Particle-size-controllable silicon carbide powder for growth of silicon carbide crystals as well as synthesis method and application of particle-size-controllable silicon carbide powder

Abstract

The invention discloses particle size controllable silicon carbide powder for silicon carbide crystal growth and a synthesis method and application thereof, and relates to the technical field of semiconductors. The preparation method comprises the following steps: reacting silicon elementary substance with carbon elementary substance in a vacuum environment to prepare silicon carbide powder; by adjusting the particle size of the silicon elementary substance, the particle size of the carbon elementary substance, the density of the carbon elementary substance and the molar ratio of carbon to silicon, the particle size of the silicon carbide powder can be efficiently controlled to be 4-6 times of the particle size of the carbon elementary substance; the synthesis method is simple in preparation process, the prepared silicon carbide powder is high in purity, the defect that the particle size of SiC powder synthesized in the prior art is small and uncontrollable is overcome, and the method is simple in used device, high in synthesis efficiency and suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a silicon carbide powder with controllable particle size for silicon carbide crystal growth, a synthesis method and an application thereof. Background Art

[0002] In the field of semiconductor technology, wide-bandgap semiconductor materials, represented by silicon carbide (SiC) and gallium nitride (GaN), have become an important cornerstone of modern electronic technology due to their excellent physical and chemical properties. SiC, in particular, offers advantages such as high breakdown field strength, high thermal conductivity, high saturated electron drift velocity, and high bonding energy, giving it significant advantages in terms of breakdown voltage, radiation resistance, and operating temperature.

[0003] Large-particle silicon carbide powder (>2000 μm) can be used to improve processing efficiency, while small-particle powder (<500 μm) can be used to improve crystallization quality. Currently, the preparation process for small-particle silicon carbide powder is relatively mature, but the particle size distribution range is wide and difficult to accurately control. With the widespread application of SiC substrates in power electronic devices, the market demand for high-quality, large-sized silicon carbide crystals is growing, which in turn drives higher requirements for SiC powder quality and particle size controllability. In the existing silicon carbide powder preparation process, there are obvious deficiencies in the technology that can achieve efficient SiC and controllable particle size, which seriously restricts the flexibility and yield of silicon carbide powder growth.

[0004] Therefore, developing a SiC powder preparation process that is easy to operate and can precisely control the particle size is of great significance for achieving high-quality, controllable particle size, especially large-scale production of large-sized silicon carbide crystals.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of the present invention is to provide a silicon carbide powder with controllable particle size for silicon carbide crystal growth, a synthesis method and application thereof, so as to solve the above technical problems.

[0007] The present invention is achieved in that: In a first aspect, an embodiment of the present invention provides a method for synthesizing silicon carbide powder with controllable particle size for growing silicon carbide crystals, comprising the following steps: Silicon and carbon are reacted in a vacuum environment to produce silicon carbide powder; Among them, the vacuum degree is 1×10 -2 torr to 1×10 2 torr; the particle size of silicon is ≤200μm, the particle size of carbon is 200μm-2000μm; the density of carbon is 0.35g / cm 3 -1g / cm3 ; The molar ratio of silicon element and carbon element is (1-1.5):1; The particle size of the prepared silicon carbide powder is 4 to 6 times the particle size of the carbon element used.

[0008] In a second aspect, an embodiment of the present invention provides a silicon carbide powder with controllable particle size obtained by the aforementioned synthesis method.

[0009] In a third aspect, an embodiment of the present invention provides a use of silicon carbide powder with controllable particle size obtained by the aforementioned synthesis method in the growth of silicon carbide crystals.

[0010] The present invention has the following beneficial effects: The embodiment of the present invention provides a method for synthesizing silicon carbide powder with controllable particle size for silicon carbide crystal growth. By adjusting the silicon element particle size, carbon element particle size, carbon element density and carbon-silicon molar ratio, the particle size of the silicon carbide powder can be efficiently controlled to be 4 to 6 times the carbon element particle size. The preparation process of the silicon carbide powder is simple and the obtained silicon carbide powder has high purity, which makes up for the shortcomings of the SiC powder synthesized in the prior art that the particle size is small and uncontrollable. The method uses a simple device, has high synthesis efficiency, and is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0012] Figure 1 The morphology pictures of carbon particles and flake graphite: (a) carbon particles, (b) flake graphite; Figure 2 The morphology pictures of the silicon carbide powder prepared in Example 1: (a) small-scale picture, (b) particle size test picture; Figure 3 The morphology images of the silicon carbide powder prepared in Example 2: (a) a small-scale image, and (b) a crucible image; Figure 4 The morphology pictures of the silicon carbide powder prepared in Example 3: (a) small-scale picture, (b) particle size test picture; Figure 5 The morphology images of the silicon carbide powder prepared in Example 4 are: (a) small-scale image, (b) microscopic image (5 times magnification); Figure 6 The morphology images of the silicon carbide powder prepared in Example 5 are: (a) small-scale image, (b) microscopic image (5 times magnification); Figure 7 This is a morphology picture of the silicon carbide powder prepared in Example 6 (small scale); Figure 8 This is a morphology picture of the silicon carbide powder prepared in Example 7 (small scale); Figure 9 The morphology pictures of the silicon carbide powder prepared in Example 8: (a) small-scale picture, (b) particle size test picture; Figure 10 This is a morphology picture of the silicon carbide powder prepared in Example 9 (small scale); Figure 11 This is a morphology picture of the silicon carbide powder prepared in Example 10 (small scale); Figure 12 The morphology pictures of the silicon carbide powder prepared in Example 12: the left picture is the picture of the flake graphite output material, and the right picture is the picture of the output material in Example 1; Figure 13 The morphology images of the silicon carbide powder prepared in Example 13 are: (a) small-scale image, (b) micrograph (5x magnification); Figure 14 Schematic diagram of XRD test results. DETAILED DESCRIPTION

[0013] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0014] In a first aspect, an embodiment of the present invention provides a method for synthesizing silicon carbide powder with controllable particle size for growing silicon carbide crystals, comprising the following steps: Silicon and carbon are reacted in a vacuum environment to produce silicon carbide powder; Among them, the vacuum degree is 1×10 -2 torr to 1×10 2 torr; the particle size of silicon is ≤200μm, the particle size of carbon is 200μm-2000μm; the density of carbon is 0.35g / cm 3 -1g / cm 3 ; The molar ratio of the silicon element to the carbon element is (1-1.5):1; The particle size of the prepared silicon carbide powder is 4 to 6 times the particle size of the carbon element used.

[0015] In an embodiment of the present invention, the particle size of the carbon element is 20μm-2000μm. The provided synthesis method can efficiently produce small-particle and large-particle silicon carbide powders. Within the set average particle size range, the particle size of the obtained silicon carbide powder is 4 times to 6 times the particle size of the carbon element used, and the yield is 45% to 60%, which is suitable for large-scale mass production.

[0016] If large-particle carbon is used to prepare silicon carbide, its smaller specific surface area will adsorb fewer impurities, which is conducive to the preparation of high-purity silicon carbide; the large particle size can also avoid excessive densification or deformation of silicon carbide; in addition, the gaps between large-particle particles are large, which is conducive to achieving a more uniform filling density and reducing lattice defects.

[0017] It should be noted that as the particle size of the carbon element increases, the particle size of the synthesized silicon carbide shows a stable trend.

[0018] The silicon carbide powder prepared in the embodiment of the present invention is a 4H crystal form and has high purity.

[0019] In an optional embodiment, the density of the carbon element is 0.35 g / cm 3 -1g / cm 3 .

[0020] It should be noted that during the synthesis of silicon carbide powder, a reasonable setting of the carbon density is beneficial for balancing porosity and particle strength, maximizing reaction efficiency. If the carbon density is too low, the carbon will be loosely packed, reducing the overall mechanical strength of the charge and making it prone to collapse at high temperatures, resulting in incomplete reaction and reduced raw material conversion rate. If the carbon density is too high, the packing is tight, and the silicon atmosphere cannot penetrate the interior, hindering mass transfer at the reaction interface, resulting in incomplete internal reaction, the formation of black-core silicon carbide particles, and a reduction in reaction rate.

[0021] In an optional embodiment, the molar ratio of silicon element and carbon element is (1-1.5):1.

[0022] It should be noted that at high temperatures, carbon element easily generates CO gas, which adheres to the surface of the carbon element, hindering the full contact between silicon element and carbon element, resulting in incomplete carbon reaction. Therefore, the heating device must be evacuated and filled with inert gas.

[0023] Setting an appropriate excess of silicon is conducive to sufficient contact between carbon and silicon, pushing the reaction in the positive direction, and thus achieving efficient synthesis of silicon carbide.

[0024] In an optional embodiment, the particle size of the prepared silicon carbide powder is 4 to 6 times the particle size of the carbon element used.

[0025] It should be noted that the method for synthesizing silicon carbide powder with controllable particle size for silicon carbide crystal growth provided by the present invention has a simple preparation process. By adjusting the silicon element particle size, carbon element particle size, carbon element density and carbon-silicon molar ratio, the particle size of the silicon carbide powder can be efficiently controlled to be 4 to 6 times the carbon element particle size, thereby obtaining high-quality, high-purity, large-size and controllable-particle-size silicon carbide powder.

[0026] In an optional embodiment, the molar ratio of silicon element and carbon element is (1.05-1.1):1.

[0027] It should be noted that, C+Si→SiC, the molar ratio is set according to the reaction equation of the two. If one of the reactants is in appropriate excess, it will promote the reaction to move to the product, which is beneficial to the efficient conversion of the reactants and can effectively inhibit the decomposition of SiC at high temperature. If the molar ratio of carbon element is too large, the density of carbon element is too high, making it impossible for silicon vapor to penetrate into the interior, resulting in insufficient internal reaction and the formation of black-core silicon carbide particles.

[0028] In an optional embodiment, the carbon element is selected from flake graphite or carbon particles, and its structure is shown in FIG. Figure 1 (a) Carbon particles, (b) flake graphite.

[0029] It should be noted that in order to ensure the high purity of SiC, in the embodiment of the present invention, both silicon and carbon are selected from high-purity raw materials with a purity greater than 99.999%; if the purity is lower, the obtained product does not belong to silicon carbide for semiconductor crystal growth.

[0030] In the embodiment of the present invention, the silicon element is silicon powder.

[0031] In an optional embodiment, the temperature for preparing silicon carbide powder is 1800° C.-2400° C., and the time is 5 h-30 h.

[0032] The time setting can be adjusted reasonably according to the amount of material being processed to ensure that the output powder reacts fully.

[0033] In an optional embodiment, when vacuuming, the pressure of the device to be heated is less than 10 -5 torr, fill with inert gas; when the pressure reaches 1×10 -2 torr to 1×10 2 torr, the temperature is raised from room temperature to 2000℃-2300℃ for reaction.

[0034] It should be noted that the vacuum pressure is less than 10 -5The primary purpose of torr (high vacuum environment) is to remove active gas impurities in the system, such as O2, H2O, N2, etc., to avoid oxidation, nitridation or the generation of other non-target phase impurities, which will destroy the integrity of the SiC crystal and reduce the purity of the product.

[0035] Inflating at low pressure can use the partial pressure of inert gas to replace residual air, ensuring that the system is mainly composed of inert gas. In addition, filling with inert gas and controlling the pressure can isolate the air, avoid corrosion reactions of the crucible material or heating device, and extend the service life of the equipment.

[0036] If the pressure is high, the silicon carbide powder obtained has a small particle size, and the particle size of the silicon carbide powder is less than 4 times the particle size of the carbon element used. The morphology of the powder is flocculent, the silicon carbide powder is loose and the grain boundaries are dispersed. After observation at a magnification factor, the silicon carbide powder has fuzzy boundaries and imperfect crystallization.

[0037] The measurement of the crystal morphology or particle size of the silicon carbide powder can be selected according to actual needs. In the embodiment of the present invention, the particle size measurement is mainly tested using a ruler, and the morphology test is mainly performed by camera shooting or conventional microscope observation.

[0038] It should be noted that the particle size of silicon carbide powder exceeding the range of electron microscopy (the imaging range of electron microscopy is less than 1000 μm) cannot be accurately measured using a microscope. Therefore, in the embodiment of the present invention, the particle size of silicon carbide powder greater than 1000 μm is measured using a ruler.

[0039] The present invention does not impose any particular limitation on the inert gas, and argon or helium can be selected according to actual needs.

[0040] The pressure is 1×10 -2 torr to 1×10 2 torr, raising the temperature from room temperature to 2000℃-2300℃ for reaction can promote the reduction of temperature difference in the heating device, avoid local overcooling or overheating, reduce the impact of environmental variables on the synthesis process, and ensure the quality consistency of different batches of products.

[0041] High temperature is often accompanied by silicon melting (Si melting point 1414℃). A low-pressure environment can reduce the volatilization temperature of silicon, avoiding composition segregation or structural unevenness caused by the liquid phase. A high-temperature, low-pressure environment is conducive to inhibiting the growth of abnormal grains and obtaining SiC with uniform microstructure. It can also promote the volatilization of low-boiling-point impurities and improve product purity.

[0042] In an optional embodiment, the internal pressure of the heating device is evacuated to a pressure less than 10 -5 torr, the pressure inside the furnace does not exceed 7.5×10 -2torr, further verifies the airtightness of the heating device; it can effectively prevent external gas infiltration and internal gas leakage, reduce the generation of impurities, and improve product yield; in addition, it can ensure the stability of the synthesis process and the reliability of the long-term operation of the equipment.

[0043] In an optional embodiment, silicon and carbon are placed in a crucible for synthesis reaction, wherein the crucible is made of graphite with an ash content of <5 ppm.

[0044] It should be noted that the crucible is made of graphite. Graphite has good thermal conductivity and can transfer heat quickly and evenly, reducing the temperature gradient in the reaction system and promoting the uniformity of the Si+C→SiC reaction. It does not react with silicon and carbon at high temperatures and will not introduce new impurities. The surface of the graphite crucible may evaporate slightly (forming CO), but its excessive loss can be avoided through process control. If there is insufficient carbon in the reaction, the graphite crucible can be used to supplement a small amount of carbon source.

[0045] In an optional embodiment, in order to reduce the loss of graphite in the synthesis process and extend the service life of the graphite crucible, before loading silicon and carbon elements, a layer of high-purity carbon powder is spread on the bottom of the crucible, and the distance between the loading surface and the top of the crucible is maintained at 50mm-150mm, where the amount of high-purity carbon powder can be reasonably set according to the actual amount of material processed.

[0046] In an optional embodiment, the heating device is selected from any one of a high-frequency induction heating furnace, a medium-frequency induction heating furnace, and a graphite resistance heating furnace.

[0047] The heating device can be reasonably selected according to actual needs.

[0048] In summary, the method for synthesizing silicon carbide powder with controllable particle size for growing silicon carbide crystals provided in an embodiment of the present invention comprises the following steps: Molar ratio (1.05-1.1): 1. Mix silicon and carbon evenly and put them into a graphite crucible. Put the crucible into a graphite resistance heating furnace and evacuate the furnace until the pressure inside is less than 10 -5 torr, fill with inert gas helium; wait until the pressure in the furnace is 1×10 -2 torr to 1×10 2 torr, the temperature is raised from room temperature to 1800℃-2400℃ and reacted for 5h-30h, then the temperature in the furnace is lowered to room temperature to obtain silicon carbide powder with controllable particle size for silicon carbide crystal growth.

[0049] Among them, silicon and carbon are reasonably selected according to actual needs.

[0050] In a second aspect, an embodiment of the present invention provides a silicon carbide powder with controllable particle size obtained by the aforementioned synthesis method.

[0051] In a third aspect, an embodiment of the present invention provides a use of silicon carbide powder with controllable particle size obtained by the aforementioned synthesis method in the growth of silicon carbide crystals.

[0052] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0053] Example 1 This embodiment provides a method for synthesizing silicon carbide powder with controllable particle size for growing silicon carbide crystals, comprising the following steps: Mix silicon powder and carbon particles in a molar ratio of 1.05:1 and put them into a graphite crucible. Put the crucible into a graphite resistance heating furnace and evacuate the furnace until the pressure inside is less than 10 -5 torr, fill with inert gas helium; wait until the pressure in the furnace is 1×10 -2 torr to 1×10 2 torr, raise the temperature from room temperature to 2200℃ and react for 25h, then lower the temperature in the furnace to room temperature to obtain silicon carbide powder.

[0054] The particle size of silicon powder is 200 μm, the particle size of carbon particles is 1000 μm, and the density of carbon particles is 0.65 g / cm 3 ; According to calculation, the yield of silicon carbide powder is 53%.

[0055] In this embodiment, the particle size of the prepared silicon carbide powder was measured: the average particle size ranged from 4000 μm to 8000 μm, which was about 5 times larger than that of the carbon particles. The powder produced had a relatively complete reaction, and there was no carbon residue inside the particles. The relevant morphology can be seen. Figure 2 : (a) Small-scale image, (b) Particle size test image.

[0056] Example 2 This embodiment provides a method for synthesizing silicon carbide powder with controllable particle size for growing silicon carbide crystals. The method differs from Example 1 only in that: Silicon powder and carbon particles were mixed evenly at a molar ratio of 1.1:1 and then loaded into a graphite crucible; the carbon particle size was 1000 μm and the carbon particle density was 0.65 g / cm 3 ; According to calculation, the yield of silicon carbide powder is 48%.

[0057] The average particle size of the prepared silicon carbide powder ranges from 4000 μm to 8000 μm, which is about 5 times larger than that of the carbon particles. The reaction is sufficient and the particle size of the silicon carbide powder is close to that of Example 1. However, the crucible is severely corroded and is not suitable for large-scale production. The relevant morphology is shown in FIG. Figure 3 : (a) Small-scale image, (b) crucible image.

[0058] Example 3 This embodiment provides a method for synthesizing silicon carbide powder with controllable particle size for growing silicon carbide crystals. The method differs from Example 1 only in that: Silicon powder and carbon particles were mixed evenly in a molar ratio of 1:1.1 and then loaded into a graphite crucible; the carbon particle size was 1000 μm and the carbon particle density was 0.65 g / cm 3 ; According to calculation, the yield of silicon carbide powder is 45%.

[0059] The average particle size of the prepared silicon carbide powder ranges from 4000μm to 8000μm, which is about 5 times larger than that of carbon particles. The increase in the carbon particle molar ratio does not affect the particle size. Excessive carbon causes some carbon to not participate in the reaction, resulting in black core material and incomplete reaction. The relevant morphology is shown in Figure 4 : (a) Small-scale image, (b) Particle size test image.

[0060] Example 4 This embodiment provides a method for synthesizing silicon carbide powder with controllable particle size for growing silicon carbide crystals. The method differs from Example 1 only in that: The particle size of silicon powder is 200μm, the particle size of carbon particles is 200μm, and the density of carbon particles is 1.2g / cm 3 ; According to calculation, the yield of silicon carbide powder is 46%.

[0061] The average particle size of the prepared silicon carbide powder ranges from 800μm to 1200μm, which is about 5 times larger than the carbon particle size. The carbon particle density is greater than the set range, so the silicon atmosphere cannot fully penetrate and the reaction is insufficient, resulting in a black core in the prepared silicon carbide powder. The specific morphology is shown in Figure 5: (a) small-scale image, (b) microscopic image (magnified 5 times).

[0062] Example 5 This embodiment provides a method for synthesizing silicon carbide powder with controllable particle size for growing silicon carbide crystals. The method differs from Example 1 only in that: The particle size of silicon powder is 200μm, the particle size of carbon particles is 200μm, and the density of carbon particles is 0.8g / cm 3 ; According to calculation, the yield of silicon carbide powder is 52%.

[0063] The average particle size of the prepared silicon carbide powder ranges from 800μm to 1200μm, which is about 5 times larger than the particle size of carbon particles. The prepared silicon carbide powder crystals have no black core and the output powder reaction is sufficient. The specific morphology is shown in Figure 6: (a) small-scale picture, (b) microscopic picture (magnified 5 times).

[0064] Example 6 This embodiment provides a method for synthesizing silicon carbide powder with controllable particle size for growing silicon carbide crystals. The method differs from Example 1 only in that: The carbon particle size is 800 μm and the carbon particle density is 0.45 g / cm 3 ; According to calculation, the yield of silicon carbide powder is 49%.

[0065] The average particle size of the prepared silicon carbide powder ranges from 3000 μm to 5000 μm, which is about 5 times larger than that of carbon particles. The density is within the set range, the reaction is complete, and there is no black core phenomenon. The specific morphology is shown in Figure 7.

[0066] Example 7 This embodiment provides a method for synthesizing silicon carbide powder with controllable particle size for growing silicon carbide crystals. The method differs from Example 1 only in that: The carbon particle size is 800 μm and the carbon particle density is 1.5 g / cm 3 ; According to calculation, the yield of silicon carbide powder is 45%.

[0067] The average particle size of the prepared silicon carbide powder ranges from 300μm to 5000μm, which is about 5 times larger than the carbon particle size. The carbon particle density is greater than the set range, the silicon atmosphere cannot be fully penetrated, the reaction is incomplete, and there is a black core material. The specific morphology is shown in Figure 8.

[0068] Example 8 This embodiment provides a method for synthesizing silicon carbide powder with controllable particle size for growing silicon carbide crystals. The method differs from Example 1 only in that: The carbon particle size is 1000 μm and the carbon particle density is 1.5 g / cm 3 ; According to calculation, the yield of silicon carbide powder is 46%.

[0069] The average particle size of the prepared silicon carbide powder ranges from 4000μm to 8000μm, which is about 5 times larger than the particle size of carbon particles. Due to the high density and denseness of the carbon particles, the silicon atmosphere cannot penetrate into the interior, and the output powder does not react fully, forming a black-core silicon carbide powder. The specific morphology is shown in Figure 9: (a) small-scale picture, (b) particle size test picture.

[0070] Example 9 This embodiment provides a method for synthesizing silicon carbide powder with controllable particle size for growing silicon carbide crystals. The method differs from Example 1 only in that: The carbon particle size is 2000 μm and the carbon particle density is 0.8 g / cm 3 ; According to calculation, the yield of silicon carbide powder is 49%.

[0071] The average particle size of the prepared silicon carbide powder ranges from 6000 μm to 10000 μm, which is about 4 times larger than that of carbon particles, indicating sufficient reaction. The specific morphology is shown in Figure 10.

[0072] Example 10 This embodiment provides a method for synthesizing silicon carbide powder with controllable particle size for growing silicon carbide crystals. The method differs from Example 1 only in that: The carbon particle size is 2000μm and the carbon particle density is 1.5g / cm 3 ; According to calculation, the yield of silicon carbide powder is 47%.

[0073] The average particle size of the prepared silicon carbide powder ranges from 6000μm to 10000μm, which is about 3.5 times larger than the carbon particle size. The carbon particle density is greater than the set range, the silicon atmosphere cannot be fully penetrated, the reaction is incomplete, and there is a black core material. The specific morphology is shown in Figure 11.

[0074] Example 11 This embodiment provides a method for synthesizing silicon carbide powder with controllable particle size for growing silicon carbide crystals. The method differs from Example 1 only in that: The carbon particle size is 2500μm and the carbon particle density is 0.6g / cm 3 ; According to calculation, the yield of silicon carbide powder is 40%.

[0075] The average particle size of the prepared silicon carbide powder is in the range of 6000 μm-10000 μm. The particle size of the carbon particles exceeds the set range, the increase of the particle size is limited, the reaction is sufficient, and the specific morphology is similar to that of Example 9.

[0076] Example 12 This embodiment provides a method for synthesizing silicon carbide powder with controllable particle size for growing silicon carbide crystals. The method differs from Example 1 only in that: The carbon element used is flake graphite with a particle size of 1000 μm and a density of 0.65 g / cm 3 ; According to calculation, the yield of silicon carbide powder is 51%.

[0077] The average particle size of the prepared silicon carbide powder ranges from 4000 μm to 8000 μm, which is about 5 times larger than the particle size of carbon particles, and the output powder reacts fully; see Figure 12 for specific morphology: the left side is the flake graphite output material, and the right side is the output material of Example 1.

[0078] Example 13 This embodiment provides a method for synthesizing silicon carbide powder with controllable particle size for growing silicon carbide crystals. The method differs from Example 1 only in that: When the pressure in the furnace is 1×10 -2 torr to 6×10 2 torr, the temperature was raised from room temperature to 2200℃ and the reaction was carried out for 25h; wherein the carbon particle size was 200μm and the carbon particle density was 0.25g / cm 3; According to calculation, the yield of silicon carbide powder is 40%.

[0079] The average particle size of the prepared silicon carbide powder ranges from 500 μm to 700 μm, which is about 5 times larger than that of carbon particles. The powder is flocculent, irregular in shape, incomplete in crystallization, fragile, and has a low yield. See Figure 13 for the specific morphology.

[0080] Test Example 1 In this test example, the silicon carbide powders prepared in Examples 1-4, 6, 8 and 12 were subjected to XRD tests, and the test results are shown in FIG. Figure 14 , the corresponding icons are 1-7, and icon 75 corresponds to the standard sample.

[0081] XRD test results show that the silicon carbide powder sample is a standard 4H crystal form.

[0082] Test Example 2 In this test example, the purity of the silicon carbide powder prepared in Example 1 was tested. The test results are shown in Table 1.

[0083] Table 1 Purity test results

[0084] From the data in Table 1, it can be seen that the purity of the silicon carbide powder prepared in Example 1 is 99.99997%. In addition, its yield is as high as 58%, and silicon carbide powder with controllable particle size is prepared with high yield and high purity.

[0085] In summary, the setting of the molar ratio has little effect on the particle size of silicon carbide powder, but has a greater impact on the crystal form, purity and yield of silicon carbide; using large-particle carbon particles with a particle size greater than 1000μm (1000μm-2500μm) can produce silicon carbide powder in the range of 4000μm-8000μm, and the average particle size of the produced silicon carbide powder increases to 3 to 5 times the particle size of the carbon particles used; as the particle size of the carbon particles increases, the particle size of the silicon carbide powder no longer increases, but the increase multiple of the particle size and the yield will decrease with the increase of the carbon particle size; and using small-particle carbon particles with a particle size less than 500μm, the average particle size of the produced silicon carbide powder increases to 6 times the particle size of the carbon particles used. Therefore, the present invention can achieve efficient control of the silicon carbide powder particle size to 4 to 6 times the carbon particle size by adjusting the silicon particle size, carbon particle size, carbon density and carbon-silicon molar ratio; the synthesis method of the present invention has a simple preparation process and the obtained silicon carbide powder has high purity, which makes up for the shortcomings of the SiC powder synthesized in the prior art that the particle size is small and uncontrollable. The method uses a simple device, has high synthesis efficiency, and is suitable for large-scale industrial production.

[0086] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for synthesizing silicon carbide powder with controllable particle size for growing silicon carbide crystals, characterized in that: The steps include: Silicon and carbon are reacted in a vacuum environment to produce silicon carbide powder; Among them, the vacuum degree is 1×10 -2 torr to 1×10 2 torr; the particle size of the silicon element is ≤200μm, the particle size of the carbon element is 200μm-2000μm; the density of the carbon element is 0.35g / cm 3 -1g / cm 3 ; The molar ratio of the silicon element to the carbon element is (1-1.5):1; The particle size of the prepared silicon carbide powder is 4 to 6 times the particle size of the carbon element used.

2. The synthesis method according to claim 1, characterized in that The molar ratio of the silicon element to the carbon element is (1.05-1.1):

1.

3. The synthesis method according to claim 1, wherein The temperature for preparing the silicon carbide powder is 1800° C.-2400° C., and the time is 5 h-30 h.

4. The synthesis method according to claim 1, characterized in that The carbon element is selected from flake graphite or carbon particles.

5. The synthesis method according to claim 1, characterized in that When vacuuming, the pressure of the device to be heated is less than 10 - 5 torr, fill with inert gas; when the pressure reaches 1×10 -2 torr to 1×10 2 torr, the temperature is raised from room temperature to 2000℃-2300℃ for reaction.

6. The synthesis method according to claim 1, characterized in that Silicon and carbon are placed in a crucible for synthesis reaction, wherein the crucible is made of graphite with an ash content of <5ppm.

7. A silicon carbide powder with controllable particle size obtained by the synthesis method according to any one of claims 1 to 6.

8. Use of silicon carbide powder with controllable particle size obtained by the synthesis method according to any one of claims 1 to 6 in silicon carbide crystal growth.

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