Silicon carbide composite seed crystal, preparation method thereof and silicon carbide crystal

Abstract

The invention discloses a silicon carbide composite seed crystal, a preparation method thereof and a silicon carbide crystal. The preparation method of the silicon carbide composite seed crystal comprises the following steps: providing the silicon carbide seed crystal; forming a silicon carbide transition layer on the silicon surface of the silicon carbide seed crystal, and enabling the carbon surface of the silicon carbide transition layer to be far away from the silicon surface of the silicon carbide seed crystal to obtain a silicon carbide composite structure; forming a diamond layer on the carbon surface of the silicon carbide transition layer to obtain a silicon carbide composite seed crystal; wherein the thermal conductivity of the silicon carbide transition layer is smaller than that of the diamond layer, and the thermal conductivity of the silicon carbide transition layer is larger than that of the silicon carbide seed crystal; and the crystal form of the silicon carbide transition layer is different from that of the silicon carbide seed crystal. The silicon carbide composite seed crystal prepared by the method ensures the growth quality of the silicon carbide crystal while realizing the growth of the large-diameter, high-thickness and low-cost silicon carbide crystal.

Description

Technical Field

[0001] This application relates to the field of semiconductor material preparation, and particularly to a silicon carbide composite seed crystal, a preparation method thereof, and a silicon carbide crystal including the silicon carbide composite seed crystal. Background Art

[0002] Silicon carbide single crystals are generally large-sized commercialized bulk crystals realized by PVT (Physical Vapor Transport) and LPE (Liquid Phase Epitaxy), but the growth rate is much lower than that of silicon crystals.

[0003] The reason for the slow growth rate of silicon carbide crystals is that the physical properties of the silicon carbide single crystal seeds used in both physical vapor deposition and flux liquid phase growth are poor. The traditional seed crystal is composed of a certain thickness of silicon carbide single crystal material, and the thermal conductivity of the silicon carbide single crystal material is only 490 W / (m·K). The factors affecting the thermal conductivity of silicon carbide single crystals include impurities and crystal structure defects, etc. During the crystal growth process, the temperature gradient is the internal driving force for single crystal crystallization, and the temperature gradient is a key factor determining the crystal growth rate. The crystal growth rate has a close positive correlation with the temperature gradient. Under a large temperature gradient, the crystal crystallization rate is faster, and vice versa. The low thermal conductivity of silicon carbide material is not conducive to forming a large temperature gradient in the vertical direction required for silicon carbide crystal growth. Therefore, the growth rate of silicon carbide crystals is not only slow, but also the growth thickness is very small, that is, the silicon carbide crystals cannot grow thick (generally only 20 - 25 mm), or when growing thick, the internal quality of the crystal is poor, and an electronic-grade silicon carbide crystal cannot be obtained.

[0004] This application solves at least one of the above problems. Summary of the Invention

[0005] The purpose of this application is to provide a preparation method of a silicon carbide composite seed crystal, which is used to solve the problem that the low thermal conductivity of silicon carbide material is not conducive to forming a large temperature gradient in the vertical direction required for silicon carbide crystal growth. Therefore, the growth rate of silicon carbide crystals is not only slow, but also the growth thickness is very small, that is, the silicon carbide crystals cannot grow thick, with a thickness generally only 20 - 25 mm, or when growing thick, the internal quality of the crystal is poor, and an electronic-grade silicon carbide crystal cannot be obtained. While realizing the growth of large-diameter, high-thickness, and low-cost silicon carbide crystals by the method of this application, the growth quality of silicon carbide crystals can also be guaranteed.

[0006] To achieve the above purpose, this application adopts the following technical solutions:

[0007] In the first aspect of the present invention, a preparation method of a silicon carbide composite seed crystal is provided, including the following steps:

[0008] Provide a silicon carbide seed crystal;

[0009] Form a silicon carbide transition layer on the silicon face of the silicon carbide seed crystal, and make the carbon face of the silicon carbide transition layer away from the silicon face of the silicon carbide seed crystal to obtain a silicon carbide composite structure;

[0010] Form a diamond layer on the carbon face of the silicon carbide transition layer to obtain a silicon carbide composite seed crystal;

[0011] Wherein, the thermal conductivity of the silicon carbide transition layer is less than that of the diamond layer, and the thermal conductivity of the silicon carbide transition layer is greater than that of the silicon carbide seed crystal; the crystal form of the silicon carbide transition layer is different from that of the silicon carbide seed crystal.

[0012] Compared with the prior art, the beneficial effects of this application are as follows:

[0013] By forming a silicon carbide transition layer with high thermal conductivity on the surface of a silicon carbide seed crystal with low thermal conductivity, the silicon face of the silicon carbide seed crystal and the silicon face of the silicon carbide transition layer are combined by silicon atom diffusion, reducing the interface stress and enhancing the bonding strength between the two phases; by forming a diamond layer with even higher thermal conductivity on the carbon face of the silicon carbide transition layer with high thermal conductivity, the silicon carbide transition layer serves as a thermal stress buffer layer, reducing interface cracks or peeling caused by the difference in thermal expansion coefficients between the silicon carbide seed crystal and the diamond layer.

[0014] By establishing a temperature gradient among the silicon carbide seed crystal with low thermal conductivity, the silicon carbide transition layer with high thermal conductivity, and the diamond layer with even higher thermal conductivity, the heat at the silicon carbide seed crystal can be quickly transferred out in the vertical and horizontal directions, so that a large temperature gradient can be achieved in the vertical and horizontal directions for the silicon carbide composite seed crystal. This can not only increase the growth rate of the silicon carbide crystal in the vertical direction, facilitating the growth of a silicon carbide crystal with a thickness of more than 50 mm; but also increase the growth rate of the silicon carbide crystal in the horizontal direction, facilitating the diameter expansion during the growth of the silicon carbide crystal and making it easy to achieve the growth of a large-diameter silicon carbide crystal, greatly reducing the growth cost of the silicon carbide material. In summary, the silicon carbide composite seed crystal prepared by the above method can achieve the growth of a large-diameter, high-thickness, and low-cost silicon carbide crystal while ensuring the growth quality of the silicon carbide crystal.

[0015] In some possible implementation manners of the first aspect, during the process of forming the silicon carbide transition layer on the silicon face of the silicon carbide seed crystal, the silicon face of the silicon carbide seed crystal and the silicon face of the silicon carbide transition layer are combined by silicon atom diffusion; the forming of the silicon carbide transition layer on the silicon face of the silicon carbide seed crystal includes:

[0016] Under the conditions that the temperature is 850 - 900 °C, the pressure is 20 - 30 Kpa, the flow rates of SiH4 and CH4 are both 2 - 20 sccm, and the flow rate of H2 is 200 - 500 sccm, a chemical vapor deposition method is used to grow on the silicon surface of the silicon carbide seed crystal with a thickness of 100 - 200 μm for 10 - 20 h to prepare an initial silicon carbide transition layer with a thickness of 50 - 200 μm;

[0017] Grind and polish the carbon surface of the initial silicon carbide transition layer to obtain a silicon carbide transition layer with a thickness of 10 - 50 μm and a surface roughness less than the first preset roughness;

[0018] Among them, the value range of the first preset roughness is 1 - 5 nm.

[0019] In some possible implementation manners of the first aspect, during the process of forming the silicon carbide transition layer on the silicon surface of the silicon carbide seed crystal, the silicon surface of the silicon carbide seed crystal and the silicon surface of the silicon carbide transition layer are combined by silicon atom diffusion; the forming of the silicon carbide transition layer on the silicon surface of the silicon carbide seed crystal includes:

[0020] Under the conditions that the temperature is 1900 - 2100 °C and the pressure is 0.001 - 0.03 pa, the silicon surface of the silicon carbide seed crystal with a thickness of 100 - 200 μm and the silicon surface of the initial silicon carbide transition layer are hetero - bonded to obtain a first hetero - bonded structure;

[0021] Among them, the surface roughness of the silicon surface of the initial silicon carbide transition layer is less than the second preset roughness, and the value range of the second preset roughness is 1 - 5 nm;

[0022] After the hetero - bonding is completed, under the conditions that the annealing temperature is 1800 - 1900 °C and the annealing atmosphere is argon or nitrogen, the first hetero - bonded structure is annealed for 20 - 40 h to convert the initial silicon carbide transition layer into the silicon carbide transition layer;

[0023] Among them, the thickness of the silicon carbide transition layer is 10 - 50 μm.

[0024] In some possible implementation manners of the first aspect, during the process of forming the diamond layer on the carbon surface of the silicon carbide transition layer, the carbon surface of the silicon carbide transition layer and the surface of the diamond layer are combined by carbon atom diffusion; the forming of the diamond layer on the carbon surface of the silicon carbide transition layer includes:

[0025] Use the chemical vapor deposition method to grow an initial diamond layer with a thickness of 500 - 900 μm on the carbon surface of the silicon carbide transition layer;

[0026] Grind and polish the initial diamond layer to obtain the diamond layer with a thickness of 300-500 μm and a surface roughness less than the third preset roughness;

[0027] Among them, the value range of the third preset roughness is 1-5 nm.

[0028] In some possible implementation manners of the first aspect, the growth of the initial diamond layer with a thickness of 500-900 μm on the carbon surface of the silicon carbide transition layer includes:

[0029] Under the conditions of a temperature of 850-900 °C, a gas pressure of 20-30 Kpa, a flow rate of CH4 of 2-20 sccm, a flow rate of H2 of 200-500 sccm, and a flow rate of O2 of 2-20 sccm, use MPCVD to grow on the carbon surface of the silicon carbide transition layer for 60-90 h to prepare the initial diamond layer with a thickness of 500-900 μm;

[0030] Or, under the conditions of a temperature of 2200-2300 °C, a gas pressure of 20-30 Kpa, a flow rate of CH4 of 2-20 sccm, and a flow rate of H2 of 200-500 sccm, use HFCVD to grow on the carbon surface of the silicon carbide transition layer for 60-90 h to prepare the initial diamond layer with a thickness of 500-900 μm;

[0031] Or, under the conditions of a temperature of 850-900 °C, a gas pressure of 20-30 Kpa, a flow rate of CH4 of 2-20 sccm, and a flow rate of H2 of 200-500 sccm, use DCPCVD to grow on the carbon surface of the silicon carbide transition layer for 5-10 h to prepare the initial diamond layer with a thickness of 500-900 μm.

[0032] In some possible implementation manners of the first aspect, during the process of forming the diamond layer on the carbon surface of the silicon carbide transition layer, the carbon surface of the silicon carbide transition layer and the surface of the diamond layer are bonded by carbon atom diffusion; the formation of the diamond layer on the carbon surface of the silicon carbide transition layer includes:[[ID=S19]]

[0033] Under the conditions of a temperature of 1900-2100 °C and a gas pressure of 0.001-0.03 pa, perform heterovalent bonding on the carbon surface of the silicon carbide transition layer and the surface of the initial diamond layer to obtain a second heterovalent bonding structure;

[0034] Among them, the surface roughness of the initial diamond layer is less than the fourth preset roughness, and the value range of the fourth preset roughness is 1-5 nm;

[0035] After the heterogeneous bonding is completed, the second heterogeneous bonding structure is annealed for 20 to 40 h under the conditions that the annealing temperature is 1800 to 1900 °C and the annealing atmosphere is argon or nitrogen, so that the initial diamond layer is transformed into the diamond layer;

[0036] Wherein, the thickness of the diamond layer is 300 - 500 um.

[0037] In some possible embodiments of the first aspect, before forming the diamond layer, the preparation method further includes: forming a plurality of first micro-channels in a convex or groove shape on the carbon surface of the silicon carbide transition layer;

[0038] And / or, before the heterogeneous bonding between the carbon surface of the silicon carbide transition layer and the surface of the initial diamond layer, the method further includes: forming a plurality of second micro-channels in a convex or groove shape on the surface of the initial diamond layer;

[0039] Wherein, the convex first micro-channels correspond to the groove-shaped second micro-channels, so that the convex first micro-channels can be embedded into the groove-shaped second micro-channels; the convex second micro-channels correspond to the groove-shaped first micro-channels, so that the convex second micro-channels can be embedded into the groove-shaped first micro-channels.

[0040] In some possible embodiments of the first aspect, forming a plurality of first micro-channels in a convex or groove shape on the carbon surface of the silicon carbide transition layer includes:

[0041] Under the conditions that the pulse width is 500 ps to 1 ns, the laser power is 10 to 15 W, and the laser repetition frequency is 20 to 100 kHz, a plurality of first micro-channels in a convex or groove shape are formed on the carbon surface of the silicon carbide transition layer by laser etching; or under the conditions that the etching temperature exceeds 1800 °C and the etching gas is CF4, O2 or Ar, a plurality of first micro-channels in a convex or groove shape are formed on the carbon surface of the silicon carbide transition layer by plasma etching;

[0042] Wherein, the width of the first micro-channel is 5 to 10 μm; and / or, the depth of the first micro-channel is 30 - 50 μm; and / or, the lateral spacing of the first micro-channels is 5 to 10 mm;

[0043] And / or, forming a plurality of second micro-channels in a convex or groove shape on the surface of the initial diamond layer includes:

[0044] Under the conditions that the pulse width is 500 ps to 1 ns, the laser power is 10 to 15 W, and the laser repetition frequency is 20 to 100 kHz, a plurality of second microchannels in a convex or groove shape are formed on the surface of the initial diamond layer by laser etching; or under the conditions that the etching temperature exceeds 1800 °C and the etching gas is CF4, O2 or Ar, a plurality of second microchannels in a convex or groove shape are formed on the surface of the initial diamond layer by plasma etching;

[0045] Wherein, the width of the second microchannel is 5 to 10 μm; and / or, the depth of the second microchannel is 30 - 50 μm; and / or, the lateral pitch of the second microchannels is 5 to 10 mm.

[0046] And / or, the thickness of the diamond layer is less than or equal to two-thirds of the thickness of the silicon carbide composite seed crystal, and the thickness of the diamond layer is greater than or equal to one-half of the thickness of the silicon carbide composite seed crystal;

[0047] And / or, the thickness of the silicon carbide seed crystal is less than one-third of the thickness of the silicon carbide composite seed crystal.

[0048] In the second aspect of the present invention, a silicon carbide composite seed crystal is provided, and the silicon carbide composite seed crystal is prepared by using the preparation method of the silicon carbide composite seed crystal described above.

[0049] In the third aspect of the present invention, a silicon carbide crystal is provided, and the silicon carbide crystal includes the silicon carbide composite seed crystal described above. Description of the Drawings

[0050] Figure 1 It is a flow chart of the overall steps of the preparation method of the silicon carbide composite seed crystal provided by the present application;

[0051] Figure 2 It is a schematic structural diagram of the silicon carbide composite seed crystal provided by the present application;

[0052] Figure 3 It is a schematic diagram of the first microchannel and the second microchannel in a spiral mosquito coil pattern provided by the present application.

[0053] In the figure, 10 is the silicon carbide composite seed crystal; 11 is the silicon carbide seed crystal; 12 is the silicon carbide transition layer; 13 is the diamond layer. Detailed Embodiments

[0054] Example embodiments will now be described more fully with reference to the accompanying drawings. However, the example embodiments can be implemented in various forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this application will be more complete and comprehensive, and will fully convey the concept of the example embodiments to those skilled in the art. Like reference numerals in the figures denote like or similar structures, and thus their repeated description will be omitted.

[0055] The words expressing positions and directions described in this application are all illustrated by taking the accompanying drawings as examples, but can be changed according to needs, and all the changes made are included in the protection scope of this application.

[0056] In the first aspect of this embodiment, a method for preparing a silicon carbide composite seed crystal is provided. As shown in the accompanying drawings, it includes the following steps S1 to S3. Figure 1 As shown, it includes the following steps S1 - S3.

[0057] Step S1: Provide a silicon carbide seed crystal.

[0058] The silicon carbide material in the silicon carbide seed crystal can be of 3C, 4H, 6H or 15R crystal forms, etc. In this embodiment, 4H crystal form is preferably used.

[0059] The thickness of the silicon carbide seed crystal is 100 - 200 μm, for example, it can be 100 μm, 120 μm, 150 μm, 180 μm or 200 μm; the diameter of the silicon carbide seed crystal matches the diameter of the silicon carbide crystal to be grown, generally being 6 - 12 inches, for example, it can be 6 inches, 7 inches, 8 inches, 9 inches, 10 inches, 11 inches or 12 inches.

[0060] It should be noted that the thickness of the silicon carbide seed crystal is less than one - third of the thickness of the silicon carbide composite seed crystal.

[0061] By controlling the thickness of the silicon carbide seed crystal within the above - mentioned range, the comprehensive thermal conductivity of the prepared silicon carbide composite seed crystal can be more than 40% higher than that of the pure silicon carbide seed crystal, and the temperature gradient of the silicon carbide composite seed crystal in the vertical direction increases by 15 - 20% and the temperature gradient in the horizontal direction increases by 10%.

[0062] Furthermore, as a preferred embodiment of this application, before forming the silicon carbide transition layer, the preparation method further includes steps S11 - S14.

[0063] Step S11: Polish the surface of the silicon carbide seed crystal.

[0064] For example, a silicon carbide crystal of a suitable size is cut from a high-quality single-crystal silicon carbide material as a silicon carbide seed crystal, and the surface of the silicon carbide seed crystal is polished to make the surface roughness of its silicon surface less than a preset roughness, and the value of the preset roughness is 1-5 nm. Exemplarily, the surface roughness of the silicon surface of the silicon carbide seed crystal can be 0.5 nm, 1 nm, 2 nm, 3 nm or 4 nm.

[0065] Further, the silicon carbide seed crystal can be first polished with a diamond grinding fluid with high precision, and then the polished silicon carbide seed crystal can be subjected to chemical mechanical polishing.

[0066] Step S12: Pickle the polished silicon carbide seed crystal.

[0067] For example, pickle the silicon carbide seed crystal by soaking it in aqua regia (a mixture of nitric acid and hydrochloric acid) for 30 min to remove the contaminant particles on the surface of the silicon carbide seed crystal.

[0068] Step S13: Ultrasonically clean the pickled silicon carbide seed crystal.

[0069] For example, ultrasonically clean the silicon carbide seed crystal with an acetone solution for 10 min to penetrate into the surface microporous structure of the silicon carbide seed crystal to achieve dead-end cleaning. It can not only further remove the contaminant particles and polishing reagent residues on the surface of the silicon carbide seed crystal, but also form micro-scratches on the surface of the silicon carbide seed crystal to optimize its surface morphology, thereby increasing the nucleation density and bonding force with the subsequent silicon carbide transition layer, and making its nucleation density as high as 10 9 / cm 2 .

[0070] Step S14: Dry the ultrasonically cleaned silicon carbide seed crystal. For example, bake the silicon carbide seed crystal in an oven at 200 °C for 15 min to dry the silicon carbide seed crystal.

[0071] After the above steps, efficient decontamination of the silicon carbide seed crystal is achieved, ensuring the integrity and high cleanliness of its surface, reducing the defects caused by contaminants during the subsequent formation of the silicon carbide transition layer, making the number of particulate matters (0.3 μm scale) on the surface of the silicon carbide seed crystal less than 500-1000, and ensuring the uniformity and adhesion of the silicon carbide transition layer on the surface of the silicon carbide seed crystal.

[0072] Step S2: Form a silicon carbide transition layer on the silicon surface of the silicon carbide seed crystal, and make the carbon surface of the silicon carbide transition layer away from the silicon surface of the silicon carbide seed crystal to obtain a silicon carbide composite structure.

[0073] The crystal plane of the silicon carbide transition layer is mainly the (111) crystal plane; the thickness of the silicon carbide transition layer is 10-50 μm, for example, it can be 10 μm, 20 μm, 30 μm, 40 μm or 50 μm.

[0074] It should be noted that the thermal conductivity of the silicon carbide transition layer is greater than that of the silicon carbide seed crystal, and the crystal form of the silicon carbide transition layer is different from that of the silicon carbide seed crystal. For the silicon carbide transition layer, the silicon carbide material in the silicon carbide transition layer can be in the crystal form of 3C, 4H, 6H, 15R, etc. In this embodiment, the 3C crystal form is preferably used.

[0075] It should be further noted that during the formation of the silicon carbide transition layer on the silicon surface of the silicon carbide seed crystal, the silicon surface of the silicon carbide seed crystal and the silicon surface of the silicon carbide transition layer are combined by silicon atom diffusion. Since the silicon atoms of the silicon carbide seed crystal and the silicon atoms of the silicon carbide transition layer are combined by forming covalent bonds, there is no transition intermediate layer between them, making their combination tighter.

[0076] Furthermore, as a preferred embodiment of the present application, forming the silicon carbide transition layer on the silicon surface of the silicon carbide seed crystal includes steps S21a - step S22a.

[0077] Step S21a: Under the conditions of a temperature of 850 - 900 °C, a pressure of 20 - 30 Kpa, the flow rates of SiH4 and CH4 both being 2 - 20 sccm, and the flow rate of H2 being 200 - 500 sccm, use chemical vapor deposition to grow on the silicon surface of a silicon carbide seed crystal with a thickness of 100 - 200 μm for 10 - 20 h to prepare an initial silicon carbide transition layer with a thickness of 50 - 200 μm.

[0078] Exemplarily, the thickness of the initial silicon carbide transition layer can be 50 μm, 70 μm, 90 μm, 110 μm, 130 μm, 150 μm, 170 μm, or 200 μm. The growth time of the initial silicon carbide transition layer can be 10 h, 12 h, 15 h, 18 h, or 20 h. The growth temperature of the initial silicon carbide transition layer can be 850 °C, 860 °C, 870 °C, 880 °C, 890 °C, or 900 °C; the pressure can be 20 Kpa, 21 Kpa, 22 Kpa, 23 Kpa, 24 Kpa, 25 Kpa, 26 Kpa, 27 Kpa, 28 Kpa, 29 Kpa, or 30 Kpa; the flow rates of SiH4 and CH4 can both be 2 sccm, 4 sccm, 6 sccm, 8 sccm, 10 sccm, 12 sccm, 14 sccm, 16 sccm, 18 sccm, or 20 sccm; the flow rate of H2 can be 200 sccm, 250 sccm, 300 sccm, 350 sccm, 400 sccm, 450 sccm, or 500 sccm; the purities of SiH4, CH4, and H2 can be 99.9999%.

[0079] The inventors' research found that during the process of growing the initial silicon carbide transition layer by chemical vapor deposition, if the temperature is lower than 850 °C, the growth is very slow; if the temperature is higher than 900 °C, although the growth rate is high, the quality of the initially grown silicon carbide transition layer is very poor. If the gas pressure is lower than 20 KPa, the plasma power density is low and the growth rate is slow; if the gas pressure is higher than 30 Kpa, the plasma density is high, and although the growth rate is fast, amorphous carbides are likely to appear.

[0080] SiH4 and CH4 are the raw material gases for growing silicon carbide by chemical vapor deposition. If the concentration is too low (flow rate less than 2 sccm), the growth rate is very slow; if the concentration is too high (flow rate greater than 20 sccm), although the growth rate is fast, the quality of the grown silicon carbide material is very poor. Hydrogen is the carrier gas for transporting the raw material gas and can etch amorphous silicon carbide in a timely manner. If the concentration is too low (flow rate less than 200 sccm), the growth rate is very slow; if the concentration is too high (flow rate greater than 500 sccm), hydrogen will etch away other amorphous carbide materials.

[0081] If the growth time of the initial silicon carbide transition layer is too short (growth time less than 10 h), an initial silicon carbide transition layer of a certain thickness cannot be produced; if the growth time is too long (growth time greater than 20 h), the quality of the initial silicon carbide transition layer is not high, which is not conducive to the preparation of the silicon carbide composite seed crystal.

[0082] Step S22a: Grind and polish the carbon surface of the initial silicon carbide transition layer to obtain a silicon carbide transition layer with a thickness of 10 - 50 μm and a surface roughness less than the first preset roughness.

[0083] The value range of the first preset roughness is 1 - 5 nm. For example, the surface roughness of the carbon surface of the silicon carbide transition layer can be 0.5 nm, 1 nm, 2 nm, 3 nm, or 4 nm.

[0084] Since the thermal conductivity of the silicon carbide transition layer of the 3C polytype silicon carbide material is (500 W / (m·K)), which is higher than the thermal conductivity of the silicon carbide seed crystal of the 4H polytype silicon carbide material (490 W / (m·K)), the silicon carbide transition layer with high thermal conductivity can quickly conduct the heat adsorbed by silicon and carbon atoms during the process of growing silicon carbide crystals on the surface of the silicon carbide seed crystal with low thermal conductivity, thereby establishing a larger temperature gradient in the vertical and horizontal directions in the silicon carbide composite seed crystal; at the same time, the silicon carbide transition layer can provide the silicon atoms required for epitaxial growth for the silicon carbide seed crystal and the carbon atoms required for epitaxial growth of the diamond layer respectively, enabling the silicon carbide seed crystal and the diamond layer to achieve a good epitaxial growth interface.

[0085] As another preferred embodiment of the present application, forming a silicon carbide transition layer on the silicon surface of the silicon carbide seed crystal includes step S21b - step S22b.

[0086] Step S21b: Under the conditions of a temperature of 1900 - 2100 °C and a pressure of 0.001 - 0.03 Pa, hetero - bond the silicon surface of a silicon carbide seed crystal with a thickness of 100 - 200 μm to the silicon surface of the initial silicon carbide transition layer to obtain a first hetero - bonded structure.

[0087] The surface roughness of the silicon surface of the initial silicon carbide transition layer is less than a second preset roughness, and the value range of the second preset roughness is 1 - 5 nm. Exemplarily, the surface roughness of the silicon surface of the initial silicon carbide transition layer can be 0.5 nm, 1 nm, 2 nm, 3 nm or 4 nm.

[0088] Exemplarily, the temperature can be 1900 °C, 1950 °C, 2000 °C, 2050 °C or 2100 °C; the pressure can be 0.001 Pa, 0.005 Pa, 0.01 Pa, 0.015 Pa, 0.02 Pa, 0.025 Pa or 0.03 Pa.

[0089] The inventors have conducted in - depth research and found that during the hetero - bonding process, if the temperature is lower than 1900 °C, the bonding is not firm and defects such as voids and micro - cracks are likely to occur at the interface; if the temperature is higher than 2100 °C, the power consumption is serious and it has little effect on improving the bonding force. If the pressure is higher than 0.03 Pa, the vacuum degree is not high and it is easy to introduce impurity gases such as air, which affects the bonding effect; if the pressure is lower than 0.001 Pa, the requirements for the system equipment are very high and the cost is large. Therefore, the temperature and pressure of the hetero - bonding need to be controlled within the above - mentioned ranges.

[0090] Under the above conditions for hetero - bonding (the bonding surfaces are all silicon surfaces), the lattice mismatch degree between the initial silicon carbide transition layer and the silicon carbide seed crystal is small, and the solid - solid interface energy is very low. It is easy to achieve silicon carbide bonding without an intermediate layer, which can not only promote the formation of chemical bonds between the two, reduce the interface defect density, but also make their surfaces in close contact, reducing micropores and gaps, thereby improving the density and mechanical strength of the first hetero - bonded structure.

[0091] Furthermore, it can also reduce the interfacial residual stress caused by the thermal expansion difference between the initial silicon carbide transition layer of the 3C polytype silicon carbide material and the silicon carbide seed crystal of the 4H polytype silicon carbide material, preventing the first hetero - bonded structure from cracking. In addition, under these conditions for hetero - bonding, the interfacial thermal resistance is low, and the silicon carbide transition layer with high thermal conductivity can quickly conduct the heat accumulated by the silicon carbide seed crystal with low thermal conductivity, thereby establishing a larger temperature gradient in the vertical and horizontal directions in the silicon carbide composite seed crystal.

[0092] Step S22b: After the heterogeneous bonding is completed, the first heterogeneous bonding structure is annealed for 20 - 40 h under the conditions that the annealing temperature is 1800 - 1900 °C and the annealing atmosphere is argon or nitrogen, so that the initial silicon carbide transition layer is transformed into a silicon carbide transition layer.

[0093] The thickness of the silicon carbide transition layer is 10 - 50 μm, and can be, for example, 10 μm, 20 μm, 30 μm, 40 μm or 50 μm. The annealing temperature can be 1800 °C, 1820 °C, 1850 °C, 1880 °C or 1900 °C; the annealing time can be 20 h, 22 h, 25 h, 28 h, 30 h, 32 h, 35 h, 38 h or 40 h.

[0094] The inventors' research found that if the annealing temperature exceeds the above temperature range and is lower than 1800 °C, the effect of removing thermal stress will be poor, and the thermal stress generated by bonding cannot be effectively removed. When the annealing temperature is 1900 °C, the internal thermal stress can be effectively removed. If the temperature continues to rise, the power cost will be high and it will not be of great significance; correspondingly, the same is true for the annealing time. Therefore, the temperature and time of the annealing treatment need to be controlled within the above ranges.

[0095] By annealing the first heterogeneous bonding structure under the above conditions, not only can the internal thermal stress generated during the bonding process be reduced, but also the physical diffusion of silicon atoms can be promoted at high temperature, reducing the interfacial thermal resistance.

[0096] Further, as a preferred embodiment of the present application, before forming the diamond layer, the above preparation method further includes step S23.

[0097] Step S23: Form a plurality of first microchannels in a convex or grooved shape on the carbon surface of the silicon carbide transition layer.

[0098] As a preferred embodiment of step S23, step S23 includes: forming a plurality of first microchannels in a convex or grooved shape on the carbon surface of the silicon carbide transition layer by laser etching under the conditions that the pulse width is 500 ps - 1 ns, the laser power is 10 - 15 W, and the laser repetition frequency is 20 - 100 kHz.

[0099] Exemplarily, the laser wavelength is 1064 nm or 532 nm or 355 nm; the pulse width is 500 ps, 600 ps, 700 ps, 800 ps, 9,00 ps or 1 ns; the laser power is 10 W, 11 W, 12 W, 13 W, 14 W or 15 W; the laser repetition frequency is 20 kHz, 30 kHz, 40 kHz, 50 kHz, 60 kHz, 70 kHz, 80 kHz, 90 kHz or 100 kHz.

[0100] As another preferred embodiment of step S23, step S23 includes: under the conditions that the etching temperature exceeds 1800 °C and the etching gas is CF4, O2 or Ar, a plurality of first microchannels in a convex or groove shape are formed on the carbon surface of the silicon carbide transition layer by plasma etching.

[0101] Exemplarily, the etching temperature can be 1800 °C, 1850 °C, 1900 °C, 2000 °C or 2100 °C.

[0102] Preferably, referring to the attached Figure 3 As shown, all the first microchannels are connected end to end in sequence and are distributed in a spiral shape (mosquito coil pattern). The etching width of the first microchannels is 5 - 10 μm, for example, it can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm; the etching depth of the first microchannels is 30 - 50 μm, for example, it can be 30 μm, 35 μm, 40 μm, 45 μm or 50 μm; the lateral spacing of the first microchannels is 5 - 10 mm, for example, it can be 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or 10 mm.

[0103] By setting the first microchannels, the contact surface area between the silicon carbide transition layer and the diamond layer can be increased, thereby enhancing the heat transfer ability of the silicon carbide transition layer and the diamond layer to accumulate heat during the growth process, which helps to establish a larger temperature gradient in the vertical and horizontal directions for the silicon carbide composite seed crystal.

[0104] Step S3: A diamond layer is formed on the carbon surface of the silicon carbide transition layer to obtain a silicon carbide composite seed crystal.

[0105] The thermal conductivity of the silicon carbide transition layer is less than that of the diamond layer; the thickness of the diamond layer is 300 - 500 μm, for example, it can be 300 μm, 350 μm, 400 μm, 450 μm or 500 μm.

[0106] It should be further noted that the thickness of the diamond layer is less than or equal to two-thirds of the thickness of the silicon carbide composite seed crystal, and the thickness of the diamond layer is greater than or equal to one-half of the thickness of the silicon carbide composite seed crystal.

[0107] By controlling the thickness of the diamond layer within the above range, the comprehensive thermal conductivity of the prepared silicon carbide composite seed crystal is more than 40% higher than that of the pure silicon carbide seed crystal. The temperature gradient of the silicon carbide composite seed crystal in the vertical direction can be increased by 15 - 20%, and the temperature gradient in the horizontal direction is increased by 10%.

[0108] For the diamond layer, the present application has no special limitation, and any suitable diamond layer in the art can be used to implement the technical solution of the present application. In some embodiments of the present application, the diamond layer used can be selected from single-crystal diamond or polycrystalline diamond, and single-crystal diamond is preferably used.

[0109] It should be further noted that during the process of forming a diamond layer on the carbon surface of the silicon carbide transition layer of the silicon carbide composite structure, the carbon surface of the silicon carbide transition layer and the surface of the diamond layer are combined by carbon atom diffusion. Since the carbon atoms of the diamond layer and the carbon atoms of the silicon carbide transition layer are combined in the form of covalent bonds, there is no transitional intermediate layer between the two, making their combination closer.

[0110] Furthermore, as a preferred embodiment of the present application, forming a diamond layer on the carbon surface of the silicon carbide transition layer includes steps S31a - S32a.

[0111] Step S31a: Growing an initial diamond layer on the carbon surface of the silicon carbide transition layer by chemical vapor deposition.

[0112] The thickness of the initial diamond layer is 500 - 900 μm. Exemplarily, the thickness of the initial diamond layer can be 500 μm, 550 μm, 600 μm, 650 μm, 700 μm, 750 μm, 800 μm, 850 μm or 900 μm.

[0113] As a preferred embodiment of step S31a, under the conditions of a temperature of 850 - 900 °C, a pressure of 20 - 30 Kpa, a flow rate of CH4 of 2 - 20 sccm, a flow rate of H2 of 200 - 500 sccm, and a flow rate of O2 of 2 - 20 sccm, an initial diamond layer with a thickness of 500 - 900 μm is prepared by growing on the carbon surface of the silicon carbide transition layer using MPCVD (Microwave Plasma Chemical Vapor Deposition) for 60 - 90 h.

[0114] Exemplarily, the temperature can be 850 °C, 860 °C, 870 °C, 880 °C, 890 °C or 900 °C; the air pressure can be 20 Kpa, 21 Kpa, 22 Kpa, 23 Kpa, 24 Kpa, 25 Kpa, 26 Kpa, 27 Kpa, 28 Kpa, 29 Kpa or 30 Kpa; the flow rate of CH4 can be 2 sccm, 4 sccm, 6 sccm, 8 sccm, 10 sccm, 12 sccm, 14 sccm, 16 sccm, 18 sccm or 20 sccm; the flow rate of H2 can be 200 sccm, 250 sccm, 300 sccm, 350 sccm, 400 sccm, 450 sccm or 500 sccm; the flow rate of O2 can be 2 sccm, 4 sccm, 6 sccm, 8 sccm, 10 sccm, 12 sccm, 14 sccm, 16 sccm, 18 sccm or 20 sccm; the growth time can be 60 h, 65 h, 70 h, 75 h, 80 h, 85 h or 90 h.

[0115] The inventors' research found that during the process of growing the initial diamond layer by MPCVD, if the temperature is lower than 850 °C, the growth is very slow; if the temperature is higher than 900 °C, although the growth rate is high, the quality of the grown initial diamond layer is very poor. If the air pressure is lower than 20 KPa, the plasma power density is low and the growth rate is slow; if the air pressure is higher than 30 Kpa, the plasma density is high, and although the growth rate is fast, non-diamond crystal forms such as graphite phase or amorphous carbon substances are likely to appear.

[0116] CH4 is the source gas for growing the initial diamond layer by MPCVD, which can increase the carbon source required for the epitaxial growth of the initial diamond layer; if the concentration of CH4 is too low (flow rate less than 2 sccm), the growth rate is very slow; if the concentration of CH4 is too high (flow rate greater than 20 sccm), although the growth rate is fast, the quality of the grown initial diamond layer is very poor. H2 is the carrier gas for transporting the source gas. It can not only etch non-diamond crystal substances in a timely manner but also etch the grown diamond, which is beneficial to improving the deposition quality of the initial diamond layer and enhancing the packing density of the initial diamond layer; if the concentration of H2 is too low (flow rate less than 200 sccm), the growth rate is very slow; if the concentration of H2 is too high (flow rate greater than 500 sccm); hydrogen will not only etch away non-diamond crystal substances but also etch the grown diamond. O2 can increase the plasma power density, etch non-diamond phases (such as graphite phase or amorphous carbon, etc.), and improve the growth rate and quality of the initial diamond layer.

[0117] If the growth time of the initial diamond layer is too short (less than 60 h), it is impossible to produce an initial diamond layer with a certain thickness; if the growth time is too long (more than 90 h), the quality of the initial diamond layer is not high, which is not conducive to the preparation of the initial diamond layer.

[0118] As another preferred embodiment of step S31a, under the conditions of a temperature of 2200 - 2300 °C, a pressure of 20 - 30 Kpa, a flow rate of CH4 of 2 - 20 sccm, and a flow rate of H2 of 200 - 500 sccm, HFCVD (Hot Filament Chemical Vapor Deposition) is used to grow on the carbon surface of the silicon carbide transition layer for 60 - 90 h to prepare an initial diamond layer with a thickness of 500 - 900 μm.

[0119] Exemplarily, the temperature can be 2200 °C, 2220 °C, 2240 °C, 2260 °C, 2280 °C or 2300 °C; the pressure can be 20 Kpa, 21 Kpa, 22 Kpa, 23 Kpa, 24 Kpa, 25 Kpa, 26 Kpa, 27 Kpa, 28 Kpa, 29 Kpa or 30 Kpa; the flow rate of CH4 can be 2 sccm, 4 sccm, 6 sccm, 8 sccm, 10 sccm, 12 sccm, 14 sccm, 16 sccm, 18 sccm or 20 sccm; the flow rate of H2 can be 200 sccm, 250 sccm, 300 sccm, 350 sccm, 400 sccm, 450 sccm or 500 sccm; the growth time can be 60 h, 65 h, 70 h, 75 h, 80 h, 85 h or 90 h.

[0120] The inventors' research found that during the growth of the initial diamond layer by HFCVD, if the temperature is lower than 2200 °C, the growth is very slow; if the temperature is higher than 2300 °C, although the growth rate is high, the quality of the grown initial diamond layer is very poor. If the pressure is lower than 20 KPa, the plasma power density is low and the growth rate is slow; if the pressure is higher than 30 Kpa, the plasma density is high, although the growth rate is fast, but it is easy to appear non-diamond crystalline states such as graphite phase or amorphous carbon substances.

[0121] CH4 is the source gas for growing the initial diamond layer by HFCVD, which can increase the carbon source required for the epitaxial growth of the initial diamond layer. If the concentration of CH4 is too low (flow rate less than 2 sccm), the growth rate is very slow. If the concentration of CH4 is too high (flow rate greater than 20 sccm), although the growth rate is fast, the quality of the grown initial diamond layer is very poor. H2 is the carrier gas for transporting the source gas. It can not only etch non-diamond crystalline substances in a timely manner, but also etch the grown diamond, which is beneficial to improving the deposition quality of the initial diamond layer and enhancing the packing density of the initial diamond layer. If the concentration of H2 is too low (flow rate less than 200 sccm), the growth rate is very slow. If the concentration of H2 is too high (flow rate greater than 500 sccm), hydrogen will not only etch away non-diamond crystalline substances, but also etch the grown diamond.

[0122] If the growth time of the initial diamond layer is too short (less than 60 h), it is impossible to produce an initial diamond layer with a certain thickness. If the growth time is too long (greater than 90 h), the quality of the initial diamond layer is not high, which is not conducive to the preparation of the initial diamond layer.

[0123] By HFCVD, a polycrystalline diamond material or a single-crystalline diamond material with a certain thickness can be grown on the silicon carbide composite structure of the silicon carbide seed crystal of 4H polytype silicon carbide material / the silicon carbide transition layer of 3C polytype silicon carbide material. As a high-thermal-conductivity heat-conducting material, the diamond material can establish a large temperature gradient for the silicon carbide composite seed crystal during the growth of silicon carbide crystals, which helps to grow silicon carbide crystals with a thicker thickness and a larger diameter on the silicon carbide composite seed crystal.

[0124] As another preferred embodiment of step S31a, under the conditions of a temperature of 850 - 900 °C, a pressure of 20 - 30 Kpa, a CH4 flow rate of 2 - 20 sccm, and an H2 flow rate of 200 - 500 sccm, DCPCVD (Direct Current Plasma Chemical Vapor Deposition) is used to grow on the carbon surface of the silicon carbide transition layer for 5 - 10 h to prepare an initial diamond layer with a thickness of 500 - 900 μm.

[0125] Exemplarily, the temperature can be 850 °C, 860 °C, 870 °C, 880 °C, 890 °C or 900 °C; the air pressure can be 20 Kpa, 21 Kpa, 22 Kpa, 23 Kpa, 24 Kpa, 25 Kpa, 26 Kpa, 27 Kpa, 28 Kpa, 29 Kpa or 30 Kpa; the flow rate of CH4 can be 2 sccm, 4 sccm, 6 sccm, 8 sccm, 10 sccm, 12 sccm, 14 sccm, 16 sccm, 18 sccm or 20 sccm; the flow rate of H2 can be 200 sccm, 250 sccm, 300 sccm, 350 sccm, 400 sccm, 450 sccm or 500 sccm; the growth time can be 5 h, 6 h, 7 h, 8 h, 9 h or 10 h.

[0126] The inventors' research found that during the process of growing the initial diamond layer by DCPCVD, if the temperature is lower than 850 °C, the growth is very slow; if the temperature is higher than 900 °C, although the growth rate is high, the quality of the grown initial diamond layer is very poor. If the air pressure is lower than 20 KPa, the plasma power density is low and the growth rate is slow; if the air pressure is higher than 30 Kpa, the plasma density is high, although the growth rate is fast, it is easy to appear non-diamond crystalline states such as graphite phase or amorphous carbon substances.

[0127] CH4 is the source gas for growing the initial diamond layer by DCPCVD, which can increase the carbon source required for the epitaxial growth of the initial diamond layer. If the concentration of CH4 is too low (flow rate less than 2 sccm), the growth rate is very slow; if the concentration of CH4 is too high (flow rate greater than 20 sccm), although the growth rate is fast, the quality of the grown initial diamond layer is very poor. H2 is the carrier gas for transporting the source gas. It can not only etch non-diamond crystalline substances in a timely manner, but also etch the grown diamond, which is beneficial to improving the deposition quality of the initial diamond layer and enhancing the packing density of the initial diamond layer; if the concentration of H2 is too low (flow rate less than 200 sccm), the growth rate is very slow; if the concentration of H2 is too high (flow rate greater than 500 sccm); hydrogen will not only etch away non-diamond crystalline substances, but also etch the grown diamond.

[0128] If the growth time of the initial diamond layer is too short (growth time less than 5 h), it is impossible to produce an initial diamond layer with a certain thickness; if the growth time is too long (growth time greater than 10 h), the quality of the initial diamond layer is not high, which is not conducive to the preparation of the initial diamond layer.

[0129] By using DCPCVD, a certain thickness of polycrystalline diamond material or single-crystalline diamond material can be grown on the silicon carbide composite structure of the silicon carbide seed crystal of 4H polytype silicon carbide material / the silicon carbide transition layer of 3C polytype silicon carbide material. As a heat-conducting material with high thermal conductivity, the diamond material can establish a large temperature gradient for the silicon carbide composite seed crystal during the growth of silicon carbide crystals, which helps to grow silicon carbide crystals with a thicker thickness and a larger diameter on the silicon carbide composite seed crystal.

[0130] Step S32a: Grind and polish the initial diamond layer to obtain a diamond layer with a thickness of 300 - 500 μm and a surface roughness less than the third preset roughness.

[0131] The value range of the third preset roughness is 1 - 5 nm. Exemplarily, the surface roughness of the diamond layer can be 0.5 nm, 1 nm, 2 nm, 3 nm or 4 nm.

[0132] Furthermore, the silicon carbide composite seed crystal can be first subjected to high-precision grinding with a diamond grinding fluid, and then the ground silicon carbide composite seed crystal can be subjected to chemical mechanical polishing to make the surface roughness of the diamond layer less than 1 - 5 nm. Post-treatment of the silicon carbide composite seed crystal includes Step S33a - Step S35a.

[0133] Step S33a: Pickle the polished silicon carbide composite seed crystal.

[0134] For example, pickle the silicon carbide composite seed crystal by soaking it in aqua regia (a mixture of nitric acid and hydrochloric acid) for 30 min to remove the contaminant particles on the surface of the silicon carbide composite seed crystal.

[0135] Step S34a: Ultrasonically clean the pickled silicon carbide composite seed crystal.

[0136] For example, ultrasonically clean the silicon carbide composite seed crystal with an acetone solution for 10 min to penetrate into the surface micropore structure of the silicon carbide composite seed crystal to achieve dead-angle-free cleaning. This can not only further remove the contaminant particles and polishing reagent residues on the surface of the silicon carbide composite seed crystal, but also form micro-scratches on the surface of the silicon carbide composite seed crystal to optimize its surface morphology, thereby increasing the nucleation density and bonding force with the subsequently grown silicon carbide crystal, so that the nucleation density can be as high as 109 / cm2.

[0137] Step S35a: Dry the ultrasonically cleaned silicon carbide composite seed crystal.

[0138] For example, bake the silicon carbide composite seed crystal in an oven at 200 °C for 15 min to dry the silicon carbide composite seed crystal.

[0139] After the above steps, the efficient decontamination of the silicon carbide composite seed crystal is achieved, ensuring the integrity and high cleanliness of its surface, reducing the defects caused by contaminants during the subsequent formation of silicon carbide crystals, so that the number of particulate matters (0.3μm scale) on the surface of the silicon carbide composite seed crystal is less than 500 - 1000, ensuring the uniformity and adhesion of the silicon carbide crystal on the surface of the silicon carbide composite seed crystal, and enabling it to be used in various silicon carbide crystal growth methods.

[0140] In the above solution, a silicon carbide transition layer and a diamond layer are sequentially grown on the silicon carbide seed crystal by chemical vapor deposition. The prepared silicon carbide composite seed crystal has higher quality, reduces the dependence of the pure silicon carbide seed crystal in the prior art on high-quality silicon carbide single crystals, and can be used to grow silicon carbide crystals with higher thickness and larger diameter.

[0141] As another preferred embodiment of the present application, forming a diamond layer on the carbon surface of the silicon carbide transition layer includes step S31b - step S32b.

[0142] Step S31b: Under the conditions of a temperature of 1900 - 2100°C and a pressure of 0.001 - 0.03 Pa, the carbon surface of the silicon carbide transition layer is heterogeneously bonded to the surface of the initial diamond layer to obtain a second heterogeneously bonded structure.

[0143] The surface roughness of the initial diamond layer is less than the fourth preset roughness, and the value range of the fourth preset roughness is 1 - 5 nm. The surface roughness of the initial diamond layer can be 0.5 nm, 1 nm, 2 nm, 3 nm, or 4 nm.

[0144] Exemplarily, the temperature can be 1900°C, 1950°C, 2000°C, 2050°C, or 2100°C; the pressure can be 0.001 Pa, 0.005 Pa, 0.01 Pa, 0.015 Pa, 0.02 Pa, 0.025 Pa, or 0.03 Pa.

[0145] The inventors have deeply studied and found that during the heterogeneous bonding process, if the temperature is lower than 1900°C, the bonding is not firm, and defects such as voids and microcracks are likely to occur at the interface; if the temperature is higher than 2100°C, the power consumption is serious, and it has little effect on improving the bonding force. If the pressure is higher than 0.03 Pa, the vacuum degree is not high, and impurity gases such as air are likely to be introduced, affecting the bonding effect; if the pressure is lower than 0.001 Pa, the requirements for the system equipment are very high, and the cost is large. Therefore, the temperature and pressure of the heterogeneous bonding need to be controlled within the above ranges.

[0146] Under the above conditions, heterogeneous bonding (the bonding surfaces are both carbon surfaces) is carried out. The lattice mismatch between the silicon carbide transition layer and the initial diamond layer is small, and the solid-solid interface energy is very low. It is easy to achieve carbon surface bonding without an intermediate layer, which can not only promote the formation of chemical bonds between the two, reduce the interface defect density, but also make their surfaces in close contact, reduce micropores and gaps, and improve the density and mechanical strength of the second heterogeneous bonding structure.

[0147] Furthermore, it can also reduce the interfacial residual stress caused by the thermal expansion difference between the silicon carbide transition layer and the initial diamond layer, and prevent the second heterogeneous bonding structure from cracking. In addition, under these conditions, the heterogeneous bonding has a low interfacial thermal resistance, and the diamond with high thermal conductivity can quickly conduct the heat accumulated in the silicon carbide transition layer, thereby establishing a larger temperature gradient in the vertical and horizontal directions in the silicon carbide composite seed crystal.

[0148] Furthermore, the initial diamond layer can be first subjected to high-precision grinding with diamond grinding fluid, and then the ground initial diamond layer is subjected to chemical mechanical polishing to make the surface roughness of the initial diamond layer less than 1-5 nm. The post-treatment of the initial diamond layer includes step S27b-step S29b.

[0149] Step S27b: Pickle the polished initial diamond layer.

[0150] For example, soak the initial diamond layer in aqua regia (a mixture of nitric acid and hydrochloric acid) for 30 min to remove the contaminant particles on the surface of the initial diamond layer.

[0151] Step S28b: Ultrasonically clean the pickled initial diamond layer.

[0152] For example, ultrasonically clean the initial diamond layer with acetone solution for 10 min to penetrate into the surface micropore structure of the initial diamond layer to achieve dead-angle-free cleaning. It can not only further remove the contaminant particles and polishing reagent residues on the surface of the initial diamond layer, but also form micro-scratches on the surface of the initial diamond layer to optimize its surface morphology, thereby improving the nucleation density and bonding force with the subsequent bonded silicon carbide transition layer, so that the nucleation density can be as high as 10 9 / cm 2 。

[0153] Step S29b: Dry the ultrasonically cleaned initial diamond layer.

[0154] For example, bake the initial diamond layer in an oven at 200 °C for 15 min to dry the initial diamond layer.

[0155] After the above steps, efficient decontamination of the initial diamond layer is achieved, ensuring the integrity and high cleanliness of its surface, reducing defects caused by contaminants during the subsequent bonding process, so that the number of particles (0.3 μm scale) on the surface of the initial diamond layer is less than 500 - 1000, ensuring the uniformity and adhesion of the bonding between the carbon surface of the silicon carbide transition layer and the surface of the initial diamond layer.

[0156] As a preferred embodiment of the present application, before the heterogeneous bonding between the carbon surface of the silicon carbide transition layer and the initial diamond layer, the preparation method further includes step S30b: forming a plurality of second microchannels in a convex or groove shape on the surface of the initial diamond layer.

[0157] As a preferred embodiment of step S30b, step S30b includes: under the conditions of a pulse width of 500 ps - 1 ns, a laser power of 10 - 15 W, and a laser repetition frequency of 20 - 100 kHz, using laser etching to form a plurality of second microchannels in a convex or groove shape on the surface of the initial diamond layer.

[0158] Exemplarily, the laser wavelength is 1064 nm or 532 nm or 355 nm; the pulse width is 500 ps, 600 ps, 700 ps, 800 ps, 900 ps or 1 ns; the laser power is 10 W, 11 W, 12 W, 13 W, 14 W or 15 W; the laser repetition frequency is 20 kHz, 30 kHz, 40 kHz, 50 kHz, 60 kHz, 70 kHz, 80 kHz, 90 kHz or 100 kHz.

[0159] As another preferred embodiment of step S30b, step S30b includes: under the conditions of an etching temperature exceeding 1800 °C and an etching gas being CF4, O2 or Ar, using plasma etching to form a plurality of second microchannels in a convex or groove shape on the surface of the initial diamond layer.

[0160] Preferably, referring to the attached Figure 3 As shown, all the second microchannels are connected end to end in sequence and are distributed in a spiral shape (mosquito coil pattern). The etching width of the second microchannels is 5 - 10 μm, for example, it can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm; the etching depth of the second microchannels is 30 - 50 μm, for example, it can be 30 μm, 35 μm, 40 μm, 45 μm or 50 μm; the lateral spacing of the second microchannels is 5 - 10 mm, for example, it can be 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or 10 mm.

[0161] Exemplarily, the etching temperature can be 1800 °C, 1850 °C, 1900 °C, 2000 °C or 2100 °C.

[0162] By setting the second microchannel, the contact surface area between the silicon carbide transition layer and the diamond layer can be increased, thereby enhancing the heat transfer ability of the silicon carbide transition layer and the diamond layer to accumulate heat during the growth process, which helps to establish a larger temperature gradient in the vertical and horizontal directions for the silicon carbide composite seed crystal.

[0163] It should be noted that the protruding first microchannel corresponds to the groove-shaped second microchannel so that the protruding first microchannel can be embedded in the groove-shaped second microchannel; the protruding second microchannel corresponds to the groove-shaped first microchannel so that the protruding second microchannel can be embedded in the groove-shaped first microchannel.

[0164] During the bonding process, the corresponding fitting of the first microchannel and the second microchannel can further increase the contact surface area between the initial diamond layer and the silicon carbide transition layer, thereby enhancing the heat transfer ability of the diamond layer and the silicon carbide transition layer to accumulate heat during the growth process, which helps to establish a larger temperature gradient in the vertical and horizontal directions for the silicon carbide composite seed crystal.

[0165] Step S32b: After the hetero-bonding is completed, under the conditions that the annealing temperature is 1800 - 1900 °C and the annealing atmosphere is argon or nitrogen, the second hetero-bonded structure is annealed for 20 - 40 h so that the initial diamond layer is transformed into a diamond layer with a thickness of 300 - 500 μm.

[0166] The function of the annealing treatment is to eliminate the lattice deformation caused by the diffusion movement of carbon atoms in the silicon carbide material and the diamond material, and reduce or eliminate the thermal stress in the bonding interface.

[0167] Exemplarily, the annealing temperature can be 1800 °C, 1820 °C, 1850 °C, 1880 °C or 1900 °C; the annealing time can be 20 h, 22 h, 25 h, 28 h, 30 h, 32 h, 35 h, 38 h or 40 h.

[0168] The inventors have found through research that if the temperature exceeds the above range and the annealing temperature is lower than 1800 °C, the effect of removing thermal stress will be poor, and the thermal stress generated by bonding cannot be effectively removed. When the annealing temperature is 1900 °C, the internal thermal stress can be effectively removed. If the temperature continues to rise, the power cost will be high and it will not be of much significance; correspondingly, the same is true for the annealing time. Therefore, the temperature and time of the annealing treatment need to be controlled within the above range.

[0169] By annealing the second hetero-bonded structure under the above conditions, not only can the internal thermal stress generated during the bonding process be reduced, but also the physical diffusion of carbon atoms can be promoted at high temperature, and the interface thermal resistance can be reduced.

[0170] In summary, in the present application, a silicon carbide transition layer can be epitaxially grown on the silicon surface of a silicon carbide seed crystal by chemical vapor deposition, and a diamond layer can be grown on the carbon surface of the silicon carbide transition layer by chemical vapor deposition, thereby realizing the preparation of a silicon carbide composite seed crystal.

[0171] In the present application, a silicon carbide transition layer can also be grown on the silicon surface of a silicon carbide seed crystal by hetero-bonding, and a diamond layer can be grown on the carbon surface of the silicon carbide transition layer by chemical vapor deposition, thereby realizing the preparation of a silicon carbide composite seed crystal.

[0172] In the present application, the silicon surface of a silicon carbide seed crystal can also be combined with the silicon surface of a silicon carbide transition layer by hetero-bonding, and the carbon surface of the silicon carbide transition layer can be combined with the surface of a diamond layer by hetero-bonding, thereby realizing the preparation of a silicon carbide composite seed crystal.

[0173] In the present application, a silicon carbide transition layer can also be epitaxially grown on the silicon surface of a silicon carbide seed crystal by chemical vapor deposition, and the carbon surface of the silicon carbide transition layer can be combined with the surface of a diamond layer by hetero-bonding, thereby realizing the preparation of a silicon carbide composite seed crystal.

[0174] In the present application, a silicon carbide transition layer can also be formed on the silicon surface of a silicon carbide seed crystal, and a first microchannel can be etched on the carbon surface of the silicon carbide transition layer, so that the carbon surface of the silicon carbide transition layer with the first microchannel is combined with the surface of a diamond layer, thereby realizing the preparation of a silicon carbide composite seed crystal.

[0175] In the present application, a silicon carbide transition layer can also be formed on the silicon surface of a silicon carbide seed crystal, and a second microchannel can be etched on the surface of a diamond layer, so that the surface of the diamond layer with the second microchannel is combined with the carbon surface of the silicon carbide transition layer, thereby realizing the preparation of a silicon carbide composite seed crystal.

[0176] In the present application, a silicon carbide transition layer can also be formed on the silicon surface of a silicon carbide seed crystal, a first microchannel can be etched on the carbon surface of the silicon carbide transition layer, and a second microchannel can be etched on the surface of a diamond layer, so that the carbon surface of the silicon carbide transition layer with the first microchannel is combined with the surface of the diamond layer with the second microchannel, thereby realizing the preparation of a silicon carbide composite seed crystal.

[0177] Furthermore, the bonding in the present application is direct bonding under normal pressure without an intermediate bonding layer; the bonding in the present application is permanent bonding. After the growth of a silicon carbide crystal is completed on the silicon carbide composite seed crystal, the diamond layer can be cut out by using a laser cutting technique, and then the diamond layer can be ground and polished for subsequent repeated use of the diamond material to prepare a silicon carbide composite seed crystal.

[0178] By utilizing the extremely high thermal conductivity of diamond materials (2000 - 2200 W / (m·K)), the heat accumulated in the silicon carbide seed crystal can be rapidly conducted out in the vertical direction, thereby reducing the temperature of the silicon carbide seed crystal. Since during the growth process of a thick crystal, the required temperature gradient in the vertical direction is determined by the temperature difference between the diamond layer at the lower part of the growth cavity and the temperature of the silicon carbide seed crystal at the upper part of the growth cavity, and the temperature of the silicon carbide seed crystal is lower than that of the diamond layer. The greater the temperature difference between the two, the greater the temperature gradient in the vertical direction within a certain spacing range. This temperature gradient in the vertical direction is the crystallization driving force required for the growth of high-thickness silicon carbide crystals. The greater the temperature gradient in the vertical direction, the greater the vertical crystallization driving force, and the faster the crystal grows in the vertical direction. A high-thickness silicon carbide crystal can be grown within the same growth period.

[0179] Since during the growth process of a large-diameter crystal, the required temperature gradient in the horizontal direction is determined by the temperature difference between the temperature of the silicon carbide seed crystal at the upper part of the growth cavity and the temperature of the inner wall of the growth cavity. The temperature of the inner wall is higher than that of the silicon carbide seed crystal. The greater the temperature difference between the two, the greater the temperature gradient in the horizontal direction within a certain spacing range. This temperature gradient in the horizontal direction is the crystallization driving force required for the growth of large-diameter silicon carbide crystals. The greater the temperature gradient in the horizontal direction, the greater the horizontal crystallization driving force, and the faster the crystal grows in the vertical direction. A large-diameter silicon carbide crystal can be grown within the same growth period.

[0180] Therefore, using the silicon carbide composite seed crystal provided by this application can establish a relatively large temperature gradient in both the vertical and horizontal directions. It can not only accelerate the growth rate of silicon carbide crystals in the vertical direction, which is beneficial to rapidly growing silicon carbide crystals with a thickness of more than 50 mm, but also increase the growth rate of silicon carbide crystals in the horizontal direction, which is beneficial to the rapid expansion of the diameter of silicon carbide crystals during growth, making it easy to achieve the growth of large-diameter silicon carbide crystals, and greatly reducing the growth cost of silicon carbide materials. This method can save more than 60% of high-quality silicon carbide materials. In summary, the silicon carbide composite seed crystal prepared by the above method can achieve the growth of large-diameter, high-thickness, and low-cost silicon carbide crystals while ensuring the growth quality of silicon carbide crystals.

[0181] In the second aspect of this embodiment, a silicon carbide composite seed crystal is provided, and the silicon carbide composite seed crystal is prepared by using the preparation method of the above-mentioned silicon carbide composite seed crystal.

[0182] As Figure 2 shown, the silicon carbide composite seed crystal 10 includes a silicon carbide seed crystal 11, a silicon carbide transition layer 12, and a diamond layer 13. The silicon carbide transition layer 12 is disposed on the silicon carbide seed crystal 11; the diamond layer 13 is disposed on the side of the silicon carbide transition layer 12 away from the silicon carbide seed crystal 11.

[0183] In the third aspect of this embodiment, a silicon carbide crystal is provided, and the silicon carbide crystal includes the above-mentioned silicon carbide composite seed crystal.

[0184] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0185] It should be noted that for the following embodiments where no specific conditions are indicated, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0186] Example 1

[0187] This embodiment provides a method for preparing a silicon carbide composite seed crystal, including the following steps:

[0188] S11: Provide a silicon carbide seed crystal with a thickness of 140 μm and a surface roughness of 1 nm.

[0189] S12: Under the conditions of a temperature of 850 °C, a pressure of 20 Kpa, a flow rate of both SiH4 and CH4 of 2 sccm, and a flow rate of H2 of 200 sccm, use chemical vapor deposition to grow an initial silicon carbide transition layer with a thickness of 50 μm on the surface of the silicon carbide seed crystal for 10 h.

[0190] S13: Grind and polish the initial silicon carbide transition layer to convert the initial silicon carbide transition layer into a silicon carbide transition layer with a thickness of 10 μm and a surface roughness of 1 nm, obtaining a silicon carbide composite structure.

[0191] S14: Under the conditions of a temperature of 850 °C, a pressure of 20 Kpa, a flow rate of both CH4 and O2 of 2 sccm, and a flow rate of H2 of 200 sccm, use MPCVD to grow an initial diamond layer with a thickness of 500 μm on the silicon surface of the silicon carbide transition layer for 60 h.

[0192] S15: Grind and polish the initial diamond layer to obtain a diamond layer with a thickness of 300 μm and a surface roughness of 1 nm, obtaining a silicon carbide composite seed crystal.

[0193] Example 2

[0194] This embodiment provides a method for preparing a silicon carbide composite seed crystal, including the following steps:

[0195] S11: Provide a silicon carbide seed crystal with a thickness of 200 μm and a surface roughness of 4 nm.

[0196] S12: Under the conditions of a temperature of 900 °C, a pressure of 30 Kpa, a flow rate of 20 sccm for both SiH4 and CH4, and a flow rate of 500 sccm for H2, use chemical vapor deposition to grow an initial silicon carbide transition layer with a thickness of 200 μm on the surface of the silicon carbide seed crystal for 20 h.

[0197] S13: Grind and polish the initial silicon carbide transition layer to convert the initial silicon carbide transition layer into a silicon carbide transition layer with a thickness of 50 μm and a surface roughness of 4 nm, obtaining a silicon carbide composite structure.

[0198] S14: Under the conditions of a temperature of 900 °C, a pressure of 30 Kpa, a flow rate of 20 sccm for both CH4 and O2, and a flow rate of 500 sccm for H2, use MPCVD to grow an initial diamond layer with a thickness of 900 μm on the silicon surface of the silicon carbide transition layer for 90 h.

[0199] S15: Grind and polish the initial diamond layer to obtain a diamond layer with a thickness of 480 μm and a surface roughness of 4 nm, obtaining a silicon carbide composite seed crystal.

[0200] Example 3

[0201] This example provides a method for preparing a silicon carbide composite seed crystal, including the following steps:

[0202] S11: Provide a silicon carbide seed crystal with a thickness of 150 μm and a surface roughness of 3 nm.

[0203] S12: Under the conditions of a temperature of 875 °C, a pressure of 25 Kpa, a flow rate of 12 sccm for both SiH4 and CH4, and a flow rate of 350 sccm for H2, use chemical vapor deposition to grow an initial silicon carbide transition layer with a thickness of 125 μm on the surface of the silicon carbide seed crystal for 15 h.

[0204] S13: Grind and polish the initial silicon carbide transition layer to convert the initial silicon carbide transition layer into a silicon carbide transition layer with a thickness of 30 μm and a surface roughness of 3 nm, obtaining a silicon carbide composite structure.

[0205] S14: Under the conditions of a temperature of 875 °C, a pressure of 25 Kpa, a flow rate of 12 sccm for both CH4 and O2, and a flow rate of 350 sccm for H2, use MPCVD to grow an initial diamond layer with a thickness of 700 μm on the silicon surface of the silicon carbide transition layer for 75 h.

[0206] S15: Grind and polish the initial diamond layer to obtain a diamond layer with a thickness of 350 μm and a surface roughness of 3 nm, and obtain a silicon carbide composite seed crystal.

[0207] Example 4

[0208] This example provides a method for preparing a silicon carbide composite seed crystal, including the following steps:

[0209] S11: Provide a silicon carbide seed crystal with a thickness of 140 μm and a surface roughness of 1 nm.

[0210] S12: Under the conditions of a temperature of 1900 °C and a pressure of 0.001 Pa, hetero - bond the silicon surface of the silicon carbide seed crystal with the silicon surface of an initial silicon carbide transition layer with a surface roughness of 1 nm and a thickness of 10 μm to obtain a first hetero - bonded structure.

[0211] S13: After the hetero - bonding is completed, perform an annealing treatment on the first hetero - bonded structure for 20 h under the conditions of an annealing temperature of 1800 °C and an annealing atmosphere of argon or nitrogen, so that the initial silicon carbide transition layer is transformed into a silicon carbide transition layer with a thickness of 10 μm, and obtain a silicon carbide composite structure.

[0212] S14: Under the conditions of a temperature of 850 °C, a pressure of 20 KPa, a flow rate of both CH4 and O2 of 2 sccm, and a flow rate of H2 of 200 sccm, use MPCVD to grow an initial diamond layer with a thickness of 500 μm on the silicon surface of the silicon carbide transition layer for 60 h.

[0213] S15: Grind and polish the initial diamond layer to obtain a diamond layer with a thickness of 300 μm and a surface roughness of 1 nm, and obtain a silicon carbide composite seed crystal.

[0214] Example 5

[0215] This example provides a method for preparing a silicon carbide composite seed crystal, including the following steps:

[0216] S11: Provide a silicon carbide seed crystal with a thickness of 200 μm and a surface roughness of 4 nm.

[0217] S12: Under the conditions of a temperature of 2100 °C and a pressure of 0.03 Pa, hetero - bond the silicon surface of the silicon carbide seed crystal with the silicon surface of an initial silicon carbide transition layer with a surface roughness of 4 nm and a thickness of 50 μm to obtain a first hetero - bonded structure.

[0218] S13: After the hetero-bonding is completed, the first hetero-bonded structure is annealed for 40 h at an annealing temperature of 1900 °C and an annealing atmosphere of argon or nitrogen, so that the initial silicon carbide transition layer is transformed into a silicon carbide transition layer with a thickness of 50 μm, and a silicon carbide composite structure is obtained.

[0219] S14: Under the conditions of a temperature of 900 °C, a pressure of 30 Kpa, a flow rate of 20 sccm for both CH4 and O2, and a flow rate of 500 sccm for H2, MPCVD is used to grow an initial diamond layer with a thickness of 900 μm on the silicon surface of the silicon carbide transition layer for 90 h.

[0220] S15: The initial diamond layer is polished to obtain a diamond layer with a thickness of 480 μm and a surface roughness of 4 nm, and a silicon carbide composite seed crystal is obtained.

[0221] Example 6

[0222] This example provides a method for preparing a silicon carbide composite seed crystal, including the following steps:

[0223] S11: Provide a silicon carbide seed crystal with a thickness of 150 μm and a surface roughness of 3 nm.

[0224] S12: Under the conditions of a temperature of 2000 °C and a pressure of 0.02 pa, the silicon surface of the silicon carbide seed crystal is hetero-bonded with the silicon surface of an initial silicon carbide transition layer with a surface roughness of 3 nm and a thickness of 30 μm to obtain a first hetero-bonded structure.

[0225] S13: After the hetero-bonding is completed, the first hetero-bonded structure is annealed for 30 h at an annealing temperature of 1850 °C and an annealing atmosphere of argon or nitrogen, so that the initial silicon carbide transition layer is transformed into a silicon carbide transition layer with a thickness of 30 μm, and a silicon carbide composite structure is obtained.

[0226] S14: Under the conditions of a temperature of 875 °C, a pressure of 25 Kpa, a flow rate of 12 sccm for both CH4 and O2, and a flow rate of 350 sccm for H2, MPCVD is used to grow an initial diamond layer with a thickness of 700 μm on the silicon surface of the silicon carbide transition layer for 75 h.

[0227] S15: The initial diamond layer is polished to obtain a diamond layer with a thickness of 350 μm and a surface roughness of 3 nm, and a silicon carbide composite seed crystal is obtained.

[0228] Example 7

[0229] This example provides a method for preparing a silicon carbide composite seed crystal, including the following steps:

[0230] S11: Provide a silicon carbide seed crystal with a thickness of 140 μm and a surface roughness of 1 nm.

[0231] S12: Under the conditions of a temperature of 1900 °C and a pressure of 0.001 Pa, heterogeneously bond the silicon surface of the silicon carbide seed crystal with the silicon surface of an initial silicon carbide transition layer with a surface roughness of 1 nm and a thickness of 10 μm to obtain a first heterogeneously bonded structure.

[0232] S13: After the heterogeneously bonding is completed, perform an annealing treatment on the first heterogeneously bonded structure for 20 h under the conditions of an annealing temperature of 1800 °C and an annealing atmosphere of argon or nitrogen, so that the initial silicon carbide transition layer is transformed into a silicon carbide transition layer with a thickness of 10 μm, obtaining a silicon carbide composite structure.

[0233] S14: Under the conditions of a temperature of 1900 °C and a pressure of 0.001 Pa, heterogeneously bond the carbon surface of the silicon carbide transition layer with the surface of an initial diamond layer with a surface roughness of 1 nm and a thickness of 300 μm to obtain a second heterogeneously bonded structure.

[0234] S15: After the heterogeneously bonding is completed, perform an annealing treatment on the second heterogeneously bonded structure for 20 h under the conditions of an annealing temperature of 1800 °C and an annealing atmosphere of argon or nitrogen, so that the initial diamond layer is transformed into a diamond layer with a thickness of 300 μm and a surface roughness of 1 nm, obtaining a silicon carbide composite seed crystal.

[0235] Example 8

[0236] This example provides a method for preparing a silicon carbide composite seed crystal, including the following steps:

[0237] S11: Provide a silicon carbide seed crystal with a thickness of 200 μm and a surface roughness of 4 nm.

[0238] S12: Under the conditions of a temperature of 2100 °C and a pressure of 0.03 Pa, heterogeneously bond the silicon surface of the silicon carbide seed crystal with the silicon surface of an initial silicon carbide transition layer with a surface roughness of 4 nm and a thickness of 50 μm to obtain a first heterogeneously bonded structure.

[0239] S13: After the heterogeneously bonding is completed, perform an annealing treatment on the first heterogeneously bonded structure for 40 h under the conditions of an annealing temperature of 1900 °C and an annealing atmosphere of argon or nitrogen, so that the initial silicon carbide transition layer is transformed into a silicon carbide transition layer with a thickness of 50 μm, obtaining a silicon carbide composite structure.

[0240] S14: Under the conditions of a temperature of 2100 °C and a pressure of 0.03 Pa, heterogeneously bond the carbon surface of the silicon carbide transition layer with the surface of an initial diamond layer with a surface roughness of 4 nm and a thickness of 480 μm to obtain a second heterogeneously bonded structure.

[0241] S15: After the heterogeneous bonding is completed, the second heterogeneous bonding structure is annealed for 40 h under the conditions that the annealing temperature is 1900 °C and the annealing atmosphere is argon or nitrogen, so that the initial diamond layer is transformed into a diamond layer with a thickness of 480 μm and a surface roughness of 5 nm, and a silicon carbide composite seed crystal is obtained.

[0242] Example 9

[0243] This example provides a method for preparing a silicon carbide composite seed crystal, including the following steps:

[0244] S11: Provide a silicon carbide seed crystal with a thickness of 150 μm and a surface roughness of 3 nm.

[0245] S12: Under the conditions that the temperature is 2000 °C and the air pressure is 0.02 Pa, the silicon surface of the silicon carbide seed crystal is heterogeneously bonded to the silicon surface of an initial silicon carbide transition layer with a surface roughness of 3 nm and a thickness of 30 μm to obtain a first heterogeneous bonding structure.

[0246] S13: After the heterogeneous bonding is completed, the first heterogeneous bonding structure is annealed for 30 h under the conditions that the annealing temperature is 1850 °C and the annealing atmosphere is argon or nitrogen, so that the initial silicon carbide transition layer is transformed into a silicon carbide transition layer with a thickness of 30 μm, and a silicon carbide composite structure is obtained.

[0247] S14: Under the conditions that the temperature is 2000 °C and the air pressure is 0.02 Pa, the carbon surface of the silicon carbide transition layer is heterogeneously bonded to an initial diamond layer with a surface roughness of 3 nm and a thickness of 350 μm to obtain a second heterogeneous bonding structure.

[0248] S15: After the heterogeneous bonding is completed, the second heterogeneous bonding structure is annealed for 30 h under the conditions that the annealing temperature is 1850 °C and the annealing atmosphere is argon or nitrogen, so that the initial diamond layer is transformed into a diamond layer with a thickness of 350 μm and a surface roughness of 3 nm, and a silicon carbide composite seed crystal is obtained.

[0249] Example 10

[0250] This example provides a method for preparing a silicon carbide composite seed crystal, including the following steps:

[0251] S11: Provide a silicon carbide seed crystal with a thickness of 140 μm and a surface roughness of 1 nm.

[0252] S12: Under the conditions of a temperature of 850 °C, a pressure of 20 Kpa, a flow rate of 2 sccm for both SiH4 and CH4, and a flow rate of 200 sccm for H2, a 50-μm-thick initial silicon carbide transition layer is grown on the surface of a silicon carbide seed crystal by chemical vapor deposition for 10 h.

[0253] S13: Grind and polish the initial silicon carbide transition layer to convert the initial silicon carbide transition layer into a 10-μm-thick silicon carbide transition layer with a surface roughness of 1 nm, obtaining a silicon carbide composite structure.

[0254] S14: Under the conditions of a temperature of 1900 °C and a pressure of 0.001 pa, hetero-bond the carbon surface of the silicon carbide transition layer with an initial diamond layer having a surface roughness of 1 nm and a thickness of 300 μm to obtain a second hetero-bonded structure.

[0255] S15: After the hetero-bonding is completed, anneal the second hetero-bonded structure for 20 h under the conditions of an annealing temperature of 1800 °C and an annealing atmosphere of argon or nitrogen, so that the initial diamond layer is converted into a 300-μm-thick diamond layer with a surface roughness of 1 nm, obtaining a silicon carbide composite seed crystal.

[0256] Example 11

[0257] This example provides a method for preparing a silicon carbide composite seed crystal, including the following steps:

[0258] S11: Provide a silicon carbide seed crystal with a thickness of 200 μm and a surface roughness of 4 nm.

[0259] S12: Under the conditions of a temperature of 900 °C, a pressure of 30 Kpa, a flow rate of 20 sccm for both SiH4 and CH4, and a flow rate of 500 sccm for H2, a 200-μm-thick initial silicon carbide transition layer is grown on the surface of the silicon carbide seed crystal by chemical vapor deposition for 20 h.

[0260] S13: Grind and polish the initial silicon carbide transition layer to convert the initial silicon carbide transition layer into a 50-μm-thick silicon carbide transition layer with a surface roughness of 4 nm, obtaining a silicon carbide composite structure.

[0261] S14: Under the conditions of a temperature of 2100 °C and a pressure of 0.03 pa, hetero-bond the carbon surface of the silicon carbide transition layer with an initial diamond layer having a surface roughness of 4 nm and a thickness of 480 μm to obtain a second hetero-bonded structure.

[0262] S15: After the hetero-bonding is completed, the second hetero-bonded structure is annealed for 40 h under the conditions that the annealing temperature is 1900 °C and the annealing atmosphere is argon or nitrogen, so that the initial diamond layer is transformed into a diamond layer with a thickness of 480 μm and a surface roughness of 4 nm, and a silicon carbide composite seed crystal is obtained.

[0263] Example 12

[0264] This example provides a method for preparing a silicon carbide composite seed crystal, which includes the following steps:

[0265] S11: Provide a silicon carbide seed crystal with a thickness of 150 μm and a surface roughness of 3 nm.

[0266] S12: Under the conditions that the temperature is 875 °C, the air pressure is 25 Kpa, the flow rates of SiH4 and CH4 are both 12 sccm, and the flow rate of H2 is 350 sccm, a chemical vapor deposition is used to grow an initial silicon carbide transition layer with a thickness of 125 μm on the surface of the silicon carbide seed crystal for 15 h.

[0267] S13: Grind and polish the initial silicon carbide transition layer to transform the initial silicon carbide transition layer into a silicon carbide transition layer with a thickness of 30 μm and a surface roughness of 3 nm, and a silicon carbide composite structure is obtained.

[0268] S14: Under the conditions that the temperature is 2000 °C and the air pressure is 0.02 pa, the carbon surface of the silicon carbide transition layer is hetero-bonded with an initial diamond layer with a surface roughness of 3 nm and a thickness of 350 μm to obtain a second hetero-bonded structure.

[0269] S15: After the hetero-bonding is completed, the second hetero-bonded structure is annealed for 30 h under the conditions that the annealing temperature is 1850 °C and the annealing atmosphere is argon or nitrogen, so that the initial diamond layer is transformed into a diamond layer with a thickness of 350 μm and a surface roughness of 3 nm, and a silicon carbide composite seed crystal is obtained.

[0270] Example 13

[0271] Similar to the preparation method of Example 1, the difference is: S14: Under the conditions that the temperature is 2200 °C, the air pressure is 20 Kpa, the flow rate of CH4 is 2 sccm, and the flow rate of H2 is 200 sccm, an initial diamond layer with a thickness of 500 μm is grown on the carbon surface of the silicon carbide transition layer by HFCVD for 60 h; the others are the same and will not be described in detail here.

[0272] Example 14

[0273] Similar to the preparation method of Example 2, the differences are as follows: S14: Under the conditions of a temperature of 2300 °C, a pressure of 30 Kpa, a flow rate of CH4 of 20 sccm, and a flow rate of H2 of 500 sccm, HFCVD is used to grow on the carbon surface of the silicon carbide transition layer for 90 h to prepare an initial diamond layer with a thickness of 900 μm; the others are the same and will not be elaborated here.

[0274] Example 15

[0275] Similar to the preparation method of Example 3, the differences are as follows: S14: Under the conditions of a temperature of 2250 °C, a pressure of 25 Kpa, a flow rate of CH4 of 12 sccm, and a flow rate of H2 of 350 sccm, HFCVD is used to grow on the carbon surface of the silicon carbide transition layer for 75 h to prepare an initial diamond layer with a thickness of 700 μm; the others are the same and will not be elaborated here.

[0276] Example 16

[0277] Similar to the preparation method of Example 4, the differences are as follows: S14: Under the conditions of a temperature of 850 °C, a pressure of 20 Kpa, a flow rate of CH4 of 2 sccm, and a flow rate of H2 of 200 sccm, DCPCVD is used to grow on the carbon surface of the silicon carbide transition layer for 5 h to prepare an initial diamond layer with a thickness of 500 μm; the others are the same and will not be elaborated here.

[0278] Example 17

[0279] Similar to the preparation method of Example 5, the differences are as follows: Under the conditions of a temperature of 900 °C, a pressure of 30 Kpa, a flow rate of CH4 of 20 sccm, and a flow rate of H2 of 500 sccm, DCPCVD is used to grow on the carbon surface of the silicon carbide transition layer for 10 h to prepare an initial diamond layer with a thickness of 900 μm.

[0280] Example 18

[0281] Similar to the preparation method of Example 6, the differences are as follows: Under the conditions of a temperature of 875 °C, a pressure of 25 Kpa, a flow rate of CH4 of 12 sccm, and a flow rate of H2 of 350 sccm, DCPCVD is used to grow on the carbon surface of the silicon carbide transition layer for 7 h to prepare an initial diamond layer with a thickness of 700 μm.

[0282] Example 19

[0283] Similar to the preparation method of Example 3, the differences are as follows: Grooved first microchannels are etched on the carbon surface of the silicon carbide transition layer; the others are the same and will not be elaborated here.

[0284] The width of the first microchannel is 5 μm, the depth of the first microchannel is 30 μm, and the lateral pitch of the first microchannel is 5 mm.

[0285] Example 20

[0286] Similar to the preparation method of Example 12, the difference is that: raised second microchannels are etched on the surface of the initial diamond layer; others are the same and will not be elaborated here.

[0287] The width of the second microchannel is 5 μm, the depth of the first microchannel is 30 μm, and the lateral pitch of the first microchannel is 5 mm.

[0288] Example 21

[0289] Similar to the preparation method of Example 9, the difference is that: grooved first microchannels are etched on the carbon surface of the silicon carbide transition layer, and raised second microchannels are etched on the surface of the initial diamond layer; others are the same and will not be elaborated here.

[0290] The width of the first microchannel is 5 μm, the depth of the first microchannel is 30 μm, and the lateral pitch of the first microchannel is 5 mm; the width of the second microchannel is 5 μm, the depth of the first microchannel is 30 μm, and the lateral pitch of the first microchannel is 5 mm.

[0291] Silicon carbide crystals are grown respectively using the silicon carbide composite seeds prepared in Examples 1 - 21. The growth conditions include: the growth temperature is 2200 - 2300 °C, the pressure is 3×10 -3 pa - 5×10 -3 pa, and the growth time is 160 - 200 hours.

[0292] The diameter of the grown silicon carbide crystal is 200 mm, the thickness is 40 mm, and the average growth rate is 200 - 250 μm / hour. The surface of the grown silicon carbide crystal is flat, has good light transmittance, and has no polycrystalline phenomenon. This silicon carbide crystal is a single 4H polytype silicon carbide crystal.

[0293] Under the above growth conditions (i.e., the growth temperature is 2200 - 2300 °C, the pressure is 3×10 -3 pa - 5×10 -3 pa, and the growth time is 160 - 200 hours), when using a pure silicon carbide seed to grow a silicon carbide crystal, the diameter of the grown silicon carbide crystal is 150 mm, the thickness is 30 mm, and the average growth rate of this silicon carbide crystal is 150 - 200 μm / hour. The surface of this silicon carbide crystal is uneven, has poor light transmittance, and has a polycrystalline structure phenomenon.

[0294] It can be seen therefrom that, compared with the existing pure silicon carbide seed crystal, when using the silicon carbide composite seed crystal provided by the present application to prepare a silicon carbide crystal, the average growth rate is relatively fast, a silicon carbide crystal with a relatively thick thickness and a relatively large diameter can be grown, and the surface of the grown silicon carbide crystal is flat, has good light transmittance, has no polycrystalline phenomenon, and has relatively good quality. Moreover, the thickness of the silicon carbide seed crystal in the silicon carbide composite seed crystal provided by the present application accounts for less than 1 / 3. Therefore, compared with the existing pure silicon carbide seed crystal, the silicon carbide composite seed crystal provided by the present application can save at least 2 / 3 of the usage amount of the silicon carbide seed crystal.

[0295] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present application. Without departing from the principle and purpose of the present application, those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the invention, and all such changes should fall within the protection scope of the claims of the present application.

Claims

1. A method for preparing a silicon carbide composite seed crystal, characterized in that, The steps are as follows: Provide a silicon carbide seed crystal; Form a silicon carbide transition layer on the silicon surface of the silicon carbide seed crystal, and make the carbon surface of the silicon carbide transition layer away from the silicon surface of the silicon carbide seed crystal to obtain a silicon carbide composite structure; Form a diamond layer on the carbon surface of the silicon carbide transition layer to obtain a silicon carbide composite seed crystal; Wherein, the thermal conductivity of the silicon carbide transition layer is less than that of the diamond layer, and the thermal conductivity of the silicon carbide transition layer is greater than that of the silicon carbide seed crystal; the crystal form of the silicon carbide transition layer is different from that of the silicon carbide seed crystal.

2. The preparation method according to claim 1, wherein During the process of forming the silicon carbide transition layer on the silicon surface of the silicon carbide seed crystal, the silicon surface of the silicon carbide seed crystal and the silicon surface of the silicon carbide transition layer are combined by silicon atom diffusion; the forming of the silicon carbide transition layer on the silicon surface of the silicon carbide seed crystal includes: Under the conditions of a temperature of 850-900°C, a pressure of 20-30 Kpa, the flow rates of SiH4 and CH4 both being 2-20 sccm, and the flow rate of H2 being 200-500 sccm, use chemical vapor deposition to grow on the silicon surface of the silicon carbide seed crystal with a thickness of 100-200 μm for 10-20 h to prepare an initial silicon carbide transition layer with a thickness of 50-200 μm; Grind and polish the carbon surface of the initial silicon carbide transition layer to obtain a silicon carbide transition layer with a thickness of 10-50 μm and a surface roughness less than the first preset roughness; Wherein, the value range of the first preset roughness is 1-5 nm.

3. The preparation method according to claim 1, wherein, During the process of forming the silicon carbide transition layer on the silicon surface of the silicon carbide seed crystal, the silicon surface of the silicon carbide seed crystal and the silicon surface of the silicon carbide transition layer are combined by silicon atom diffusion; the forming of the silicon carbide transition layer on the silicon surface of the silicon carbide seed crystal includes: Under the conditions of a temperature of 1900-2100°C and a pressure of 0.001-0.03 pa, heterogeneously bond the silicon surface of the silicon carbide seed crystal with a thickness of 100-200 μm to the silicon surface of the initial silicon carbide transition layer to obtain a first heterogeneously bonded structure; Wherein, the surface roughness of the silicon surface of the initial silicon carbide transition layer is less than the second preset roughness, and the value range of the second preset roughness is 1-5 nm; After the heterogeneously bonding is completed, under the conditions of an annealing temperature of 1800-1900°C and an annealing atmosphere of argon or nitrogen, perform an annealing treatment on the first heterogeneously bonded structure for 20-40 h to make the initial silicon carbide transition layer transform into the silicon carbide transition layer; Wherein, the thickness of the silicon carbide transition layer is 10-50 μm.

4. The preparation method according to any one of claims 1-3, characterized in that, During the process of forming the diamond layer on the carbon surface of the silicon carbide transition layer, the carbon surface of the silicon carbide transition layer and the surface of the diamond layer are combined by carbon atom diffusion; the forming of the diamond layer on the carbon surface of the silicon carbide transition layer includes: Use chemical vapor deposition to grow an initial diamond layer with a thickness of 500-900 μm on the carbon surface of the silicon carbide transition layer; Grind and polish the initial diamond layer to obtain the diamond layer with a thickness of 300-500 μm and a surface roughness less than the third preset roughness; Among them, the value range of the third preset roughness is 1-5 nm.

5. The preparation method according to claim 4, characterized in that, Growing an initial diamond layer with a thickness of 500-900 μm on the carbon surface of the silicon carbide transition layer includes: Under the conditions of a temperature of 850-900 °C, a pressure of 20-30 Kpa, a flow rate of CH4 of 2-20 sccm, a flow rate of H2 of 200-500 sccm, and a flow rate of O2 of 2-20 sccm, using MPCVD to grow on the carbon surface of the silicon carbide transition layer for 60-90 h to prepare the initial diamond layer with a thickness of 500-900 μm; Or, under the conditions of a temperature of 2200-2300 °C, a pressure of 20-30 Kpa, a flow rate of CH4 of 2-20 sccm, and a flow rate of H2 of 200-500 sccm, using HFCVD to grow on the carbon surface of the silicon carbide transition layer for 60-90 h to prepare the initial diamond layer with a thickness of 500-900 μm; Or, under the conditions of a temperature of 850-900 °C, a pressure of 20-30 Kpa, a flow rate of CH4 of 2-20 sccm, and a flow rate of H2 of 200-500 sccm, using DCPCVD to grow on the carbon surface of the silicon carbide transition layer for 5-10 h to prepare the initial diamond layer with a thickness of 500-900 μm.

6. The preparation method according to any one of claims 1-3, characterized in that, During the process of forming a diamond layer on the carbon surface of the silicon carbide transition layer, the carbon surface of the silicon carbide transition layer and the surface of the diamond layer are combined by carbon atom diffusion; forming a diamond layer on the carbon surface of the silicon carbide transition layer includes: Under the conditions of a temperature of 1900-2100 °C and a pressure of 0.001-0.03 pa, heterogeneously bonding the carbon surface of the silicon carbide transition layer and the surface of the initial diamond layer to obtain a second heterogeneously bonded structure; Among them, the surface roughness of the initial diamond layer is less than the fourth preset roughness, and the value range of the fourth preset roughness is 1-5 nm; After the heterogeneously bonding is completed, under the conditions of an annealing temperature of 1800-1900 °C and an annealing atmosphere of argon or nitrogen, annealing the second heterogeneously bonded structure for 20-40 h to convert the initial diamond layer into the diamond layer; Among them, the thickness of the diamond layer is 300-500 um.

7. The preparation method according to claim 6, characterized in that, Before forming the diamond layer, the preparation method further includes: forming a plurality of first microchannels in a convex or groove shape on the carbon surface of the silicon carbide transition layer; And / or, before the heterogeneously bonding of the carbon surface of the silicon carbide transition layer and the surface of the initial diamond layer, the preparation method further includes: Forming a plurality of second microchannels in a convex or groove shape on the surface of the initial diamond layer; Among them, the convex first microchannels correspond to the groove-shaped second microchannels so that the convex first microchannels can be embedded in the groove-shaped second microchannels; the convex second microchannels correspond to the groove-shaped first microchannels so that the convex second microchannels can be embedded in the groove-shaped first microchannels.

8. The preparation method according to claim 7, characterized in that, Forming a plurality of first microchannels in a convex or groove shape on the carbon surface of the silicon carbide transition layer, including: Under the conditions of a pulse width of 500 ps to 1 ns, a laser power of 10 to 15 W, and a laser repetition frequency of 20 to 100 kHz, forming a plurality of first microchannels in a convex or groove shape on the carbon surface of the silicon carbide transition layer by laser etching; or under the conditions of an etching temperature exceeding 1800 °C and an etching gas being CF4, O2, or Ar, forming a plurality of first microchannels in a convex or groove shape on the carbon surface of the silicon carbide transition layer by plasma etching; Wherein, the width of the first microchannel is 5 to 10 μm; and / or, the depth of the first microchannel is 30 - 50 μm; and / or, the lateral spacing of the first microchannels is 5 to 10 mm; And / or, forming a plurality of second microchannels in a convex or groove shape on the surface of the initial diamond layer, including: Under the conditions of a pulse width of 500 ps to 1 ns, a laser power of 10 to 15 W, and a laser repetition frequency of 20 to 100 kHz, forming a plurality of second microchannels in a convex or groove shape on the surface of the initial diamond layer by laser etching; or under the conditions of an etching temperature exceeding 1800 °C and an etching gas being CF4, O2, or Ar, forming a plurality of second microchannels in a convex or groove shape on the surface of the initial diamond layer by plasma etching; Wherein, the width of the second microchannel is 5 to 10 μm; and / or, the depth of the second microchannel is 30 - 50 μm; and / or, the lateral spacing of the second microchannels is 5 to 10 mm. And / or, the thickness of the diamond layer is less than or equal to two-thirds of the thickness of the silicon carbide composite seed crystal, and the thickness of the diamond layer is greater than or equal to one-half of the thickness of the silicon carbide composite seed crystal; And / or, the thickness of the silicon carbide seed crystal is less than one-third of the thickness of the silicon carbide composite seed crystal.

9. A silicon carbide composite seed crystal, characterized in that, The silicon carbide composite seed crystal is prepared by using the preparation method of the silicon carbide composite seed crystal according to any one of claims 1 - 8.

10. A silicon carbide crystal, characterized in that, The silicon carbide crystal contains the silicon carbide composite seed crystal according to claim 9.

Images