Preparation method of high-purity silicon carbide powder

Abstract

The invention belongs to the technical field of semiconductor materials, and particularly relates to a preparation method of high-purity silicon carbide powder. The preparation method comprises the following steps: reacting a mixture of fluosilicate and carbon powder at 1500-1600 DEG C in an inert atmosphere for 2-5 hours, cooling to 600-700 DEG C, preserving heat for 2-4 hours in an oxidizing atmosphere, cooling to room temperature, washing with water, and drying to obtain the high-purity silicon carbide powder. According to the method, the high-value silicon carbide is prepared from cheap fluosilicate as a raw material and carbon powder through a one-step reaction, and the method is low in cost, simple in process, free of corrosive byproducts and suitable for industrial application. Furthermore, the cheaper fluosilicic acid is taken as a raw material and is subjected to nano mixing with the carbon powder in a precipitation form, so that not only is new impurities prevented from being introduced by mechanical grinding, but also the two reaction raw materials are fully contacted and reacted, and the product yield reaches 98% or above. Furthermore, fluorine elements in the raw materials can be combined with impurities to form fluoride to be volatilized in a gas form, the impurities are removed while the product is prepared, and the impurity removal process is simplified.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of semiconductor materials, and particularly relates to a preparation method of high-purity silicon carbide powder. BACKGROUND

[0002] Silicon carbide is an important basic material for the development of the third-generation semiconductor industry. Silicon carbide power devices can effectively meet the requirements of high efficiency, miniaturization and light weight of power electronic systems due to their excellent high-voltage resistance, high-temperature resistance and low loss, and are gradually becoming the mainstream in the field of semiconductor materials.

[0003] There are mainly two process routes for the production of silicon carbide powder in the prior art. One is to use high-purity silicon dioxide or silicon powder and high-purity carbon powder to sinter in a graphite dry pan of a resistance furnace to prepare silicon carbide, such as CN119976852A and CN119118132A. The main disadvantages are that new impurities are introduced during mixing and grinding, the reaction is insufficient, and the conversion rate of raw materials is low. The other is to use high-purity silicon tetrachloride, hydrogen and hydrocarbon to prepare silicon carbide by chemical vapor deposition, such as JP2025503260A. The main disadvantages are that three chemicals are used for vapor deposition in a specific ratio, the reaction control is difficult, and the hydrogen chloride gas generated during the reaction is highly corrosive under high-temperature conditions, which requires high requirements for equipment materials.

[0004] Further, the method for preparing SiC single crystals is mainly the physical vapor transport (PVT) method, and SiC powder is the raw material for growing SiC single crystals by the PVT method. Obviously, in order to improve the quality of SiC single crystals, in addition to a suitable single crystal growth process, the SiC powder used for growing single crystals is also very important, and its purity and other physical property parameters will directly affect the quality of SiC single crystals, and further affect the performance of SiC devices. Therefore, the preparation of high-purity SiC powder is the key to growing high-quality SiC single crystals by the PVT method.

[0005] CN120463200A discloses a preparation method of 6N high-purity silicon carbide powder, which comprises multiple steps such as batching, acoustic resonance mixing, high-temperature pyrolysis and calcination, acid washing purification and washing, and vacuum shock drying, which is relatively complicated. SUMMARY

[0006] To overcome the above-mentioned shortcomings, the application provides a preparation method of high-purity silicon carbide powder.

[0007] The mixture of fluorosilicate and carbon powder is reacted at 1500-1600℃ for 2-5h under an inert atmosphere, cooled to 600-700℃, and kept at the temperature for 2-4h under an oxidizing atmosphere, then cooled to room temperature, washed with water, and dried to obtain high-purity silicon carbide powder.

[0008] The fluorosilicate, on one hand, can be directly commercially available, and then mixed with high-purity carbon powder; on the other hand, the fluorosilicate can be self-made, and mixed with carbon powder at the same time, and the specific method is as follows: first, the fluorosilicate solution is uniformly mixed with high-purity carbon powder, and then the aqueous solution of soluble alkali metal salt is slowly added dropwise, the fluorosilicate of alkali metal is precipitated together with carbon powder, filtered, and dried to obtain a mixture of fluorosilicate and carbon powder. It can be understood that the solubility of the fluorosilicate of alkali metal salt is low, and the newly generated fluorosilicate is precipitated in the form of precipitation, and the uniformly precipitated fluorosilicate is precipitated together with the uniformly dispersed carbon powder, so that a uniformly mixed mixture is directly obtained.

[0009] The high-purity carbon powder is selected from at least one of carbon nanotubes, carbon nanowires, graphene, graphite, and amorphous carbon, and the particle size is preferably nanoscale. The nanoscale carbon powder is mixed with the fluorosilicate precipitate to achieve molecular-level mixing, which lays a foundation for subsequent uniform and sufficient reaction of the two. The soluble alkali metal salt is selected from at least one of sodium chloride, sodium sulfate, sodium nitrate, potassium chloride, potassium sulfate, and potassium nitrate.

[0010] The fluorosilicate solution is prepared by purifying fluorosilicic acid by-product of phosphate fertilizer or phosphoric acid. In view of the fact that anion impurities can be removed by volatilization during subsequent high-temperature sintering, the focus here is to remove metal ion impurities, so that the content of metal ions is ≤100 ppm, for example, removing silica gel particle impurities by microfiltration membrane filtration, removing impurity metal ions by resin adsorption, etc. The concentration of fluorosilicic acid is preferably 10-30 wt%. The fluorosilicic acid in this concentration range is relatively stable and is not easy to generate silica gel precipitate, thereby avoiding introducing impurities to the subsequent reaction.

[0011] Further, in order to enhance the dispersibility of the carbon powder in the aqueous solution, 0.1-3% surfactant, such as polyvinylpyrrolidone (PVP), Tween 80, sodium dodecyl sulfate (SDS), etc., is added to the fluorosilicic acid solution before the carbon powder is mixed with the fluorosilicic acid solution.

[0012] The mixture of fluorosilicate and carbon powder is rapidly heated to 1500-1600°C at a heating rate of 10-20°C / min. At this temperature and in an inert atmosphere, the molecularly mixed fluorosilicate and carbon powder directly react to generate silicon carbide, fluoride salt, and carbon tetrafluoride. For example, the reaction formula of sodium fluorosilicate is as follows:

[0013] Na2SiF6 + 2C → SiC + 2NaF + CF4↑

[0014] It should be noted that trace impurity elements in the reactants, such as iron, aluminum, boron, sulfur, etc., combine with fluorine elements to form fluorides at high temperatures, which are carried away by carbon tetrafluoride gas, thereby playing an auxiliary effect of removing impurities.

[0015] Preferably, the molar ratio of silicon to carbon elements in the mixture of fluorosilicate and carbon powder is 1:2-2.2, in which range the carbon powder is in excess, ensuring that trace amounts of oxygen elements in the reactants (such as alcohol adsorbed on the surface of the carbon powder, trace amounts of oxygen elements brought in by silica gel, etc.) can fully react to generate gaseous carbon monoxide to escape.

[0016] After the above reaction is completed, in order to remove the remaining carbon powder, the reaction product is kept at 600-700°C for 2-4h in an oxidizing atmosphere, so that the carbon powder is oxidized to gaseous carbon monoxide to escape, further improving the purity of the silicon carbide product.

[0017] The above inert atmosphere is one or both of argon and helium, and the oxidizing atmosphere is oxygen or clean air.

[0018] The beneficial effects of the present application are:

[0019] The high-value silicon carbide is prepared by one-step reaction of the inexpensive fluorosilicate with carbon powder, which is low in cost, simple in process, free of corrosive by-products, and suitable for industrial application. Further, the more inexpensive fluorosilicate is used as raw material, and the nanometer mixing is achieved in the form of precipitation with carbon powder, which not only avoids the introduction of new impurities by mechanical grinding, but also enables the two reaction raw materials to fully contact and fully react, with a product yield of more than 98%. Further, the fluorine element in the raw material can combine with impurities to form fluorides that volatilize in the form of gas, removing impurities while preparing the product and simplifying the impurity removal process. Moreover, the addition of a surfactant in the fluorosilicate not only promotes the uniform dispersion of the carbon powder, but also helps the fluorosilicate to form a fluffy rather than dense solid when it is precipitated, so that small particle size silicon carbide powder is directly obtained after high temperature reaction of the carbon powder, without the need for a special crushing process. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 XRD detection result graph of the silicon carbide product obtained in Example 7. DETAILED DESCRIPTION

[0021] The technical solutions of the present application will be further described in detail below in conjunction with specific embodiments. The purity of the obtained product is detected according to the national standard GB / T37254-2018.

[0022] Example 1

[0023] Silicon carbide powder was prepared.

[0024] Commercially available 200 mesh sodium fluorosilicate (purity 99.9wt%) 200 g and high purity graphite (99.999wt%) with particle size less than 10 μm 26.82 g were mixed by stirring thoroughly, the molar ratio of silicon to carbon in the mixture was 1:2.1, and the mixture was transferred into a tube furnace, the tube was replaced with helium, and the temperature was raised to 1600°C at a rate of 15°C / min, the temperature was maintained for 4 h, the temperature was lowered to 650°C, and oxygen was introduced, the temperature was maintained for 3 h, and then the temperature was lowered to room temperature, the mixture was washed with purified water, and vacuum drying was performed at 120°C to obtain 25.67 g of silicon carbide powder product, the yield was 60.2%, and the detection purity was 99.9994%.

[0025] Example 2

[0026] Silicon carbide powder was prepared.

[0027] Commercially available 200 mesh sodium fluorosilicate (purity 99.9wt%) 200 g and single-walled carbon nanotubes (99.99wt%) 26.82 g were mixed by stirring thoroughly, the molar ratio of silicon to carbon in the mixture was 1:2.1, and the mixture was transferred into a tube furnace, the tube was replaced with helium, and the temperature was raised to 1500°C at a rate of 20°C / min, the temperature was maintained for 5 h, the temperature was lowered to 600°C, and oxygen was introduced, the temperature was maintained for 3 h, and then the temperature was lowered to room temperature, the mixture was washed with purified water, and vacuum drying was performed at 120°C to obtain 31.3 g of silicon carbide powder product, the yield was 73.4%, and the detection purity was 99.9991%.

[0028] Example 3

[0029] Silicon carbide powder was prepared.

[0030] Commercially available 200 mesh potassium fluorosilicate (purity 99.9wt%) 200 g and graphene (99.9wt%) 24.0 g were mixed by stirring thoroughly, the molar ratio of silicon to carbon in the mixture was 1:2.2, and the mixture was transferred into a tube furnace, the tube was replaced with argon, and the temperature was raised to 1550°C at a rate of 10°C / min, the temperature was maintained for 5 h, the temperature was lowered to 650°C, and oxygen was introduced, the temperature was maintained for 4 h, and then the temperature was lowered to room temperature, the mixture was washed with purified water, and vacuum drying was performed at 120°C to obtain 25.41 g of silicon carbide powder product, the yield was 69.8%, and the detection purity was 99.9990%.

[0031] Example 4

[0032] Fluorosilicate was prepared.

[0033] The fluorosilicic acid with concentration of 18wt% from a domestic phosphoric acid enterprise was selected, and insoluble substances were filtered out by using 5 μm and 2 μm microporous filter membranes in turn. Then the fluorosilicic acid solution was treated by D401 amino phosphonic acid type chelating resin and D851 imino diacetic acid type chelating resin in turn to remove trivalent and divalent metal ions including iron, aluminum, calcium, magnesium and other ions, so that the fluorosilicic acid solution with high purity was obtained, and the content of single metal ion was less than 5 ppm.

[0034] 500 g of the purified fluorosilicic acid was taken, 1.5 g of PVP surfactant was added and stirred to dissolve, then 15.1 g of high-purity graphite (particle size <10 μm, purity 99.999wt%) was added and stirred to assist ultrasonic mixing and uniform dispersion, and then 25wt% sodium chloride aqueous solution was slowly added dropwise until no precipitation was generated. After filtration and vacuum drying at 120°C, 127.9 g of a mixture of sodium fluorosilicate and graphite was obtained, and the molar ratio of silicon to carbon in the mixture was 1:2.1.

[0035] Example 5

[0036] Self-made fluorosilicate.

[0037] 500 g of the purified fluorosilicic acid in Example 4 was taken, 8 g of SDS surfactant was added and stirred to dissolve, then 15.7 g of single-walled carbon nanotubes (purity 99.99wt%) was added and stirred to assist ultrasonic mixing and uniform dispersion, and then 25wt% potassium chloride aqueous solution was slowly added dropwise until no precipitation was generated. After filtration and vacuum drying at 120°C, 128.5 g of a mixture of sodium fluorosilicate and carbon nanotubes was obtained, and the molar ratio of silicon to carbon in the mixture was 1:2.19.

[0038] Example 6

[0039] Self-made fluorosilicate.

[0040] 500 g of the purified fluorosilicic acid in Example 4 was taken, 13 g of Tween 80 surfactant was added and stirred to dissolve, then 14.8 g of graphene (purity 99.9wt%) was added and stirred to assist ultrasonic mixing and uniform dispersion, and then 25wt% potassium chloride aqueous solution was slowly added dropwise until no precipitation was generated. After filtration and vacuum drying at 120°C, 149.7 g of a mixture of potassium fluorosilicate and graphene was obtained, and the molar ratio of silicon to carbon in the mixture was 1:2.02.

[0041] Example 7

[0042] Preparation of silicon carbide powder.

[0043] The mixture of 100 g of sodium fluorosilicate prepared in Example 4 and graphite was transferred into a tube furnace, the tube was replaced with helium, and the temperature was raised to 1600°C at a rate of 15°C / min, the temperature was maintained for 4 h, the temperature was lowered to 650°C, oxygen was introduced, the temperature was maintained for 3 h, the temperature was lowered to room temperature, the product was washed with purified water, and vacuum drying was performed at 120°C to obtain 18.0 g of silicon carbide powder product at a yield of 95.7% and a purity of 99.99997%.

[0044] Example 8

[0045] Silicon carbide powder was prepared.

[0046] The mixture of 100 g of sodium fluorosilicate prepared in Example 5 and carbon nanotubes was transferred into a tube furnace, the tube was replaced with helium, and the temperature was raised to 1500°C at a rate of 20°C / min, the temperature was maintained for 5 h, the temperature was lowered to 600°C, oxygen was introduced, the temperature was maintained for 3 h, the temperature was lowered to room temperature, the product was washed with purified water, and vacuum drying was performed at 120°C to obtain 18.48 g of silicon carbide powder product at a yield of 98.8% and a purity of 99.99995%.

[0047] Example 9

[0048] Silicon carbide powder was prepared.

[0049] The mixture of 100 g of potassium fluorosilicate prepared in Example 6 and graphene was transferred into a tube furnace, the tube was replaced with argon, and the temperature was raised to 1550°C at a rate of 10°C / min, the temperature was maintained for 5 h, the temperature was lowered to 650°C, oxygen was introduced, the temperature was maintained for 4 h, the temperature was lowered to room temperature, the product was washed with purified water, and vacuum drying was performed at 120°C to obtain 18.22 g of silicon carbide powder product at a yield of 96.5% and a purity of 99.99992%.

[0050] Comparative Example 1

[0051] Silicon carbide powder was prepared.

[0052] The same as Example 1, except that the stirring mixing was replaced with ball milling mixing. The silicon carbide powder product was prepared at a yield of 91.7% and a purity of 99.996%.

[0053] Comparative Example 2

[0054] Silicon carbide powder was prepared.

[0055] 100g of sodium silicate (purity 99.9wt%) was first dissolved in 400g of water, 1.5g of PVP surfactant was added, then mixed and dispersed with 31.5g of high-purity graphite (99.999wt%) with a particle size of 10μm or less, then evaporated to remove water to obtain a solid mixture, the molar ratio of silicon to carbon in the mixture was 1:3.2, and then transferred to a tube furnace, the tube was replaced with helium, heated to 1600℃ at a rate of 15℃ / min, kept for 4h, cooled to 650℃ and oxygen was introduced, kept for 3h, then cooled to room temperature, washed with pure water, and vacuum dried at 120℃ to obtain a mixture of silicon carbide and silicon dioxide 37.5g, silicon carbide accounted for 62.7%, and the yield of silicon carbide was 71.6%. Further dissolved with electronic grade hydrofluoric acid to remove silicon dioxide, and the purity of the obtained silicon carbide was 99.993%.

[0056] The above examples and comparative example data are summarized in the following table: Yield / % Purity / % Particle size distribution / μm Example 1 60.2 99.9994 500-1500 Example 2 73.4 99.9991 400-1300 Example 3 69.8 99.9990 400-1400 Example 7 95.7 99.99997 300-800 Example 8 98.8 99.99995 200-800 Example 9 96.5 99.99992 300-800 Comparative Example 1 91.7 99.996 600-1800 Comparative Example 2 71.6 99.993 100-500

[0057] As can be seen from the data in the table, in Examples 1-3, the fluorosilicate and carbon powder were not fully mixed and contacted, and the reaction was not fully carried out, part of the sodium fluorosilicate was decomposed into sodium fluoride and silicon tetrafluoride, resulting in a lower yield of silicon carbide. In Comparative Example 1, the reactants were mixed by ball milling to achieve better contact, resulting in a significant increase in yield, but the purity of the product was reduced. In Examples 7-9, the fluorosilicate and carbon powder were fully contacted and reacted, resulting in a higher yield of silicon carbide, and the pretreatment of fluorosilicic acid reduced the impurity content, resulting in a higher purity product of 6N grade. In Comparative Example 2, the fluorosilicate was replaced by silicate, the silicate and carbon powder were fully mixed, but the reaction did not fully proceed, resulting in a lower yield, and the final product purity was also lower due to the lack of fluorine element for impurity removal.

Claims

1. A method for preparing high-purity silicon carbide powder, characterized in that, A mixture of fluorosilicate and carbon powder is reacted at 1500-1600℃ for 2-5 hours under an inert atmosphere, then cooled to 600-700℃ and kept at that temperature for 2-4 hours under an oxidizing atmosphere. Finally, it is cooled to room temperature, washed with water, and dried to obtain high-purity silicon carbide powder.

2. The preparation method according to claim 1, characterized in that, The mixture of fluorosilicate and toner is prepared by the following method: first, high-purity toner is mixed evenly with fluorosilicic acid solution, and then an aqueous solution of soluble alkali metal salt is slowly added dropwise. The alkali metal fluorosilicate precipitates together with the toner. After filtration and drying, the mixture of fluorosilicate and toner is obtained.

3. The preparation method according to claim 2, characterized in that, The high-purity carbon powder is selected from at least one of carbon nanotubes, carbon nanowires, graphene, graphite, and amorphous carbon, and the soluble alkali metal salt is selected from at least one of sodium chloride, sodium sulfate, sodium nitrate, potassium chloride, potassium sulfate, and potassium nitrate.

4. The preparation method according to claim 2, characterized in that, The concentration of the fluorosilicic acid solution is 10-30 wt%. Before mixing the high-purity carbon powder with the fluorosilicic acid solution, 0.1-3% surfactant is added to the fluorosilicic acid solution, which is selected from at least one of polyvinylpyrrolidone, Tween 80, and sodium dodecyl sulfate.

5. The preparation method according to claim 2, characterized in that, The fluorosilicic acid solution is prepared by purifying fluorosilicic acid from phosphate fertilizer or phosphoric acid by-products, and the impurity content is ≤0.01wt%.

6. The preparation method according to claim 1, characterized in that, The molar ratio of silicon to carbon in the mixture of fluorosilicate and carbon powder is 1:2-2.

2.

7. The preparation method according to claim 1, characterized in that, The inert atmosphere is one or both of argon and helium, and the oxidizing atmosphere is oxygen or clean air.

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