A composite silicon carbide substrate and a method of making the same

Abstract

The application provides a composite silicon carbide substrate and a preparation method thereof. The preparation method comprises the following steps: (1) a first surface of a silicon carbide single crystal substrate is bonded with a graphite plate, a second surface of the silicon carbide single crystal substrate is irradiated by laser, and a modified surface is formed in the silicon carbide single crystal substrate; an external force is applied to separate the silicon carbide single crystal substrate along the modified surface, and a composite crystal layer structure composed of the silicon carbide single crystal substrate and the graphite plate is obtained; (2) after a crystal layer is grown on the modified surface of the silicon carbide single crystal substrate in the composite crystal layer structure, the graphite plate is separated, and a composite silicon carbide substrate composed of the silicon carbide single crystal substrate and the crystal layer is obtained. According to the preparation method, the graphite plate is used as a supporting layer, a thin high-quality silicon carbide single crystal substrate is obtained through laser cutting, and then a low-quality crystal layer is grown on the silicon carbide single crystal substrate, so that a bonding interface layer is not formed, the preparation efficiency of the composite silicon carbide substrate is improved, and the preparation time is reduced.

Description

Technical Field

[0001] This invention relates to the field of technology, and in particular to a composite silicon carbide substrate and its preparation method. Background Technology

[0002] Devices fabricated on silicon carbide single crystal substrates have advantages such as high temperature resistance, high voltage resistance, high frequency, high power, radiation resistance, and high efficiency, and have important application value in fields such as radio frequency and new energy vehicles.

[0003] The conventional manufacturing method for silicon carbide single-crystal substrates includes the following steps: growing silicon carbide single crystals using the physical vapor transport method to obtain silicon carbide single-crystal ingots; processing the outer periphery of the ingots to obtain the required diameter and surface quality; slicing the ingots into thin slices; and grinding and polishing the slices to the required thickness and flatness to obtain the final silicon carbide single-crystal substrate. The physical vapor transport method for growing silicon carbide single crystals has very low efficiency, resulting in high costs for a single silicon carbide single-crystal substrate. One solution to reduce the cost of silicon carbide substrates is to use a composite substrate structure: bonding a thin layer of single-crystal silicon carbide onto a lower-cost support substrate. This solution requires separately processing the surfaces of the low-quality and high-quality substrates to meet the bonding requirements before bonding. High-quality surface processing presents certain complexities and difficulties. Furthermore, this solution forms a bonding interface layer, which may negatively affect the vertical conductivity of the substrate.

[0004] CN114746980A discloses a method for manufacturing a composite substrate: forming a pre-embedded weakening layer in a high-quality single-crystal substrate by ion implantation; depositing a low-quality crystal layer or polycrystalline layer on the surface of the single-crystal substrate by CVD; and separating along the weakening layer to obtain the composite substrate.

[0005] The problem with this method is that, due to the high temperature of the CVD process, the pre-embedded weakening layer may crack prematurely during the CVD process, forcing the CVD process to be interrupted.

[0006] Therefore, it is of great significance to develop a simple and efficient method for preparing composite silicon carbide substrates without pre-burying a weakening layer before depositing low-quality crystals or polycrystalline materials. Summary of the Invention

[0007] In view of the problems existing in the prior art, the present invention provides a composite silicon carbide substrate and its preparation method. The preparation method first uses a graphite plate as a support layer and obtains a thin, high-quality silicon carbide single crystal substrate by laser cutting. Then, a low-quality crystal layer is grown on the high-quality silicon carbide single crystal substrate, which does not form a bonding interface layer, thus greatly improving the preparation efficiency of the composite silicon carbide substrate. The interface of the obtained composite silicon carbide substrate has a low surface quality of more than 5 nm, which can reduce the surface processing difficulty and cost of the silicon carbide single crystal substrate, while making the materials on both sides of the interface have better bonding quality.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a composite silicon carbide substrate, the method comprising the following steps:

[0010] (1) The first surface of the silicon carbide single crystal substrate is bonded to the graphite plate, and the second surface of the silicon carbide single crystal substrate is irradiated with a laser to form a modified surface inside the silicon carbide single crystal substrate; an external force is applied to break the silicon carbide single crystal substrate along the modified surface to obtain a composite crystal layer structure composed of the silicon carbide single crystal substrate and the graphite plate; the thickness of the silicon carbide single crystal substrate in the composite crystal layer structure is 1 to 50 μm.

[0011] (2) After growing a crystal layer on the modified surface of the silicon carbide single crystal substrate in the composite crystal layer structure, the graphite plate is separated to obtain a composite silicon carbide substrate composed of a silicon carbide single crystal substrate and a crystal layer.

[0012] The silicon carbide single crystal substrate in the preparation method of the composite silicon carbide substrate of the present invention is a high-quality silicon carbide single crystal substrate with fewer defects such as microtubes, dislocations, phase transitions, and polycrystalline inclusions. First, the first surface of the silicon carbide single crystal substrate is bonded to a graphite plate, which serves as a support layer for the silicon carbide single crystal substrate. Then, the second surface of the silicon carbide single crystal substrate is irradiated with a laser to break the silicon carbide single crystal substrate along the modified surface, resulting in a composite crystal layer structure composed of a very thin silicon carbide single crystal substrate and a graphite plate. Next, a low-quality crystal layer is grown on the Si or C surface of the high-quality silicon carbide single crystal substrate. This low-quality crystal layer is allowed to contain more defects such as microtubes, dislocations, phase transitions, and polycrystalline inclusions, and can be single-crystal or polycrystalline. Finally, the graphite plate is separated to obtain the composite silicon carbide substrate composed of the silicon carbide single crystal substrate and the crystal layer. The preparation method described in this invention involves growing a low-quality crystal layer on a high-quality silicon carbide single crystal substrate, which does not form a bonding interface layer. Therefore, it does not adversely affect the vertical conductivity of the high-quality silicon carbide single crystal substrate.

[0013] In the composite crystal layer structure described in this invention, the thickness of the silicon carbide single crystal substrate is 1 to 50 μm, for example, it can be 1 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm or 50 μm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0014] Silicon carbide single crystal substrates with a thickness of only 1 to 50 μm are difficult to exist independently and are prone to breakage. In this invention, a thicker silicon carbide single crystal substrate is first bonded to a graphite plate, with the graphite plate serving as a support layer. Then, a very thin silicon carbide single crystal substrate can be obtained through laser cutting.

[0015] Preferably, the thickness of the silicon carbide single crystal substrate in step (1) is 150 to 1000 μm, for example, it can be 150 μm, 200 μm, 400 μm, 700 μm, 900 μm or 1000 μm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0016] Preferably, the silicon carbide single crystal substrate has a crystal form of 4H or 6H.

[0017] Preferably, the first surface of the silicon carbide single crystal substrate includes a Si surface or a C surface.

[0018] Preferably, the diameter of the single crystal substrate is 2 to 8 inches, for example, it can be 2 inches, 3 inches, 4 inches, 5 inches, 6 inches or 8 inches, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] Preferably, the angle between the {0001} crystal plane of the silicon carbide single crystal substrate and the surface of the silicon carbide single crystal substrate is 0° to 8°, for example, it can be 0°, 1°, 1.5°, 2°, 3°, 5° or 8°, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] In the preferred embodiment of this invention, the angle between the {0001} crystal plane and the surface of the single-crystal substrate in step (1) is 0° to 8° because cracks are generated within the crystal when it is irradiated with a laser. The fracture toughness of the {1100} and {1120} crystal planes is approximately 1.5 times that of the {0001} plane; therefore, the cracks tend to propagate towards the {0001} crystal plane. In other words, the modified surface is approximately parallel to the {0001} crystal plane.

[0021] Preferably, the bonding step (1) includes sequentially applying adhesive and heating for carbonization.

[0022] Preferably, the adhesive comprises any one or a combination of at least two of acrylate, epoxy resin, or phenolic resin, wherein typical but non-limiting combinations include a combination of acrylate and epoxy resin, a combination of phenolic resin and acrylate, or a combination of epoxy resin, phenolic resin, and acrylate.

[0023] Preferably, the heating and carbonization temperature is 200 to 800°C, for example, it can be 200°C, 300°C, 400°C, 500°C, 700°C or 800°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] This invention applies pressure to the silicon carbide single crystal substrate and the graphite plate during heating and carbonization, making them adhere more tightly and increasing the bonding strength.

[0025] The method for separating the graphite plate in this invention involves using tools such as knives, blade saws, or wire saws to crack the carbonized layer formed by the adhesive, or heating it in an atmospheric environment to oxidize and remove the carbonized layer or graphite plate formed by the adhesive, thereby separating the graphite plate from the silicon carbide single crystal substrate. The separated graphite plate can be returned to step (1) for reuse.

[0026] Preferably, the laser in step (1) is a pulsed laser.

[0027] Preferably, the pulsed laser includes a solid-state laser or a fiber laser.

[0028] Preferably, the pulse width of the pulsed laser is 100 to 300 fs, for example, it can be 100 fs, 120 fs, 150 fs, 200 fs, 240 fs or 300 fs, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] The pulse width of the pulsed laser in this invention is preferably 100-300 fs. When the pulse width is too small, the single crystal substrate cannot be cut well along the modified surface; when the pulse width is too large, cracks will be generated on the modified surface, which will seriously affect the quality of the composite substrate.

[0030] Preferably, the scanning path of the laser irradiation includes any one of parallel straight lines, concentric circles, zigzag lines, or curves.

[0031] Preferably, the laser irradiation scanning path in step (2) is as follows: parallel scanning paths are divided into groups of N, assuming M groups, and the first scanning path of group 1 to M, the second scanning path of group 1 to M, the third scanning path of group 1 to M, and so on, until all paths are scanned. The scanning directions of two consecutive paths can be the same or opposite.

[0032] The purpose of optimizing the laser scanning path in this invention is to make the internal stress generated by laser irradiation in the crystal as uniform as possible, and to prevent or reduce substrate warping and deformation caused by excessive stress concentration after the modified surface is broken.

[0033] Preferably, the modified surface of the silicon carbide single crystal substrate in the composite crystal layer structure is subjected to surface treatment so that the roughness Ra of the modified surface after treatment is 5 to 500 nm.

[0034] In this invention, the modified surface of the silicon carbide single crystal substrate in the composite crystal layer structure is surface treated without chemical mechanical polishing (CMP), or even just simple surface cleaning. As long as the roughness Ra is 5 to 500 nm, the surface quality in this roughness range can meet the requirements for growing low-quality crystal layers, further reducing the preparation cost.

[0035] Preferably, the remaining portion of the silicon carbide single crystal substrate after being broken along the modified surface in step (1) is ground and polished and then reused as a seed crystal.

[0036] Preferably, the crystal layer in step (2) comprises a single crystal or a polycrystalline material.

[0037] Preferably, the thickness of the crystal layer is 100 to 1000 μm, for example, it can be 100 μm, 300 μm, 500 μm, 700 μm, 900 μm or 1000 μm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0038] Preferably, the growth rate of the crystal layer is 300–5000 μm / h, for example, it can be 300 μm / h, 400 μm / h, 500 μm / h, 600 μm / h, 700 μm / h, 800 μm / h, 900 μm / h, 1000 μm / h, 2000 μm / h, 3000 μm / h, 4000 μm / h, 4500 μm / h, or 5000 μm / h, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0039] Generally, the quality of the grown crystal layer decreases as the growth rate increases. Therefore, low-quality crystal layers can be grown at higher growth rates, allowing for more defects such as microtubes, dislocations, phase transitions, and polycrystalline inclusions, and even transitioning from single crystal to polycrystalline. In this invention, the preferred growth rate of the crystal layer is 300–5000 μm / h. At lower growth rates, the composite substrate requires longer fabrication times and has lower efficiency; at higher growth rates, impurities or voids may appear in the crystal layer, resulting in a poor-quality composite substrate.

[0040] Preferably, the crystal layer growth method includes any one of physical vapor transport (PVT), solution vapor deposition (LPE), or high-temperature chemical vapor deposition (HTCVD).

[0041] Preferably, both surfaces of the composite silicon carbide substrate described in step (2) are ground and polished.

[0042] The present invention uses chemical mechanical polishing (CMP) to grind and polish both surfaces of the composite silicon carbide substrate described in step (2) to achieve the required surface quality. One of the surfaces is the laser-modified surface. Assuming that the angle between the {0001} crystal plane of the high-quality silicon carbide single crystal substrate and the substrate surface is θ (i.e., off-axis θ), when grinding and polishing the modified surface of the composite substrate, adjusting the angle between the grinding and polishing reference plane and the modified surface to θ can ensure that the substrate after grinding and polishing is still off-axis θ, 0° to 8°.

[0043] Preferably, the roughness Ra of both surfaces of the composite silicon carbide substrate is <0.5nm, for example, it can be 0.49nm, 0.45nm, 0.4nm, 0.3nm, 0.2nm or 0.1nm, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0044] The roughness Ra of both surfaces of the composite silicon carbide substrate described in this invention is <0.5 nm. When using this composite silicon carbide substrate to manufacture semiconductor devices, an epitaxial layer is manufactured on the modified surface of the silicon carbide single crystal substrate, and then the semiconductor device structure is manufactured in the epitaxial layer.

[0045] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0046] (1) The first surface of the silicon carbide single crystal substrate is bonded to the graphite plate, and the second surface of the silicon carbide single crystal substrate is irradiated with a laser to form a modified surface inside the silicon carbide single crystal substrate; an external force is applied to break the silicon carbide single crystal substrate along the modified surface to obtain a composite crystal layer structure composed of the silicon carbide single crystal substrate and the graphite plate; the thickness of the silicon carbide single crystal substrate in the composite crystal layer structure is 1 to 50 μm.

[0047] The thickness of the silicon carbide single crystal substrate is 150-1000 μm, and the crystal form is 4H or 6H; the first surface of the silicon carbide single crystal substrate includes a Si plane or a C plane; the angle between the {0001} crystal plane of the silicon carbide single crystal substrate and the surface of the silicon carbide single crystal substrate is 0°-8°.

[0048] The bonding steps include sequentially applying adhesive and heating and carbonizing at a temperature of 200-800°C;

[0049] The laser is a pulsed laser; the pulsed laser includes a solid-state laser or a fiber laser; the pulse width of the pulsed laser is 100–300 fs; the scanning path of the laser irradiation includes any one of parallel straight lines, concentric circles, zigzag lines, or curves; the scanning path of the laser irradiation is as follows: dividing the mutually parallel scanning paths into groups of N from beginning to end, assuming they are divided into M groups, and sequentially scanning the first scanning path of the first group to the M group, the second scanning path of the first group to the M group, the third scanning path of the first group to the M group, and so on, until all paths have been scanned;

[0050] The modified surface of the silicon carbide single crystal substrate in the composite crystal layer structure is surface treated to make the roughness Ra of the modified surface 5-500 nm; the remaining part of the silicon carbide single crystal substrate after being broken along the modified surface is ground and polished and reused as a seed crystal.

[0051] (2) After growing a crystal layer on the modified surface of the silicon carbide single crystal substrate in the composite crystal layer structure, the graphite plate is separated to obtain a composite silicon carbide substrate composed of a silicon carbide single crystal substrate and a crystal layer.

[0052] The crystal layer comprises a single crystal or a polycrystalline crystal; the thickness of the crystal layer is 100–1000 μm, and the growth rate is 300–5000 μm / h; the growth method of the crystal layer includes any one of physical vapor transport (PVT), solution vapor deposition (LPE), or high-temperature chemical vapor deposition (HTCVD); both surfaces of the composite silicon carbide substrate are ground and polished so that the roughness Ra of both surfaces is <0.5 nm.

[0053] One of the surfaces is the laser-modified surface. When grinding and polishing the modified surface of the composite substrate, the angle between the grinding and polishing reference surface and the modified surface is adjusted to θ, so that the substrate after grinding and polishing is still off-axis θ, 0°~8°.

[0054] In a second aspect, the present invention also provides a composite silicon carbide substrate, wherein the composite silicon carbide substrate is prepared by the method for preparing a composite silicon carbide substrate described in the first aspect;

[0055] The roughness Ra of the interface between the silicon carbide single crystal substrate and the crystal layer in the composite silicon carbide substrate is 5 to 500 nm.

[0056] The roughness Ra of the interface between the silicon carbide single crystal substrate and the crystal layer in the composite silicon carbide substrate of the present invention is 5 to 500 nm, which can reduce the surface processing difficulty and cost of the silicon carbide single crystal substrate, and at the same time make the materials on both sides of the interface have better bonding quality.

[0057] Compared with the prior art, the present invention has at least the following beneficial effects:

[0058] (1) The method for preparing composite silicon carbide substrate provided by the present invention does not form a bonding interface layer, the bonding quality between silicon carbide single crystal substrate and crystal layer is high, and the excess part of silicon carbide single crystal substrate is removed by laser cutting, which effectively shortens the preparation time and significantly improves the preparation efficiency.

[0059] (2) The composite silicon carbide substrate provided by the present invention has a high surface roughness Ra at the interface between the silicon carbide single crystal substrate and the crystal layer, which can greatly reduce the surface processing difficulty of the silicon carbide single crystal substrate in the composite substrate, thereby reducing the processing cost. Attached Figure Description

[0060] Figure 1 This is a schematic diagram of the method for preparing the composite substrate provided in Example 1.

[0061] Figure 2 This is a schematic diagram of the modified surface in Example 1.

[0062] Figure 3 This is a schematic diagram of the scanning path of laser irradiation in Example 1.

[0063] Figure 4 This is a schematic diagram of the composite silicon carbide substrate in Example 1.

[0064] Figure 5 This is a schematic diagram of the apparatus for growing crystals using the induction heating physical vapor transport method in Example 1.

[0065] Figure 6 This is a schematic diagram of the scanning path of laser irradiation in Example 2.

[0066] Figure 7 This is a schematic diagram of the apparatus for growing crystals using the resistance heating physical vapor transport method in Example 2.

[0067] Figure 8 This is a schematic diagram of the scanning path of laser irradiation in Example 3.

[0068] Figure 9 This is a schematic diagram of the apparatus for growing crystals using the induction heating solution method in Example 3.

[0069] Figure 10 This is a schematic diagram of the apparatus for growing crystals using the resistance heating solution method in Example 4.

[0070] Figure 11 This is a schematic diagram of the apparatus for growing crystals by induction heating high-temperature chemical vapor deposition in Example 5.

[0071] Figure 12 This is a schematic diagram of the apparatus for growing crystals by resistance heating high-temperature chemical vapor deposition in Example 6.

[0072] In the figure: 1-Silicon carbide single crystal substrate; 1'-Single crystal substrate remaining on the composite silicon carbide substrate; 1”-Remaining silicon carbide single crystal substrate after being broken along the modified surface; 2-Crystal layer; 20-Silicon carbide powder; 21-Crucible lid; 3-Graphite plate; 4-Seed crystal rod; 40-Laser; 5-Graphite crucible; 6-Crucible support; 7-Insulated box; 8-Induction heating coil; 9-Cavity; 10-Reaction chamber; 11-Resistance heater. Detailed Implementation

[0073] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0074] The present invention will now be described in further detail. However, the examples described below are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0075] Example 1

[0076] This embodiment provides a method for preparing a composite silicon carbide substrate, and a schematic diagram of the preparation method is shown below. Figure 1 As shown, it includes the following steps:

[0077] (1) The first surface of the silicon carbide single crystal substrate 1 is bonded to the graphite plate 3. The laser 40 irradiates the second surface of the silicon carbide single crystal substrate 1, forming a modified surface inside the silicon carbide single crystal substrate 1. A schematic diagram of the modified surface is shown below. Figure 2 As shown; an external force is applied to break the silicon carbide single crystal substrate 1 along the modified surface to obtain a composite crystal layer structure composed of the silicon carbide single crystal substrate and the graphite plate 3; the thickness of the silicon carbide single crystal substrate in the composite crystal layer structure is 2 μm;

[0078] The silicon carbide single crystal substrate 1 has a thickness of 800 μm and a crystal form of 4H; the first surface of the silicon carbide single crystal substrate 1 is the C-plane; the angle between the {0001} crystal plane of the silicon carbide single crystal substrate 1 and the surface of the silicon carbide single crystal substrate 1 is 4°, that is, 4° off-axis.

[0079] The bonding steps include sequentially applying adhesive and heating and carbonizing at a temperature of 500°C;

[0080] The laser 40 is a pulsed laser; the pulsed laser is a solid-state laser; the pulse width of the pulsed laser is 170 fs; the scanning path irradiated by the laser 40 is as follows: parallel scanning paths are divided into groups of N from beginning to end, assuming they are divided into M groups, and the first scanning path of the first group to the M group, the second scanning path of the first group to the M group, the third scanning path of the first group to the M group, and so on, until all paths are scanned; specifically, the scanning order is: 1-1, 2-1, 3-1, 4-1, 1-2, 2-2, 3-2, 4-2, 1-3, 2-3, 3-3, ...; the scanning directions of two consecutive scanning paths are opposite, as shown in the schematic diagram. Figure 3 As shown;

[0081] The modified surface of the silicon carbide single crystal substrate 1 in the composite crystal layer structure is surface treated to make the roughness Ra of the modified surface 300nm; the remaining part 1” of the silicon carbide single crystal substrate 1 after being broken along the modified surface is ground and polished and then reused as a seed crystal.

[0082] (2) After growing crystal layer 2 on the modified surface of the single crystal substrate 1' remaining on the composite silicon carbide substrate in the composite crystal layer structure, the graphite plate 3 is separated to obtain a composite silicon carbide substrate composed of the silicon carbide single crystal substrate and crystal layer 2, as shown in the schematic diagram. Figure 4 As shown;

[0083] The crystal layer 2 comprises a single crystal or polycrystalline material; the thickness of the crystal layer 2 is 350 μm, and the growth rate is 3000 μm / h; the growth method of the crystal layer 2 is physical vapor transport; both surfaces of the composite silicon carbide substrate are ground and polished to ensure that the roughness Ra of both surfaces is <0.5 nm. One of the surfaces is the modified surface of laser 40. When grinding and polishing the modified surface of the composite substrate, the angle between the grinding and polishing reference plane and the modified surface is adjusted to 4°, so that the substrate remains off-axis by 4° after grinding and polishing.

[0084] This embodiment is performed in an apparatus for growing crystals using the induction heating physical vapor transport method. A schematic diagram of the apparatus is shown below. Figure 5 As shown, the structure includes a graphite crucible 5, a single crystal substrate 1' remaining on the composite silicon carbide substrate in the composite crystal layer structure, a graphite plate 3, a crucible support 6, a heat insulation box 7, an induction heating coil 8, and a chamber 9; the chamber 9 has at least one exhaust port and at least one inlet port. The graphite crucible 5 contains silicon carbide powder 20.

[0085] The graphite plate 3 is connected to the single crystal substrate 1' remaining on the composite silicon carbide substrate in the composite crystal layer structure. One surface of the single crystal substrate 1' is opposite to the silicon carbide powder 20. The crucible holder 6 supports the graphite crucible 5 and drives the graphite crucible 5 to rotate or move vertically. The graphite crucible 5 is surrounded by a heat insulation box 7, which is located in a chamber 9. An induction heating coil 8 is arranged on the outer periphery of the chamber 9. The induction coil 8 is helical, has a current frequency of 8kHz, and is hollow, allowing for water cooling. The energized induction coil 8 heats the silicon carbide powder 20 in the crucible, causing the silicon carbide powder 20 to sublimate. The crucible holder 6 passes through the wall of the chamber 9.

[0086] Example 2

[0087] This embodiment provides a method for preparing a composite silicon carbide substrate, the method comprising the following steps:

[0088] (1) The first surface of the silicon carbide single crystal substrate 1 is bonded to the graphite plate 3. The second surface of the silicon carbide single crystal substrate 1 is irradiated by the laser 40, and a modified surface is formed inside the silicon carbide single crystal substrate 1. An external force is applied to break the silicon carbide single crystal substrate 1 along the modified surface to obtain a composite crystal layer structure composed of the silicon carbide single crystal substrate and the graphite plate 3. The thickness of the silicon carbide single crystal substrate in the composite crystal layer structure is 37 μm.

[0089] The silicon carbide single crystal substrate 1 has a thickness of 1000 μm and a crystal form of 6H; the first surface of the silicon carbide single crystal substrate 1 is a Si plane; the angle between the {0001} crystal plane of the silicon carbide single crystal substrate 1 and the surface of the silicon carbide single crystal substrate 1 is 2°, that is, 2° off-axis.

[0090] The bonding steps include sequentially applying adhesive and heating and carbonizing at a temperature of 300°C;

[0091] The laser 40 is a pulsed laser; the pulsed laser is a fiber laser; the pulse width of the pulsed laser is 300 fs; the scanning path illuminated by the laser 40 is a series of parallel straight lines, with the spacing between adjacent paths remaining constant; the scanning direction of each path is opposite, as shown in the schematic diagram. Figure 6 As shown;

[0092] The modified surface of the silicon carbide single crystal substrate in the composite crystal layer structure is surface treated to make the roughness Ra of the modified surface 500nm; the remaining part 1” of the silicon carbide single crystal substrate 1 after being broken along the modified surface is ground and polished and then reused as a seed crystal.

[0093] (2) After growing crystal layer 2 on the modified surface of silicon carbide single crystal substrate in the composite crystal layer structure, the graphite plate 3 is separated to obtain a composite silicon carbide substrate composed of silicon carbide single crystal substrate and crystal layer 2.

[0094] The crystal layer 2 is polycrystalline; the thickness of the crystal layer 2 is 100 μm, and the growth rate is 4800 μm / h; the growth method of the crystal layer 2 is physical vapor transport; both surfaces of the composite silicon carbide substrate are ground and polished so that the roughness Ra of both surfaces is <0.5 nm. One of the surfaces is the laser-modified surface. When grinding and polishing the modified surface of the composite substrate, the angle between the grinding and polishing reference plane and the modified surface is adjusted to 2°, so that the substrate remains off-axis by 2° after grinding and polishing.

[0095] This embodiment is performed in an apparatus for growing crystals using the resistance heating physical vapor transport method. A schematic diagram of the apparatus is shown below. Figure 7 As shown, the structure includes a graphite crucible 5, a single crystal substrate 1' remaining on a composite silicon carbide substrate in a composite crystal layer structure, a graphite plate 3, a crucible support 6, a heat insulation box 7, a resistance heater 11, and a chamber 9; the chamber 9 has at least one exhaust port and at least one inlet port. The graphite crucible 5 contains silicon carbide powder 20.

[0096] Graphite plate 3 is connected to silicon carbide single crystal substrate 1, with one surface of silicon carbide single crystal substrate 1 facing silicon carbide powder 20. Crucible holder 6 supports graphite crucible 5, causing graphite crucible 5 to rotate or move vertically. Resistance heater 11 surrounds the outside of graphite crucible 5 and is surrounded by heat insulation box 7. Resistance heater 11 is a graphite heater; when energized, the graphite heater heats the silicon carbide powder 20 in graphite crucible 5, causing the silicon carbide powder 20 to sublimate. Crucible holder 6 passes through the wall of chamber 9.

[0097] Example 3

[0098] This embodiment provides a method for preparing a composite silicon carbide substrate, the method comprising the following steps:

[0099] (1) The first surface of the silicon carbide single crystal substrate 1 is bonded to the graphite plate 3. The second surface of the silicon carbide single crystal substrate 1 is irradiated by the laser 40, and a modified surface is formed inside the silicon carbide single crystal substrate 1. An external force is applied to break the silicon carbide single crystal substrate 1 along the modified surface to obtain a composite crystal layer structure composed of the silicon carbide single crystal substrate and the graphite plate 3. The thickness of the silicon carbide single crystal substrate in the composite crystal layer structure is 33 μm.

[0100] The silicon carbide single crystal substrate 1 has a thickness of 820 μm and a crystal form of 4H; the first surface of the silicon carbide single crystal substrate 1 is a Si plane; the angle between the {0001} crystal plane of the silicon carbide single crystal substrate 1 and the surface of the silicon carbide single crystal substrate 1 is 6°, that is, 6° off-axis.

[0101] The bonding steps include sequentially applying adhesive and heating and carbonizing at a temperature of 200°C;

[0102] The laser 40 is a pulsed laser; the pulsed laser is a fiber laser; the pulse width of the pulsed laser is 100 fs; the scanning path illuminated by the laser 40 is a series of parallel straight lines, with the spacing between adjacent paths remaining constant; the scanning direction of each path is the same, as shown in the schematic diagram. Figure 8 As shown;

[0103] The modified surface of the silicon carbide single crystal substrate in the composite crystal layer structure is surface treated to make the roughness Ra of the modified surface 5nm; the remaining part 1” of the silicon carbide single crystal substrate after being broken along the modified surface is ground and polished and then reused as a seed crystal.

[0104] (2) After growing crystal layer 2 on the modified surface of silicon carbide single crystal substrate in the composite crystal layer structure, the graphite plate 3 is separated to obtain a composite silicon carbide substrate composed of silicon carbide single crystal substrate and crystal layer 2.

[0105] The crystal layer 2 is a single crystal; the thickness of the crystal layer 2 is 880 μm, and the growth rate is 300 μm / h; the growth method of the crystal layer 2 is a solution method; both surfaces of the composite silicon carbide substrate are ground and polished so that the roughness Ra of both surfaces is <0.5 nm. One of the surfaces is the laser-modified surface. When grinding and polishing the modified surface of the composite substrate, the angle between the grinding and polishing reference plane and the modified surface is adjusted to 6°, so that the substrate remains off-axis by 6° after grinding and polishing.

[0106] This embodiment is carried out in an apparatus for crystal growth using induction heating solution method, and the structural schematic diagram of the apparatus is shown below. Figure 9 As shown, the structure includes a graphite crucible 5, a seed crystal rod 4, a graphite plate 3, a single crystal substrate 1' remaining on the composite silicon carbide substrate in the composite crystal layer structure, a crucible holder 6, a heat-insulating box 7, an induction heating coil 8, and a chamber 9. The chamber 9 has at least one evacuation port and at least one inlet port. The graphite crucible 5 contains a flux solution.

[0107] The seed crystal rod 4 is connected to the graphite plate 3. A composite seed crystal can be attached to the bottom of the graphite plate 3. The seed crystal rod 4 can rotate and move vertically. The crucible holder 6 supports the graphite crucible 5 and can drive the graphite crucible 5 to rotate and move vertically. The graphite crucible 5 is surrounded by a heat insulation box 7, and an induction heating coil 8 is arranged around the outer periphery of the heat insulation box 7. The induction coil 8 is helical, with a current frequency of 3kHz, and is hollow, allowing for water cooling. The energized induction coil 8 heats and melts the flux in the graphite crucible 5. The chamber 9 provides an atmospheric environment for crystal growth. The seed crystal rod 4 and the crucible holder 6 pass through the wall of the chamber 9.

[0108] Example 4

[0109] This embodiment provides a method for preparing a composite silicon carbide substrate, the method comprising the following steps:

[0110] (1) The first surface of the silicon carbide single crystal substrate 1 is bonded to the graphite plate 3. The second surface of the silicon carbide single crystal substrate 1 is irradiated by the laser 40, and a modified surface is formed inside the silicon carbide single crystal substrate 1. An external force is applied to break the silicon carbide single crystal substrate 1 along the modified surface to obtain a composite crystal layer structure composed of the silicon carbide single crystal substrate and the graphite plate 3. The thickness of the silicon carbide single crystal substrate in the composite crystal layer structure is 1 μm.

[0111] The silicon carbide single crystal substrate 1 has a thickness of 720 μm and a crystal form of 6H; the first surface of the silicon carbide single crystal substrate 1 is the C-plane; the angle between the {0001} crystal plane of the silicon carbide single crystal substrate 1 and the surface of the silicon carbide single crystal substrate 1 is 0°, i.e., the off-axis is 0°.

[0112] The bonding steps include sequentially applying adhesive and heating and carbonizing at a temperature of 710°C;

[0113] The laser 40 is a pulsed laser; the pulsed laser is a solid-state laser; the pulse width of the pulsed laser is 250 fs; the scanning path of the laser irradiation is a series of parallel straight lines, and the spacing between adjacent paths remains unchanged; the scanning direction of each path is the same;

[0114] The modified surface of the silicon carbide single crystal substrate in the composite crystal layer structure is surface treated to make the roughness Ra of the modified surface 160nm; the remaining part 1” of the silicon carbide single crystal substrate after being broken along the modified surface is ground and polished and then reused as a seed crystal.

[0115] (2) After growing crystal layer 2 on the modified surface of silicon carbide single crystal substrate in the composite crystal layer structure, the graphite plate 3 is separated to obtain a composite silicon carbide substrate composed of silicon carbide single crystal substrate and crystal layer 2.

[0116] The crystal layer 2 comprises a single crystal or polycrystalline material; the thickness of the crystal layer 2 is 200 μm, and the growth rate is 1000 μm / h; the growth method of the crystal layer 2 is a solution method; both surfaces of the composite silicon carbide substrate are ground and polished to ensure that the roughness Ra of both surfaces is <0.5 nm. One of the surfaces is a laser-modified surface. When grinding and polishing the modified surface of the composite substrate, adjusting the angle between the grinding and polishing reference plane and the modified surface to 0° ensures that the substrate remains off-axis by 0° after grinding and polishing.

[0117] This embodiment is carried out in an apparatus for crystal growth using the resistance heating solution method. A schematic diagram of the apparatus is shown below. Figure 10 As shown, the structure includes a graphite crucible 5, a seed crystal rod 4, a graphite plate 3, a single crystal substrate 1' remaining on the composite silicon carbide substrate in the composite crystal layer structure, a crucible holder 6, a heat insulation box 7, a resistance heater 11, and a chamber 9. The chamber 9 has at least one evacuation port and at least one inlet port. The graphite crucible 5 contains a flux solution.

[0118] The seed crystal rod 4 is connected to the graphite plate 3. A composite seed crystal can be attached to the bottom of the graphite plate 3. The seed crystal rod 4 can rotate and move vertically. The crucible holder 6 supports the graphite crucible 5 and can drive the graphite crucible 5 to rotate and move vertically. The graphite crucible 5 is surrounded by a resistance heater 11 and is enclosed by a heat insulation box 7. The resistance heater 11 is a graphite heater, which heats and melts the flux in the graphite crucible 5 when energized. The chamber 9 provides an atmospheric environment for crystal growth. The seed crystal rod 4 and the crucible holder 6 pass through the wall of the chamber 9.

[0119] Example 5

[0120] This embodiment provides a method for preparing a composite silicon carbide substrate, the method comprising the following steps:

[0121] (1) The first surface of the silicon carbide single crystal substrate 1 is bonded to the graphite plate 3. The second surface of the silicon carbide single crystal substrate 1 is irradiated by the laser 40, and a modified surface is formed inside the silicon carbide single crystal substrate 1. An external force is applied to break the silicon carbide single crystal substrate 1 along the modified surface to obtain a composite crystal layer structure composed of the silicon carbide single crystal substrate and the graphite plate 3. The thickness of the silicon carbide single crystal substrate in the composite crystal layer structure is 50 μm.

[0122] The silicon carbide single crystal substrate 1 has a thickness of 150 μm and a crystal form of 4H; the first surface of the silicon carbide single crystal substrate 1 is a Si plane; the angle between the {0001} crystal plane of the silicon carbide single crystal substrate 1 and the surface of the silicon carbide single crystal substrate 1 is 7°, that is, 7° off-axis.

[0123] The bonding steps include sequentially applying adhesive and heating and carbonizing at a temperature of 800°C;

[0124] The laser 40 is a pulsed laser; the pulsed laser is a fiber laser; the pulse width of the pulsed laser is 190 fs; the scanning path of the laser irradiation is a series of parallel straight lines, and the spacing between adjacent paths remains constant; the scanning direction of each path is opposite.

[0125] The modified surface of the silicon carbide single crystal substrate in the composite crystal layer structure is surface treated to make the roughness Ra of the modified surface 50 nm; the remaining part 1” of the silicon carbide single crystal substrate after being broken along the modified surface is ground and polished and then reused as a seed crystal.

[0126] (2) After growing crystal layer 2 on the modified surface of silicon carbide single crystal substrate in the composite crystal layer structure, the graphite plate 3 is separated to obtain a composite silicon carbide substrate composed of silicon carbide single crystal substrate and crystal layer 2.

[0127] The crystal layer 2 comprises a single crystal or polycrystalline material; the thickness of the crystal layer 2 is 500 μm, and the growth rate is 1800 μm / h; the growth method of the crystal layer 2 is high-temperature chemical vapor deposition; both surfaces of the composite silicon carbide substrate are ground and polished to ensure that the roughness Ra of both surfaces is <0.5 nm. One of the surfaces is the laser-modified surface. When grinding and polishing the modified surface of the composite substrate, the angle between the grinding and polishing reference plane and the modified surface is adjusted to 7°, so that the substrate remains off-axis by 7° after grinding and polishing.

[0128] This embodiment is carried out in an apparatus for growing crystals using induction heating high-temperature chemical vapor deposition. A schematic diagram of the apparatus is shown below. Figure 11 As shown, the structure includes a seed crystal rod 4, a graphite plate 3, a single crystal substrate 1' remaining on the composite silicon carbide substrate in the composite crystal layer structure, a reaction chamber 10, a heat insulation box 7, an induction heating coil 8, and a cavity 9. The cavity 9 has at least one exhaust port and at least one inlet port.

[0129] The seed crystal rod 4 is connected to the graphite plate 3. A composite seed crystal can be attached to the bottom of the graphite plate 3. The seed crystal rod 4 can rotate and move vertically. The reaction chamber 10 is made of graphite and is surrounded by a heat insulation box 7, which is located inside the chamber 9. An induction heating coil 8 is arranged around the outer periphery of the chamber 9. The induction coil 8 is helical, with a current frequency of 20kHz, and is hollow, allowing for water cooling. The seed crystal rod 4 passes through the wall of the chamber 9. The energized induction coil 8 heats the reaction chamber 10 to the temperature required for crystal growth.

[0130] The chamber 9 is filled with reaction gas through its air inlet. The reaction gas includes silicon source gas and carbon source gas. The silicon source gas is silane, and the carbon source gas is propane.

[0131] Example 6

[0132] This embodiment provides a method for preparing a composite silicon carbide substrate, the method comprising the following steps:

[0133] (1) The first surface of the silicon carbide single crystal substrate 1 is bonded to the graphite plate 3. The second surface of the silicon carbide single crystal substrate 1 is irradiated by a laser to form a modified surface inside the silicon carbide single crystal substrate 1. An external force is applied to break the silicon carbide single crystal substrate 1 along the modified surface to obtain a composite crystal layer structure composed of the silicon carbide single crystal substrate and the graphite plate 3. The thickness of the silicon carbide single crystal substrate in the composite crystal layer structure is 27 μm.

[0134] The silicon carbide single crystal substrate 1 has a thickness of 860 μm and a crystal form of 6H; the first surface of the silicon carbide single crystal substrate 1 is the C-plane; the angle between the {0001} crystal plane of the silicon carbide single crystal substrate 1 and the surface of the silicon carbide single crystal substrate 1 is 8°, that is, 8° off-axis.

[0135] The bonding steps include sequentially applying adhesive and heating and carbonizing at a temperature of 440°C;

[0136] The laser 40 is a pulsed laser; the pulsed laser includes a solid-state laser or a fiber laser; the pulse width of the pulsed laser is 290 fs; the scanning path of the laser 40 is as follows: parallel scanning paths are divided into groups of N from beginning to end, assuming they are divided into M groups, and the first scanning path of the first group to the M group, the second scanning path of the first group to the M group, the third scanning path of the first group to the M group, and so on, until all paths are scanned; specifically, the scanning order is: 1-1, 2-1, 3-1, 4-1, 1-2, 2-2, 3-2, 4-2, 1-3, 2-3, 3-3, ...; the scanning directions of two consecutive scanning paths are opposite; the modified surface of the silicon carbide single crystal substrate in the composite crystal layer structure is surface treated to make the roughness Ra of the modified surface 340 nm; the remaining part 1” of the silicon carbide single crystal substrate after being broken along the modified surface is ground and polished and reused as a seed crystal;

[0137] (2) After growing crystal layer 2 on the modified surface of silicon carbide single crystal substrate in the composite crystal layer structure, the graphite plate 3 is separated to obtain a composite silicon carbide substrate composed of silicon carbide single crystal substrate and crystal layer 2.

[0138] The crystal layer 2 comprises a single crystal or polycrystalline material; the thickness of the crystal layer 2 is 1000 μm, and the growth rate is 600 μm / h; the growth method of the crystal layer 2 is high-temperature chemical vapor deposition; both surfaces of the composite silicon carbide substrate are ground and polished to ensure that the roughness Ra of both surfaces is <0.5 nm. One of the surfaces is the laser-modified surface. When grinding and polishing the modified surface of the composite substrate, adjusting the angle between the grinding and polishing reference plane and the modified surface to 8° ensures that the substrate remains off-axis by 8° after grinding and polishing.

[0139] This embodiment is carried out in an apparatus for growing crystals using resistance heating high-temperature chemical vapor deposition. A schematic diagram of the apparatus is shown below. Figure 12 As shown, the structure includes a seed crystal rod 4, a graphite plate 3, a single crystal substrate 1' remaining on the composite silicon carbide substrate in the composite crystal layer structure, a reaction chamber 10, a heat insulation box 7, a resistance heater 11, and a cavity 9. The cavity 9 has at least one exhaust port and at least one inlet port.

[0140] The seed crystal rod 4 is connected to the graphite plate 3. A composite seed crystal can be attached to the bottom of the graphite plate 3. The seed crystal rod 4 can rotate and move vertically. The reaction chamber 10 is made of graphite, and a resistance heater 11 is installed on its outer side. The resistance heater 11 is located in the heat insulation box 7, which is located in the chamber 9. The seed crystal rod 4 passes through the wall of the chamber 9. The resistance heater 11 is a graphite heater. When energized, the graphite heater heats the reaction chamber 10 to the temperature required for crystal growth.

[0141] The chamber 9 is filled with reaction gas through its air inlet. The reaction gas includes silicon source gas and carbon source gas. The silicon source gas is silane, and the carbon source gas is propane.

[0142] Example 7

[0143] This embodiment provides a method for preparing a composite silicon carbide substrate. The preparation method is the same as in Example 1, except that the growth rate of the crystal layer is replaced by 150 μm / h instead of 3000 μm / h.

[0144] Example 8

[0145] This embodiment provides a method for preparing a composite substrate. The preparation method is the same as in Example 1, except that the growth rate of the crystal layer is replaced by 5500 μm / h instead of 3000 μm / h.

[0146] Comparative Example 1

[0147] This comparative example provides a method for preparing a composite substrate, comprising the following steps:

[0148] Single-crystal substrates and crystal layers were fabricated using physical vapor transport method. Both crystal types were 4H and both had a thickness of 350 μm. The angle between the {0001} crystal plane of the single-crystal substrate and the surface of the single-crystal substrate was 4°.

[0149] Ion implantation or laser irradiation is performed on one surface of a single-crystal substrate to form a pre-embedded weakening layer at a depth of about 2 μm from the surface;

[0150] The ion-implanted or laser-irradiated surface of the single-crystal substrate is bonded to one surface of the crystal layer to obtain a composite substrate comprising a single-crystal substrate, a crystal layer, and a bonding interface layer between the two.

[0151] The composite substrate was subjected to heat treatment, which caused the single crystal substrate to break along the pre-embedded weakening layer, resulting in a composite substrate with a single crystal substrate thickness of 2 μm.

[0152] The resistance values ​​of the composite substrates obtained in the above embodiments and comparative examples were measured using the following method: a back electrode was formed on the surface of the crystal layer of the composite silicon carbide substrate, and a circular surface electrode with a diameter of 0.3 mm was formed on the surface of the single crystal substrate. A voltage V was applied between the surface electrode and the back electrode, and the corresponding current I was recorded to obtain the VI curve, from which the resistance value was calculated.

[0153] (1) As can be seen from the comparison between Example 1 and Comparative Example 1, the resistance value of Example 1 is 3.8Ω, while the resistance value of Comparative Example 1 is higher, reaching 4.1Ω, due to the negative impact of the bonding interface layer on the vertical conductivity of the composite substrate. The composite substrate prepared by the method of the present invention has high quality and better vertical conductivity.

[0154] (2) It can be seen from the combined examples 1 and 7-8 that in example 7, the composite substrate prepared by the crystal layer growth rate was only 150 μm / h, and the quality of the composite substrate was high with a resistance value of 3.7Ω. However, the preparation time of the composite substrate was long and the preparation efficiency was low. In example 8, the crystal layer growth rate was too high, and impurities or holes appeared in the crystal layer, resulting in poor quality of the composite substrate with a resistance value of 4.0Ω.

[0155] In summary, the method for preparing composite silicon carbide substrates provided by this invention uses a graphite plate as a support layer and obtains a thin, high-quality silicon carbide single crystal substrate through laser cutting. Then, a low-quality crystal layer is grown on the high-quality silicon carbide single crystal substrate, without forming a bonding interface layer. This significantly improves the preparation efficiency of composite silicon carbide substrates and has prospects for industrial application.

[0156] The applicant declares that the above description is only a specific embodiment 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 conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a composite silicon carbide substrate, characterized in that, The preparation method includes the following steps: (1) The first surface of the silicon carbide single crystal substrate is bonded to the graphite plate, and the second surface of the silicon carbide single crystal substrate is irradiated by laser to form a modified surface inside the silicon carbide single crystal substrate; an external force is applied to break the silicon carbide single crystal substrate along the modified surface to obtain a composite crystal layer structure composed of silicon carbide single crystal substrate and graphite plate; the thickness of the silicon carbide single crystal substrate in the composite crystal layer structure is 1~50μm; The scanning path for laser irradiation in step (1) includes any one of parallel straight lines, concentric circles, zigzag lines, or curves; (2) After growing a crystal layer on the modified surface of the silicon carbide single crystal substrate in the composite crystal layer structure, the graphite plate is separated to obtain a composite silicon carbide substrate composed of a silicon carbide single crystal substrate and a crystal layer. The growth rate of the crystal layer is 300~5000 μm / h.

2. The preparation method according to claim 1, characterized in that, The thickness of the silicon carbide single crystal substrate in step (1) is 150~1000μm; The silicon carbide single crystal substrate has a crystal form of 4H or 6H; The first surface of the silicon carbide single crystal substrate includes a Si surface or a C surface; The angle between the {0001} crystal plane of the silicon carbide single crystal substrate and the surface of the silicon carbide single crystal substrate is 0°~8°.

3. The preparation method according to claim 1, characterized in that, The bonding steps in step (1) include applying adhesive and heating for carbonization in sequence; The temperature for heating and carbonization is 200~800℃.

4. The preparation method according to claim 1, characterized in that, The laser mentioned in step (1) is a pulsed laser; The pulsed laser includes a solid-state laser or a fiber laser; The pulse width of the pulsed laser is 100~300 fs.

5. The preparation method according to claim 1, characterized in that, The scanning path of laser irradiation in step (1) is as follows: divide the parallel scanning paths into groups of N from beginning to end, assuming they are divided into M groups, and scan the first scanning path of the first group to the M group, the second scanning path of the first group to the M group, the third scanning path of the first group to the M group, and so on, until all paths are scanned.

6. The preparation method according to claim 1, characterized in that, The modified surface of the silicon carbide single crystal substrate in the composite crystal layer structure described in step (1) is subjected to surface treatment so that the roughness Ra of the modified surface after treatment is 5~500nm. The remaining portion of the silicon carbide single crystal substrate after being broken along the modified surface is ground and polished, and then reused as a seed crystal.

7. The preparation method according to claim 1, characterized in that, The crystal layer in step (2) includes single crystal or polycrystalline; The thickness of the crystal layer is 100~1000μm; The crystal layer growth method includes any one of physical vapor transport (PVT), solution vapor deposition (LPE), or high-temperature chemical vapor deposition (HTCVD).

8. The preparation method according to claim 1, characterized in that, Both surfaces of the composite silicon carbide substrate described in step (2) are ground and polished; The roughness Ra of both surfaces of the composite silicon carbide substrate is <0.5 nm.

9. The preparation method according to any one of claims 1 to 8, characterized in that, The preparation method includes the following steps: (1) The first surface of the silicon carbide single crystal substrate is bonded to the graphite plate, and the second surface of the silicon carbide single crystal substrate is irradiated by laser to form a modified surface inside the silicon carbide single crystal substrate; an external force is applied to break the silicon carbide single crystal substrate along the modified surface to obtain a composite crystal layer structure composed of silicon carbide single crystal substrate and graphite plate; the thickness of the silicon carbide single crystal substrate in the composite crystal layer structure is 1~50μm; The thickness of the silicon carbide single crystal substrate is 150~1000μm, and the crystal form is 4H or 6H; the first surface of the silicon carbide single crystal substrate includes a Si plane or a C plane; the angle between the {0001} crystal plane of the silicon carbide single crystal substrate and the surface of the silicon carbide single crystal substrate is 0°~8°. The bonding steps include sequentially applying adhesive and heating and carbonizing at a temperature of 200~800℃; The laser is a pulsed laser; the pulsed laser includes a solid-state laser or a fiber laser; the pulse width of the pulsed laser is 100~300 fs; the scanning path of the laser irradiation includes any one of parallel straight lines, concentric circles, zigzag lines or curves; the scanning path of the laser irradiation is as follows: divide the mutually parallel scanning paths into groups of N from beginning to end, assuming they are divided into M groups, and scan the first scanning path of the first group to the M group, the second scanning path of the first group to the M group, the third scanning path of the first group to the M group, and so on, until all paths have been scanned; The modified surface of the silicon carbide single crystal substrate in the composite crystal layer structure is surface treated to make the roughness Ra of the modified surface 5~500nm; the remaining part of the silicon carbide single crystal substrate after being broken along the modified surface is ground and polished and reused as a seed crystal. (2) After growing a crystal layer on the modified surface of the silicon carbide single crystal substrate in the composite crystal layer structure, the graphite plate is separated to obtain a composite silicon carbide substrate composed of a silicon carbide single crystal substrate and a crystal layer. The crystal layer includes single crystal or polycrystalline; the thickness of the crystal layer is 100~1000μm, and the growth rate is 300~5000μm / h; the growth method of the crystal layer includes any one of physical vapor transport (PVT), solution vapor deposition (LPE), or high-temperature chemical vapor deposition (HTCVD); both surfaces of the composite silicon carbide substrate are ground and polished so that the roughness Ra of both surfaces is <0.5nm.

10. A composite silicon carbide substrate, characterized in that, The composite silicon carbide substrate is prepared by the method for preparing a composite silicon carbide substrate according to any one of claims 1 to 9; The roughness Ra of the interface between the silicon carbide single crystal substrate and the crystal layer in the composite silicon carbide substrate is 5~500 nm.

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