A high-purity silicon carbide and its preparation method

Abstract

The present invention relates to the field of semiconductor materials, and discloses a high-purity silicon carbide and a preparation method thereof. The preparation method includes: (1) performing decarbonization treatment on silicon carbide powder to obtain first silicon carbide powder; (2) performing ultrasonic cleaning treatment and drying on the first silicon carbide powder to obtain second silicon carbide powder; (3) performing mixing treatment on carbon powder, silicon powder and the second silicon carbide powder to obtain mixture I; (4) reacting the mixture I by a three-stage programmed temperature rising method to obtain high-purity silicon carbide. The method for preparing high-purity silicon carbide provided by the present invention can improve the purity of silicon carbide crystals and can also increase the yield ratio of large-size silicon carbide crystals.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor materials, and specifically, to a high-purity silicon carbide and a preparation method thereof. Background Art

[0002] As a third-generation semiconductor material, silicon carbide crystals have advantages such as a wide bandgap, high thermal conductivity, high critical breakdown field strength, and high electron saturation drift rate, and have great application prospects in the field of semiconductor manufacturing.

[0003] Currently, silicon carbide single crystals are mainly grown by the PVT method. The specific growth method is as follows: The silicon carbide seed crystal is bonded to the seed crystal stage at the top of the graphite crucible, silicon carbide powder is placed at the bottom of the crucible, and then the graphite crucible is placed in a crystal growth furnace for heating. As the temperature rises, the silicon carbide powder at the bottom of the crucible evaporates and crystallizes at the top of the graphite crucible. However, during this process, the purity, particle size, and crystal form of the silicon carbide powder have a great influence on the growth of silicon carbide crystals.

[0004] In addition, the synthesis of silicon carbide powder mainly uses the self-propagating high-temperature synthesis method for growth. The high-purity carbon powder and high-purity silicon powder are fully mixed in a ratio of 1:1. After mixing, it is placed in a high-purity graphite crucible, and then the high-purity graphite crucible is placed in a furnace, evacuated, and then high-purity argon gas is introduced as a protective atmosphere, and then heated up immediately. When the reaction is over, the silicon carbide powder is taken out, and then crushed, screened, carbon-removed, screened, cleaned, and dried to obtain silicon carbide powder. However, when preparing silicon carbide powder by this method, silicon carbide powder with different particle sizes will be produced, and the finer silicon carbide is not suitable for the growth of silicon carbide crystals.

[0005] Therefore, in order to further expand the application of silicon carbide crystals, improving the quality of silicon carbide crystals and reducing the preparation cost on the basis of the existing technology have become the main development trends in the current preparation of silicon carbide crystals.

[0006] CN115124040A discloses a solid-phase synthesis method for increasing the proportion of large-particle-size silicon carbide powder. By adding a certain proportion of small-particle-size high-purity silicon carbide powder as nucleation points during raw material mixing, the growth of silicon carbide grains is induced, so that the proportion of large-particle-size powder in the synthesized silicon carbide powder is increased to more than 65%; however, when using this method to increase the proportion of large-particle-size silicon carbide powder, the purity requirement for the silicon carbide raw material powder is relatively high, resulting in a reduction in raw material utilization rate.

[0007] CN114182357A discloses a method for using crushed grains of silicon carbide crystals to regrow silicon carbide single crystals. By stacking silicon carbide powders with different particle sizes in sequence and heating, high-quality silicon carbide single crystals can be prepared; however, when using this method to prepare silicon carbide single crystals, the preparation process is relatively cumbersome and the preparation process is relatively complex.

[0008] CN113564712A discloses a method for recycling waste materials during the growth of silicon carbide single crystals. The method comprises the following steps: subjecting the recovered materials to a calcination treatment to remove carbon, a mixed acid washing treatment to remove trace elements, and an alkali oxidation treatment to remove silicon, thereby purifying and recovering silicon carbide powder, thereby achieving the recycling and reuse of the silicon carbide waste materials. However, when pre-treating the silicon carbide powder using this recycling method, a large amount of acid washing solvent and alkaline solvent are used, which will cause a certain degree of environmental pollution and increase the production cost of the silicon carbide crystals. Summary of the Invention

[0009] The purpose of the present invention is to overcome the defects of the prior art in the process of preparing silicon carbide crystals, that is, low utilization rate of small-particle size (180-230 μm) silicon carbide powder and low yield of large-particle size silicon carbide crystals.

[0010] In the process of preparing silicon carbide crystals in the prior art, the utilization rate of small-particle silicon carbide powder with a particle size of 180-230μm is very low. In order to utilize this part of the small-particle material, the prior art usually requires the application of a large amount of acid and / or alkali for pickling and alkali washing. The inventor found in the study that when the purity of the existing small-particle silicon carbide powder with a particle size of 180-230μm reaches 99.9wt% or more, this part of the small-particle silicon carbide powder is decarbonized in advance under specific conditions (specifically, a temperature of 800-900℃ and a time of 5-8h), and the material obtained after the decarbonization treatment is ultrasonically cleaned at a frequency of 40-60Hz for 60-180min. When this part of the specially treated small-particle silicon carbide powder is mixed with conventional carbon powder and silicon powder in a certain proportion and grown, the yield ratio of large-particle silicon carbide crystals can be significantly improved.

[0011] In order to achieve the above object, the first aspect of the present invention provides a method for preparing high-purity silicon carbide, the method comprising:

[0012] (1) decarbonizing silicon carbide powder having a particle size of 180-230 μm and a purity of not less than 99.9 wt % to obtain a first silicon carbide powder; the decarbonizing treatment is performed in the presence of compressed air, and the decarbonizing treatment conditions at least meet the following conditions: a temperature of 800-900° C. and a time of 5-8 hours;

[0013] (2) ultrasonically cleaning the first silicon carbide powder and drying it to obtain a second silicon carbide powder; the ultrasonic cleaning conditions at least meet the following requirements: an ultrasonic frequency of 40-60 Hz and a cleaning time of 60-180 min;

[0014] (3) Mix the carbon powder, silicon powder and the second silicon carbide powder in a weight ratio of 1 - 1.2:1 - 1.2:1 to obtain mixture I;

[0015] (4) In the presence of a protective atmosphere, react mixture I by the three - stage programmed heating method to obtain high - purity silicon carbide with a purity of not less than 99.99 wt%.

[0016] Preferably, in step (3), the purity of the carbon powder is not less than 99.999 wt%.

[0017] Preferably, in step (3), the purity of the silicon powder is not less than 99.999 wt%.

[0018] Preferably, in step (3), the particle sizes of the silicon powder and the carbon powder are each independently 60 - 100 μm.

[0019] Preferably, in step (3), the weight ratio of the carbon powder, the silicon powder and the second silicon carbide powder is 1 - 1.03:1 - 1.03:1.

[0020] Preferably, in step (3), the mixing time is more than 20 min and the stirring speed is 80 - 120 rpm.

[0021] More preferably, in step (3), the mixing treatment is carried out in a three - dimensional mixer.

[0022] Preferably, in step (4), the operation of the three - stage programmed heating method includes:

[0023] S1: Under the first pressure, heat mixture I at the first heating rate to the first temperature and keep it at the first temperature for the first time to obtain the first intermediate material;

[0024] S2: Under the second pressure, heat the first intermediate material at the second heating rate to the second temperature and keep it at the second temperature for the second time to obtain the second intermediate material;

[0025] S3: Under the third pressure, heat the second intermediate material at the third heating rate to the third temperature and keep it at the third temperature for the third time to obtain the high - purity silicon carbide.

[0026] Preferably, in step (4), in the operation of the three - stage programmed heating method,

[0027] In S1, the first pressure is 1.5 - 2.5 Torr, the first heating rate is 4 - 6 °C / min, the first temperature is 1300 - 1400 °C, and the first time is 2.5 - 4 h;

[0028] And / or, in S2, the second pressure is 95 - 100 Torr, the second heating rate is 5 - 6.5 °C / min, the second temperature is 1650 - 1750 °C, and the second time is 4 - 7 h;

[0029] And / or, in S3, the third pressure is 40 - 60 Torr, the third heating rate is 4.5 - 5.5 °C / min, the third temperature is 2250 - 2350 °C, and the third time is 16 - 24 h.

[0030] The second aspect of the present invention provides high-purity silicon carbide obtained by the method described in the first aspect.

[0031] Using the method provided by the present invention can improve the utilization rate of small-particle-size silicon carbide powder and can increase the yield ratio of large-particle-size silicon carbide crystals.

[0032] In particular, using the method provided by the present invention can improve the purity of silicon carbide crystals and does not use acid-base solvents during the preparation process, meeting the requirements of green chemistry. Description of the Drawings

[0033] Figure 1 It is a spectrogram of glow discharge mass spectrometry (GDMS) of the high-purity silicon carbide prepared in Example 1. Detailed Embodiments

[0034] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0035] As described above, the first aspect of the present invention provides a method for preparing high-purity silicon carbide, and the method includes:

[0036] (1) Carbon removal treatment is performed on silicon carbide powder with a particle size of 180 - 230 μm and a purity of not less than 99.9 wt% to obtain first silicon carbide powder; the carbon removal treatment is carried out in the presence of compressed air, and the conditions of the carbon removal treatment at least satisfy: the temperature is 800 - 900 °C and the time is 5 - 8 h;

[0037] (2) The first silicon carbide powder is subjected to ultrasonic cleaning treatment and dried to obtain second silicon carbide powder; the conditions of the ultrasonic cleaning at least satisfy: the ultrasonic frequency is 40 - 60 Hz and the cleaning time is 60 - 180 min;

[0038] (3) Mix the carbon powder, silicon powder and the second silicon carbide powder in a weight ratio of 1 - 1.2:1 - 1.2:1 to obtain mixture I;

[0039] (4) React mixture I using a three-stage programmed heating method in the presence of a protective atmosphere to obtain high-purity silicon carbide with a purity of not less than 99.99 wt%.

[0040] Preferably, in step (1), the method further includes: performing screening process I on the silicon carbide raw material powder to obtain the silicon carbide powder with a particle size of 180 - 230 μm and a purity of not less than 99.9 wt%, loading the silicon carbide powder into a quartz boat, and performing the decarbonization treatment in a tube furnace.

[0041] Preferably, the purity of the silicon carbide powder with a particle size of 180 - 230 μm is 99.9 - 99.99 wt%.

[0042] The present invention has no specific requirements for the specific process and specific equipment of screening process I. Those skilled in the art can carry out the screening process known in the art. The invention will not be elaborated herein, and those skilled in the art should not consider it as a limitation to the present invention.

[0043] According to a particularly preferred specific embodiment, step (2) of the present invention includes: performing ultrasonic cleaning treatment on the first silicon carbide powder in water and drying to obtain the second silicon carbide powder; the conditions of the ultrasonic cleaning at least satisfy: the ultrasonic frequency is 40 - 60 Hz, and the cleaning time is 60 - 180 min.

[0044] Preferably, in step (2), the drying conditions at least satisfy: the temperature is 200 - 250 °C, and the time is 2 - 5 h.

[0045] Preferably, in step (3), the purity of the carbon powder is not less than 99.999 wt%. More preferably, in step (3), the purity of the carbon powder is 99.999 wt% - 99.9999 wt%.

[0046] Preferably, in step (3), the purity of the silicon powder is not less than 99.999 wt%. More preferably, in step (3), the purity of the silicon powder is 99.999 wt% - 99.9999 wt%.

[0047] Preferably, in step (3), the particle sizes of the silicon powder and the carbon powder are each independently 60 - 100 μm.

[0048] Preferably, in step (3), the weight ratio of the carbon powder, the silicon powder, and the second silicon carbide powder is 1-1.03:1-1.03:1. The inventors have found that in this preferred embodiment, the prepared silicon carbide crystals have a larger particle size and a higher purity.

[0049] Preferably, in step (3), the mixing treatment time is more than 20 minutes, and the stirring speed is 80-120 rpm.

[0050] More preferably, in step (3), the mixing process is carried out in a three-dimensional mixer.

[0051] According to a preferred embodiment, the operation of step (4) includes: loading the mixed material I into a 12-15L crucible, placing the crucible in a furnace chamber, evacuating the chamber, and performing the three-stage programmed temperature method in the presence of a protective atmosphere.

[0052] More preferably, in step (4), the vacuum treatment conditions at least meet the following requirements: the time is 15-20 hours, the vacuum degree is not less than 10 -6 Torr, and replace it with a protective atmosphere with a purity of not less than 99.999 volume %, and the replacement times are 2-5 times.

[0053] Further preferably, in step (4), the protective atmosphere is selected from at least one of argon and helium.

[0054] Preferably, in step (4), the operation of the three-stage programmed temperature method includes:

[0055] S1: heating the mixed material I to a first temperature at a first heating rate under a first pressure, and maintaining the temperature at the first temperature for a first time to obtain a first intermediate material;

[0056] S2: heating the first intermediate material to a second temperature at a second heating rate under a second pressure, and maintaining the temperature at the second temperature for a second time to obtain a second intermediate material;

[0057] S3: Under a third pressure, heating the second intermediate material to a third temperature at a third heating rate, and maintaining the temperature at the third temperature for a third time to obtain the high-purity silicon carbide.

[0058] Preferably, in step (4), in step S1 of the three-stage programmed temperature method, the first pressure is 1.5-2.5 Torr, the first heating rate is 4-6°C / min, the first temperature is 1300-1400°C, and the first time is 2.5-4h.

[0059] Preferably, in step (4), in step S2 of the three-stage programmed temperature rise method, the second pressure is 95-100 Torr, the second heating rate is 5-6.5 °C / min, the second temperature is 1650-1750 °C, and the second time is 4-7 h.

[0060] Preferably, in step (4), in step S3 of the three-stage programmed temperature rise method, the third pressure is 40-60 Torr, the third heating rate is 4.5-5.5 °C / min, the third temperature is 2250-2350 °C, and the third time is 16-24 h.

[0061] Preferably, in step (4), the method further includes: cooling the material obtained by the three-stage programmed temperature rise method to 20-40 °C, and performing screening treatment II on the cooled material to obtain the high-purity silicon carbide.

[0062] The present invention has no specific requirements for the specific process and specific equipment of the screening treatment II. Those skilled in the art can perform it in combination with the known screening treatments in the art. The invention will not be elaborated here, and those skilled in the art should not understand it as a limitation of the present invention.

[0063] As described above, the second aspect of the present invention provides high-purity silicon carbide obtained by the method of the first aspect. [[ID=I4]]

[0064] The present invention will be described in detail below by way of examples. In the following examples, unless otherwise specified, the raw materials used are all commercially available.

[0065] Crucible: graphite crucible, model SGL-R6510, purchased from SGL Carbon (Shanghai) Co., Ltd.;

[0066] Three-dimensional mixer: model SYH-200, purchased from Changzhou Shengwanda Drying Equipment Co., Ltd.;

[0067] Carbon powder: purity 99.99 wt%, purchased from SGL Carbon (Shanghai) Co., Ltd.;

[0068] Carbon powder: purity 99.9999 wt%, purchased from SGL Carbon (Shanghai) Co., Ltd.;

[0069] Silicon powder: purity 99.99 wt%, purchased from Wacker Chemie (China) Co., Ltd.;

[0070] Silicon powder: purity 99.9999 wt%, purchased from Wacker Chemie (China) Co., Ltd.;

[0071] In the following examples, the silicon carbide powder with a particle size of 180 - 230 μm is obtained through screening treatment I. The purity of the silicon carbide powder is 99.99 wt%, and the amount of the silicon carbide powder used is 3400 g.

[0072] Example 1

[0073] This example provides a method for preparing high-purity silicon carbide, which includes:

[0074] (1) Loading the silicon carbide powder with a particle size of 180 - 230 μm into a quartz boat, and performing decarbonization treatment in a tubular furnace to obtain the first silicon carbide powder;

[0075] (2) Ultrasonically cleaning and drying the first silicon carbide powder in water to obtain the second silicon carbide powder;

[0076] (3) Mixing carbon powder, silicon powder and the second silicon carbide powder in a three-dimensional mixer at a weight ratio of 1:1.02:1 to obtain mixture I, and loading mixture I into a 15L graphite crucible;

[0077] (4) Placing the graphite crucible in the furnace cavity, after vacuum treatment, reacting under the presence of argon with a purity of 99.9999 vol% by using a three-stage programmed temperature rise method to obtain high-purity silicon carbide precursor I;

[0078] (5) Cooling the high-purity silicon carbide precursor I to 30°C, and performing screening treatment II on the cooled high-purity silicon carbide precursor I to obtain high-purity silicon carbide M1.

[0079] Unless otherwise specified, the remaining examples and comparative examples of the present invention are carried out using the same process flow as in Example 1. The difference is that the process parameters for preparing high-purity silicon carbide are different. For details, see Table 1.

[0080] Example 2

[0081] Prepare high-purity silicon carbide according to the process flow of Example 1. The difference is that the process parameters for preparing high-purity silicon carbide are different, and in this example, the weight ratio of the carbon powder, the silicon powder and the second silicon carbide powder used is 1.02:1:1.

[0082] The remaining steps are the same as in Example 1 to obtain high-purity silicon carbide M2.

[0083] Example 3

[0084] Prepare high-purity silicon carbide according to the process flow of Example 1. The difference is that the process parameters for preparing high-purity silicon carbide are different, and in this example, the weight ratio of the carbon powder, the silicon powder and the second silicon carbide powder used is 1:1:1.

[0085] The remaining steps are the same as those in Example 1 to obtain high-purity silicon carbide M3.

[0086] Example 4

[0087] Prepare high-purity silicon carbide according to the method of Example 1, except that in this example, the purity of the carbon powder is 99.99 wt%, and the purity of the silicon powder is 99.99 wt%.

[0088] The remaining steps are the same as those in Example 1 to obtain high-purity silicon carbide M4.

[0089] Table 1

[0090]

[0091]

[0092] Comparative Example 1

[0093] Prepare high-purity silicon carbide according to the method of Example 1, except that in this comparative example, the two-step heating method is used to replace the three-stage programmed heating method. Specifically:

[0094] (1) Load silicon carbide powder with a particle size of 180 - 230 μm into a quartz boat, and perform decarburization treatment in a tube furnace to obtain the first silicon carbide powder;

[0095] (2) Perform ultrasonic cleaning treatment on the first silicon carbide powder in water and dry it to obtain the second silicon carbide powder;

[0096] (3) Mix the carbon powder, silicon powder and the second silicon carbide powder in a three-dimensional mixer at a weight ratio of 1:1.02:1 to obtain mixture I, and load mixture I into a 15L graphite crucible;

[0097] (4) Place the graphite crucible in the furnace cavity, after vacuum treatment, react under the presence of argon with a purity of 99.9999 vol% using the two-step heating method to obtain high-purity silicon carbide precursor II;

[0098] (5) Cool the high-purity silicon carbide precursor II to 30 °C, and perform screening treatment II on the cooled high-purity silicon carbide precursor II to obtain high-purity silicon carbide DM1;

[0099] Among them, the operating conditions of the two-step heating method are:

[0100] DS1: Under a pressure of 2 Torr, heat mixture I to 1350 °C at a heating rate of 5.5 °C / min, and keep it at 1350 °C for 3 h to obtain intermediate material I;

[0101] DS2: At a pressure of 50 Torr, the intermediate material I is heated to 2300 °C at a heating rate of 5 °C / min and held at 2300 °C for 19 h to obtain high-purity silicon carbide DM1.

[0102] Comparative Example 2

[0103] High-purity silicon carbide is prepared according to the method of Example 1, except that the carbon removal treatment, ultrasonic cleaning treatment, and drying are carried out after the three-stage programmed heating method. Specifically:

[0104] (1) Carbon powder, silicon powder, and the silicon carbide powder with a particle size of 180 - 230 μm are mixed in a three-dimensional mixer at a weight ratio of 1:1.02:1 to obtain mixture I, and the mixture I is loaded into a 15 L graphite crucible.

[0105] (2) The graphite crucible is placed in the furnace chamber. After vacuum treatment, reaction is carried out using the three-stage programmed heating method in the presence of argon with a purity of 99.9999 vol%, to obtain high-purity silicon carbide precursor III.

[0106] (3) The high-purity silicon carbide precursor III is loaded into a quartz boat and carbon removal treatment is carried out in a tube furnace to obtain silicon carbide powder I.

[0107] (4) The silicon carbide powder I is ultrasonically cleaned in water and dried to obtain silicon carbide powder II.

[0108] (5) The silicon carbide powder II is subjected to screening treatment II to obtain high-purity silicon carbide DM2.

[0109] Comparative Example 3

[0110] High-purity silicon carbide is prepared according to the method of Example 1, except that the weight ratio of the carbon powder, the silicon powder, and the second silicon carbide powder in this comparative example is 0.25:0.25:1.

[0111] The remaining steps are the same as those in Example 1 to obtain high-purity silicon carbide DM3.

[0112] Among them, the obtained silicon carbide product has a large hardness and cannot be taken out from the graphite crucible, and the particle size of the silicon carbide powder does not grow.

[0113] Test Example

[0114] Using a glow discharge mass spectrometer (model VG - 90), the high-purity silicon carbide prepared in the examples and comparative examples is tested respectively. The specific test results are shown in Table 2.

[0115] Table 2

[0116]

[0117] As can be seen from the above results, the method provided by the present invention can further improve the yield ratio of large-size silicon carbide crystals while obtaining high-purity silicon carbide.

[0118] The present invention exemplarily provides a spectrogram of glow discharge mass spectrometry detection of the high-purity silicon carbide prepared in Example 1, as Figure 1 shown in. It can be seen from Figure 1 that the prepared silicon carbide has few impurities and high purity.

[0119] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for preparing high-purity silicon carbide, characterized in that, The method includes: (1) Subjecting silicon carbide powder with a particle size of 180 - 230 μm and a purity of not less than 99.9 wt% to decarbonization treatment to obtain first silicon carbide powder; the decarbonization treatment is carried out in the presence of compressed air, and the conditions of the decarbonization treatment at least satisfy: the temperature is 800 - 900 °C, and the time is 5 - 8 h; (2) Subjecting the first silicon carbide powder to ultrasonic cleaning treatment and drying to obtain second silicon carbide powder; the conditions of the ultrasonic cleaning at least satisfy: the ultrasonic frequency is 40 - 60 Hz, and the cleaning time is 60 - 180 min; (3) Mixing carbon powder, silicon powder and the second silicon carbide powder in a weight ratio of 1 - 1.2:1 - 1.2:1 to obtain mixture I; (4) Reacting the mixture I by a three-stage programmed heating method in the presence of a protective atmosphere to obtain high-purity silicon carbide with a purity of not less than 99.99 wt%; Among them, in step (4), the operation of the three-stage programmed heating method includes: S1: Under a first pressure, heating the mixture I at a first heating rate to a first temperature and holding at the first temperature for a first time to obtain a first intermediate material; the first pressure is 1.5 - 2.5 Torr, the first heating rate is 4 - 6 °C / min, the first temperature is 1300 - 1400 °C, and the first time is 2.5 - 4 h; S2: Under a second pressure, heating the first intermediate material at a second heating rate to a second temperature and holding at the second temperature for a second time to obtain a second intermediate material; the second pressure is 95 - 100 Torr, the second heating rate is 5 - 6.5 °C / min, the second temperature is 1650 - 1750 °C, and the second time is 4 - 7 h; S3: Under a third pressure, heating the second intermediate material at a third heating rate to a third temperature and holding at the third temperature for a third time to obtain the high-purity silicon carbide with a purity of not less than 99.99 wt%; the third pressure is 40 - 60 Torr, the third heating rate is 4.5 - 5.5 °C / min, the third temperature is 2250 - 2350 °C, and the third time is 16 - 24 h.

2. The method according to claim 1, characterized in that In step (3), the purity of the carbon powder is not less than 99.999 wt%.

3. The method according to claim 1 or 2, characterized in that, In step (3), the purity of the silicon powder is not less than 99.999 wt%.

4. The method according to claim 1 or 2, characterized in that, In step (3), the particle sizes of the silicon powder and the carbon powder are each independently 60 - 100 μm.

5. The method according to claim 1 or 2, characterized in that, In step (3), the weight ratio of the carbon powder, the silicon powder and the second silicon carbide powder is 1 - 1.03:1 - 1.03:

1.

6. The method according to claim 1 or 2, characterized in that, In step (3), the mixing treatment time is more than 20 min, and the stirring speed is 80 - 120 rpm.

7. The method according to claim 1 or 2, characterized in that In step (3), the mixing treatment is carried out in a three-dimensional mixer.

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