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

Abstract

The invention discloses a silicon carbide composite seed crystal and a preparation method thereof. The preparation method of the silicon carbide composite seed crystal comprises the following steps: providing a diamond substrate; forming a silicon carbide transition layer on the surface of the diamond substrate, and enabling the silicon surface of the silicon carbide transition layer to be far away from the surface of the diamond substrate to obtain a diamond / silicon carbide composite structure; forming a silicon carbide seed crystal on the silicon surface of the diamond / silicon carbide composite structure, and enabling the carbon surface of the silicon carbide seed crystal to be far away from the silicon 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 substrate, 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] The present 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] Due to the characteristics of wide bandgap width, high thermal conductivity, and high breakdown field strength, silicon carbide crystal materials are widely used in fields such as electric vehicles, photovoltaics, and radio frequency communications, and are one of the most important third-generation semiconductor materials. Because silicon carbide crystals have a high optical refractive index and high thermal conductivity, they have currently been used as optical wafers on augmented reality (AR) glasses, and the market application prospect is very broad.

[0003] Silicon carbide single crystals generally achieve large-size commercialized bulk crystals through PVT (Physical Vapor Transport) and LPE (Liquid Phase Epitaxy), but the growth rate is far lower than that of silicon crystals. Currently, silicon carbide single crystals are mainly crystals with two specifications of 6 inches and 8 inches in diameter. The growth cycle of a single crystal is about 7 to 10 days, and the growth rate is extremely slow. The growth rate of most domestic manufacturers is between 100 and 150 microns per hour, and the thickness of the single crystal is only 20 to 25 mm. The yield rate is much lower than that of mature single-crystal silicon growth. The growth process is a black-box operation, and the ingot is opaque, so the quality cannot be timely feedback. Wolfspeed Company in the United States grows 8-inch ingots in batches, and its growth rate of silicon carbide substrates has achieved a growth rate of more than 300 microns per hour, with a thickness of 60 mm, which is at the world-leading level.

[0004] 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 methods are poor. Traditional seeds are 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. For example, the increase in the impurity nitrogen content will reduce the thermal conductivity of the material, and the existence of crystal structure defects will lead to a decrease in thermal conductivity. During the crystal growth process, the temperature gradient is the internal driving force for single-crystal crystallization. The temperature gradient is a key factor determining the crystal growth rate. The growth rate of the crystal 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 materials is not conducive to forming a large temperature gradient in the vertical direction required for silicon carbide crystals. Therefore, the growth rate of silicon carbide crystals is not only slow, but the growth thickness is also very small, that is, silicon carbide crystals cannot grow thick, and the thickness is generally only 20 to 25 mm, or when growing thick, the internal quality of the crystal is poor, and an electronic-grade silicon carbide crystal cannot be obtained.

[0005] This application solves at least one of the above problems. Summary of the Invention

[0006] The purpose of this application is to provide a method for preparing a silicon carbide composite seed crystal, which is used to solve the problem that the low thermal conductivity of silicon carbide materials is not conducive to forming a large temperature gradient in the vertical direction required for growing silicon carbide crystals. Therefore, the growth rate of silicon carbide crystals is not only slow, but the growth thickness is also very small, that is, the silicon carbide crystals cannot grow thick, and the thickness is generally only 20-25 mm, or when growing thick, the internal quality of the crystal is poor, and it is impossible to obtain electronic-grade silicon carbide crystals. The silicon carbide composite seed crystal prepared by the method of this application can ensure the growth quality of silicon carbide crystals while realizing the growth of large-diameter, high-thickness, and low-cost silicon carbide crystals.

[0007] To achieve the above purpose, this application adopts the following technical solutions:

[0008] In the first aspect of this application, a method for preparing a silicon carbide composite seed crystal is provided, including the following steps:

[0009] Provide a diamond substrate;

[0010] Form a silicon carbide transition layer on the surface of the diamond substrate, and make the silicon surface of the silicon carbide transition layer away from the surface of the diamond substrate to obtain a diamond / silicon carbide composite structure;

[0011] Form a silicon carbide seed crystal on the silicon surface of the diamond / silicon carbide composite structure, and make the carbon surface of the silicon carbide seed crystal away from the silicon surface of the silicon carbide transition layer to obtain a silicon carbide composite seed crystal;

[0012] Wherein, the thermal conductivity of the silicon carbide transition layer is less than that of the diamond substrate, 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.

[0013] Compared with the prior art, the beneficial effects of this application are as follows:

[0014] By forming a silicon carbide transition layer with low thermal conductivity on the surface of a diamond substrate with high thermal conductivity, the surface of the diamond substrate and the carbon surface of the silicon carbide transition layer are combined by carbon atom diffusion, reducing the interfacial stress and enhancing the bonding strength between the two phases; by forming a silicon carbide seed crystal with even lower thermal conductivity on the silicon surface of the silicon carbide transition layer with low thermal conductivity, the silicon carbide transition layer serves as a thermal stress buffer layer to reduce interfacial cracks or peeling caused by the difference in thermal expansion coefficients between the diamond substrate and the silicon carbide seed crystal.

[0015] By establishing a temperature gradient among a diamond substrate with high thermal conductivity, a silicon carbide transition layer with low thermal conductivity, and a silicon carbide seed crystal with even lower thermal conductivity, the heat at the silicon carbide seed crystal can be rapidly transferred out in the vertical and horizontal directions, thereby achieving a relatively large temperature gradient 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 over 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 easier to achieve the growth of a large-diameter silicon carbide crystal, significantly reducing the growth cost of the silicon carbide material. In summary, the silicon carbide composite seed crystal prepared by the above method can, while achieving the growth of a large-diameter, high-thickness, and low-cost silicon carbide crystal, also ensure the growth quality of the silicon carbide crystal.

[0016] In some possible implementation manners of the first aspect, during the process of forming the silicon carbide transition layer on the surface of the diamond substrate, the surface of the diamond substrate and the carbon surface of the silicon carbide transition layer are combined through carbon atom diffusion; forming the silicon carbide transition layer on the surface of the diamond substrate includes:

[0017] Under the conditions of a temperature of 850 - 900 °C, a pressure of 20 - 30 Kpa, a flow rate of both SiH4 and CH4 of 2 - 20 sccm, and a flow rate of H2 of 200 - 500 sccm, the surface of the diamond substrate is subjected to chemical vapor deposition to prepare the silicon carbide transition layer; wherein, the growth time of the silicon carbide transition layer is 10 - 20 h.

[0018] In some possible implementation manners of the first aspect, during the process of forming the silicon carbide transition layer on the surface of the diamond substrate, the surface of the diamond substrate and the carbon surface of the silicon carbide transition layer are combined through carbon atom diffusion; forming the silicon carbide transition layer on the surface of the diamond substrate includes:

[0019] Under the conditions of a temperature of 1900 - 2100 °C and a pressure of 0.001 - 0.03 pa, the surface of the diamond substrate and the carbon surface of the initial silicon carbide transition layer are subjected to hetero-bonding to obtain a first hetero-bonded structure;

[0020] After the hetero-bonding is completed, under the conditions of an annealing temperature of 1800 - 1900 °C and an annealing atmosphere of argon or nitrogen, the first hetero-bonded structure is subjected to an annealing treatment for 20 - 40 h to form the silicon carbide transition layer.

[0021] In some possible embodiments of the first aspect, during the process of forming a silicon carbide seed crystal on the silicon surface of the diamond / silicon carbide composite structure, the silicon surface of the silicon carbide transition layer and the silicon surface of the silicon carbide seed crystal are bonded together by silicon atom diffusion; forming the silicon carbide seed crystal on the silicon surface of the diamond / silicon carbide composite structure includes:

[0022] Under the conditions of a temperature of 850 - 900 °C, a pressure of 20 - 30 Kpa, a flow rate of both SiH4 and CH4 of 2 - 20 sccm, and a flow rate of H2 of 200 - 500 sccm, chemically vapor deposit the silicon carbide seed crystal on the surface of the diamond / silicon carbide composite structure; wherein, the growth time of the silicon carbide seed crystal is 10 - 20 h.

[0023] In some possible embodiments of the first aspect, during the process of forming a silicon carbide seed crystal on the silicon surface of the silicon carbide composite structure, the silicon surface of the silicon carbide transition layer and the silicon surface of the silicon carbide seed crystal are bonded together by silicon atom diffusion; forming the silicon carbide seed crystal on the silicon surface of the diamond / silicon carbide composite structure includes:

[0024] 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 the diamond / silicon carbide composite structure and the silicon surface of the initial silicon carbide seed crystal to obtain a second hetero - bonded structure;

[0025] After the hetero - bonding is completed, under the conditions of an annealing temperature of 1800 - 190 [0] °C and an annealing atmosphere of argon or nitrogen, perform an annealing treatment on the second hetero - bonded structure for 20 - 40 h to form the silicon carbide seed crystal.

[0026] In some possible embodiments of the first aspect, after forming the silicon carbide transition layer, the method further includes:

[0027] Form a groove - shaped first micro - channel on the silicon surface of the silicon carbide transition layer; or form a protruding first micro - channel on the silicon surface of the silicon carbide transition layer;

[0028] Wherein, the width of the first micro - channel is 5 - 10 μm; and / or the depth of the first micro - channel is 30 - 50 μm; and / or the lateral pitch of the first micro - channel is 5 - 10 mm.

[0029] In some possible embodiments of the first aspect, before forming the silicon carbide seed crystal, the method further includes:

[0030] Form a groove - shaped second micro - channel on the silicon surface of the initial silicon carbide seed crystal; or form a protruding second micro - channel on the silicon surface of the initial silicon carbide seed crystal;

[0031] Note: There seems to be a typo in the original text where "2100]" and "190 [0]" are incorrect notations. I've translated it as it is but it should be corrected in the original.Among them, the width of the second microchannel is 5-10 μm; and / or the depth of the second microchannel is 30-50 μm; and / or the lateral pitch of the second microchannels is 5-10 mm;

[0032] The convex second microchannel corresponds to the groove-shaped first microchannel, so that the convex second microchannel can be embedded into the groove-shaped first microchannel;

[0033] The convex first microchannel corresponds to the groove-shaped second microchannel, so that the convex first microchannel can be embedded into the groove-shaped second microchannel.

[0034] In some possible embodiments of the first aspect, the diamond substrate is single-crystal diamond or polycrystalline diamond;

[0035] and / or, the thickness of the diamond substrate is 300-500 μm;

[0036] and / or, the thickness of the diamond substrate is less than or equal to two-thirds of the thickness of the silicon carbide composite seed crystal, and the thickness of the diamond substrate is greater than or equal to one-half of the thickness of the silicon carbide composite seed crystal;

[0037] and / or, the surface roughness of the diamond substrate is less than a first preset roughness, and the value range of the first preset roughness is 1-5 nm.

[0038] and / or, the silicon carbide material in the silicon carbide transition layer is of 3C, 4H, AH or 15R crystal form;

[0039] and / or, the thickness of the silicon carbide transition layer is 10-50 μm;

[0040] and / or, the surface roughness of the silicon surface of the silicon carbide transition layer is less than a second preset roughness, and the value range of the second preset roughness is 1-5 nm;

[0041] and / or, the thickness of the silicon carbide seed crystal is 100-200 μm;

[0042] 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;

[0043] and / or, the surface roughness of the silicon surface of the silicon carbide seed crystal is less than a third preset roughness, and the value range of the third preset roughness is 1-5 nm.

[0044] In a second aspect of the present application, there is provided a silicon carbide composite seed crystal prepared by the preparation method of the above-mentioned silicon carbide composite seed crystal.

[0045] In a third aspect of the present application, a silicon carbide crystal is provided, and the silicon carbide crystal includes the above-mentioned silicon carbide composite seed crystal. Description of the Drawings

[0046] Figure 1 is an overall step flow chart of the preparation method of the silicon carbide composite seed crystal provided by the present application;

[0047] Figure 2 is a schematic structural diagram of the silicon carbide composite seed crystal provided by the present application;

[0048] Figure 3 is a schematic diagram of the first microchannel and the second microchannel in a spiral mosquito coil pattern provided by the present application.

[0049] In the figure, 10 is the silicon carbide composite seed crystal; 11 is the diamond substrate; 12 is the silicon carbide transition layer; 13 is the silicon carbide seed crystal. Detailed Embodiments

[0050] 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 the same or similar structures, and thus their repeated description will be omitted.

[0051] In the present application, the words expressing position and direction are described with reference to the drawings as examples, but can be changed according to needs, and all changes made are included in the protection scope of the present application.

[0052] In a first aspect of this embodiment, a method for preparing a silicon carbide composite seed crystal is provided. With reference to the attached Figure 1 shown, it includes the following steps S1 to S3.

[0053] Step S1: Provide a diamond substrate.

[0054] The surface roughness of the diamond substrate is less than a first preset roughness, and the value range of the first preset roughness is 1 to 5 nm. The surface roughness of the diamond substrate can be, for example, 0.5 nm, 1 nm, 2 nm, 3 nm, or 4 nm.

[0055] It should be noted that the thickness of the diamond substrate is 300 to 500 μm, and can be, for example, 300 μm, 350 μm, 400 μm, 450 μm, or 500 μm; the thickness of the diamond substrate is less than or equal to two-thirds of the thickness of the silicon carbide composite seed crystal, and the thickness of the diamond substrate is greater than or equal to one-half of the thickness of the silicon carbide composite seed crystal.

[0056] By controlling the thickness of the diamond substrate 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%.

[0057] For the diamond substrate, the present application does not particularly limit it, and any suitable diamond substrate in the art can be used to implement the technical solution of the present application. In some embodiments of the present application, the diamond substrate used may be selected from single crystal diamond or polycrystalline diamond, and preferably single crystal diamond.

[0058] Further, as a preferred embodiment of the present application, before forming the silicon carbide transition layer, the preparation method further includes steps S11-S14.

[0059] Step S11: Polish the surface of the diamond substrate.

[0060] For example, polish the surface of the diamond substrate by mechanical grinding to make its surface roughness less than 1-5 nm. For example, the surface roughness of the diamond substrate can be 0.5 nm, 1 nm, 2 nm, 3 nm or 4 nm.

[0061] Step S12: Pickle the polished diamond substrate.

[0062] For example, pickle the diamond substrate by soaking it in aqua regia (a mixture of nitric acid and hydrochloric acid) for 30 min to remove the contaminated particles on the surface of the diamond substrate.

[0063] Step S13: Ultrasonically clean the pickled diamond substrate.

[0064] For example, ultrasonically clean the diamond substrate with an acetone solution for 10 min to penetrate into the surface microporous structure of the diamond substrate to achieve dead-angle-free cleaning. It can not only further remove the contaminated particles on the surface of the diamond substrate, but also form minute scratches on the surface of the diamond substrate to optimize its surface morphology, thereby improving the nucleation density and bonding force with the subsequent silicon carbide transition layer, so that the nucleation density can be as high as 10 9 / cm 2 .

[0065] A Step S14: Dry the ultrasonically cleaned diamond substrate. For example, bake the diamond substrate in an oven at 200 °C for 15 min to dry the diamond substrate.

[0066] After the above steps, efficient decontamination of the diamond substrate is achieved, ensuring the integrity and high cleanliness of its surface, reducing defects caused by contaminants during the subsequent formation of the silicon carbide transition layer, so that the number of particles (0.3μm scale) on the surface of the diamond substrate is less than 500 - 1000, ensuring the uniformity and adhesion of the silicon carbide transition layer on the surface of the diamond substrate.

[0067] Step S2: Form a silicon carbide transition layer on the surface of the diamond substrate, and make the silicon surface of the silicon carbide transition layer away from the surface of the diamond substrate to obtain a diamond / silicon carbide composite structure.

[0068] The thickness of the silicon carbide transition layer is 10 - 50μm, for example, it can be 10μm, 20μm, 30μm, 40μm or 50μm; the surface roughness of the silicon surface of the silicon carbide transition layer is less than the second preset roughness, and the value range of the second preset roughness is 1 - 5nm. For example, the surface roughness of the silicon surface of the silicon carbide transition layer can be 0.5nm, 1nm, 2nm, 3nm or 4nm.

[0069] It should be noted that the thermal conductivity of the silicon carbide transition layer is less than that of the diamond substrate. For the silicon carbide transition layer, the silicon carbide material in the silicon carbide transition layer can be 3C, 4H, 6H or 15R crystal form, etc. In this embodiment, 3C crystal form is preferably used.

[0070] It should be further noted that during the process of forming the silicon carbide transition layer on the surface of the diamond substrate, the surface of the diamond substrate and the carbon surface of the silicon carbide transition layer are bonded by carbon atom diffusion. Since the carbon atoms of the diamond substrate and the carbon atoms of the silicon carbide transition layer are bonded in the form of covalent bonds, there is no transition intermediate layer between the two, making their combination closer.

[0071] Further, as a preferred embodiment of the present application, forming a silicon carbide transition layer on the surface of the diamond substrate includes steps S21a - step S22a.

[0072] Step S21a: Under the conditions of a temperature of 1900 - 2100°C and a pressure of 0.001 - 0.03pa, perform hetero - bonding between the surface of the diamond substrate and the carbon surface of the initial silicon carbide transition layer to obtain a first hetero - bonded structure.

[0073] The temperature can be 1900°C, 1950°C, 2000°C, 2050°C or 2100°C; the pressure can be 0.001pa, 0.005pa, 0.01pa, 0.015pa, 0.02pa, 0.025pa or 0.03pa.

[0074] The inventors' in-depth research 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 strength. If the air 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 air 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 air pressure of the heterogeneous bonding need to be controlled within the above ranges.

[0075] Under the above conditions, heterogeneous bonding (the bonding surfaces are both carbon surfaces) is carried out. The lattice mismatch degree between the silicon carbide transition layer and the diamond substrate 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 closely contact, reduce micropores and gaps, and improve the densification and mechanical strength of the first heterogeneous bonding structure; furthermore, it can also reduce the interface residual stress caused by the thermal expansion difference between the silicon carbide transition layer and the diamond substrate, and prevent the second heterogeneous bonding structure from cracking. In addition, under these conditions, heterogeneous bonding is carried out, the interface thermal resistance is low, and the diamond with high thermal conductivity can quickly conduct the heat accumulated in the silicon carbide transition layer, so as to establish a larger temperature gradient in the vertical and horizontal directions in the silicon carbide composite seed crystal.

[0076] Step S22a: After the heterogeneous bonding is completed, the first heterogeneous bonding structure is annealed for 20 - 40 h under the conditions of an annealing temperature of 1800 - 1900 °C and an annealing atmosphere of argon or nitrogen to form a silicon carbide transition layer.

[0077] 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.

[0078] The inventors' research found 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 is high and it is of little 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.

[0079] 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 carbon atoms can be promoted at high temperature, and the interface thermal resistance can be reduced.

[0080] As another preferred embodiment of the present application, forming a silicon carbide transition layer on the surface of the diamond substrate includes step S21b.

[0081] Step S21b: Under the conditions that the temperature is 850 - 900 °C, the air 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, chemically vapor deposit on the surface of the diamond substrate to prepare a silicon carbide transition layer.

[0082] The growth time of the silicon carbide transition layer is 10 - 20 h. For example, the growth time can be 10 h, 12 h, 15 h, 18 h, or 20 h. The temperature can be 850 °C, 860 °C, 870 °C, 880 °C, 890 °C, or 900 °C; the air pressure can be 20 Kpa, 22 Kpa, 25 Kpa, 28 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%.

[0083] The inventors' research found that during the process of chemically vapor depositing the silicon carbide transition layer, 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 silicon carbide transition 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, amorphous carbides are likely to appear.

[0084] SiH4 and CH4 are the raw material gases for chemically vapor depositing silicon carbide. 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 transport gas for 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.

[0085] If the growth time of the silicon carbide transition layer is too short (less than 10 h), a silicon carbide transition layer of a certain thickness cannot be produced; if the growth time is too long (greater than 20 h), the quality of the silicon carbide transition layer is not high, which is not conducive to the preparation of the silicon carbide composite seed crystal.

[0086] Using the above conditions, a silicon carbide transition layer is prepared by chemical vapor deposition on the surface of a diamond substrate, which can not only provide a good material basis for the homoepitaxial growth or bonding of the silicon carbide transition layer and the silicon carbide seed crystal, but also prevent the dislocation defects inside the diamond from extending to the silicon carbide seed crystal, thus avoiding affecting the quality of the grown silicon carbide crystal.

[0087] Further, as a preferred embodiment of the present application, after forming the silicon carbide transition layer, the preparation method further includes step S23.

[0088] Step S23: Etch a groove-shaped first microchannel or a raised first microchannel on the silicon surface of the silicon carbide transition layer.

[0089] Preferably, as shown in the attached Figure 3 The first microchannel is in a spiral shape (mosquito coil pattern). The etching width of the first microchannel 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 microchannel 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.

[0090] Further, as a preferred embodiment of the present application, before forming the silicon carbide seed crystal, the preparation method further includes steps S24 - S27.

[0091] Step S24: Polish the silicon surface of the silicon carbide transition layer in the diamond / silicon carbide composite structure.

[0092] For example, polish the silicon surface of the silicon carbide transition layer by mechanical grinding to make its surface roughness less than 1 - 5 nm.

[0093] Step S25: Pickle the polished diamond / silicon carbide composite structure.

[0094] For example, soak and pickle the diamond / silicon carbide composite structure in aqua regia (a mixture of nitric acid and hydrochloric acid) for 30 min to remove the contaminated particles on the silicon surface of the silicon carbide transition layer.

[0095] Step S26: Ultrasonically clean the pickled diamond / silicon carbide composite structure.

[0096] For example, ultrasonic cleaning of the diamond / silicon carbide composite structure with an acetone solution for 10 min is used to penetrate the surface micropore structure of the diamond / silicon carbide composite structure to achieve dead - angle - free cleaning. This can not only further remove the contaminant particles on the surface of the diamond / silicon carbide composite structure, but also form micro - scratches on the surface of the diamond / silicon carbide composite structure, optimize its surface morphology, thereby increasing the nucleation density and bonding force with the silicon carbide seed crystal in the subsequent process, so that the nucleation density can be as high as 10 9 / cm 2 .

[0097] Step S27: Dry the diamond / silicon carbide composite structure after ultrasonic cleaning.

[0098] For example, bake the diamond / silicon carbide composite structure in an oven at 200 °C for 15 min to dry the diamond / silicon carbide composite structure.

[0099] After the above steps, efficient decontamination of the diamond / silicon carbide composite structure is achieved, ensuring the integrity and high cleanliness of its surface. This can reduce the defects caused by contaminants during the subsequent formation of the silicon carbide seed crystal, so that the number of particulate matters (0.3 - μm scale) on the surface of the diamond / silicon carbide composite structure is less than 500 - 1000, ensuring the uniformity and adhesion of the silicon carbide seed crystal on the silicon surface of the silicon carbide transition layer.

[0100] Further, as a preferred embodiment of the present application, before forming the silicon carbide seed crystal, the preparation method further includes steps S24b - S27b.

[0101] Step S24b: Polish the silicon surface of the silicon carbide seed crystal.

[0102] For example, polish the silicon surface of the silicon carbide seed crystal by mechanical grinding to make its surface roughness less than the third preset roughness, and the value range of the third preset roughness is 1 - 5 nm. The surface roughness of the silicon surface of the silicon carbide seed crystal can be, for example, 0.5 nm, 1 nm, 2 nm, 3 nm, or 4 nm.

[0103] Step S25b: Pickle the polished silicon carbide seed crystal.

[0104] For example, soak and pickle the silicon carbide seed crystal in aqua regia (a mixture of nitric acid and hydrochloric acid) for 30 min to remove the contaminant particles on the silicon surface of the silicon carbide seed crystal.

[0105] Step S26b: Ultrasonically clean the pickled silicon carbide seed crystal.

[0106] For example, the silicon carbide seed crystal is ultrasonically cleaned in an acetone solution for 10 minutes to penetrate the surface micropore structure of the silicon carbide seed crystal and achieve dead - end cleaning. This can not only further remove the contaminant particles on the surface of the silicon carbide seed crystal but also form minute scratches on the surface of the silicon carbide seed crystal to optimize its surface morphology, thereby increasing the nucleation density and bonding strength of the subsequent diamond / silicon carbide composite structure, so that the nucleation density can be as high as 10 9 / cm 2 。

[0107] Step S27b: Dry the ultrasonically cleaned silicon carbide seed crystal.

[0108] For example, the silicon carbide seed crystal is baked in an oven at 200°C for 15 minutes to dry the silicon carbide seed crystal.

[0109] After the above steps, efficient decontamination of the silicon carbide seed crystal is achieved, ensuring the integrity and high cleanliness of its surface. This can reduce defects caused by contaminants during the subsequent formation of the silicon carbide seed crystal, so that the number of particulate matters (0.3μm scale) on the surface of the silicon carbide seed crystal is less than 500 - 1000, ensuring the uniformity and adhesion of the silicon carbide seed crystal on the silicon surface of the silicon carbide transition layer.

[0110] Further, as a preferred embodiment of the present application, before forming the silicon carbide seed crystal (which can be before the hetero - bonding of the silicon surface of the diamond / silicon carbide composite structure and the silicon surface of the initial silicon carbide seed crystal), the preparation method further includes step S28.

[0111] Step S28: Etch a groove - shaped second micro - channel or a raised second micro - channel on the silicon surface of the initial silicon carbide seed crystal.

[0112] Preferably, as shown in the attached Figure 3 figure, the second micro - channel is spiral (mosquito - coil pattern). The etching width of the second micro - channel is 5 - 10μm, for example, it can be 5μm, 6μm, 7μm, 8μm, 9μm or 10μm; the etching depth of the second micro - channel is 30 - 50μm, for example, it can be 30μm, 35μm, 40μm, 45μm or 50μm; the lateral spacing of the second micro - channel is 5 - 10mm, for example, it can be 5mm, 6mm, 7mm, 8mm, 9mm or 10mm.

[0113] It should be noted that the raised second micro - channel corresponds to the groove - shaped first micro - channel so that the raised second micro - channel can be embedded in the groove - shaped first micro - channel; the raised first micro - channel corresponds to the groove - shaped second micro - channel so that the raised first micro - channel can be embedded in the groove - shaped second micro - channel.

[0114] The corresponding chimerism of the first microchannel and the second microchannel can increase the contact surface area between the silicon carbide seed crystal and the silicon carbide transition layer during the bonding process, thereby enhancing the heat transfer ability of the silicon carbide seed crystal and the silicon carbide transition layer to accumulate heat during the growth process, and contributing to establishing a larger temperature gradient in the vertical and horizontal directions for the silicon carbide composite seed crystal.

[0115] Step S3: Form a silicon carbide seed crystal on the silicon surface of the diamond / silicon carbide composite structure, and make the carbon surface of the silicon carbide seed crystal away from the silicon surface of the silicon carbide transition layer to obtain a silicon carbide composite seed crystal.

[0116] 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.

[0117] 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.

[0118] By controlling the thickness of the silicon carbide seed crystal within the above 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%.

[0119] It should be noted that 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. The silicon carbide material in the silicon carbide seed crystal can be 3C, 4H, 6H or 15R crystal form, etc., and in this embodiment, it is preferably 4H crystal form.

[0120] It should be further noted that during the process of forming the silicon carbide seed crystal on the silicon surface of the diamond / silicon carbide composite structure, the silicon surface of the silicon carbide transition layer and the silicon surface of the silicon carbide seed crystal are combined by silicon atom diffusion. Since the silicon atoms of the silicon carbide transition layer and the silicon atoms of the silicon carbide seed crystal are combined in the form of forming covalent bonds, and there is no transition intermediate layer between the two, the combination of the two is tighter.

[0121] Furthermore, as a preferred embodiment of the present application, forming the silicon carbide seed crystal on the silicon surface of the diamond / silicon carbide composite structure includes steps S31a - S32a.

[0122] Step S31a: Under the conditions of a temperature of 1900 - 2100 °C and a pressure of 0.001 - 0.03 Pa, perform hetero - bonding on the silicon surface of the diamond / silicon carbide composite structure and the silicon surface of the initial silicon carbide seed crystal to obtain a second hetero - bonded structure.

[0123] The temperature can be 1900 °C, 1950 °C, 2000 °C, 2050 °C or 2100 °C; the air 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.

[0124] The inventors' in-depth research 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 strength. If the air 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 affect the bonding effect; if the air pressure is lower than 0.001 Pa, the requirements for the system equipment are very high and the cost is large. Therefore, it is necessary to control the temperature and air pressure of the heterogeneous bonding within the above ranges.

[0125] Under the above conditions, heterogeneous bonding is carried out (the bonding surfaces are all silicon surfaces). The lattice mismatch between the silicon carbide transition layer and the initial 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, reduce micropores and gaps, and improve the density and mechanical strength of the second heterogeneous bonding structure; further, it can also reduce the interface residual stress caused by the thermal expansion difference between the diamond / silicon carbide composite structure and the initial silicon carbide seed crystal, and prevent the second heterogeneous bonding structure from cracking.

[0126] Step S32a: After the heterogeneous bonding is completed, under the conditions that the annealing temperature is 1800 - 1900 °C and the annealing atmosphere is argon or nitrogen, the second heterogeneous bonding structure is annealed for 20 - 40 h to form a silicon carbide seed crystal.

[0127] 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.

[0128] The inventors' further research found 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 is high and it is of little significance; correspondingly, the same is true for the annealing time.

[0129] Annealing the second heterogeneous bonding structure under the above conditions can not only reduce the internal thermal stress generated during the bonding process, but also promote the physical diffusion of silicon atoms at high temperature and reduce the interface thermal resistance.

[0130] As another preferred embodiment of the present application, forming a silicon carbide seed crystal on the silicon surface of the diamond / silicon carbide composite structure includes step S31b.

[0131] Step S31b: Under the conditions of a temperature of 850 - 900 °C, a pressure of 20 - 30 Kpa, a flow rate of both SiH4 and CH4 of 2 - 20 sccm, and a flow rate of H2 of 200 - 500 sccm, chemical vapor deposition is performed on the silicon surface of the diamond / silicon carbide composite structure to prepare a silicon carbide seed crystal.

[0132] The growth time of the silicon carbide seed crystal is 10 - 20 h. For example, the growth time can be 10 h, 12 h, 15 h, 18 h, or 20 h. The temperature can be 850 °C, 860 °C, 870 °C, 880 °C, 890 °C, or 900 °C; the pressure can be 20 Kpa, 22 Kpa, 25 Kpa, 28 Kpa, or 30 Kpa; the flow rates of both SiH4 and 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.

[0133] The inventors further studied and found that during the process of chemical vapor deposition growth of silicon carbide seed crystals, 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 silicon carbide seed crystals 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, and although the growth rate is fast, amorphous carbides are likely to appear.

[0134] SiH4 and CH4 are the source gas for chemical vapor deposition growth of silicon carbide. 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 H2 is the carrier transport gas for the source 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 other amorphous carbide materials.

[0135] If the growth time is too short (less than 10 h), a silicon carbide seed crystal of a certain thickness cannot be produced; if the growth time is too long (greater than 20 h), the quality of the silicon carbide seed crystal is not high, which is not conducive to the preparation of the silicon carbide composite seed crystal.

[0136] Using the above conditions, silicon carbide seeds are prepared by chemical vapor deposition on the silicon surface of the diamond / silicon carbide composite structure. This not only provides a good material basis for the homoepitaxial growth or bonding of the silicon carbide transition layer and the silicon carbide seeds, but also prevents the extension of dislocation defects inside the diamond to the silicon carbide seeds, affecting the quality of the grown silicon carbide crystals.

[0137] In this application, by utilizing the extremely high thermal conductivity of diamond materials (2000 - 2200 W / (m·K)), the heat accumulated by the silicon carbide seeds can be quickly conducted out in the vertical direction, thereby reducing the temperature of the silicon carbide seeds. Since during the growth of thick crystals, the required temperature gradient in the vertical direction is determined by the temperature difference between the diamond / silicon carbide composite structure located at the lower part of the growth cavity and the temperature of the silicon carbide seeds located at the upper part of the growth cavity. The temperature of the diamond / silicon carbide composite structure is higher than that of the silicon carbide seeds. The greater the temperature difference between the two, the greater the temperature gradient in the vertical direction within a certain spacing range. This vertical temperature gradient is the crystallization driving force required for the growth of high-thickness silicon carbide crystals. The greater the vertical temperature gradient, the greater the vertical crystallization driving force, and the faster the crystal growth rate in the vertical direction. High-thickness silicon carbide crystals can be grown within the same growth period.

[0138] Since during the growth of large-diameter crystals, the required temperature gradient in the horizontal direction is determined by the temperature difference between the temperature of the silicon carbide seeds located 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 seeds. The greater the temperature difference between the two, the greater the temperature gradient in the horizontal direction within a certain spacing range. This horizontal temperature gradient is the crystallization driving force required for the growth of large-diameter silicon carbide crystals. The greater the horizontal temperature gradient, the greater the horizontal crystallization driving force, and the faster the crystal growth rate in the vertical direction. Large-diameter silicon carbide crystals can be grown within the same growth period.

[0139] Therefore, using the silicon carbide composite seeds provided in this application can establish relatively large temperature gradients 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 quickly 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. In summary, the silicon carbide composite seeds prepared by the above method can ensure the growth quality of silicon carbide crystals while achieving the growth of large-diameter, high-thickness, and low-cost silicon carbide crystals.

[0140] In the second aspect of this embodiment, a silicon carbide composite seed is provided, and the silicon carbide composite seed is prepared by using the preparation method of the above-mentioned silicon carbide composite seed.

[0141] As Figure 2 shown, the silicon carbide composite seed crystal 10 includes a diamond substrate 11, a silicon carbide transition layer 12, and a silicon carbide seed crystal 13. The silicon carbide transition layer 12 is disposed on the diamond substrate 11; the silicon carbide seed crystal 13 is disposed on a side of the silicon carbide transition layer 12 away from the diamond substrate 11.

[0142] In a 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.

[0143] 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.

[0144] It should be noted that for the following embodiments where specific conditions are not indicated, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments where the manufacturer is not indicated, they are all conventional products that can be obtained through commercial purchase.

[0145] Example 1

[0146] This embodiment provides a method for preparing a silicon carbide composite seed crystal, including the following steps:

[0147] S11: Provide a diamond substrate with a thickness of 300 μm and a roughness of 1 nm.

[0148] S12: Under the conditions of a temperature of 850 °C, a pressure of 20 Kpa, a flow rate of SiH4 and CH4 both being 2 sccm, and a flow rate of H2 being 200 sccm, use chemical vapor deposition to grow a silicon carbide transition layer with a thickness of 10 μm on the surface of the diamond substrate for 10 h.

[0149] S13: Under the conditions of a temperature of 850 °C, a pressure of 20 Kpa, a flow rate of SiH4 and CH4 both being 2 sccm, and a flow rate of H2 being 200 sccm, use chemical vapor deposition to grow a silicon carbide seed crystal with a thickness of 140 μm on the silicon surface of the diamond / silicon carbide composite structure for 10 h, thereby obtaining the silicon carbide composite seed crystal.

[0150] Example 2

[0151] This embodiment provides a method for preparing a silicon carbide composite seed crystal, including the following steps:

[0152] S11: Provide a diamond substrate with a thickness of 480 μm and a roughness of 4 nm.

[0153] 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 silicon carbide transition layer with a thickness of 50 μm is grown on the surface of a diamond substrate by chemical vapor deposition for 20 h.

[0154] S13: 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 silicon carbide seed crystal with a thickness of 200 μm is grown on the surface of a diamond / silicon carbide composite structure by chemical vapor deposition for 20 h, thereby obtaining a silicon carbide composite seed crystal.

[0155] Example 3

[0156] This example provides a method for preparing a silicon carbide composite seed crystal, including the following steps:

[0157] S11: Provide a diamond substrate with a thickness of 350 μm and a roughness of 3 nm.

[0158] S12: Under the conditions of a temperature of 875 °C, a pressure of 25 Kpa, a flow rate of 11 sccm for both SiH4 and CH4, and a flow rate of 350 sccm for H2, a silicon carbide transition layer with a thickness of 30 μm is grown on the surface of a diamond substrate by chemical vapor deposition for 15 h.

[0159] S13: Under the conditions of a temperature of 875 °C, a pressure of 25 Kpa, a flow rate of 11 sccm for both SiH4 and CH4, and a flow rate of 350 sccm for H2, a silicon carbide seed crystal with a thickness of 150 μm is grown on the surface of a diamond / silicon carbide composite structure by chemical vapor deposition for 15 h, thereby obtaining a silicon carbide composite seed crystal.

[0160] Example 4

[0161] This example provides a method for preparing a silicon carbide composite seed crystal, including the following steps:

[0162] S11: Provide a diamond substrate with a thickness of 300 μm and a roughness of 1 nm.

[0163] 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 silicon carbide transition layer with a thickness of 10 μm is grown on the surface of a diamond substrate by chemical vapor deposition for 10 h to prepare the silicon carbide transition layer.

[0164] S14: Under the conditions of a temperature of 1900 °C and a pressure of 0.001 Pa, hetero - bond the silicon surface of the diamond / silicon carbide composite structure with the silicon surface of the initial silicon carbide seed crystal to obtain a second hetero - bonded structure.

[0165] 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 to form a silicon carbide seed crystal with a thickness of 140 μm, thereby obtaining a silicon carbide composite seed crystal.

[0166] Example 5

[0167] This example provides a method for preparing a silicon carbide composite seed crystal, including the following steps:

[0168] S11: Provide a diamond substrate with a thickness of 480 μm and a roughness of 4 nm.

[0169] S12: Under the conditions of a temperature of 900 °C, a pressure of 30 KPa, a flow rate of both SiH4 and CH4 of 20 sccm, and a flow rate of H2 of 500 sccm, use chemical vapor deposition to grow on the surface of the diamond substrate for 20 h to prepare a silicon carbide transition layer with a thickness of 50 μm.

[0170] S14: Under the conditions of a temperature of 2100 °C and a pressure of 0.03 Pa, hetero - bond the silicon surface of the diamond / silicon carbide composite structure with the silicon surface of the initial silicon carbide seed crystal to obtain a second hetero - bonded structure.

[0171] S15: After the hetero - bonding is completed, anneal the second hetero - bonded structure for 40 h under the conditions of an annealing temperature of 1900 °C and an annealing atmosphere of argon or nitrogen to form a silicon carbide seed crystal with a thickness of 200 μm, thereby obtaining a silicon carbide composite seed crystal.

[0172] Example 6

[0173] This example provides a method for preparing a silicon carbide composite seed crystal, including the following steps:

[0174] S11: Provide a diamond substrate with a thickness of 350 μm and a roughness of 3 nm.

[0175] S12: Under the conditions of a temperature of 875 °C, a pressure of 25 KPa, a flow rate of both SiH4 and CH4 of 11 sccm, and a flow rate of H2 of 350 sccm, use chemical vapor deposition to grow on the surface of the diamond substrate for 15 h to form a silicon carbide transition layer with a thickness of 30 μm.

[0176] S14: Under the conditions of a temperature of 2000 °C and a pressure of 0.02 Pa, hetero - bond the silicon surface of the diamond / silicon carbide composite structure with the silicon surface of the initial silicon carbide seed crystal to obtain a second hetero - bonded structure.

[0177] S15: After the hetero - bonding is completed, anneal the second hetero - bonded structure for 30 h under the conditions of an annealing temperature of 1850 °C and an annealing atmosphere of argon or nitrogen to form a silicon carbide seed crystal with a thickness of 150 μm, thereby obtaining a silicon carbide composite seed crystal.

[0178] Example 7

[0179] This example provides a method for preparing a silicon carbide composite seed crystal, including the following steps:

[0180] S11: Provide a diamond substrate with a thickness of 300 μm and a roughness of 1 nm.

[0181] S12: Under the conditions of a temperature of 1900 °C and a pressure of 0.001 Pa, hetero - bond the surface of the diamond substrate with the carbon surface of the initial silicon carbide transition layer to obtain a first hetero - bonded structure.

[0182] S13: After the hetero - bonding is completed, anneal 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 to form a silicon carbide transition layer with a thickness of 10 μm.

[0183] S14: 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 H2 flow rate of 200 sccm, use chemical vapor deposition to grow a silicon carbide seed crystal with a thickness of 140 μm on the silicon surface of the diamond / silicon carbide composite structure for 10 h, thereby obtaining a silicon carbide composite seed crystal.

[0184] Example 8

[0185] This example provides a method for preparing a silicon carbide composite seed crystal, including the following steps:

[0186] S11: Provide a diamond substrate with a thickness of 480 μm and a roughness of 4 nm.

[0187] S12: Under the conditions of a temperature of 2100 °C and a pressure of 0.03 Pa, hetero - bond the surface of the diamond substrate with the carbon surface of the initial silicon carbide transition layer to obtain a first hetero - bonded structure.

[0188] S13: After the hetero - bonding is completed, anneal the first hetero - bonded structure for 40 h under the conditions of an annealing temperature of 1900 °C and an annealing atmosphere of argon or nitrogen to form a silicon carbide transition layer with a thickness of 50 μm.

[0189] S14: 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 silicon carbide seed crystal with a thickness of 200 μm is grown on the surface of the diamond / silicon carbide composite structure for 20 h by chemical vapor deposition, thereby obtaining a silicon carbide composite seed crystal.

[0190] Example 9

[0191] This example provides a method for preparing a silicon carbide composite seed crystal, including the following steps:

[0192] S11: Provide a diamond substrate with a thickness of 350 μm and a roughness of 3 nm.

[0193] S12: Under the conditions of a temperature of 2000 °C and a pressure of 0.02 pa, the surface of the diamond substrate is hetero-bonded with the carbon surface of the initial silicon carbide transition layer to obtain a first hetero-bonded structure.

[0194] S13: After the hetero-bonding is completed, the first hetero-bonded structure is annealed for 30 h under the conditions of an annealing temperature of 1850 °C and an annealing atmosphere of argon or nitrogen to form a silicon carbide transition layer with a thickness of 30 μm.

[0195] S14: Under the conditions of a temperature of 875 °C, a pressure of 25 Kpa, a flow rate of 11 sccm for both SiH4 and CH4, and a flow rate of 350 sccm for H2, a silicon carbide seed crystal with a thickness of 150 μm is grown on the surface of the diamond / silicon carbide composite structure for 15 h by chemical vapor deposition, thereby obtaining a silicon carbide composite seed crystal.

[0196] Example 10

[0197] This example provides a method for preparing a silicon carbide composite seed crystal, including the following steps:

[0198] S11: Provide a diamond substrate with a thickness of 300 μm and a roughness of 1 nm.

[0199] S12: Under the conditions of a temperature of 1900 °C and a pressure of 0.001 pa, the surface of the diamond substrate is hetero-bonded with the carbon surface of the initial silicon carbide transition layer to obtain a first hetero-bonded structure.

[0200] S13: After the hetero-bonding is completed, the first hetero-bonded structure is annealed for 20 h under the conditions of an annealing temperature of 1800 °C and an annealing atmosphere of argon or nitrogen to form a silicon carbide transition layer with a thickness of 10 μm.

[0201] S14: Under the conditions of a temperature of 1900 °C and a pressure of 0.001 Pa, hetero-bond the silicon surface of the diamond / silicon carbide composite structure with the silicon surface of the initial silicon carbide seed crystal to obtain a second hetero-bonded structure.

[0202] 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 to form a silicon carbide seed crystal with a thickness of 140 μm, so as to obtain a silicon carbide composite seed crystal.

[0203] Example 11

[0204] This example provides a method for preparing a silicon carbide composite seed crystal, including the following steps:

[0205] S11: Provide a diamond substrate with a thickness of 480 μm and a roughness of 4 nm.

[0206] S12: Under the conditions of a temperature of 2100 °C and a pressure of 0.03 Pa, hetero-bond the surface of the diamond substrate with the carbon surface of the initial silicon carbide transition layer to obtain a first hetero-bonded structure.

[0207] S13: After the hetero-bonding is completed, anneal the first hetero-bonded structure for 40 h under the conditions of an annealing temperature of 1900 °C and an annealing atmosphere of argon or nitrogen to form a silicon carbide transition layer with a thickness of 50 μm.

[0208] S14: Under the conditions of a temperature of 2100 °C and a pressure of 0.03 Pa, hetero-bond the silicon surface of the diamond / silicon carbide composite structure with the silicon surface of the initial silicon carbide seed crystal to obtain a second hetero-bonded structure.

[0209] S15: After the hetero-bonding is completed, anneal the second hetero-bonded structure for 40 h under the conditions of an annealing temperature of 1900 °C and an annealing atmosphere of argon or nitrogen to form a silicon carbide seed crystal with a thickness of 200 μm, so as to obtain a silicon carbide composite seed crystal.

[0210] Example 12

[0211] This example provides a method for preparing a silicon carbide composite seed crystal, including the following steps:

[0212] S11: Provide a diamond substrate with a thickness of 350 μm and a roughness of 3 nm.

[0213] S12: Under the conditions of a temperature of 2000 °C and a pressure of 0.02 Pa, hetero-bond the surface of the diamond substrate with the carbon surface of the initial silicon carbide transition layer to obtain a first hetero-bonded structure.

[0214] S13: After the heterogeneous bonding is completed, the first heterogeneous bonding structure is annealed for 30 h at an annealing temperature of 1850 °C and an annealing atmosphere of argon or nitrogen to form a silicon carbide transition layer with a thickness of 30 μm.

[0215] S14: Under the conditions of a temperature of 2000 °C and a pressure of 0.03 Pa, the silicon surface of the diamond / silicon carbide composite structure is heterogeneously bonded to the silicon surface of the initial silicon carbide seed crystal to obtain a second heterogeneous bonding structure.

[0216] S15: After the heterogeneous bonding is completed, the second heterogeneous bonding structure is annealed for 30 h at an annealing temperature of 1850 °C and an annealing atmosphere of argon or nitrogen to form a silicon carbide seed crystal with a thickness of 150 μm to obtain a silicon carbide composite seed crystal.

[0217] Example 13

[0218] Similar to the preparation method of Example 11, the difference is that: a groove-shaped first microchannel is etched on the silicon surface of the silicon carbide transition layer; the others are the same and will not be elaborated here.

[0219] The width of the first microchannel is 5 μm, the depth of the first microchannel is 30 μm, and the lateral spacing of the first microchannels is 5 mm.

[0220] Example 14

[0221] Similar to the preparation method of Example 11, the difference is that: a convex second microchannel is etched on the silicon surface of the initial silicon carbide seed crystal; the others are the same and will not be elaborated here.

[0222] The width of the second microchannel is 5 μm, the depth of the first microchannel is 30 μm, and the lateral spacing of the first microchannels is 5 mm.

[0223] Example 15

[0224] Similar to the preparation method of Example 11, the difference is that: a groove-shaped first microchannel is etched on the silicon surface of the silicon carbide transition layer and a convex second microchannel is etched on the silicon surface of the initial silicon carbide seed crystal; the others are the same and will not be elaborated here.

[0225] The width of the first microchannel is 5 μm, the depth of the first microchannel is 30 μm, and the lateral spacing of the first microchannels is 5 mm; the width of the second microchannel is 5 μm, the depth of the first microchannel is 30 μm, and the lateral spacing of the first microchannels is 5 mm.

[0226] The silicon carbide composite seed crystals prepared in Examples 1-15 are used to grow silicon carbide crystals respectively, and the growth conditions include: a growth temperature of 2200-2300 °C, a pressure of 3×10 -3 Pa - 5×10-3 The growth temperature is 2200 - 2300 °C, the pressure is 3×10

[0227] 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.

[0228] 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 growing silicon carbide crystals using a pure silicon carbide seed 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.

[0229] It can be seen from this that compared with the existing pure silicon carbide seed crystal, when using the silicon carbide composite seed crystal provided by this application to prepare silicon carbide crystals, the average growth rate is relatively fast, and it is possible to grow silicon carbide crystals with a thicker thickness and a larger diameter. Moreover, the surface of the grown silicon carbide crystal is flat, has good light transmittance, has no polycrystalline phenomenon, and has better quality.

[0230] Although the embodiments of this application have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limitations on this application. Without departing from the principles and purposes of this 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 these changes should fall within the protection scope of the claims of this application.

Claims

1. A preparation method of a silicon carbide composite seed crystal, characterized in that, It includes the following steps: Provide a diamond substrate; Form a silicon carbide transition layer on the surface of the diamond substrate, and make the silicon surface of the silicon carbide transition layer away from the surface of the diamond substrate to obtain a diamond / silicon carbide composite structure; Form a silicon carbide seed crystal on the silicon surface of the diamond / silicon carbide composite structure, and make the carbon surface of the silicon carbide seed crystal away from the silicon 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 substrate, 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 surface of the diamond substrate, the surface of the diamond substrate and the carbon surface of the silicon carbide transition layer are bonded by carbon atom diffusion; the forming of the silicon carbide transition layer on the surface of the diamond substrate 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, perform chemical vapor deposition on the surface of the diamond substrate to prepare the silicon carbide transition layer; wherein, the growth time of the silicon carbide transition layer is 10-20 h.

3. The preparation method according to claim 1, wherein, During the process of forming the silicon carbide transition layer on the surface of the diamond substrate, the surface of the diamond substrate and the carbon surface of the silicon carbide transition layer are bonded by carbon atom diffusion; the forming of the silicon carbide transition layer on the surface of the diamond substrate includes: Under the conditions of a temperature of 1900-2100 °C and a pressure of 0.001-0.03 pa, perform hetero-bonding on the surface of the diamond substrate and the carbon surface of the initial silicon carbide transition layer to obtain a first hetero-bonded structure; After the hetero-bonding is completed, perform an annealing treatment on the first hetero-bonded structure for 20-40 h under the conditions of an annealing temperature of 1800-1900 °C and an annealing atmosphere of argon or nitrogen to form the silicon carbide transition layer.

4. The preparation method according to claim 1, characterized in that During the process of forming the silicon carbide seed crystal on the silicon surface of the diamond / silicon carbide composite structure, the silicon surface of the silicon carbide transition layer and the silicon surface of the silicon carbide seed crystal are bonded by silicon atom diffusion; the forming of the silicon carbide seed crystal on the silicon surface of the diamond / silicon carbide composite structure 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, perform chemical vapor deposition on the surface of the diamond / silicon carbide composite structure to prepare the silicon carbide seed crystal; wherein, the growth time of the silicon carbide seed crystal is 10-20 h.

5. The preparation method according to claim 1, characterized in that, During the process of forming the silicon carbide seed crystal on the silicon surface of the diamond / silicon carbide composite structure, the silicon surface of the silicon carbide transition layer and the silicon surface of the silicon carbide seed crystal are bonded by silicon atom diffusion; The forming of the silicon carbide seed crystal on the silicon surface of the diamond / silicon carbide composite structure includes: Under the conditions of a temperature of 1900 - 2100 °C and a pressure of 0.001 - 0.03 Pa, the silicon surface of the diamond / silicon carbide composite structure is hetero-bonded with the silicon surface of the initial silicon carbide seed crystal to obtain a second hetero-bonded structure; After the hetero-bonding is completed, under the conditions of an annealing temperature of 1800 - 1900 °C and an annealing atmosphere of argon or nitrogen, the second hetero-bonded structure is annealed for 20 - 40 h to form the silicon carbide seed crystal.

6. According to the preparation method described in any one of claims 1-5, characterized in that, After forming the silicon carbide transition layer, the method further includes: Forming a grooved first microchannel on the silicon surface of the silicon carbide transition layer; or forming a raised first microchannel on the silicon surface of the silicon carbide transition layer; Wherein, the width of the first microchannel is 5 - 10 μm; and / or the depth of the first microchannel is 30 - 50 μm; and / or the lateral pitch of the first microchannel is 5 - 10 mm.

7. The preparation method according to claim 6, characterized in that, Before forming the silicon carbide seed crystal, the method further includes: Forming a grooved second microchannel on the silicon surface of the initial silicon carbide seed crystal; or forming a raised second microchannel on the silicon surface of the initial silicon carbide seed crystal; Wherein, the width of the second microchannel is 5 - 10 μm; and / or the depth of the second microchannel is 30 - 50 μm; and / or the lateral pitch of the second microchannel is 5 - 10 mm; The raised second microchannel corresponds to the grooved first microchannel so that the raised second microchannel can be embedded in the grooved first microchannel; The raised first microchannel corresponds to the grooved second microchannel so that the raised first microchannel can be embedded in the grooved second microchannel.

8. The preparation method according to claim 1, wherein The diamond substrate is single-crystal diamond or polycrystalline diamond; and / or, the thickness of the diamond substrate is 300 - 500 μm; and / or, the thickness of the diamond substrate is less than or equal to two-thirds of the thickness of the silicon carbide composite seed crystal and greater than or equal to one-half of the thickness of the silicon carbide composite seed crystal; and / or, the surface roughness of the diamond substrate is less than a first preset roughness, and the value range of the first preset roughness is 1 - 5 nm; and / or, the silicon carbide material in the silicon carbide transition layer is of 3C, 4H, 6H or 15R crystal form; and / or, the thickness of the silicon carbide transition layer is 10 - 50 μm; and / or, the surface roughness of the silicon surface of the silicon carbide transition layer is less than a second preset roughness, and the value range of the second preset roughness is 1 - 5 nm; and / or, the thickness of the silicon carbide seed crystal is 100 - 200 μm; 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; and / or, the surface roughness of the silicon surface of the silicon carbide seed crystal is less than a third preset roughness, and the value range of the third preset roughness is 1 - 5 nm.

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 comprises the silicon carbide composite seed crystal as described in Claim 9.

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