Preparation method of high-purity hot-pressed sintered silicon carbide

Abstract

The invention relates to the technical field of preparation of advanced ceramic materials, and particularly discloses a preparation method of high-purity hot-pressed sintered silicon carbide. The preparation method mainly comprises the following steps: selecting high-purity submicron silicon carbide powder, and sequentially carrying out acid washing, alkali washing and plasma-assisted high-temperature gas phase impurity removal treatment to realize deep purification; mixing with an organic forming aid in a metal-pollution-free environment, and performing cold isostatic pressing forming; degreasing and presintering are completed through gradient heating; then carrying out hot pressed sintering without a sintering aid under an ultrahigh vacuum condition; and finally, a finished product is obtained through polishing, vacuum annealing and hot isostatic pressing treatment. According to the method, through multistage purification and whole-process clean process control, impurity introduction and grain boundary enrichment are effectively avoided, the silicon carbide ceramic with the metal impurity content lower than 5 ppm, high density and excellent mechanical property can be stably prepared, and the method is particularly suitable for key components needing ultra-high purity and reliability in semiconductor manufacturing equipment.

Description

Technical Field

[0001] This application relates to the field of advanced ceramic material preparation technology, and more specifically, it relates to a method for preparing high-purity hot-pressed sintered silicon carbide. Background Technology

[0002] Silicon carbide ceramics, with their excellent high-temperature stability, good thermal conductivity, corrosion resistance, and low coefficient of thermal expansion, have become key structural materials in high-end process equipment such as semiconductor epitaxy, etching, and rapid thermal processing. As semiconductor manufacturing moves towards 12-inch wafers and more advanced processes, the requirements for the cleanliness and purity of materials in core equipment components are becoming increasingly stringent. In particular, the content of metal impurities must be controlled at extremely low levels to avoid contaminating the wafer and affecting process precision. High-purity silicon carbide materials have become a core foundation for ensuring the stability of equipment operation.

[0003] Currently, the industry commonly uses hot pressing sintering to prepare silicon carbide components. To reduce the sintering temperature and achieve densification, sintering aids such as boron, carbon, or aluminum are usually introduced. However, these aids and their reaction byproducts tend to accumulate at the grain boundaries of the material. At the same time, traditional powder purification processes and processing are not perfect in controlling trace impurities, making it difficult to systematically avoid metal contamination. As a result, the total metal impurity content of the final product is difficult to stably control at an extremely low level, which cannot meet the application requirements of advanced semiconductor equipment for extremely high cleanliness. Summary of the Invention

[0004] To address the problem in the existing hot-pressed sintered silicon carbide preparation process that the use of sintering aids and insufficient control of trace impurities during powder purification and processing lead to the easy accumulation of metallic impurities, making it difficult to meet the ultra-high purity requirements of advanced semiconductor equipment, this application provides a method for preparing high-purity hot-pressed sintered silicon carbide.

[0005] A method for preparing high-purity hot-pressed sintered silicon carbide includes the following steps: S1. Multi-stage purification of high-purity silicon carbide powder: Submicron-sized β-SiC powder is selected as raw material and subjected to acid washing to remove impurities, alkali washing to remove impurities, and high-temperature gas phase de-purification treatment in sequence. The high-temperature gas phase de-purification adopts plasma-assisted degassing. S2. Metal-free mixing and billet forming: In a metal-free environment, silicon carbide powder purified by S1 is mixed with organic forming aids, and high-purity silicon carbide balls are used as the mixing medium. The mixed powder is then dried and sieved, and then cold isostatically pre-formed to obtain a high-purity silicon carbide billet. S3, Gradient heating degreasing and pre-firing: The green body obtained in S2 is placed in an inert atmosphere and subjected to gradient heating treatment to complete the degreasing and pre-firing of organic matter in sequence. S4. Hot pressing sintering without sintering aids: The pre-fired blank of S3 is placed in a high-purity mold free of metal contamination that has been vacuum baked, and multi-stage hot pressing sintering is carried out in an ultra-high vacuum environment; hot pressing sintering includes a high-temperature holding stage under pressure; controlled cooling is carried out after sintering. S5. Post-treatment: The sintered body obtained in S4 is subjected to precision surface polishing, vacuum high-temperature annealing and hot isostatic pressing in sequence.

[0006] By adopting the above technical solution, submicron-sized β-SiC powder is selected as the raw material, leveraging its large specific surface area to lay the foundation for deep impurity removal. A multi-stage purification system is constructed through acid washing, alkali washing, and plasma-assisted high-temperature gas-phase depurification. Acid washing specifically dissolves metallic impurities, alkali washing removes free silicon and oxides, and plasma-assisted technology activates impurity molecules to enhance the removal of trace impurities. In the mixing and forming stage, a non-metallic liner and high-purity silicon carbide spheres are used to avoid metal contamination. High-purity organic forming aids are used to ensure mixing uniformity and formability. High-quality green bodies are obtained through cold isostatic pressing. Subsequently, degreasing and pre-firing are carried out in an inert atmosphere gradient temperature rise to avoid thermal stress cracking and oxidation, remove aids, and stabilize the green body structure. Sintering without sintering aids is carried out in an ultra-high vacuum multi-stage hot pressing sintering process. Mold baking eliminates contamination, high temperature and high pressure achieve densification, and controlled cooling reduces thermal stress. Finally, post-treatment eliminates internal stress and micropores. All stages work together to construct a high-purity preparation system throughout the entire process, ensuring the purity and structural integrity of the material.

[0007] Preferably, in step S1, the particle size D of the submicron β-SiC powder is... 50 The particle size is 0.3 μm to 1.0 μm, and the initial purity is not less than 99.999%.

[0008] By employing the above technical solution and selecting high-initial-purity submicron-sized β-SiC powder, the impurity base is controlled at the source, reducing the subsequent purification load. This particle size range ensures sufficient specific surface area, allowing the purification medium to fully contact impurities on the powder surface and inside, improving impurity removal efficiency, while avoiding the problems of agglomeration caused by excessively small particle sizes or the difficulty in removing deep impurities caused by excessively large particle sizes. The particle size characteristics synergize with the subsequent plasma-assisted high-temperature gas-phase depurification process, facilitating the diffusion and volatilization of impurity molecules, further ensuring the purification effect, and providing high-quality raw materials with a low impurity base for the entire high-purity preparation process.

[0009] Preferably, in step S1, the acid washing to remove impurities is performed by soaking in a mixed solution of high-purity hydrofluoric acid and high-purity nitric acid for 2 to 4 hours; the alkaline washing to remove impurities is performed by soaking in a high-purity ammonium hydroxide solution for 1 to 3 hours.

[0010] By adopting the above technical solution, acid washing uses a mixed solution of high-purity hydrofluoric acid and nitric acid, utilizing their synergistic effect to achieve targeted impurity removal, while the high-purity reagent avoids the introduction of new impurities. Hydrofluoric acid selectively dissolves silicon-based impurities and some metal oxides, while nitric acid, with its strong oxidizing properties, promotes the dissolution of insoluble metal impurities, significantly improving the impurity removal efficiency. A reasonable soaking time ensures thorough impurity removal while avoiding excessive etching of the powder surface. Alkaline washing uses a high-purity ammonium hydroxide solution to specifically remove residual free silicon, metal hydroxides, and oxides from acid washing, forming a complementary purification logic with acid washing. The high-purity reagent avoids metal ion contamination, and the reaction-transformation of impurities facilitates their removal, reducing the load on subsequent high-temperature gas-phase depurification and ensuring the continuous effectiveness of the multi-stage purification system.

[0011] Preferably, in step S1, the vacuum level of the high-temperature gas phase depurification process is 10. -6 The process involves processing at Pa levels, with temperatures ranging from 1600℃ to 1900℃ and processing times from 2 hours to 4 hours. The total metal impurity content of the silicon carbide powder after multi-stage purification is ≤5ppm.

[0012] By employing the above technical solution, high-temperature vapor-phase impurity removal utilizes an ultra-high vacuum environment, which reduces the vapor pressure of impurity molecules, providing thermodynamic conditions for the volatilization of trace impurities while simultaneously isolating them from external contamination. The appropriate temperature provides sufficient energy to convert trace impurities and volatile oxides into the gas phase, achieving selective removal without affecting the silicon carbide powder itself. The reasonable processing time, combined with the high-temperature, high-vacuum environment, ensures the full diffusion and volatilization of deep-seated trace impurities, preventing abnormal particle growth or agglomeration. This process, as the final stage of multi-stage purification, complements the preceding acid and alkali washing processes, specifically removing residual trace and insoluble impurities, ultimately achieving the goal of low metal impurity content and providing high-quality raw materials for subsequent high-purity preparation.

[0013] Preferably, in step S2, the organic forming aid is selected from one or a combination of two of high-purity polyvinyl alcohol and high-purity polyethylene glycol; the mixing process uses an inner liner made of alumina or silicon carbide.

[0014] By adopting the above technical solution, high-purity polyvinyl alcohol, polyethylene glycol, and combinations thereof are selected as organic molding aids. Their excellent film-forming and adhesive properties ensure the formation of the preform, and their easy decomposition at high temperatures leaves no residue, meeting the high-purity requirements. The high purity level avoids the introduction of trace impurities. The combination of the two aids synergistically optimizes the molding effect and degreasing efficiency. The mixing process uses an alumina or silicon carbide liner to avoid metal debris contamination from traditional metal liners. These materials have excellent chemical stability and wear resistance, do not react with powders or aids, and maintain a clean mixing environment. This forms a metal-free mixing system with the high-purity silicon carbide balls, avoiding secondary powder contamination and reducing powder adsorption residue, ensuring uniform mixing and laying the foundation for obtaining a high-purity preform with a uniform structure.

[0015] Preferably, in step S2, the drying temperature is 80°C to 120°C, and the drying time is 4h to 8h; the cold isostatic pressing preforming pressure is 100MPa to 200MPa, and the holding time is 1h to 3h.

[0016] By employing the above technical solutions, the drying process removes residual moisture from the mixed powder using a gentle thermal environment, while simultaneously preventing premature decomposition or volatilization of organic forming aids. The synergistic effect of appropriate temperature and time, combined with the characteristics of submicron-sized powders, ensures sufficient escape of deep moisture, preventing the formation of pores by water vapor in subsequent processes, and maintaining powder dispersibility, laying the foundation for sieving and forming. Cold isostatic pressing preforming uses uniform isostatic pressing to ensure close packing of the powder, forming a structurally stable and appropriately strong green body, ensuring uniform density. A reasonable holding time ensures uniform pressure transmission, resulting in consistent internal density within the green body and improving overall integrity. This process, in conjunction with the preceding metal-free mixing and drying processes, ensures that the green body maintains high purity while possessing good structural stability, supporting the smooth implementation of subsequent processes.

[0017] Preferably, in step S3, the heating rate of the gradient heating process is 0.5℃ / min to 2℃ / min; the degreasing temperature of the organic matter is 600℃ to 800℃; and the pre-calcination temperature is 1200℃ to 1500℃.

[0018] By adopting the above technical solutions, gradient heating can achieve slow and uniform heating, avoiding cracking and deformation of the green body due to thermal stress caused by internal and external temperature differences. Simultaneously, an inert atmosphere prevents oxidation of the green body during heating, maintaining the high-purity control approach throughout the entire process. The degreasing temperature is matched to the thermal decomposition characteristics of organic forming aids, ensuring that the aids are completely decomposed into gaseous products and detach from the green body, leaving no carbonaceous impurities. This temperature, in conjunction with the gradient heating rate, allows for gradual decomposition of the aids and smooth escape of gaseous products, ensuring the integrity of the green body. Pre-firing allows the silicon carbide particles inside the green body to form a preliminary sintering neck, improving strength and stabilizing the microstructure without causing over-sintering. It also further removes trace amounts of volatile impurities, working in conjunction with previous processes to optimize the microstructure while maintaining high purity of the green body, laying the foundation for subsequent hot pressing sintering without sintering aids.

[0019] Preferably, in step S4, the vacuum level of the ultra-high vacuum environment is 10. -6 The second stage of the multi-stage hot pressing sintering is heated to 1600°C to 2000°C while applying a pressure of 30MPa to 60MPa; the controlled cooling rate is 5°C / min to 10°C / min.

[0020] By employing the above technical solutions, the ultra-high vacuum environment can effectively remove gaseous impurities such as oxygen and water vapor, preventing oxidation of the green body during high-temperature sintering. Simultaneously, it provides a channel for the escape of residual gases and decomposition products, reducing porosity defects. The high-temperature environment of multi-stage hot-pressing sintering provides energy for atomic diffusion of silicon carbide particles, while high pressure pushes the particles to fit tightly together, compressing voids. The synergy of these two factors enables efficient densification of the green body without sintering aids. Controlled cooling after sintering slows the cooling rate, reduces the temperature gradient between the surface and core, minimizes thermal stress, and prevents cracking and deformation. Maintaining vacuum during cooling further prevents oxidation, ensuring the high purity of the material.

[0021] Preferably, in step S4, the temperature of the vacuum baking process is 800°C to 1000°C, and the baking time is 2 hours to 3 hours.

[0022] By employing the above technical solution, a vacuum baking pretreatment is performed on high-purity molds free from metal contamination. The appropriate temperature activates volatile impurities such as water vapor and oil adsorbed on the mold surface, reducing their adhesion to the mold surface and promoting their detachment and extraction. A reasonable baking time and temperature work in tandem to ensure that surface and shallow impurities fully escape, avoiding residue. This treatment eliminates the mold's own sources of contamination, preventing the release of impurities from the mold during subsequent high-temperature, high-pressure sintering and contamination of the silicon carbide material. Combined with the ultra-high vacuum sintering environment, this strengthens the entire process impurity control system at the equipment level, providing a clean mold environment for the densification sintering of high-purity silicon carbide without sintering aids, ensuring material purity and structural uniformity.

[0023] Preferably, in step S5, the vacuum high-temperature annealing temperature is 1400℃ to 1600℃, and the holding time is 2h to 3h; the hot isostatic pressing is carried out in an argon atmosphere, with a processing pressure of 100MPa to 200MPa, a processing temperature of 1800℃ to 2000℃, and a processing time of 1h to 2h.

[0024] By employing the above technical solutions, vacuum high-temperature annealing can prevent abnormal growth of silicon carbide grains, and the vacuum environment isolates oxygen to prevent oxidation. This treatment effectively releases the internal stress generated by hot pressing sintering, alleviates lattice distortion and grain boundary stress concentration, optimizes grain arrangement and grain boundary bonding, and provides a structurally stable matrix for subsequent hot isostatic pressing. Hot isostatic pressing is carried out in an argon inert atmosphere to avoid material oxidation or reaction with external gases under high temperature and high pressure. High temperature provides energy for atomic diffusion, and high pressure acts uniformly on all parts of the sintered body, eliminating internal closed micropores and micro-defects, and improving density and particle bonding. These two processes, together with surface precision polishing, form a complete post-processing system that connects with previous processes, ensuring the structural integrity and high purity of the final product.

[0025] In summary, this application has the following beneficial effects: 1. Because this application adopts a multi-stage purification process, metal impurities and oxides are removed sequentially by acid washing and alkali washing, and plasma-assisted high-temperature gas phase depurification is combined with the control of no metal contamination throughout the mixing, forming and hot pressing sintering process, and no sintering aids are added, the introduction and enrichment of impurities are effectively avoided, and the purity of the material is improved.

[0026] 2. In this application, a mixing equipment with an alumina or silicon carbide liner is preferred, along with a high-purity organic forming aid, and combined with drying treatment with specific parameters and cold isostatic pressing preforming. This reduces the risk of contamination during mixing and forming, ensures the uniformity and purity of the green body, and achieves the effect of optimizing the quality of the green body.

[0027] 3. The method of this application uses a gradient heating method for degreasing and pre-firing, and reasonably controls the heating rate and degreasing and pre-firing temperatures to fully remove organic matter from the green body, while forming a stable microstructure, which improves the strength of the green body and provides a good foundation for subsequent sintering, thus achieving the effect of improving the sintering adaptability of the green body.

[0028] 4. This application employs multi-stage hot pressing sintering under ultra-high vacuum environment, combined with mold vacuum baking treatment and precise temperature and pressure control, to achieve efficient densification of materials without sintering aids. At the same time, by controlling the cooling rate to reduce thermal stress, the density of the material is improved.

[0029] 5. This application utilizes a multi-stage post-processing technique combining precision surface polishing, vacuum high-temperature annealing, and hot isostatic pressing to effectively eliminate micropores, internal stresses, and grain boundary defects within the sintered body, further optimizing the microstructure of the material and achieving an improved overall performance. Attached Figure Description

[0030] Figure 1 This is a flowchart of the preparation process of a method for preparing high-purity hot-pressed sintered silicon carbide provided in this application; Figure 2 This is the X-ray diffraction pattern of the high-purity hot-pressed sintered silicon carbide sample prepared in Example 1 of this application; Figure 3 This is a trace element content analysis diagram of the high-purity hot-pressed sintered silicon carbide sample prepared in Example 1 of this application; Figure 4 This is a stress-strain curve of the bending strength of the high-purity hot-pressed sintered silicon carbide sample prepared in Example 1 of this application. Detailed Implementation

[0031] The present application will be further described in detail below with reference to embodiments and comparative examples. Unless otherwise specified, the experimental methods used below are conventional methods. Unless otherwise specified, the materials, reagents, methods and instruments used are all conventional materials, reagents, methods and instruments in the art, which can be obtained by those skilled in the art through commercial channels or prepared according to literature methods.

[0032] Technical concept: The core problem with existing hot-pressing sintered silicon carbide preparation technology in high-end semiconductor applications is that the material purity cannot meet stringent requirements. This stems from two main issues: First, to reduce sintering temperature and promote densification, sintering aids are commonly added. These aids and their byproducts tend to accumulate at grain boundaries, introducing additional metallic impurities. Second, traditional processes lack systematic impurity control, and powder purification methods are limited, making it difficult to completely remove impurities of various forms. Furthermore, secondary contamination can easily occur during processing steps such as mixing, forming, and sintering due to metal contact and mold contamination. These multiple factors combined result in the material purity failing to meet standards.

[0033] This technical solution revolves around a synergistic approach to impurity control and additive-free densification throughout the entire process. It achieves deep impurity removal from raw materials through multi-stage purification processes, utilizing the complementarity of different purification methods to specifically remove various impurities. The entire process employs a metal-free contamination design, avoiding new contamination at the source through non-metallic linings, high-purity media, and a formulation free of sintering aids. Supporting processes such as mold pretreatment, ultra-high vacuum sintering, and gradient temperature degreasing pre-firing ensure the cleanliness of the processing environment and the stability of the green body structure. Finally, post-treatment optimization eliminates internal stress and micropores. These steps form a synergistic system, achieving densification without relying on sintering aids, while systematically solving the problems of impurity residue and secondary contamination, thus achieving stable preparation of high-purity silicon carbide.

[0034] Example 1: This example provides a method for preparing high-purity hot-pressed sintered silicon carbide, including the following steps: S1. Multi-stage purification of high-purity silicon carbide powder: Submicron-sized β-SiC powder is selected as raw material and is subjected to acid washing to remove impurities, alkali washing to remove impurities, and high-temperature gas phase de-purification treatment in sequence. High-temperature gas phase de-purification adopts plasma-assisted degassing. Among them, the particle size D of submicron β-SiC powder 50 The particle size is 0.6 μm, and the initial purity is not less than 99.999%. Pickling and impurity removal are performed by soaking in a mixed solution of high-purity hydrofluoric acid and high-purity nitric acid, wherein the purity of the high-purity hydrofluoric acid is ≥99.99% and the purity of the high-purity nitric acid is ≥99.99%, and the volume ratio of the two is 1:4. The mixed solution is prepared and used immediately at room temperature to avoid volatilization affecting the impurity removal effect. The soaking time is 3 hours. During the pickling process, the mixed solution is stirred at a constant speed of 60 r / min to ensure that the powder and the acid solution are in full contact and improve the dissolution efficiency of metal impurities. Alkaline washing for impurity removal involves immersion in a high-purity ammonium hydroxide solution with a purity ≥99.99% and a solution concentration of 7.5%. The immersion time is 2 hours. During the alkaline washing process, the solution temperature is kept stable at around 25℃ to avoid temperature fluctuations affecting the removal of free silicon and oxide impurities. After alkaline washing, the powder is rinsed with high-purity deionized water with a resistivity ≥18.2 MΩ・cm. Each rinse uses 5 times the mass of the powder, and the powder is rinsed a total of 4 times. After the last rinse, the washing solution is tested with a precision pH meter. A pH value of 6.8-7.2 indicates that there is no residual alkali solution. The vacuum level of the high-temperature gas phase depurification process is 3×10⁻⁶. -6 Pa, the treatment temperature is 1750℃, and the treatment time is 3h; After multi-stage purification, the total metal impurity content of the silicon carbide powder is ≤5ppm. After purification, high-purity nitrogen with a purity of ≥99.999% is used to blow away the residual liquid on the powder surface at a flow rate of 10L / min for 30min to avoid secondary contamination.

[0035] S2. Metal-free mixing and billet forming: In a metal-free environment, silicon carbide powder purified by S1 is mixed with organic forming aids, and high-purity silicon carbide balls are used as the mixing medium. The mixed powder is then dried and sieved, and then cold isostatically pre-formed to obtain a high-purity silicon carbide billet. The organic molding aid is selected from high-purity polyvinyl alcohol with a purity of ≥99.99%. The mixing process uses an alumina liner to prevent the introduction of metal impurities during the mixing process; The drying process was carried out at 100℃ for 6 hours using a vacuum drying method, with the vacuum level maintained at 1×10⁻⁶. -3 Pa, to prevent the powder from absorbing moisture or adsorbing impurities from the atmosphere; The pressure for cold isostatic pressing preforming is 150 MPa, and the holding time is 2 hours. The screening process uses a 250-mesh sieve to remove any small agglomerates that may be generated during the mixing process. The mass ratio of the powder to the ball is controlled at 6:1 during the mixing process, and the mixing time is 2 hours to ensure that the silicon carbide powder and the organic forming agent are mixed evenly.

[0036] S3, Gradient heating degreasing and pre-firing: The green body obtained in S2 is placed in an inert atmosphere and subjected to gradient heating treatment to complete the degreasing and pre-firing of organic matter in sequence. Argon gas is used as the inert atmosphere, and the purity of argon gas is not less than 99.999%. The heating rate for the gradient heating treatment was 1.25℃ / min; The organic matter degreasing process is carried out at a temperature of 700℃ and a holding time of 3 hours to ensure that the organic forming aids are completely decomposed and removed without any residual carbon impurities. The pre-firing temperature is 1350℃ and the holding time is 4.5h. Pre-firing causes the initial sintering neck to form inside the green body, which improves the strength of the green body, stabilizes the microstructure, and avoids cracks or deformation during subsequent sintering.

[0037] S4. Hot pressing sintering without sintering aids: The pre-fired blank of S3 is placed in a high-purity mold free of metal contamination that has been vacuum baked, and multi-stage hot pressing sintering is carried out in an ultra-high vacuum environment; hot pressing sintering includes a high-temperature holding stage under pressure; controlled cooling is carried out after sintering. Among them, the vacuum degree of the ultra-high vacuum environment is 3×10⁻⁶. -6 Pa; The vacuum baking process is carried out at a temperature of 900℃ for 2.5 hours. During the baking process, a vacuum is continuously drawn to remove moisture, oil, and other impurities adsorbed on the surface of the mold. The first stage of multi-stage hot pressing sintering is heated to 800℃ and held for 2.5 hours to carry out preliminary degassing, removing residual gas and a small amount of unremoved organic decomposition products from the interior of the green body. In the second stage, the temperature is raised to 1800℃, and a pressure of 45MPa is applied. The temperature is held for 2.5 hours to achieve densification and sintering of the green body through the synergistic effect of high temperature and high pressure. The cooling rate is controlled at 7.5℃ / min. During the cooling process, a vacuum environment is maintained to prevent the sintered body from oxidizing due to contact with air. When the temperature drops below 200℃, high-purity argon gas is introduced to atmospheric pressure to prevent thermal stress caused by excessively rapid cooling.

[0038] S5. Post-treatment: The sintered body obtained in S4 is subjected to precision surface polishing, vacuum high-temperature annealing and hot isostatic pressing in sequence. Among them, the surface precision polishing uses diamond polishing fluid and undergoes two steps of rough polishing and fine polishing. After polishing, the surface roughness of the sintered body Ra≤0.05μm, removing the oxide layer and processing traces on the surface of the sintered body. The vacuum high-temperature annealing temperature was 1500℃, the holding time was 2.5h, and the vacuum degree was maintained at 5×10 during the annealing process. -4 Pa eliminates internal stress generated during sintering and optimizes grain structure; Hot isostatic pressing (HIP) is performed in an argon atmosphere with an argon purity of not less than 99.999%, at a pressure of 150 MPa, a temperature of 1900 °C, and a time of 1.5 h.

[0039] Example 2: This example provides a method for preparing high-purity hot-pressed sintered silicon carbide, including the following steps: S1. Multi-stage purification of high-purity silicon carbide powder: Submicron-sized β-SiC powder is selected as raw material and is subjected to acid washing to remove impurities, alkali washing to remove impurities, and high-temperature gas phase de-purification treatment in sequence. High-temperature gas phase de-purification adopts plasma-assisted degassing. Among them, the particle size D of submicron β-SiC powder 50 The particle size is 0.3 μm, and the initial purity is not less than 99.999%. Pickling and impurity removal are performed by soaking in a mixed solution of high-purity hydrofluoric acid and high-purity nitric acid, wherein the purity of the high-purity hydrofluoric acid is ≥99.99% and the purity of the high-purity nitric acid is ≥99.99%, and the volume ratio of the two is 1:3. The mixed solution is prepared under refrigeration at 0-5℃ to reduce the generation of volatile impurities. The soaking time is 2 hours. During the pickling process, the mixed solution is stirred at a constant speed of 40 r / min to ensure that the fine-particle powder is in full contact with the acid solution and to avoid powder agglomeration that would affect the removal of impurities. Alkaline washing and impurity removal involves soaking in a high-purity ammonium hydroxide solution with a purity ≥99.99% and a solution concentration of 5% for 1 hour. After alkaline washing, the powder is rinsed with high-purity deionized water with a resistivity ≥18.2 MΩ·cm, using 4 times the powder mass for each rinse, for a total of 3 rinses. After the last rinse, the washing solution is tested with a precision pH meter, and a pH value of 6.5-7.0 indicates that there is no residual alkali solution. The vacuum level of the high-temperature gas phase depurification process is 1×10⁻⁶. -6 Pa, the treatment temperature is 1600℃, and the treatment time is 2h; The total metal impurity content of the silicon carbide powder after multi-stage purification is ≤5ppm. After purification, the powder is sealed and stored in a desiccator under high-purity nitrogen protection for later use. The humidity inside the desiccator is controlled at ≤5%.

[0040] S2. Metal-free mixing and billet forming: In a metal-free environment, silicon carbide powder purified by S1 is mixed with organic forming aids, and high-purity silicon carbide balls are used as the mixing medium. The mixed powder is then dried and sieved, and then cold isostatically pre-formed to obtain a high-purity silicon carbide billet. The organic molding aid is selected from high-purity polyethylene glycol with a purity of ≥99.99%. The mixing process uses a silicon carbide liner to further reduce the risk of impurities being introduced during the mixing process; The drying temperature is 80℃, the drying time is 4 hours, and the drying method is blower drying with the wind speed controlled at 1m / s to ensure that the powder dries quickly and does not clump. The pressure for cold isostatic pressing preforming is 100 MPa, and the holding time is 1 hour; The screening process uses a 200-mesh sieve to remove large particles and agglomerates. During the mixing process, the mass ratio of the ball to the material is controlled at 5:1, and the mixing time is 1 hour. This ensures uniform mixing while avoiding excessive crushing of the powder.

[0041] S3, Gradient heating degreasing and pre-firing: The green body obtained in S2 is placed in an inert atmosphere and subjected to gradient heating treatment to complete the degreasing and pre-firing of organic matter in sequence. Nitrogen gas is used as the inert atmosphere, and the purity of nitrogen gas is not less than 99.999%. The heating rate of the gradient heating treatment is 0.5℃ / min, and the slow heating avoids micro-cracks in the billet due to thermal stress. The organic matter degreasing process is carried out at a temperature of 600℃ and a holding time of 2 hours. Low-temperature and long-term degreasing ensures that the organic additives decompose gradually and avoids rapid decomposition that could cause the green body to bubble. The pre-firing temperature is 1200℃ and the holding time is 3h. Pre-firing initially stabilizes the structure of the green body, providing a good foundation for subsequent high-temperature sintering.

[0042] S4. Hot pressing sintering without sintering aids: The pre-fired blank of S3 is placed in a high-purity mold free of metal contamination that has been vacuum baked, and multi-stage hot pressing sintering is carried out in an ultra-high vacuum environment; hot pressing sintering includes a high-temperature holding stage under pressure; controlled cooling is carried out after sintering. Among them, the vacuum level of the ultra-high vacuum environment is 1×10⁻⁶. -6 Pa; The vacuum baking process is carried out at a temperature of 800℃ for 2 hours to thoroughly remove impurities and moisture adsorbed on the surface of the mold. The first stage of multi-stage hot pressing sintering is heated to 600℃ and held for 2 hours to fully remove the residual gas inside the green body; The second stage involves heating to 1600℃ while applying a pressure of 30MPa and holding for 1 hour to achieve initial densification of the billet. The cooling rate is controlled at 5℃ / min. Slow cooling reduces internal thermal stress in the sintered body and ensures structural stability.

[0043] S5. Post-treatment: The sintered body obtained in S4 is subjected to precision surface polishing, vacuum high-temperature annealing and hot isostatic pressing in sequence. Among them, the surface precision polishing uses cubic boron nitride polishing liquid, and the surface roughness Ra of the sintered body after polishing is Ra≤0.05μm, which meets the requirements of high cleanliness surface; The vacuum high-temperature annealing temperature was 1400℃, the holding time was 2 hours, and the annealing vacuum degree was maintained at 1×10⁻⁶. -3 Pa effectively releases the internal stress generated during the sintering process; Hot isostatic pressing (HIP) is performed in an argon atmosphere with an argon purity of not less than 99.999%, at a pressure of 100 MPa, a temperature of 1800 °C, and a time of 1 hour.

[0044] Example 3: This example provides a method for preparing high-purity hot-pressed sintered silicon carbide, including the following steps: S1. Multi-stage purification of high-purity silicon carbide powder: Submicron-sized β-SiC powder is selected as raw material and is subjected to acid washing to remove impurities, alkali washing to remove impurities, and high-temperature gas phase de-purification treatment in sequence. High-temperature gas phase de-purification adopts plasma-assisted degassing. Among them, the particle size D of submicron β-SiC powder 50 The particle size is 1.0 μm, and the initial purity is not less than 99.999%. Pickling and impurity removal are performed by soaking in a mixed solution of high-purity hydrofluoric acid and high-purity nitric acid, wherein the purity of the high-purity hydrofluoric acid is ≥99.99% and the purity of the high-purity nitric acid is ≥99.99%, and the volume ratio of the two is 1:5. The mixed solution is stirred at room temperature for 15 minutes before use to ensure that the two acids are fully mixed and uniform. The soaking time is 4 hours. During the pickling process, the mixed solution is stirred at a constant speed of 80 r / min to ensure that the metal impurities on the surface and inside of the large-particle powder are fully dissolved. Alkaline washing for impurity removal involves immersion in a high-purity ammonium hydroxide solution with a purity ≥99.99% and a solution concentration of 10%. The immersion time is 3 hours, and the solution temperature is controlled at 30℃ during the alkaline washing process to improve the removal efficiency of free silicon and oxide impurities. After alkaline washing, the powder is rinsed with high-purity deionized water with a resistivity ≥18.2 MΩ・cm. The amount of water used for each rinse is 6 times the mass of the powder, and a total of 5 rinses are performed. After the last rinse, the washing solution is tested with a precision pH meter. A pH value of 7.0-7.5 indicates that there is no residual alkali solution. The vacuum level of the high-temperature gas phase depurification process is 5×10⁻⁶. -6 Pa, the treatment temperature is 1900℃, and the treatment time is 4h; The total metal impurity content of the silicon carbide powder after multi-stage purification is ≤5ppm. The purified powder is then vacuum dried at 120℃ for 2 hours, with the vacuum degree maintained at 5×10⁻⁶. -3 Pa removes residual moisture from the surface.

[0045] S2. Metal-free mixing and billet forming: In a metal-free environment, silicon carbide powder purified by S1 is mixed with organic forming aids, and high-purity silicon carbide balls are used as the mixing medium. The mixed powder is then dried and sieved, and then cold isostatically pre-formed to obtain a high-purity silicon carbide billet. The organic molding aid is selected from a mixture of high-purity polyvinyl alcohol and high-purity polyethylene glycol in a mass ratio of 1:1, and the purity of both aids is ≥99.99%. The mixing process uses an alumina lining to ensure that the mixing environment is free of metal contamination; The drying temperature was 120℃ and the drying time was 8 hours. A combination of vacuum drying and forced air drying was used. First, vacuum drying was carried out for 4 hours to remove most of the moisture, and then forced air drying was carried out for 4 hours to completely remove the residual moisture. The pressure for cold isostatic pressing preforming is 200 MPa, and the holding time is 3 hours. The sieving process uses a 300-mesh sieve to obtain finer and more uniform powder particles. During the mixing process, the ball-to-material mass ratio is controlled at 8:1, and the mixing time is 3 hours to ensure that the silicon carbide powder and the composite organic forming aid are fully integrated, thereby improving the quality of the green body forming.

[0046] S3, Gradient heating degreasing and pre-firing: The green body obtained in S2 is placed in an inert atmosphere and subjected to gradient heating treatment to complete the degreasing and pre-firing of organic matter in sequence. Argon gas is used as the inert atmosphere, and the purity of argon gas is not less than 99.9995%. The gradient heating process has a heating rate of 2℃ / min, which improves the processing efficiency while ensuring that the billet is free of cracks. The organic matter degreasing treatment temperature is 800℃ and the holding time is 4h to completely remove the composite organic forming aids and avoid residual carbon impurities from affecting the purity of the material. The pre-firing temperature is 1500℃ and the holding time is 6h, which greatly improves the strength and structural stability of the green body and ensures that the green body does not deform or crack during the subsequent high temperature and high pressure sintering process.

[0047] S4. Hot pressing sintering without sintering aids: The pre-fired blank of S3 is placed in a high-purity mold free of metal contamination that has been vacuum baked, and multi-stage hot pressing sintering is carried out in an ultra-high vacuum environment; hot pressing sintering includes a high-temperature holding stage under pressure; controlled cooling is carried out after sintering. Among them, the vacuum degree of the ultra-high vacuum environment is 5×10⁻⁶. -6 Pa; The vacuum baking process is carried out at a temperature of 1000℃ for 3 hours to thoroughly remove impurities and adsorbed gases from the surface and interior of the mold. The first stage of multi-stage hot pressing sintering is heated to 1000℃ and held for 3 hours to completely remove residual gaseous impurities from the blank and mold. In the second stage, the temperature is raised to 2000℃, and a pressure of 60MPa is applied. The temperature is held for 4 hours. Through the synergistic effect of high temperature and high pressure, the green body is completely densified and sintered. The cooling rate is controlled at 10℃ / min. During the cooling process, a small amount of high-purity argon is introduced into the vacuum environment as a protective gas. The argon flow rate is controlled at 5L / min to further prevent oxidation of the sintered body and to assist in heat dissipation.

[0048] S5. Post-treatment: The sintered body obtained in S4 is subjected to precision surface polishing, vacuum high-temperature annealing and hot isostatic pressing in sequence. Among them, the surface precision polishing adopts a diamond and cubic boron nitride composite polishing liquid, and is processed by three steps of rough polishing, medium polishing and fine polishing. After polishing, the surface roughness of the sintered body Ra≤0.03μm, which meets the high cleanliness surface requirements for advanced semiconductor equipment. The vacuum high-temperature annealing temperature was 1600℃, the holding time was 3 hours, and the annealing vacuum degree was maintained at 1×10⁻⁶. -4 Pa, to minimize sintering internal stress and grain boundary defects, and optimize the material microstructure; Hot isostatic pressing (HIP) is performed in an argon atmosphere with an argon purity of not less than 99.9995%, at a pressure of 200 MPa, a temperature of 2000 °C, and a duration of 2 hours.

[0049] Comparative Example 1: The only difference between this comparative example and Example 1 is that during the mixing process in S2, 1% by mass of boron carbide B4C was added as a sintering aid. The other raw material types, purity, and process parameters are completely consistent with those in Example 1.

[0050] Comparative Example 2: The only difference between this comparative example and Example 1 is that only acid washing is performed in S1, and the acid washing parameters are the same as those in Example 1. Alkali washing and high-temperature gas phase impurity removal are omitted. The remaining steps and parameters are completely the same as those in Example 1.

[0051] Comparative Example 3: The only difference between this comparative example and Example 1 is that a ball mill with a stainless steel liner is used instead of an alumina liner in the S2 mixing process. All other mixing parameters and steps are completely consistent with Example 1.

[0052] Comparative Example 4: The only difference between this comparative example and Example 1 is that the hot isostatic pressing process is completely omitted in the S5 post-processing. The sintered body is the final product after surface precision polishing and vacuum high-temperature annealing. The remaining steps and parameters are completely consistent with Example 1.

[0053] Comparative Example 5: This comparative example differs from Example 1 only in that it adopts conventional preparation methods of existing technology. Specifically, the raw material is commercial-grade SiC powder with a purity of 99.9%; S1 only undergoes single industrial-grade hydrochloric acid pickling treatment, without alkaline washing and high-temperature vapor phase impurity removal; S2 mixing uses a cast iron-lined ball mill with steel balls as the ball milling media, and 1.5wt% Al2O3 + 0.5wt% C is added as a composite sintering aid; S4 hot pressing sintering is carried out under a non-ultra-high vacuum argon protective atmosphere; S5 only undergoes conventional mechanical polishing, without vacuum high-temperature annealing and hot isostatic pressing treatment, and the remaining temperature, pressure, and time parameters are the same as in Example 1.

[0054] Test Item 1: Total Metal Impurity Content Test This test was conducted according to ASTM E1508-2017, "Standard Method for Determination of Trace Elements in Ceramic Materials by Glow Discharge Mass Spectrometry." The total metallic impurity content of high-purity hot-pressed sintered silicon carbide samples prepared in Examples 1-3 and Comparative Examples 1-5 was determined. First, three 10mm × 10mm × 5mm samples were cut from the center and edge regions of each sample. After removing the surface oxide layer and contaminants, the samples were ultrasonically cleaned for 15 minutes with anhydrous ethanol of at least 99.999% purity, followed by vacuum drying at 120°C for 2 hours. After cooling to room temperature, the samples were placed in the sample chamber of the glow discharge mass spectrometer. The discharge power was set to 30W, the argon flow rate to 0.8L / min, and the detection range covered common metallic impurity elements such as B, Al, Fe, Ni, and Cu. Each sample was tested three times, and the average of the three results was taken as the total metallic impurity content of the sample. Finally, the total metallic impurity content data for each example and comparative example sample were recorded.

[0055] Test Item 2: Density Test This test was conducted according to GB / T25995-2010 "Test Method for Density and Apparent Porosity of Fine Ceramics". The Archimedes displacement method was used to determine the density of samples from Examples 1-3 and Comparative Examples 1-5. First, all samples were processed into cubic specimens with dimensions of 15mm × 15mm × 15mm. After removing surface burrs, they were dried at 110℃ for 4 hours. After cooling to room temperature, the dry mass of each specimen was accurately weighed using an electronic balance. Then, the specimens were completely immersed in a container filled with high-purity deionized water with a resistivity ≥18.2 MΩ・cm, ensuring the specimens were completely submerged and not in contact with the container walls. The suspended mass of the specimens in the water was weighed. The density of each specimen was calculated using the formula: Density = Dry Mass / (Dry Mass - Suspended Mass) × Density of Water. Five specimens were tested in parallel for each sample, and the average value was taken as the final density data for that sample.

[0056] Test Item 3: Bending Strength Test This test was conducted according to GB / T6569-2006 "Test Method for Bending Strength of Fine Ceramics". The bending strength of samples from Examples 1 to 3 and Comparative Examples 1 to 5 was tested. First, all samples were processed into strip-shaped specimens with dimensions of 3mm × 4mm × 40mm and a surface roughness Ra ≤ 0.05μm. Then, the specimens were placed on the three-point bending test fixture of a universal testing machine. The span was set to 30mm, and the loading rate was 0.5mm / min. Pressure was applied uniformly until the specimen fractured, and the fracture load of each specimen was recorded. The bending strength was calculated using the formula: Bending strength = 3 × fracture load × span / (2 × specimen width × specimen thickness). 2), calculate the bending strength of each specimen, test 10 specimens in parallel for each sample, remove the maximum and minimum values ​​and take the average of the remaining 8 data as the final bending strength of the sample.

[0057] Test Item 4: Phase Structure Analysis Test This test was conducted according to GB / T6536-2023 "General Rules for X-ray Diffraction Analysis Methods" on the high-purity hot-pressed sintered silicon carbide sample prepared in Example 1. The sample from Example 1 was ground to a particle size ≤5μm. 0.2g of the ground powder was spread evenly on the XRD sample stage and compacted. The test parameters were set as follows: scanning range 2θ = 20°~80°, scanning rate 2° / min, tube voltage 40kV, tube current 30mA. Continuous scanning of the sample was performed to obtain the X-ray diffraction pattern of the sample from Example 1, as shown below. Figure 2 As shown. From Figure 2 It can be seen that the diffraction peaks of the sample match the characteristic peaks of the standard crystal form of silicon carbide, and there are no obvious impurity phase diffraction peaks, indicating that the sample of Example 1 has a single phase and a pure structure.

[0058] Test Item 5: Precise Analysis Test of High-Purity Trace Elements This test follows ASTM E1508-2017, "Standard Method for Determination of Trace Elements in Ceramic Materials by Glow Discharge Mass Spectrometry," and only the high-purity hot-pressed sintered silicon carbide sample prepared in Example 1 was tested. Three 10mm × 10mm × 5mm samples were cut from the central region of the sample from Example 1. After removing surface contaminants, the samples were ultrasonically cleaned for 15 minutes with anhydrous ethanol of at least 99.999% purity, then vacuum dried at 120°C for 2 hours. After cooling to room temperature, the samples were placed in the sample chamber of the glow discharge mass spectrometer. The discharge power was set to 30W, the argon flow rate to 0.8L / min, and the detection range covered more than 70 trace elements, including Li, B, Al, and Fe. Each sample was measured three times consecutively, and the average value was taken to obtain the trace element content data of the sample from Example 1. Figure 3 As shown. From Figure 3 The data shows that the content of most trace elements in the sample is below the detection limit, and the overall purity reaches 99.9999%, which meets the impurity control requirements for high-purity silicon carbide.

[0059] Test Item 6: Bending Strength Stress-Strain Curve Test This test was conducted according to GB / T6569-2006 "Test Method for Bending Strength of Fine Ceramics", using the high-purity hot-pressed sintered silicon carbide sample prepared in Example 1. The sample from Example 1 was processed into a strip-shaped specimen with dimensions of 3mm × 4mm × 40mm, ensuring a surface roughness Ra ≤ 0.05μm. The specimen was then placed on the three-point bending test fixture of a universal testing machine, with a span of 30mm and a loading rate of 0.5mm / min. Pressure was applied uniformly to the specimen, and stress and strain data were recorded synchronously and in real time during the loading process. The bending strength stress-strain curve of the sample from Example 1 was plotted, as shown below. Figure 4 As shown. From Figure 4 As can be seen from the curve, the stress of the sample rapidly climbs to the peak value after being loaded, and then fractures after the strain stabilizes slightly. This reflects the typical ceramic brittle mechanical properties and good load-bearing strength of this high-purity silicon carbide material.

[0060] The key performance test data of Examples 1-3 and Comparative Examples 1-5 are shown in Table 1.

[0061] Table 1:

[0062] As can be seen from Examples 1-3 and Comparative Example 1, adding traditional sintering aids during the preparation process introduces additional impurities. These impurities tend to accumulate at the grain boundaries of the material. Although they can help improve the density of sintering to a certain extent, the presence of impurities will destroy the structural integrity of the grain boundaries, thereby adversely affecting the mechanical properties of the material.

[0063] As can be seen from Examples 1-3 and Comparative Example 2, a single acid pickling treatment cannot completely remove various impurities from the raw materials. Alkali washing and high-temperature vapor phase de-purification can specifically remove impurities such as free silicon and oxides. Without these steps, impurities will remain and accumulate in the material, which will not only affect the purity of the material, but also interfere with the densification effect of the subsequent sintering process, and thus affect the mechanical properties of the material.

[0064] As can be seen from Examples 1-3 and Comparative Example 3, the contact of the inner lining with the metal material during the mixing process will introduce additional metal impurities. These impurities will enter the material system, destroy the high-purity environment of the material, and thus have a negative impact on the mechanical properties of the material. This also reflects the importance of a metal-free mixing environment for maintaining the purity and performance of the material.

[0065] As can be seen from Examples 1-3 and Comparative Example 4, hot isostatic pressing plays a key role in eliminating closed micropores inside the material. Without this step, micropores are likely to remain inside the material, which will reduce the overall density. Insufficient density will directly affect the mechanical properties of the material.

[0066] As can be seen from Examples 1-3 and Comparative Example 5, in the conventional preparation process of the prior art, the defects of low-purity raw materials, single purification method, metal contact mixing environment and traditional sintering aids will be superimposed. This will not only introduce a large number of impurities, but also affect the densification effect of sintering and post-treatment, thus making it difficult for the various properties of the material to meet the requirements of high-purity preparation.

[0067] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing high-purity hot-pressed sintered silicon carbide, characterized in that: Includes the following steps: S1. Multi-stage purification of high-purity silicon carbide powder: Submicron-sized β-SiC powder is selected as raw material and subjected to acid washing to remove impurities, alkali washing to remove impurities, and high-temperature gas phase de-purification treatment in sequence. The high-temperature gas phase de-purification adopts plasma-assisted degassing. S2. Metal-free mixing and billet forming: In a metal-free environment, silicon carbide powder purified by S1 is mixed with organic forming aids, and high-purity silicon carbide balls are used as the mixing medium. The mixed powder is then dried and sieved, and then cold isostatically pre-formed to obtain a high-purity silicon carbide billet. S3, Gradient heating degreasing and pre-firing: The green body obtained in S2 is placed in an inert atmosphere and subjected to gradient heating treatment to complete the degreasing and pre-firing of organic matter in sequence. S4. Hot pressing sintering without sintering aids: The pre-fired blank of S3 is placed in a high-purity mold free of metal contamination after vacuum baking, and multi-stage hot pressing sintering is carried out in an ultra-high vacuum environment; hot pressing sintering includes a high-temperature holding stage under pressure. Controlled cooling is performed after sintering. S5. Post-treatment: The sintered body obtained in S4 is subjected to precision surface polishing, vacuum high-temperature annealing and hot isostatic pressing in sequence.

2. The method for preparing high-purity hot-pressed sintered silicon carbide according to claim 1, characterized in that: In step S1, the particle size D of the submicron β-SiC powder 50 The particle size is 0.3 μm to 1.0 μm, and the initial purity is not less than 99.999%.

3. The method for preparing high-purity hot-pressed sintered silicon carbide according to claim 1, characterized in that: In step S1, the acid washing to remove impurities is performed by soaking in a mixed solution of high-purity hydrofluoric acid and high-purity nitric acid for 2 to 4 hours; the alkaline washing to remove impurities is performed by soaking in a high-purity ammonium hydroxide solution for 1 to 3 hours.

4. The method for preparing high-purity hot-pressed sintered silicon carbide according to claim 1, characterized in that: In step S1, the vacuum level of the high-temperature gas phase depurification process is 10. -6 The process involves processing at Pa levels, with temperatures ranging from 1600℃ to 1900℃ and processing times from 2 hours to 4 hours. The total metal impurity content of the silicon carbide powder after multi-stage purification is ≤5ppm.

5. The method for preparing high-purity hot-pressed sintered silicon carbide according to claim 1, characterized in that: In step S2, the organic forming aid is selected from one or a combination of two of high-purity polyvinyl alcohol and high-purity polyethylene glycol; the mixing process uses an inner liner made of alumina or silicon carbide.

6. The method for preparing high-purity hot-pressed sintered silicon carbide according to claim 1, characterized in that: In step S2, the drying temperature is 80°C to 120°C, and the drying time is 4h to 8h; the pressure of the cold isostatic pressing preforming is 100MPa to 200MPa, and the holding time is 1h to 3h.

7. The method for preparing high-purity hot-pressed sintered silicon carbide according to claim 1, characterized in that: In step S3, the heating rate of the gradient heating process is 0.5℃ / min to 2℃ / min; the degreasing temperature of the organic matter is 600℃ to 800℃; and the pre-calcination temperature is 1200℃ to 1500℃.

8. The method for preparing high-purity hot-pressed sintered silicon carbide according to claim 1, characterized in that: In step S4, the vacuum level of the ultra-high vacuum environment is 10. -6 The second stage of the multi-stage hot pressing sintering is heated to 1600°C to 2000°C while applying a pressure of 30MPa to 60MPa; the controlled cooling rate is 5°C / min to 10°C / min.

9. The method for preparing high-purity hot-pressed sintered silicon carbide according to claim 1, characterized in that: In step S4, the temperature of the vacuum baking process is 800°C to 1000°C, and the baking time is 2 hours to 3 hours.

10. The method for preparing high-purity hot-pressed sintered silicon carbide according to claim 1, characterized in that: In step S5, the vacuum high-temperature annealing temperature is 1400℃ to 1600℃, and the holding time is 2h to 3h; the hot isostatic pressing is carried out in an argon atmosphere, with a processing pressure of 100MPa to 200MPa, a processing temperature of 1800℃ to 2000℃, and a processing time of 1h to 2h.

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