Silicon carbide composite substrate and preparation method and application thereof

Abstract

The invention provides a silicon carbide composite substrate and a preparation method and application thereof. The preparation method comprises the following steps: (1) performing stripping layer injection treatment on a donor substrate to form a stripping layer; (2) respectively performing mask treatment on the bottom substrate and the donor substrate, and respectively forming floating junctions on the bottom substrate and the donor substrate through ion implantation treatment to obtain a modified bottom substrate and a modified donor substrate; (3) respectively carrying out photoresist removal treatment on the modified bottom layer substrate and the modified donor substrate, bonding ion implantation surfaces of the modified bottom layer substrate and the modified donor substrate, and carrying out heat treatment stripping to remove a stripping layer so as to obtain a semi-finished product composite substrate; and (4) carrying out ion implantation after carrying out mask treatment on the semi-finished product composite substrate, and carrying out photoresist removal and annealing to obtain the silicon carbide composite substrate. According to the silicon carbide composite substrate, multiple times of epitaxy are not needed, a deep floating junction can be formed without high-energy injection in the preparation process, the preparation cost is greatly reduced, the needed dosage is greatly reduced, and the injection time is greatly shortened.

Description

Technical Field

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

[0002] Unipolar devices do not have minority carriers in their structures to modulate conductivity, and their switching frequencies are much higher than those of bipolar devices. Therefore, they are widely used in high-switching-frequency circuits. As a typical representative, the SBD (Schottky barrier diode) has very important applications in high-frequency circuits and the microwave field because of its low switching power loss.

[0003] Compared with silicon-based materials, silicon carbide has a larger bandgap (about 3 times that of silicon), a stronger critical breakdown electric field (about 10 times that of silicon), and a higher thermal conductivity (about 3 times that of Si). Due to the larger bandgap of silicon carbide, the drift region length of silicon carbide devices is smaller under the same breakdown voltage premise, which greatly reduces the on-resistance of the devices. The higher thermal conductivity also makes the heat dissipation of the devices better. When working in a high-temperature environment, no additional heat dissipation device is required, which can greatly reduce the volume and cost of the system. Because of these excellent properties of silicon carbide materials, silicon carbide SBD devices produced have higher breakdown voltages and can work at higher temperatures, which also makes up for the deficiencies of silicon SBDs.

[0004] Although silicon carbide has many excellent properties, due to problems such as slow crystal growth rate, low yield, and difficulty in expanding the diameter, its production capacity is low and the price is very expensive. And if a silicon carbide SBD device is to have a higher breakdown voltage, thick silicon carbide epitaxy needs to be grown. During the epitaxial growth process, due to technical reasons, there are usually many defects, which seriously affect the performance of the device.

[0005] CN118156319A discloses a silicon carbide SBD device with a uniformly distributed epitaxial layer and a manufacturing method thereof, which includes: depositing the N-type SiC epitaxial layer on the upper surface of the 4H-SiC substrate layer, and depositing the P-type SiC epitaxial layer on one side of the surface of the N-type SiC epitaxial layer; the P-type SiC epitaxial layer includes: a SiO2 protective layer, a plurality of P-type trapezoidal islands with 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; depositing an anode on the other side of the surface of the N-type SiC epitaxial layer, and connecting the last P-type trapezoidal island far from the SiO2 protective layer to the anode, and depositing a cathode on the lower surface of the 4H-SiC substrate layer.

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

[0007] The above solution forms a floating junction (FJ) through multiple epitaxial methods. Multiple epitaxies may lead to the generation of defects during the epitaxial process, which in turn affects the device performance; or a floating junction is formed through high-energy ion implantation. This method requires extremely high energy for the equipment and the equipment cost is very expensive; the deep implantation and multiple epitaxies involved in the above solution are difficult to implement in commercial processes. Summary of the Invention

[0008] The purpose of the present invention is to provide a silicon carbide composite substrate, its preparation method and application. The silicon carbide composite substrate of the present invention does not require multiple epitaxies, reduces the defects caused by multiple epitaxies, and can form a relatively deep floating junction without high-energy implantation during the preparation process, greatly reducing the preparation cost. Moreover, compared with high-energy implantation, the required dose and implantation time of low-energy implantation will also be reduced synchronously, and the production efficiency is improved.

[0009] To achieve the purpose of this invention, the present invention adopts the following technical solutions:

[0010] In the first aspect, the present invention provides a preparation method of a silicon carbide composite substrate. The preparation method includes the following steps:

[0011] (1) Provide two silicon carbide substrates as the bottom substrate and the donor substrate respectively. Perform a stripping layer implantation treatment on the donor substrate to form a stripping layer on one side surface of the donor substrate;

[0012] (2) After performing the first masking treatment on one side surface of the bottom substrate and the other side of the stripping layer of the donor substrate respectively, perform the first ion implantation treatment to form floating junctions on one side surface of the bottom substrate and the other side of the stripping layer of the donor substrate respectively, obtaining a modified bottom substrate and a modified donor substrate;

[0013] (3) After performing the first degluing treatment on the modified bottom substrate and the modified donor substrate respectively, bond the ion implantation surfaces of the modified bottom substrate and the modified donor substrate, and then thermally treat and strip off the stripping layer to obtain a semi-finished composite substrate;

[0014] (4)Perform a second masking process on the surface of the side of the semi-finished composite substrate that has been peeled off, and then perform a second ion implantation process to obtain a modified semi-finished composite substrate. After performing a second de-gluing process on the modified semi-finished composite substrate, anneal it to obtain the silicon carbide composite substrate;

[0015] Among them, the ion implantation energy of the stripping layer implantation process ≤ the ion implantation energy of the first ion implantation process + the ion implantation energy of the second ion implantation process.

[0016] In the present invention, the positions and widths of the first masking process and the second masking process are exactly the same, so that the positions of the floating junctions formed by the first ion implantation process and the second ion implantation process are exactly the same. When bonding, alignment can be performed through the mark points, and the two can be perfectly matched. The ion implantation surface is the side of the substrate that has undergone ion implantation, and the surface of the side of the semi-finished composite substrate that has been peeled off is the surface after removing the stripping layer.

[0017] In the preparation process of a conventional floating junction Schottky barrier diode (FJ-SBD) or a hybrid power diode (FJ-MPS) substrate, a floating junction (FJ) needs to be formed by multiple epitaxial growths or high-energy ion implantations. However, multiple epitaxial growths may generate defects during the epitaxial process, affecting the performance of the substrate, and the cost of high-energy ion implantation is extremely high. In the method of the present invention, the bottom substrate and the donor substrate are respectively subjected to ion implantation to form floating junctions, and then the two are bonded and the donor substrate is removed by heat treatment and peeling to make a semi-finished composite silicon carbide substrate. After that, the semi-finished composite silicon carbide substrate is subjected to ion implantation again to form a floating junction, and the composite silicon carbide substrate is obtained after annealing treatment. The composite silicon carbide substrate prepared by the method of the present invention not only does not require multiple epitaxial growths and can be produced according to normal epitaxial growth, but also does not require the use of high-energy ion implantation. A relatively deep FJ can be achieved using medium and low energies, and a floating junction with a certain range of depths can be fabricated according to requirements. Moreover, the use of the composite silicon carbide substrate can also reduce the material cost.

[0018] Preferably, before the stripping layer implantation process in step (1), the bottom substrate and the donor substrate are respectively subjected to a cleaning process.

[0019] The cleaning process of the present invention can clean impurities such as particles, metals, and organic substances on the surface of the silicon carbide substrate, ensuring a clean surface.

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

[0021] Preferably, the ion implantation energy for 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. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0022] Preferably, the ion implantation energy for 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. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0023] Preferably, the ion implantation dose for the stripping layer implantation treatment in step (1) is 1×10 16 ions / cm² to 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. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0024] Preferably, the tilt angle for the stripping layer implantation treatment in step (1) is 0° to 10°. For example: 0°, 5°, 7°, 8°, or 10°, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0025] Preferably, the twist angle for the stripping layer implantation treatment in step (1) is 0° to 45°. For example: 0°, 11°, 22°, 23°, 45°, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0026] Preferably, the temperature for the stripping layer implantation treatment in step (1) is 20°C to 600°C. For example: 20°C, 100°C, 300°C, 500°C, or 600°C, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0027] Preferably, the thickness of the stripping 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. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0028] Preferably, the first masking process in step (2) includes spin coating and exposure and development.

[0029] The purpose of the first masking process in the present invention is to form an implantation window for the floating junction, preparing for subsequent ion implantation.

[0030] Preferably, the thickness of the photoresist formed by spin coating is 1 μm to 3 μm, for example: 1 μm, 1.5 μm, 2 μm, 2.5 μm, or 3 μm, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0031] Preferably, the exposure and development includes development using a positive photoresist developer.

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

[0033] Preferably, the ion implantation energy in the first ion implantation process in step (2) is 10 keV to 400 keV, for example: 1 keV, 20 keV, 50 keV, 100 keV, or 400 keV, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0034] Preferably, the ion implantation energy in the first ion implantation process in step (2) is 45 keV to 350 keV, for example: 45 keV, 80 keV, 100 keV, 200 keV, or 350 keV, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0035] Preferably, the ion implantation dose in the first ion implantation process in step (2) is 1×10 13 ions / cm² to 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. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0036] Preferably, the tilt angle in the first ion implantation process in step (2) is 0° to 60°, for example: 0°, 5°, 7°, 8°, or 10°, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0037] Preferably, the twisting angle of the first ion implantation treatment in step (2) is 0° to 45°, for example: 0°, 11°, 22°, 23°, 45°, etc., not limited to the listed values, and other unlisted values within this numerical range are equally 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., not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0039] Preferably, the thickness of the floating junction formed by the first ion implantation treatment on one surface of the bottom substrate and the other side of the release 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., not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

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

[0041] The purpose of the degumming treatment (including the first degumming treatment and the second degumming treatment) in the present invention is to remove residual glue, particles, metals, organic substances and other impurities on the surfaces of the bottom substrate and the donor substrate, facilitating subsequent bonding.

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

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

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

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

[0046] Before bonding in the present invention, it is necessary to clean the substrate to remove residual glue, particles, metals, organic substances and other impurities on the surfaces of the bottom substrate and the donor substrate, facilitating subsequent bonding.

[0047] The bonding in the present invention includes injecting surface bonding of the underlying substrate and the donor substrate, aligning through mark points to ensure the position matching of the implanted floating junctions of the underlying substrate and the donor substrate; and the bonding strength ≥ 1.4 J / cm 2 to ensure subsequent production.

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

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

[0050] In the present invention, through heat treatment, the bonded wafers are broken along the peeled implanted layer, thereby forming a composite substrate (underlying substrate + peeled donor substrate), 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., not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0052] Preferably, before the second mask treatment in step (4), the semi-finished composite substrate is subjected to a cleaning treatment.

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

[0054] The purpose of the second mask treatment in the present invention is to form the implantation window of the floating junction again.

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

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

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

[0058] Preferably, the ion implantation energy of the second ion implantation process in step (4) is 1 keV to 400 keV. For example: 1 keV, 20 keV, 50 keV, 100 keV, 400 keV, etc. It is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0059] Preferably, the ion implantation energy of the second ion implantation process in step (4) is 50 keV to 370 keV. For example: 50 keV, 80 keV, 100 keV, 200 keV, 370 keV, etc. It is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0060] Preferably, the ion implantation dose of the second ion implantation process in step (4) is 1×10 13 ions / cm² to 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. It is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0061] Preferably, the tilt angle of the second ion implantation process in step (4) is 0° to 10°. For example: 0°, 5°, 7°, 8°, 10°, etc. It is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0062] Preferably, the twist angle of the second ion implantation process in step (4) is 0° to 45°. For example: 0°, 11°, 22°, 23°, 45°, etc. It is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0063] Preferably, the temperature of the second ion implantation process in step (4) is 20°C to 600°C. For example: 20°C, 100°C, 300°C, 500°C, 600°C, etc. It is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0064] Preferably, the thickness of the floating junction formed by the second ion implantation process 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, 0.5 μm, etc. It is not limited to the listed values, and other unlisted values within this value range are equally applicable.

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

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

[0067] Preferably, the temperature for annealing in step (4) is 1600°C to 1950°C. For example: 1600°C, 1650°C, 1700°C, 1800°C, or 1950°C, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0068] Preferably, the time for annealing in step (4) is 5 min to 30 min. For example: 5 min, 10 min, 15 min, 20 min, or 30 min, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

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

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

[0071] In a second aspect, the present invention provides a silicon carbide composite substrate, and the silicon carbide composite substrate is obtained by the preparation method as 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, the unipolar device includes 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 epitaxial growths, reducing the defects caused by multiple epitaxial growths. Moreover, a relatively deep floating junction can be formed without high-energy implantation during the preparation process, greatly reducing the preparation cost. And compared with high-energy implantation, the required dose and implantation time for low-energy implantation will also be reduced synchronously, improving the 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 within 0.83 μA under a reverse voltage of 1200 V. When the reverse current reaches 0.1 mA, the reverse breakdown voltage BV can reach above 1398.14 V. 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 below 0.78 μA under a reverse voltage of 1200 V. When the reverse current reaches 0.1 mA, the reverse breakdown voltage BV can reach above 1428.22 V. The reverse electrical characteristics are significantly improved compared to conventional SBDs. Description of the Drawings

[0077] Figure 1 It 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 implantation of the release layer, 12 is the gluing, exposure and development of the donor substrate, 13 is the ion implantation of the donor substrate, 14 is the removal of the glue from the donor substrate, 21 is the gluing, exposure and development of the bottom substrate, 22 is the ion implantation of the bottom substrate, 23 is the removal of the glue from the bottom substrate, 30 is the bonding of the donor substrate and the bottom substrate, 31 is the release annealing, 32 is the gluing, exposure and development of the semi-finished composite substrate, 33 is the ion implantation of the semi-finished composite substrate, 34 is the removal of the glue and annealing of the semi-finished composite substrate, and 35 is chemical mechanical polishing.

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

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

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

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

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

[0083] Figure 7 It is a comparison chart of the reverse characteristic curves of the silicon carbide FJ-SBD prepared in Application Example 1 and Comparative Application Example 2. Specific Embodiments

[0084] The technical solution of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0085] Embodiment 1

[0086] This embodiment provides a silicon carbide composite substrate. The process flow chart for preparing the silicon carbide composite substrate is as Figure 1 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. After removing surface particles, metals, organic substances and other impurities, they are used as the bottom substrate and the donor substrate respectively. Perform a stripping layer implantation 11 treatment on the donor substrate. The implantation conditions are H ions, an implantation energy of 120 keV, an implantation dose of 6×10 16 ions / cm², an inclination angle of 7°, a twist angle of 0°, an implantation temperature of 100 °C, and form a stripping layer with a thickness of 0.8 μm on one side surface of the donor substrate;

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

[0089] (3) Perform dry degluing, wet degluing, ICP and RCA cleaning processes on the bottom substrate and the donor substrate respectively to remove residual glue, particles, metals, organic substances and other impurities on the surfaces of the bottom substrate and the donor substrate. Bond the ion implantation surfaces of the modified bottom substrate and the modified donor substrate at 25 °C, an absolute vacuum degree ≤ 10 -6 Pa, a pressure of 50 kN for 30, and then perform a stripping annealing 31 at 1050 °C for 20 min in a nitrogen atmosphere to remove the excess donor substrate along the stripping layer to obtain a semi-finished composite substrate;

[0090] (4)Clean, apply glue, expose and develop the surface of the semi-finished composite substrate on the peeled side, and then perform ion implantation 33. The ion species for ion implantation is aluminum ions, the implantation energy is 280 keV, the implantation dose is 5×10 14 ions / cm², the tilt angle is 7°, the twist angle is 0°, the implantation temperature is 500 °C, to obtain a modified semi-finished composite substrate. Perform dry and wet glue removal, ICP and RCA cleaning processes on the modified semi-finished composite substrate to remove residual glue, particles, metals, organic substances and other impurities on the surface of the composite substrate. Anneal at 1750 °C for 30 min in an argon atmosphere (glue removal and annealing 34 of the semi-finished composite substrate). After 100 s of CMP (chemical mechanical polishing 35) treatment and a removal amount of 1000 Å, the silicon carbide composite substrate is obtained.

[0091] The distribution schematic diagram of the floating junctions in the silicon carbide composite substrate is as Figure 2 shown.

[0092] Example 2

[0093] This example provides a silicon carbide composite substrate. The process flow chart for preparing the silicon carbide composite substrate is as Figure 1 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. After removing surface particles, metals, organic substances and other impurities, they are used as the bottom substrate and the donor substrate respectively. Perform a stripping layer implantation 11 on the donor substrate. The implantation conditions are H ions, the implantation energy is 150 keV, the implantation dose is 8×10 16 ions / cm², the tilt angle is 7°, the twist angle is 0°, the implantation temperature is 100 °C, to form a stripping layer with a thickness of 1.21 μm on one side surface of the donor substrate;

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

[0096] (3) Dry and wet degumming, ICP and RCA cleaning processes are respectively carried out on the bottom substrate and the donor substrate to remove residual glue, particles, metals, organic substances and other impurities on the surfaces of the bottom substrate and the donor substrate. The ion implantation surfaces of the modified bottom substrate and the modified donor substrate are bonded at 30 °C and an absolute vacuum of ≤ 10 -6 Pa under a pressure of 80 kN for 30 s, and then subjected to stripping annealing at 1100 °C for 20 min in a nitrogen atmosphere . After removing the excess donor substrate along the stripping layer, a semi-finished composite substrate is obtained;

[0097] (4) The surface of the semi-finished composite substrate on the side where the stripping occurs is cleaned, coated with glue, exposed and developed , and then ion implantation

[0098] is carried out. The ion species for ion implantation is aluminum ions, the implantation energy is 360 keV, the implantation dose is 5.5×10 14 ions / cm², the tilt angle is 7°, the twist angle is 0°, and the implantation temperature is 500 °C to obtain a modified semi-finished composite substrate. Dry and wet degumming, ICP and RCA cleaning processes are carried out on the modified semi-finished composite substrate to remove residual glue, particles, metals, organic substances and other impurities on the surface of the composite substrate. Annealing is carried out at 1800 °C for 5 min in an argon atmosphere (degumming and annealing of the semi-finished composite substrate Figure 3 ). After 100 s of CMP (chemical mechanical polishing ) treatment with an amount of removal of 1000 Å, the silicon carbide composite substrate is obtained.

[0098] The distribution schematic diagram of the floating junctions in the silicon carbide composite substrate is as Figure 3 shown.

[0099] Example 3

[0100] This example provides a silicon carbide composite substrate. The process flow chart for preparing the silicon carbide composite substrate is as Figure 1 shown, and the silicon carbide composite substrate is specifically obtained by the following method:

[0101] (1) Provide an N-type SiC bottom substrate and a donor substrate for standard RCA cleaning. After removing surface particles, metals, organic substances and other impurities, they are used as the bottom substrate and the donor substrate respectively. Stripping layer implantation is carried out on the donor substrate. The implantation conditions are H ions, the implantation energy is 20 keV, the implantation dose is 5.5×10 16 ions / cm², the tilt angle is 7°, the twist angle is 0°, and the implantation temperature is 100 °C to form a stripping layer with a thickness of 0.15 μm on one side surface of the donor substrate;

[0102] (2) After applying glue, exposing, and developing one side surface of the bottom substrate, a photoresist 21 with a thickness of 1 μm is formed. After applying glue, exposing, and developing the other side of the release layer of the donor substrate 12, a photoresist with a thickness of 1 μm is formed. After ion implantation treatment (donor substrate ion implantation 13, bottom substrate ion implantation 22), a floating junction with a thickness of 0.045 μm is formed on one side surface of the bottom substrate and the other side of the release layer of the donor substrate, obtaining a modified bottom substrate and a modified donor substrate. The ion species for ion implantation is aluminum ions, the implantation energy is 45 keV, the implantation dose is 4.0×10 14 ions / cm², the tilt angle is 7°, the twist angle is 0°, and the implantation temperature is 500 °C;

[0103] (3) The bottom substrate and the donor substrate are respectively subjected to dry degluing, wet degluing, ICP, and RCA cleaning processes to remove residual glue, particles, metals, organic substances, and other impurities on the surfaces of the bottom substrate and the donor substrate. The ion implantation surfaces of the modified bottom substrate and the modified donor substrate are bonded 30 at 20 °C and an absolute vacuum of ≤10 -6 Pa and a pressure of 30 kN. Then, a 20-minute peel annealing 31 is carried out in a nitrogen atmosphere at 1000 °C. The excess donor substrate is removed along the release layer to obtain a semi-finished composite substrate;

[0104] (4) The surface of the semi-finished composite substrate from which the donor substrate has been peeled is cleaned, coated with glue, exposed, developed 32, and then subjected to ion implantation 33. The ion species for ion implantation is aluminum ions, the implantation energy is 50 keV, the implantation dose is 4.0×10 14 ions / cm², the tilt angle is 7°, the twist angle is 0°, and the implantation temperature is 500 °C, obtaining a modified semi-finished composite substrate. The modified semi-finished composite substrate is subjected to dry degluing, wet degluing, ICP, and RCA cleaning processes to remove residual glue, particles, metals, organic substances, and other impurities on the surface of the composite substrate. Annealing is carried out at 1650 °C for 45 minutes in an argon atmosphere (degumming and annealing of the semi-finished composite substrate 34). After 100 s of CMP (chemical mechanical polishing 35) treatment and a removal amount of 1000 Å, the silicon carbide composite substrate is obtained.

[0105] The distribution schematic diagram of the floating junctions in the silicon carbide composite substrate is as Figure 4 shown.

[0106] Example 4

[0107] The difference between this example and Example 1 is only that the ion implantation energy for the release layer implantation treatment is 360 keV, and other conditions and parameters are exactly the same as those in Example 1.

[0108] Example 5

[0109] The difference between this embodiment and Embodiment 1 is only that the ion implantation energy for the implantation treatment of the stripping layer is 40 keV, and other conditions and parameters are exactly the same as those in Embodiment 1.

[0110] Embodiment 6

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

[0112] Embodiment 7

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

[0114] Embodiment 8

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

[0116] Embodiment 9

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

[0118] Comparative Example 1

[0119] The difference between this comparative example and Embodiment 1 is only that the ion implantation energy of the stripping layer ion implantation described in step (1) is 300 keV, the ion implantation energy of the ion implantation (the first ion implantation) described in step (2) is 100 keV, and the ion implantation energy described 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 process flow chart for the preparation of the silicon carbide FJ-SBD is as Figure 2 shown, and the silicon carbide FJ-SBD is obtained by the following method:

[0124] (1) Provide an N-type SiC bottom substrate and a donor substrate for standard RCA cleaning. After removing surface particles, metals, organic substances and other impurities, they are used as the bottom substrate and the donor substrate respectively. Perform a lift-off layer implantation 11 treatment on the donor substrate. The implantation conditions are H ions, an implantation energy of 120 keV, an implantation dose of 6×10 16 ions / cm², an inclination angle of 7°, a twist angle of 0°, an implantation temperature of 100 °C, and form a lift-off layer with a thickness of 0.8 μm on one surface of the donor substrate;

[0125] (2) After coating, exposing and developing one surface of the bottom substrate, form a photoresist 21 with a thickness of 2 μm. After coating, exposing and developing 12 the other side of the lift-off layer of the donor substrate, form a photoresist with a thickness of 2 μm. After ion implantation treatment (donor substrate ion implantation 13, bottom substrate ion implantation 22), form a floating junction with a thickness of 0.8 μm on one surface of the bottom substrate and the other side of the lift-off layer of the donor substrate respectively, and obtain a modified bottom substrate and a modified donor substrate. The ion species for ion implantation is aluminum ions, the implantation energy is 270 keV, and the implantation dose is 4.5×10 14 ions / cm², an inclination angle of 7°, a twist angle of 0°, and an implantation temperature of 500 °C;

[0126] (3) Perform dry and wet photoresist stripping, ICP and RCA cleaning processes on the bottom substrate and the donor substrate respectively to remove residual photoresist, particles, metals, organic substances and other impurities on the surfaces of the bottom substrate and the donor substrate. Bond 30 the ion implantation surfaces of the modified bottom substrate and the modified donor substrate at 25 °C and an absolute vacuum of ≤10 -6 Pa and a pressure of 50 kN. Then perform a 20-minute lift-off annealing 31 at 1050 °C in a nitrogen atmosphere to remove the excess donor substrate along the lift-off layer to obtain a semi-finished composite substrate;

[0127] (4) Perform cleaning, coating, exposing and developing 32 on the stripped surface of the semi-finished composite substrate, and then perform ion implantation 33 treatment. The ion species for ion implantation is aluminum ions, the implantation energy is 280 keV, and the implantation dose is 5×10 14ions / cm², with an inclination angle of 7°, a torsion angle of 0°, and an implantation temperature of 500 °C, a modified semi-finished composite substrate is obtained. The modified semi-finished composite substrate is subjected to dry and wet degumming, ICP and RCA cleaning processes to remove residual gum, particles, metals, organic substances and other impurities on the surface of the composite substrate. Annealing is carried out at 1750 °C for 30 min in an argon atmosphere (degumming and annealing of the semi-finished composite substrate 34). After 100 s of CMP (chemical mechanical polishing 35) treatment, a removal amount of 1000 Å is obtained to get a silicon carbide composite substrate. N-epitaxial growth is carried out on the silicon carbide composite substrate, with an epitaxial thickness of 10 μm, a doping type of N, and a doping concentration of 1×10 16 atoms / cm 3 , after back thinning (epitaxial growth and back thinning 36), an epitaxial silicon carbide composite substrate is obtained;

[0128] (5) Sputter nickel on the epitaxial silicon carbide composite substrate to form an ohmic contact 37, with a thickness of 1000 Å, anneal at 900 °C in a nitrogen atmosphere for 10 min, and then evaporate metal titanium with a thickness of 800 Å. Sputter titanium to form a Schottky contact 38 and then evaporate metal aluminum with a thickness of 2 μm, and carry out Schottky contact annealing at 500 °C in a nitrogen atmosphere for 10 min to obtain the silicon carbide FJ-SBD.

[0129] Application Example 2

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

[0131] Application Example 3

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

[0133] Application Example 4

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

[0135] Application Example 5

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

[0137] Application Example 6

[0138] The difference between this application example and Application Example 1 is only that the silicon carbide composite substrate is prepared by the method described in Example 6, and 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 by the method described in Example 7, and 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 by the method described in Example 8, and 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 by the method described in Example 9, and 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 by 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. Subsequent steps: Epitaxy: N-epitaxial growth is carried out with an epitaxial thickness of 10 μm, doping type N, and doping concentration of 1×10 16 atoms / cm 3 ; SBD: Sputter nickel to form an ohmic contact with a thickness of 1000 Å, anneal at 900 °C in a nitrogen atmosphere for 10 min, then evaporate metal titanium with a thickness of 800 Å. Sputter titanium to form a Schottky contact, and then evaporate metal aluminum with a thickness of 2 μm, and perform Schottky contact annealing at 500 °C in a nitrogen atmosphere for 10 min to obtain the silicon carbide SBD.

[0149] Performance Test:

[0150] Perform electrical tests and TCAD simulation analysis on the silicon carbide FJ-SBDs obtained from the application examples and comparative application examples. The test results are shown in Table 1 and Figure 7 as follows:

[0151] Table 1

[0152]

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

[0154] From the comparison between Application Example 1 and Application Examples 4-5, it can be obtained that during the preparation process of the silicon carbide composite substrate of the present invention, the ion implantation energy of the stripping layer implantation treatment will affect its performance. When the ion implantation energy of the stripping layer implantation treatment is controlled within 45 keV - 350 keV, the performance of the silicon carbide composite substrate is better. If the ion implantation energy of the stripping layer implantation treatment is too large, the BV and IR characteristics cannot reach the set targets, resulting in process waste and increased costs. If the ion implantation energy of the stripping layer implantation treatment is too small, the BV and IR characteristics cannot reach the set targets, and the floating junction cannot be utilized maximally, losing its cost advantage.

[0155] From the comparison between Application Example 1 and Application Examples 6-7, it can be obtained that during the preparation process of the silicon carbide composite substrate of the present invention, the ion implantation energy of the first ion implantation treatment will affect its performance. When the ion implantation energy of the first ion implantation treatment is controlled within 45 keV - 350 keV, the performance of the silicon carbide composite substrate is better. If the ion implantation energy of the first ion implantation treatment is too large, the BV and IR characteristics cannot reach the set targets, and the equipment operating at the highest energy for a long time will cause stability problems. If the ion implantation energy of the first ion implantation treatment is too small, the BV and IR characteristics cannot reach the set targets, and the floating junction cannot be utilized maximally, losing its cost advantage.

[0156] From the comparison between Application Example 1 and Application Examples 8-9, it can be obtained that during the preparation process of the silicon carbide composite substrate of the present invention, the ion implantation energy of the second ion implantation treatment will affect its performance. When the ion implantation energy of the second ion implantation treatment is controlled within 50 keV - 370 keV, the performance of the silicon carbide composite substrate is better. If the ion implantation energy of the second ion implantation treatment is too large, the BV and IR characteristics cannot reach the set targets, and the equipment operating at the highest energy for a long time will cause stability problems. If the ion implantation energy of the second ion implantation treatment is too small, the BV and IR characteristics cannot reach the set targets, and the floating junction cannot be utilized maximally, losing its cost advantage.

[0157] From the comparison between Application Example 1 and Comparative Application Example 1, it can be obtained that if the ion implantation depth of the stripping layer 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 Rp of the stripping depth > the Rp1 of the first implantation depth + the Rp2 of the second implantation depth, it will cause the junction depth of the first ion implantation process + the junction depth of the second ion implantation process to be unable to cover the thickness of the stripping layer, and the floating junction range coverage is insufficient. When the ion implantation energy controllable range of a single device is the same, the controllable range with a shallower ion implantation depth should be considered first, that is, the Rp of the ion depth ≤ the Rp1 of the first implantation depth + the Rp2 of the second implantation depth, and generally the energy: 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 comparison chart of the forward characteristic curves of the silicon carbide FJ-SBD prepared by Application Example 1 and Comparative Application Example 2 is as Figure 6 shown. From Figure 6 it can be seen that compared with the SBD prepared by single crystal, the forward VF is not much different.

[0159] The comparison chart of the reverse characteristic curves of the silicon carbide FJ-SBD prepared by Application Example 1 and Comparative Application Example 2 is as Figure 7 shown. From Figure 7 it can be seen that compared with the SBD prepared by single crystal, the reverse characteristics (breakdown voltage and reverse leakage current) of the FJ-SBD are better than those of the single crystal SBD.

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

[0161] The applicant declares that the above is only the specific implementation manner of the present invention, but the protection scope 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 protection scope and the disclosure scope 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 a surface of one side of the donor substrate; (2) performing a first mask treatment on one side surface of the bottom substrate and the other side of the peeling layer of the donor substrate, respectively, and then performing a first ion implantation treatment to form a floating junction on one side surface of the bottom substrate and the other side of the peeling layer of the donor substrate, respectively, to obtain a modified bottom substrate and a modified donor substrate; (3) After performing a first degumming treatment on the modified bottom substrate and the modified donor substrate respectively, the ion implanted surfaces of the modified bottom 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 peeled side surface 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; The ion implantation energy of the stripping 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.

2. The preparation method according to claim 1, characterized in that The ion species injected in the stripping layer injection treatment in step (1) include hydrogen and / or helium; And / or, the ion implantation energy of the stripping layer implantation treatment in step (1) is 45keV~350keV; And / or, the ion implantation dose of the peeling layer implantation treatment in step (1) is 1×10 16 ions / cm²~1×10 18 ions / cm²; And / or, the thickness of the peeling layer in step (1) is 0.1 μm to 3 μm.

3. The preparation method according to claim 1, characterized in that: Step (2) the first mask processing includes coating, exposure and development; And / or, the ion types implanted in the first ion implantation process in step (2) include any one of B, P, As, N, Al or In, or a combination of at least two thereof; And / or, the ion implantation energy of the first ion implantation treatment in step (2) is 45keV~350keV; And / or, the ion implantation dose of the first ion implantation treatment in step (2) is 1×10 13 ions / cm²~1×10 17 ions / cm²; And / or, the thickness of the floating junction formed by the first ion implantation treatment on one side surface of the bottom substrate and the other side of the release layer of the donor substrate in step (2) is independently 0.1 μm to 0.5 μm.

4. The preparation method according to claim 1, characterized in that: The bonding temperature in step (3) is 20°C to 30°C; And / or, the absolute vacuum degree of bonding in step (3) is ≤10 -6 Pa; And / or, the bonding pressure in step (3) is 10 kN to 100 kN; And / or, the bonding strength of the bonding in step (3) is ≥ 1.4 J / cm 2 .

5. The preparation method according to claim 1, characterized in that: The temperature of the heat treatment peeling in step (3) is 800°C to 1200°C; And / or, the time of the heat treatment peeling in step (3) is 1 min to 60 min.

6. The preparation method according to claim 1, characterized in that: Step (4) the second mask processing includes coating, exposure and development; And / or, the ion types implanted in the second ion implantation process in step (4) include any one of B, P, As, N, Al or In, or a combination of at least two thereof; And / or, the ion implantation energy of the second ion implantation treatment in step (4) is 50 keV to 370 keV; And / or, the ion implantation dose of the second ion implantation treatment in step (4) is 1×10 13 ions / cm²~1×10 17 ions / cm²; And / or, the thickness of the floating junction formed by the second ion implantation in step (4) is 0.1 μm to 0.5 μm.

7. The preparation method according to claim 1, characterized in that: Step (4) the second degumming process includes dry degumming and / or wet degumming; And / or, the annealing temperature in step (4) is 1600° C. to 1950° C.; And / or, the annealing time in step (4) is 5 min to 30 min.

8. The preparation method according to claim 1, characterized in that: The annealing in step (4) is followed by chemical mechanical polishing.

9. 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 8.

10. A unipolar device, characterized in that: The unipolar device comprises the silicon carbide composite substrate as claimed in claim 9; The unipolar device includes a Schottky barrier diode and / or a hybrid power diode.

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