

[0029] The purpose of the first mask processing of the present invention is to form an implantation window of the floating junction in preparation for subsequent ion implantation.

[0030] Preferably, the thickness of the photoresist formed by the coating is 1 μm to 3 μm, for example, 1 μm, 1.5 μm, 2 μm, 2.5 μm or 3 μm, etc., and is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0031] Preferably, the exposure and development comprises developing with a positive photoresist developer.

[0032] Preferably, the ion species implanted in the first ion implantation treatment in step (2) include any one of B, P, As, N, Al or In, or a combination of at least two of them.

[0033] Preferably, the ion implantation energy of the first ion implantation treatment in step (2) is 10 keV to 400 keV, for example, 1 keV, 20 keV, 50 keV, 100 keV or 400 keV, etc., and is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0034] Preferably, the ion implantation energy of the first ion implantation treatment in step (2) is 45 keV to 350 keV, for example, 45 keV, 80 keV, 100 keV, 200 keV or 350 keV, etc., and is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0035] Preferably, the ion implantation dose of the first ion implantation treatment in step (2) is 1×10 13 ions / cm²~1×10 17 ions / cm², for example: 1×10 13 ions / cm²、1×10 14 ions / cm²、1×10 15 ions / cm²、1×10 16 ions / cm² or 1×10 17 ions / cm², is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0036] Preferably, the tilt angle of the first ion implantation treatment in step (2) is 0° to 60°, for example, 0°, 5°, 7°, 8° or 10°, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0037] Preferably, the twist angle of the first ion implantation treatment in step (2) is 0° to 45°, for example, 0°, 11°, 22°, 23°, 45°, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0038] Preferably, the temperature of the first ion implantation treatment in step (2) is 20°C to 600°C, for example, 20°C, 100°C, 300°C, 500°C or 600°C, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0039] Preferably, the thickness of the floating junction formed by the first ion implantation treatment on one side surface of the underlying substrate and the other side of the peeling layer of the donor substrate in step (2) is independently 0.01 μm to 0.5 μm, for example: 0.01 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm or 0.5 μm, etc., and is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0040] Preferably, the first degumming treatment in step (3) includes dry degumming and / or wet degumming.

[0041] The purpose of the stripping treatment (including the first stripping treatment and the second stripping treatment) of the present invention is to remove residual adhesive and impurities such as particles, metals, and organic matter on the surface of the bottom substrate and the donor substrate to facilitate subsequent bonding.

[0042] Preferably, the bonding temperature in step (3) is 20°C to 30°C, for example, 20°C, 22°C, 25°C, 28°C or 30°C, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0043] Preferably, the absolute vacuum degree of the bonding in step (3) is ≤10 -6 Pa.

[0044] Preferably, the bonding pressure in step (3) is 10 kN to 100 kN, for example, 10 kN, 20 kN, 50 kN, 80 kN or 100 kN, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0045] Preferably, the bonding strength of the bonding in step (3) is ≥1.4 J / cm 2 .

[0046] Before bonding in the present invention, the substrates need to be cleaned to remove residual glue and impurities such as particles, metals, and organic matter on the surfaces of the bottom substrate and the donor substrate to facilitate subsequent bonding.

[0047] The bonding method of the present invention includes bonding the bottom substrate and the donor substrate to the implant surface, and aligning the bottom substrate and the donor substrate by mark points to ensure that the positions of the implanted floating junctions match; and the bonding strength is ≥1.4J / cm 2 , to ensure subsequent production.

[0048] Preferably, the atmosphere for the heat treatment stripping in step (3) includes nitrogen.

[0049] Preferably, the temperature of the heat treatment peeling in step (3) is 800°C~1200°C, for example: 800°C, 900°C, 1000°C, 1100°C or 1200°C, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0050] The present invention causes the bonded wafer to break along the stripping injection layer through heat treatment, thereby forming a composite substrate (bottom substrate + donor substrate after stripping), and the remaining donor substrate can be reused.

[0051] Preferably, the time for the heat treatment peeling in step (3) is 1 min to 60 min, for example, 1 min, 5 min, 10 min, 20 min or 60 min, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0052] Preferably, in step (4), the semi-finished composite substrate is cleaned before the second mask processing.

[0053] Preferably, the second mask processing in step (4) includes coating, exposure and development.

[0054] The purpose of the second mask process of the present invention is to form an injection window of the floating junction again.

[0055] Preferably, the thickness of the photoresist formed by the coating is 1 μm to 3 μm, for example, 1 μm, 1.5 μm, 2 μm, 2.5 μm or 3 μm, etc., and is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0056] Preferably, the exposure and development comprises developing with a positive photoresist developer.

[0057] Preferably, the ion species implanted in the second ion implantation treatment in step (4) include any one or a combination of at least two of B, P, As, N, Al or In. Typical but non-limiting combinations include a combination of N and P, a combination of As and N, or a combination of Al and N.

[0058] Preferably, the ion implantation energy of the second ion implantation treatment in step (4) is 1 keV to 400 keV, for example, 1 keV, 20 keV, 50 keV, 100 keV or 400 keV, etc., and is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0059] Preferably, the ion implantation energy of the second ion implantation treatment in step (4) is 50 keV to 370 keV, for example, 50 keV, 80 keV, 100 keV, 200 keV or 370 keV, etc., and is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0060] Preferably, the ion implantation dose of the second ion implantation treatment in step (4) is 1×10 13 ions / cm²~1×10 17 ions / cm², for example: 1×10 13 ions / cm²、1×10 14 ions / cm²、1×10 15 ions / cm²、1×10 16 ions / cm² or 1×10 17 ions / cm², is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0061] Preferably, the inclination angle of the second ion implantation treatment in step (4) is 0° to 10°, for example, 0°, 5°, 7°, 8° or 10°, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0062] Preferably, the twist angle of the second ion implantation treatment in step (4) is 0° to 45°, for example, 0°, 11°, 22°, 23°, 45°, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0063] Preferably, the temperature of the second ion implantation treatment in step (4) is 20°C to 600°C, for example, 20°C, 100°C, 300°C, 500°C or 600°C, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0064] Preferably, the thickness of the floating junction formed by the second ion implantation treatment in step (4) is 0.01 μm to 0.5 μm, for example, 0.01 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm or 0.5 μm, etc., and is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0065] Preferably, the second degumming treatment in step (4) includes dry degumming and / or wet degumming.

[0066] Preferably, the annealing atmosphere in step (4) includes argon.

[0067] Preferably, the annealing temperature in step (4) is 1600°C to 1950°C, for example, 1600°C, 1650°C, 1700°C, 1800°C or 1950°C, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0068] Preferably, the annealing time in step (4) is 5 min to 30 min, for example, 5 min, 10 min, 15 min, 20 min or 30 min, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0069] The purpose of the annealing treatment in the present invention is to repair the damage caused by ion implantation.

[0070] Preferably, chemical mechanical polishing (CMP) is performed after the annealing in step (4).

[0071] In a second aspect, the present invention provides a silicon carbide composite substrate, which is manufactured by the manufacturing method described in the first aspect.

[0072] The lateral width of the floating junction in the silicon carbide composite substrate of the present invention can be modified according to design requirements, and the shape can also be changed according to design requirements, such as hexagonal, circular, etc.

[0073] In a third aspect, the present invention provides a unipolar device, wherein the unipolar device comprises the silicon carbide composite substrate as described in the second aspect, and the unipolar device includes a Schottky barrier diode and / or a hybrid power diode.

[0074] Compared with the prior art, the present invention has the following beneficial effects:

[0075] (1) The silicon carbide composite substrate of the present invention does not require multiple epitaxy, which reduces the defects caused by multiple epitaxy. In addition, a deeper floating junction can be formed without high-energy injection during the preparation process, which greatly reduces the preparation cost. In addition, compared with high-energy injection, the required dose and injection time of low-energy injection are also reduced simultaneously, thereby improving production efficiency.

[0076] (2) The reverse leakage current IR of the silicon carbide FJ-SBD prepared using the silicon carbide composite substrate of the present invention can reach less than 0.83 μA at a reverse voltage of 1200 V, and the reverse breakdown voltage BV can reach more than 1398.14 V when the reverse current reaches 0.1 mA. By adjusting the preparation conditions, the reverse leakage current IR of the silicon carbide FJ-SBD prepared using the silicon carbide composite substrate can reach less than 0.78 μA at a reverse voltage of 1200 V, and the reverse breakdown voltage BV can reach more than 1428.22 V when the reverse current reaches 0.1 mA. The reverse electrical characteristics are significantly improved compared with conventional SBDs. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] Figure 1 This is a schematic diagram of the preparation process of the silicon carbide composite substrate provided by an embodiment of the present invention, 11 is the peeling layer injection, 12 is the donor substrate coating, exposure and development, 13 is the donor substrate ion injection, 14 is the donor substrate degumming, 21 is the bottom substrate coating, exposure and development, 22 is the bottom substrate ion injection, 23 is the bottom substrate degumming, 30 is the bonding between the donor substrate and the bottom substrate, 31 is the peeling annealing, 32 is the semi-finished composite substrate coating, exposure and development, 33 is the semi-finished composite substrate ion injection, 34 is the semi-finished composite substrate degumming and annealing, and 35 is chemical mechanical polishing.

[0078] Figure 2 Schematic diagram of the distribution of floating junctions in the silicon carbide composite substrate described in Example 1.

[0079] Figure 3 This is a schematic diagram of the distribution of floating junctions in the silicon carbide composite substrate described in Example 2.

[0080] Figure 4 This is a schematic diagram of the distribution of floating junctions in the silicon carbide composite substrate described in Example 3.

[0081] Figure 5 This is a flow chart of the preparation process of silicon carbide FJ-SBD provided by the application example of the present invention, 11 is peeling layer injection, 12 is donor substrate coating, exposure and development, 13 is donor substrate ion injection, 14 is donor substrate degumming, 21 is bottom substrate coating, exposure and development, 22 is bottom substrate ion injection, 23 is bottom substrate degumming, 30 is bonding between the donor substrate and the bottom substrate, 31 is peeling annealing, 32 is semi-finished composite substrate coating, exposure and development, 33 is semi-finished composite substrate ion injection, 34 is semi-finished composite substrate degumming and annealing, 35 is chemical mechanical polishing, 36 is epitaxial growth and back thinning, 37 is ohmic contact, and 38 is formation of Schottky contact.

[0082] Figure 6 This is a comparison chart of the forward characteristic curves of the silicon carbide FJ-SBD prepared in Application Example 1 and Comparative Application Example 2.

[0083] Figure 7 This is a comparison diagram of the reverse characteristic curves of the silicon carbide FJ-SBD prepared in Application Example 1 and Comparative Application Example 2. DETAILED DESCRIPTION

[0084] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0085] Example 1

[0086] This embodiment provides a silicon carbide composite substrate, the preparation process flow chart of the silicon carbide composite substrate is as follows: Figure 1 As shown, the silicon carbide composite substrate is specifically prepared by the following method:

[0087] (1) Provide an N-type SiC bottom substrate and a donor substrate for standard RCA cleaning to remove surface particles, metals, organic matter and other impurities, and then use them as the bottom substrate and donor substrate respectively. The donor substrate is subjected to a peeling layer implantation 11 treatment. The implantation conditions are H ions, the implantation energy is 120keV, and the implantation dose is 6×10 16 ions / cm², a tilt angle of 7°, a twist angle of 0°, an injection temperature of 100°C, and a 0.8 μm thick peeling layer was formed on one surface of the donor substrate;

[0088] (2) After coating, exposing and developing one side of the bottom substrate, a photoresist 21 with a thickness of 2 μm is formed. After coating, exposing and developing 12, a photoresist with a thickness of 2 μm is formed on the other side of the peeling layer of the donor substrate. After ion implantation (donor substrate ion implantation 13, bottom substrate ion implantation 22), floating junctions with a thickness of 0.28 μm are formed on one side of the bottom substrate and on the other side of the peeling layer of the donor substrate, respectively, to obtain a modified bottom substrate and a modified donor substrate. The ion species of the ion implantation is aluminum ion, the implantation energy is 270 keV, and the implantation dose is 4.5×10 14 ions / cm², the tilt angle is 7°, the twist angle is 0°, and the injection temperature is 500°C;

[0089] (3) The bottom substrate and the donor substrate are subjected to dry and wet degumming, ICP and RCA cleaning processes respectively to remove the residual glue and particles, metals, organic matter and other impurities on the surface of the bottom substrate and the donor substrate, and the ion implantation surface of the modified bottom substrate and the modified donor substrate is kept at 25°C and absolute vacuum ≤10 -6 After bonding 30 at a pressure of 50 kN, a peeling annealing 31 is performed at 1050° C. in a nitrogen atmosphere for 20 min, and the excess donor substrate is removed along the peeling layer to obtain a semi-finished composite substrate;

[0090] (4) The peeled side of the semi-finished composite substrate is cleaned, coated, exposed and developed 32, and then ion implanted 33. The ion species of the ion implantation is aluminum ion, the implantation energy is 280keV, and the implantation dose is 5×10 14 ions / cm², a tilt angle of 7°, a twist angle of 0°, and an injection temperature of 500°C to obtain a modified semi-finished composite substrate. The modified semi-finished composite substrate is subjected to dry and wet debonding, ICP and RCA cleaning processes to remove residual adhesive and impurities such as particles, metals, and organic matter on the surface of the composite substrate. The substrate is annealed at 1750°C for 30 minutes in an argon atmosphere (semi-finished composite substrate debonding and annealing 34). After 100 seconds of CMP (chemical mechanical polishing 35) with a removal amount of 1000 Å, the silicon carbide composite substrate is obtained.

[0091] The distribution diagram of the floating junction in the silicon carbide composite substrate is shown in FIG. Figure 2 shown.

[0092] Example 2

[0093] This embodiment provides a silicon carbide composite substrate, the preparation process flow chart of the silicon carbide composite substrate is as follows: Figure 1 As shown, the silicon carbide composite substrate is specifically prepared by the following method:

[0094] (1) Provide an N-type SiC bottom substrate and a donor substrate for standard RCA cleaning to remove surface particles, metals, organic matter and other impurities, and then use them as the bottom substrate and donor substrate respectively. The donor substrate is subjected to peeling layer implantation 11 treatment. The implantation conditions are H ions, the implantation energy is 150keV, and the implantation dose is 8×10 16 ions / cm², a tilt angle of 7°, a twist angle of 0°, and an injection temperature of 100°C to form a 1.21 μm thick exfoliation layer on one surface of the donor substrate;

[0095] (2) After coating, exposing and developing one side of the bottom substrate, a photoresist 21 with a thickness of 3 μm is formed. After coating, exposing and developing 12, a photoresist with a thickness of 3 μm is formed on the other side of the peeling layer of the donor substrate. After ion implantation (donor substrate ion implantation 13, bottom substrate ion implantation 22), floating junctions with a thickness of 0.4 μm are formed on one side of the bottom substrate and on the other side of the peeling layer of the donor substrate, respectively, to obtain a modified bottom substrate and a modified donor substrate. The ion species of the ion implantation is aluminum ion, the implantation energy is 350 keV, and the implantation dose is 5.5×10 14 ions / cm², the tilt angle is 7°, the twist angle is 0°, and the injection temperature is 500°C;

[0096] (3) The bottom substrate and the donor substrate are subjected to dry and wet degumming, ICP and RCA cleaning processes respectively to remove the residual glue and particles, metals, organic matter and other impurities on the surface of the bottom substrate and the donor substrate, and the ion implantation surface of the modified bottom substrate and the modified donor substrate is kept at 30°C and absolute vacuum ≤10 -6 After bonding 30 at a pressure of 80 kN, a peeling annealing 31 was performed in a nitrogen atmosphere at 1100° C. for 20 min, and excess donor substrate was removed along the peeling layer to obtain a semi-finished composite substrate;

[0097] (4) The surface of the semi-finished composite substrate that has been peeled off is cleaned, coated, exposed and developed 32, and then ion implanted 33. The ion species implanted is aluminum ion, the implantation energy is 360keV, and the implantation dose is 5.5×10 14 ions / cm², a tilt angle of 7°, a twist angle of 0°, and an injection temperature of 500°C to obtain a modified semi-finished composite substrate. The modified semi-finished composite substrate is subjected to dry and wet debonding, ICP and RCA cleaning processes to remove residual adhesive and impurities such as particles, metals, and organic matter on the surface of the composite substrate. The substrate is annealed at 1800°C for 5 minutes in an argon atmosphere (semi-finished composite substrate debonding and annealing 34). After 100 seconds of CMP (chemical mechanical polishing 35) with a removal amount of 1000 Å, the silicon carbide composite substrate is obtained.

[0098] The distribution diagram of the floating junction in the silicon carbide composite substrate is shown in FIG. Figure 3 shown.

[0099] Example 3

[0100] This embodiment provides a silicon carbide composite substrate, the preparation process flow chart of the silicon carbide composite substrate is as follows: Figure 1 As shown, the silicon carbide composite substrate is specifically prepared by the following method:

[0101] (1) Provide an N-type SiC bottom substrate and a donor substrate for standard RCA cleaning to remove surface particles, metals, organic matter and other impurities, and then use them as the bottom substrate and donor substrate respectively. The donor substrate is subjected to peeling layer implantation 11 treatment. The implantation conditions are H ions, the implantation energy is 20 keV, and the implantation dose is 5.5×10 16 ions / cm², a tilt angle of 7°, a twist angle of 0°, an injection temperature of 100°C, and a 0.15 μm thick peeling layer was formed on one surface of the donor substrate;

[0102] (2) After coating, exposing and developing one side of the bottom substrate, a photoresist 21 with a thickness of 1 μm is formed. After coating, exposing and developing 12, a photoresist with a thickness of 1 μm is formed on the other side of the peeling layer of the donor substrate. After ion implantation (donor substrate ion implantation 13, bottom substrate ion implantation 22), floating junctions with a thickness of 0.045 μm are formed on one side of the bottom substrate and on the other side of the peeling layer of the donor substrate, respectively, to obtain a modified bottom substrate and a modified donor substrate. The ion species of the ion implantation is aluminum ion, the implantation energy is 45 keV, and the implantation dose is 4.0×10 14 ions / cm², the tilt angle is 7°, the twist angle is 0°, and the injection temperature is 500°C;

[0103] (3) The bottom substrate and the donor substrate are subjected to dry and wet degumming, ICP and RCA cleaning processes respectively to remove the residual glue and particles, metals, organic matter and other impurities on the surface of the bottom substrate and the donor substrate, and the ion implantation surface of the modified bottom substrate and the modified donor substrate is kept at 20°C and absolute vacuum ≤10 -6 After bonding 30 at a pressure of 30 kN, a peeling annealing 31 is performed at 1000° C. for 20 min in a nitrogen atmosphere to remove excess donor substrate along the peeling layer to obtain a semi-finished composite substrate;

[0104] (4) The surface of the semi-finished composite substrate that has been peeled off is cleaned, coated, exposed and developed 32, and then ion implanted 33. The ion species implanted is aluminum ion, the implantation energy is 50keV, and the implantation dose is 4.0×10 14 ions / cm², a tilt angle of 7°, a twist angle of 0°, and an injection temperature of 500°C to obtain a modified semi-finished composite substrate. The modified semi-finished composite substrate is subjected to dry and wet debonding, ICP and RCA cleaning processes to remove residual adhesive and impurities such as particles, metals, and organic matter on the surface of the composite substrate. The substrate is annealed at 1650°C for 45 minutes in an argon atmosphere (semi-finished composite substrate debonding and annealing 34). After 100 seconds of CMP (chemical mechanical polishing 35) with a removal amount of 1000 Å, the silicon carbide composite substrate is obtained.

[0105] The distribution diagram of the floating junction in the silicon carbide composite substrate is shown in FIG. Figure 4 shown.

[0106] Example 4

[0107] The only difference between this embodiment and embodiment 1 is that the ion implantation energy of the lift-off layer implantation process is 360 keV, and the other conditions and parameters are exactly the same as those of embodiment 1.

[0108] Example 5

[0109] The only difference between this embodiment and embodiment 1 is that the ion implantation energy of the lift-off layer implantation process is 40 keV, and the other conditions and parameters are exactly the same as those of embodiment 1.

[0110] Example 6

[0111] The only difference between this embodiment and embodiment 1 is that the ion implantation energy of the ion implantation (first ion implantation) in step (2) is 380 keV, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0112] Example 7

[0113] The only difference between this embodiment and embodiment 1 is that the ion implantation energy of the ion implantation (first ion implantation) in step (2) is 20 keV, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0114] Example 8

[0115] The only difference between this embodiment and embodiment 1 is that the ion implantation energy of the ion implantation (second ion implantation) in step (4) is 390 keV, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0116] Example 9

[0117] The only difference between this embodiment and embodiment 1 is that the ion implantation energy of the ion implantation (second ion implantation) in step (4) is 25 keV, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0118] Comparative Example 1

[0119] The only difference between this comparative example and Example 1 is that the ion implantation energy of the stripping layer ion implantation in step (1) is 300 keV, the ion implantation energy of the ion implantation (first ion implantation) in step (2) is 100 keV, and the ion implantation energy in step (4) is 100 keV, that is, the ion implantation energy of the stripping layer implantation treatment > the ion implantation energy of the first ion implantation treatment + the ion implantation energy of the second ion implantation treatment.

[0120] Comparative Example 2

[0121] This comparative example uses a conventional single crystal SiC substrate.

[0122] Application Example 1

[0123] This application example provides a silicon carbide FJ-SBD, and the preparation process flow chart of the silicon carbide FJ-SBD is as follows: Figure 2 As shown, the silicon carbide FJ-SBD is prepared by the following method:

[0124] (1) Provide an N-type SiC bottom substrate and a donor substrate for standard RCA cleaning to remove surface particles, metals, organic matter and other impurities, and then use them as the bottom substrate and donor substrate respectively. The donor substrate is subjected to a peeling layer implantation 11 treatment. The implantation conditions are H ions, the implantation energy is 120keV, and the implantation dose is 6×10 16 ions / cm², a tilt angle of 7°, a twist angle of 0°, an injection temperature of 100°C, and a 0.8 μm thick peeling layer was formed on one surface of the donor substrate;

[0125] (2) After coating, exposing and developing one side of the bottom substrate, a photoresist 21 with a thickness of 2 μm is formed. After coating, exposing and developing 12, a photoresist with a thickness of 2 μm is formed on the other side of the peeling layer of the donor substrate. After ion implantation (donor substrate ion implantation 13, bottom substrate ion implantation 22), floating junctions with a thickness of 0.8 μm are formed on one side of the bottom substrate and on the other side of the peeling layer of the donor substrate, respectively, to obtain a modified bottom substrate and a modified donor substrate. The ion species of the ion implantation is aluminum ion, the implantation energy is 270 keV, and the implantation dose is 4.5×10 14 ions / cm², the tilt angle is 7°, the twist angle is 0°, and the injection temperature is 500°C;

[0126] (3) The bottom substrate and the donor substrate are subjected to dry and wet degumming, ICP and RCA cleaning processes respectively to remove the residual glue and particles, metals, organic matter and other impurities on the surface of the bottom substrate and the donor substrate, and the ion implantation surface of the modified bottom substrate and the modified donor substrate is kept at 25°C and absolute vacuum ≤10 -6 After bonding at a pressure of 50 kN for 30 min, a peel annealing process was performed at 1050° C. for 20 min in a nitrogen atmosphere for 31 , and the excess donor substrate was removed along the peel layer to obtain a semi-finished composite substrate;

[0127] (4) The peeled side of the semi-finished composite substrate is cleaned, coated, exposed and developed 32, and then ion implanted 33. The ion species of the ion implantation is aluminum ion, the implantation energy is 280keV, and the implantation dose is 5×10 14ions / cm², a tilt angle of 7°, a twist angle of 0°, and an injection temperature of 500°C to obtain a modified semi-finished composite substrate. The modified semi-finished composite substrate was subjected to dry and wet debonding, ICP and RCA cleaning processes to remove residual adhesive and impurities such as particles, metals, and organic matter on the surface of the composite substrate. The substrate was annealed at 1750°C for 30 minutes in an argon atmosphere (semi-finished composite substrate debonding and annealing 34). After 100 seconds of CMP (chemical mechanical polishing 35), a silicon carbide composite substrate was obtained with a removal amount of 1000A. The silicon carbide composite substrate was subjected to N-epitaxial growth with an epitaxial thickness of 10μm, a doping type of N, and a doping concentration of 1×10 16 atoms / cm 3 , after backside thinning (epitaxial growth and backside thinning 36), an epitaxial silicon carbide composite substrate is obtained;

[0128] (5) Nickel was sputtered onto the epitaxial silicon carbide composite substrate to form an ohmic contact 37 with a thickness of 1000 Å. The contact was annealed at 900°C in a nitrogen atmosphere for 10 min, and then titanium was evaporated to a thickness of 800 Å. Titanium was sputtered to form a Schottky contact 38, and then aluminum was evaporated to a thickness of 2 μm. The Schottky contact was annealed at 500°C in a nitrogen atmosphere for 10 min to obtain the silicon carbide FJ-SBD.

[0129] Application Example 2

[0130] The only difference between this application example and application example 1 is that the silicon carbide composite substrate is prepared using the method described in Example 2, and the other conditions and parameters are exactly the same as those in application example 1.

[0131] Application Example 3

[0132] The only difference between this application example and application example 1 is that the silicon carbide composite substrate is prepared using the method described in Example 3, and the other conditions and parameters are exactly the same as those in application example 1.

[0133] Application Example 4

[0134] The only difference between this application example and application example 1 is that the silicon carbide composite substrate is prepared using the method described in Example 4, and the other conditions and parameters are exactly the same as those in application example 1.

[0135] Application Example 5

[0136] The only difference between this application example and application example 1 is that the silicon carbide composite substrate is prepared using the method described in Example 5, and the other conditions and parameters are exactly the same as those in application example 1.

[0137] Application Example 6

[0138] The only difference between this application example and application example 1 is that the silicon carbide composite substrate is prepared using the method described in Example 6, and the other conditions and parameters are exactly the same as those in application example 1.

[0139] Application Example 7

[0140] The only difference between this application example and application example 1 is that the silicon carbide composite substrate is prepared using the method described in Example 7, and the other conditions and parameters are exactly the same as those in application example 1.

[0141] Application Example 8

[0142] The only difference between this application example and application example 1 is that the silicon carbide composite substrate is prepared using the method described in Example 8, and the other conditions and parameters are exactly the same as those in application example 1.

[0143] Application Example 9

[0144] The only difference between this application example and application example 1 is that the silicon carbide composite substrate is prepared using the method described in Example 9, and the other conditions and parameters are exactly the same as those in application example 1.

[0145] Comparative Application Example 1

[0146] The only difference between this comparative application example and application example 1 is that the silicon carbide composite substrate is prepared using the method described in comparative example 1, and other conditions and parameters are exactly the same as those in application example 1.

[0147] Comparative Application Example 2

[0148] The only difference between this comparative application example and application example 1 is that the single crystal SiC substrate described in comparative example 2 is used. The subsequent steps are: epitaxy: N-epitaxial growth is performed, the epitaxial thickness is 10 μm, the doping type is N, and the doping concentration is 1×10 16 atoms / cm 3 SBD: Nickel was sputtered to form an ohmic contact with a thickness of 1000 Å, annealed at 900°C in a nitrogen atmosphere for 10 minutes, and then titanium was evaporated to a thickness of 800 Å. Titanium was sputtered to form a Schottky contact, and then aluminum was evaporated to a thickness of 2 μm. The Schottky contact was annealed at 500°C in a nitrogen atmosphere for 10 minutes to obtain the silicon carbide SBD.

[0149] Performance testing:

[0150] The electrical properties and TCAD simulation analysis of the silicon carbide FJ-SBD obtained from the corresponding use case and comparative application example are shown in Table 1 and Figure 7 As shown:

[0151] Table 1

[0152]

[0153] As can be seen from Table 1, it can be obtained from Application Examples 1-9 that the reverse leakage current IR of the silicon carbide FJ-SBD prepared using the silicon carbide composite substrate of the present invention at a reverse voltage of 1200V can reach less than 0.83μA, and the reverse breakdown voltage BV can reach more than 1398.14V when the reverse current reaches 0.1mA. By adjusting the preparation conditions, the reverse leakage current IR of the silicon carbide FJ-SBD prepared using the silicon carbide composite substrate at a reverse voltage of 1200V can reach less than 0.78μA, and the reverse breakdown voltage BV can reach more than 1428.22V when the reverse current reaches 0.1mA. The reverse electrical characteristics are significantly improved compared with conventional SBDs.

[0154] By comparing Application Example 1 with Application Examples 4-5, it can be seen that in the preparation process of the silicon carbide composite substrate described in the present invention, the ion injection energy of the stripping layer injection treatment will affect its performance. When the ion injection energy of the stripping layer injection treatment is controlled at 45keV~350keV, the performance of the silicon carbide composite substrate is better. If the ion injection energy of the stripping layer injection treatment is too large, the BV and IR characteristics will not meet the set targets, and it will cause process waste and increased costs. If the ion injection energy of the stripping layer injection treatment is too small, the BV and IR characteristics will not meet the set targets, the floating junction utilization cannot be maximized, and its cost advantage is lost.

[0155] By comparing Application Example 1 with Application Examples 6-7, it can be seen that in the preparation process of the silicon carbide composite substrate described in the present invention, the ion injection energy of the first ion injection treatment will affect its performance. When the ion injection energy of the first ion injection treatment is controlled within 45keV~350keV, the performance of the silicon carbide composite substrate is better. If the ion injection energy of the first ion injection treatment is too large, the BV and IR characteristics will not meet the set targets, and the equipment will operate at the highest energy for a long time, causing stability problems. If the ion injection energy of the first ion injection treatment is too small, the BV and IR characteristics will not meet the set targets, the floating junction utilization cannot be maximized, and its cost advantage is lost.

[0156] By comparing Application Example 1 with Application Examples 8-9, it can be seen that in the preparation process of the silicon carbide composite substrate described in the present invention, the ion injection energy of the second ion injection treatment will affect its performance. When the ion injection energy of the second ion injection treatment is controlled within 50keV~370keV, the performance of the silicon carbide composite substrate is better. If the ion injection energy of the second ion injection treatment is too large, the BV and IR characteristics will not meet the set targets, and the equipment will cause stability problems if it operates at the highest energy for a long time. If the ion injection energy of the second ion injection treatment is too small, the BV and IR characteristics will not meet the set targets, the floating junction utilization cannot be maximized, and its cost advantage is lost.

[0157] A comparison between Application Example 1 and Comparative Application Example 1 shows that if the ion implantation depth of the stripping layer described in the present invention is greater than the ion implantation energy of the first ion implantation process + the ion implantation energy of the second ion implantation process, that is, the stripping depth Rp > the first implantation depth Rp1 + the second implantation depth Rp2, the first ion implantation process node depth + the second ion implantation process node depth will not cover the stripping layer thickness, resulting in insufficient coverage of the floating junction range. When a single device has the same controllable range of implantation energies, the controllable range of shallow ion implantation depths should be prioritized, that is, the stripping depth Rp ≤ the first implantation depth Rp1 + the second implantation depth Rp2. Generally, the stripping implantation energy ≤ the ion implantation energy of the first ion implantation process + the ion implantation energy of the second ion implantation process.

[0158] The forward characteristic curve comparison of silicon carbide FJ-SBD obtained in Application Example 1 and Comparative Application Example 2 is shown in the figure below: Figure 6 As shown by Figure 6 It can be seen that the forward VF is not much different from that of the single crystal SBD.

[0159] The reverse characteristic curve comparison of silicon carbide FJ-SBD obtained in application example 1 and comparative application example 2 is shown in the figure below: Figure 7 As shown by Figure 7 It can be seen that compared with single crystal SBD, the reverse characteristics (breakdown voltage and reverse leakage current) of FJ-SBD are better than those of single crystal SBD.

[0160] From the comparison between Application Example 1 and Comparative Application Example 2, it can be seen that in the reverse blocking state, the internal floating junction forms a depletion region expansion, which plays an electric field shielding effect, thereby reducing leakage current and increasing voltage resistance.

[0161] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a silicon carbide composite substrate, characterized in that: The preparation method comprises the following steps: (1) providing two silicon carbide substrates as a bottom substrate and a donor substrate, respectively, performing a peeling layer implantation process on the donor substrate, and forming a peeling layer on one surface of the donor substrate; (2) performing a first mask treatment on one side surface of the underlying substrate and the other side of the peeling layer of the donor substrate, respectively, and then performing a first ion implantation treatment to form floating junctions on one side surface of the underlying substrate and the other side of the peeling layer of the donor substrate, respectively, to obtain a modified underlying substrate and a modified donor substrate; (3) After performing a first debonding treatment on the modified base substrate and the modified donor substrate, the ion implanted surfaces of the modified base substrate and the modified donor substrate are bonded, and then the peeling layer is removed by heat treatment to obtain a semi-finished composite substrate; (4) performing a second masking treatment on the surface of the peeled side of the semi-finished composite substrate and then performing a second ion implantation treatment to obtain a modified semi-finished composite substrate, performing a second debonding treatment on the modified semi-finished composite substrate, and then annealing to obtain the silicon carbide composite substrate; Wherein, the ion implantation energy of the peeling layer implantation process is less than or equal to the ion implantation energy of the first ion implantation process + the ion implantation energy of the second ion implantation process; The ion implantation energy of the stripping layer implantation treatment in step (1) is 45 keV to 350 keV, the ion implantation energy of the first ion implantation treatment in step (2) is 45 keV to 350 keV, and the ion implantation energy of the second ion implantation treatment in step (4) is 50 keV to 370 keV; The positions and widths of the first mask process and the second mask process are exactly the same, thereby making the positions of the floating junctions formed by the first ion implantation process and the second ion implantation process exactly the same; The bonding includes implantation surface bonding of the bottom substrate and the donor substrate. During the bonding, alignment is performed through mark points to ensure that the positions of the bottom substrate and the donor substrate implanted into the floating junction match.

2. The preparation method according to claim 1, wherein The ion species injected in the stripping layer injection treatment in step (1) include hydrogen and / or helium.

3. The preparation method according to claim 1, wherein The ion implantation dose of the peeling layer implantation treatment in step (1) is 1×10 16 ions / cm²~1×10 18 ions / cm².

4. The preparation method according to claim 1, wherein The thickness of the peeling layer in step (1) is 0.1 μm to 3 μm.

5. The preparation method according to claim 1, wherein Step (2) The first mask processing includes coating, exposure and development.

6. The preparation method according to claim 1, wherein Step (2) The ion species implanted in the first ion implantation treatment include any one of B, P, As, N, Al or In, or a combination of at least two of them.

7. The preparation method according to claim 1, wherein The ion implantation dose of the first ion implantation treatment in step (2) is 1×10 13 ions / cm²~1×10 17 ions / cm².

8. The preparation method according to claim 1, wherein In step (2), the thickness of the floating junction formed by the first ion implantation treatment on one side surface of the underlying substrate and the other side of the peeling layer of the donor substrate is independently 0.1 μm to 0.5 μm.

9. The preparation method according to claim 1, wherein The bonding temperature in step (3) is 20°C to 30°C.

10. The preparation method according to claim 1, wherein The absolute vacuum degree of the bonding in step (3) is ≤10 - 6 Pa.

11. The preparation method according to claim 1, wherein The bonding pressure in step (3) is 10 kN to 100 kN.

12. The preparation method according to claim 1, wherein The bonding strength of the bonding in step (3) is ≥1.4 J / cm 2 .

13. The preparation method according to claim 1, wherein The temperature of the heat treatment peeling in step (3) is 800°C~1200°C.

14. The preparation method according to claim 1, wherein The time for the heat treatment peeling in step (3) is 1 min to 60 min.

15. The preparation method according to claim 1, wherein Step (4) The second mask processing includes coating, exposure and development.

16. The preparation method according to claim 1, wherein Step (4) The ion species injected in the second ion implantation treatment include any one of B, P, As, N, Al or In, or a combination of at least two of them.

17. The preparation method according to claim 1, wherein The ion implantation dose of the second ion implantation treatment in step (4) is 1×10 13 ions / cm²~1×10 17 ions / cm².

18. The preparation method according to claim 1, wherein The thickness of the floating junction formed by the second ion implantation in step (4) is 0.1 μm to 0.5 μm.

19. The preparation method according to claim 1, wherein Step (4) The second degumming process includes dry degumming and / or wet degumming.

20. The preparation method according to claim 1, wherein The annealing temperature in step (4) is 1600°C to 1950°C.

21. The preparation method according to claim 1, wherein The annealing time in step (4) is 5 min to 30 min.

22. The preparation method according to claim 1, wherein After the annealing in step (4), chemical mechanical polishing is performed.

23. A silicon carbide composite substrate, characterized in that: The silicon carbide composite substrate is prepared by the preparation method according to any one of claims 1 to 22.

24. A unipolar device, characterized in that: The unipolar device comprises the silicon carbide composite substrate according to claim 23; The unipolar device includes a Schottky barrier diode and / or a hybrid power diode.

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