Preparation method of in-situ large-size high-density semiconductor-grade high-purity silicon carbide multi-crystal grains
By employing a catalytic-free suspension polymerization method and high-temperature crystallization treatment, the problems of small silicon carbide polycrystalline particles, high energy consumption, and low yield in existing technologies have been solved. This method enables the efficient preparation of large-size, high-purity, and high-density silicon carbide polycrystalline grains, which is suitable for the growth of large-size silicon carbide single crystals.
Patent Information
- Application Number
- CN202511617240.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-06
- Publication Date
- 2026-01-16
AI Technical Summary
Existing methods produce small polycrystalline silicon carbide particles, require high energy consumption for secondary crystallization, and have low yields, making it difficult to meet the growth requirements of large-size silicon carbide ingots.
A precursor resin was prepared by a catalytic-free suspension polymerization method to serve as a nucleation seed crystal and binder. Pre-sintered spheres were prepared through a high-intensity granulation process. The spheres were then cured, subjected to a self-propagating synergistic carbothermal reduction reaction and densification treatment in a high-temperature crystallization furnace, and combined with rapid cooling to achieve the growth of large-size, high-density semiconductor-grade high-purity silicon carbide polycrystalline grains.
High-purity silicon carbide polycrystalline grains with a particle size of 0.8~20mm, a purity of 6N, and a density of 1.6~2.5g/cm3 were prepared with a yield of 85%~90%, which is suitable for large-size single crystal growth and reduces energy consumption and crucible material consumption.
Smart Images
Figure SMS_1
Abstract
Description
Technical Field
[0001] This invention belongs to the field of semiconductor materials, specifically relating to a method for preparing high-purity semiconductor-grade silicon carbide polycrystalline material. Background Technology
[0002] In the development of third-generation semiconductor substrate fabrication, the grain size of polycrystalline silicon carbide (SiC) has evolved from small to large. 4-inch SiC substrate growth requires 200-300 micrometers of high-purity polycrystalline SiC powder, while 6-inch SiC substrates require 500-800 micrometers of high-purity SiC substrate powder. With the increasing size of ingots, higher requirements have been placed on the size, morphology, and purity of polycrystalline SiC raw materials. Grain sizes are now required to reach millimeter levels, and even 5 millimeters or larger, while maintaining consistent morphology, higher purity (approaching the lower limit of GDMS detection), and higher density (close to intrinsic density). Only high-purity, high-density, large-particle semiconductor SiC polycrystalline raw materials can meet the requirements for growing crystals larger than 8 inches. These grains exhibit rapid thermal conductivity, uniform gas channel formation, and a reasonable gas phase transport rate, making them suitable for the growth requirements of 8-inch or even 12-inch SiC ingots in resistance furnaces.
[0003] There are currently three main methods for preparing substrate-level polycrystalline carbide: self-propagating sintering, precursor method, and CVD method.
[0004] (1) Self-propagating sintering method: This method uses high-purity silicon particles and high-purity carbon powder or graphite powder to undergo a self-propagating sintering reaction at high temperature to generate polycrystalline silicon carbide. This method has two main drawbacks. First, the purity of the silicon carbide product is heavily dependent on the purity of the silicon and carbon sources, especially since high-purity carbon sources are difficult to obtain. Due to the complexity of the graphite purification process, graphite contains residual elements such as B, Fe, Al, V, Ti, and W, which affects the purity of the product. Second, the silicon carbide grains prepared by this method are small, with primary particles only tens of micrometers and aggregated particles only a few hundred micrometers. To meet the growth requirements of large-size silicon carbide ingots, a sublimation crystallization process is necessary to grow them to the millimeter level, which inevitably leads to increased energy consumption, reduced yield, and high consumption of crucible auxiliary materials.
[0005] (2) Precursor method: The precursor method uses organosilicon compounds as silicon sources and organic matter as carbon sources, or organosilicon provides both silicon and carbon sources. Gels or resins are prepared through chemical processes such as hydrolysis polymerization and the Wutz reaction. Silicon carbide polycrystalline powder is then obtained through high-temperature pyrolysis and carbothermal reduction. This method also suffers from the problem of small initial particle size, requiring a sublimation crystallization process to grow to the millimeter scale. This inevitably leads to increased energy consumption, reduced yield, and high consumption of crucible auxiliary materials.
[0006] (3) CVD method: Using methylchlorosilane, chlorosilane, silane, alkanes, or aromatic hydrocarbons as raw materials, silicon carbide bulk materials can be prepared under a reducing atmosphere. This method has high requirements for the materials of the production equipment, which must be corrosion-resistant, and the equipment processing precision is extremely high. The reactants are all toxic or explosive raw materials, making them extremely dangerous. During the preparation of silicon carbide, the reaction parameters are also difficult to control, and more than ten byproducts such as monomethyltrichlorosilane, dimethyldichlorosilane, hydrochlorosilane, trichlorosilane, and silicon tetrachloride are produced. The treatment of large quantities of chlorine-containing byproducts and environmental protection costs are huge, and the low primary conversion rate keeps the production cost high. Summary of the Invention
[0007] The present invention aims to solve the technical problems of small silicon carbide polycrystalline particles, high energy consumption for secondary crystallization, and low yield prepared by existing methods, and provides an in-situ method for preparing large-size, high-density semiconductor-grade high-purity silicon carbide polycrystalline particles.
[0008] The method for preparing in-situ large-size, high-density semiconductor-grade high-purity silicon carbide polycrystalline grains according to the present invention is carried out according to the following steps:
[0009] I. Precursor resins were prepared using a catalytic-free suspension polymerization method, serving as nucleation seed crystals and binders:
[0010] Monoaromatic cyclosilanes and linear silanes are added in a certain proportion to a solvent of methanol or ethanol and water, and a small amount of chlorosilane is added as a hydrolysis catalyst for hydrolysis. Then, basic silanes are added to the hydrolysate as a polymerization catalyst for polymerization to obtain two precursor resins, solid and liquid.
[0011] II. Preparation of silicon-carbon pre-sintered bodies:
[0012] High-purity silicon material, high-purity graphite powder, and solid precursor resin are premixed at a mass ratio of (28~32):(12~13):(1~5) to obtain a premixed powder. The premixed powder is added to a high-intensity granulator, and liquid precursor resin is added as a binder at the same time. The mass ratio of premixed powder to binder is 100:(3~10). The mixture is mixed and granulated at a rotation speed of 50~500 r / min and a granulation temperature of 20~50℃ to obtain pre-sintered spheres with a particle size of 1~25 mm. The pre-sintered spheres do not break during a free fall from a height of 1 m. Pre-sintered spheres with a certain bonding force are prepared through the high-intensity granulation process.
[0013] III. In-situ preparation of large-size, high-purity semiconductor-grade silicon carbide polycrystalline materials:
[0014] The pre-sintered spheres are added non-contactly to the feeding hopper of the high-temperature crystallization furnace through a high-level hopper. The feeding hopper then feeds the silicon-carbon pre-sintered spheres into the high-temperature crystallization furnace through a quantitative feeding system. In the high-temperature crystallization furnace, the following processes are sequentially performed: solidification, self-propagating synergistic carbothermal reduction reaction, in-situ silicon carbide grain growth, in-situ silicon carbide grain densification, and cooling annealing. The operation of each process is as follows:
[0015] (1) Curing process: Evacuate the system to 10 -3 Up to 10 -5 Pa, the system is heated to 80-120℃ at a heating rate of 5-10℃ / min and held at that temperature for 2-4 hours; then the system is heated to 200-240℃ at a heating rate of 5-10℃ / min and held at that temperature for 4-6 hours; this is the first stage;
[0016] (2) Self-propagating synergistic carbothermic reduction reaction process: The system vacuum is maintained at 10 -3 Up to 10 -5 Pa, the system is heated to 1200~1400℃ at a heating rate of 10~15℃ / min and held at that temperature for 8~12 hours; this is the second stage. During this process, the seed crystal precursor undergoes a pyrolysis reaction to generate silicon carbide pre-seed crystal precursor. Under the condition of 1200-1400℃, silicon and carbon undergo a self-propagating reaction. The strong exothermic process of the self-propagating reaction causes the seed crystal precursor to undergo a carbothermic reduction reaction, resulting in an in-situ silicon carbide crystallization center - silicon carbide seed crystal.
[0017] (3) In-situ silicon carbide grain growth process: The system vacuum is maintained at 2000~80000Pa, and the system is heated to 2200~2400℃ at a heating rate of 10~15℃ / min and held for 12~24 hours to obtain in-situ large-size high-purity semiconductor-grade silicon carbide polycrystalline material; this is the third stage. In this process, the carbon and silicon in the granulated silicon-carbon pre-sintered body will react further to generate new silicon carbide. These newly generated silicon carbide will crystallize and grow around the silicon carbide seed crystal to obtain silicon carbide grains of 0.8~20mm.
[0018] (4) In-situ silicon carbide grain densification process: Adjust the system vacuum to 2000~2000 Pa and reduce the system temperature to 1500~2000℃; then introduce reaction gas from the bottom of the high-temperature crystallization furnace for densification. The partial pressure of the reaction gas in the whole system is maintained at 200~5000 Pa, and the densification process is controlled for 8~24 hours; wherein the reaction gas is a mixture of methylchlorosilane, hydrogen and argon.
[0019] Or it can be a mixture of trichlorosilane, methane, ethylene, and hydrogen;
[0020] Or it could be a mixture of trichlorosilane, acetylene, ethylene, and hydrogen.
[0021] Or it could be a mixture of silicon tetrachloride, methane, ethylene, and hydrogen.
[0022] Or it could be a mixture of silicon tetrachloride, acetylene, ethylene, and hydrogen.
[0023] Or it could be a mixture of silane, methane, and hydrogen.
[0024] Or it could be a mixture of silane, acetylene, ethylene, and hydrogen.
[0025] (5) Cooling and annealing stage: High-purity low-temperature argon gas is introduced into the system to reduce the temperature from 1500~2000℃ to 1000~1500℃ within 30min~2h, and then the system is naturally cooled to room temperature to obtain large-size high-density semiconductor-grade high-purity silicon carbide polycrystalline grains; during this process, the adhesion and breakage between the grains are achieved by rapid cooling.
[0026] Furthermore, the monoaromatic silane mentioned in step one is phenyltrimethoxysilane, phenyltriethoxysilane, methylphenyldimethoxysilane, methylphenyldiethoxysilane, dimethylphenylmethoxysilane, or dimethylphenylethoxysilane.
[0027] Furthermore, the linear silane mentioned in step one is trimethylmethoxysilane, trimethyltriethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, butyltrimethoxysilane, butyltriethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, dodecylsilane, or hydrogen-substituted diekoxysilanes of the above silanes.
[0028] Furthermore, in step one, the volume ratio of ethanol to water in the solvent mixture is 1:(0.1~5).
[0029] Furthermore, the chlorosilane mentioned in step one is an acidic catalytic silane monomer, namely trichlorosilane, silicon tetrachloride, dichlorosilane, methylchlorosilane, or methylhydrochlorosilane.
[0030] Furthermore, the basic silane mentioned in step one is aminopropyltrimethoxysilane, aminopropyltriethoxysilane, hexamethyldisilazane, aminoethylaminopropyltrimethoxysilane, or secondary aminosilane.
[0031] Furthermore, the molar ratio of the monoaromatic cyclosilane to the linear silane in step one is 1:(0.1~0.5).
[0032] Furthermore, the ratio of the total mass of the monoaromatic cyclosilane and the straight-chain silane mentioned in step one to the volume of the solvent is 1 kg: (1~15) L.
[0033] Furthermore, the amount of chlorosilane added in step one is 0.1% to 0.5% of the total mass of monoaromatic cyclosilane and linear silane.
[0034] Furthermore, the amount of basic silane added in step one is 1.5% to 10% of the total mass of monoaromatic cyclosilane and linear silane.
[0035] Furthermore, the polymerization described in step one is carried out at a temperature of 40~135℃ and a stirring speed of 100~500r / min.
[0036] Furthermore, the solid precursor resin described in step one has a molecular weight of 4000-6000 and is solid at room temperature (25°C). The precursor resin is synthesized under conditions of a high proportion of catalyst, a polymerization temperature above 75°C, and a stirring speed below 200 r / min.
[0037] Furthermore, the liquid precursor resin described in step one has a molecular weight of less than 4000 and is in a liquid state at room temperature (25°C). It is synthesized under conditions of low catalyst concentration, polymerization temperature below 75°C, and stirring speed above 200 r / min.
[0038] Furthermore, the high-purity silicon material mentioned in step two is high-purity silicon granules with a purity ≥ 6N.
[0039] Furthermore, the purity of the high-purity graphite powder mentioned in step two is ≥6N.
[0040] Furthermore, in step three (4), the silicon-containing gas and carbon-containing gas in the reaction gas are based on silicon atoms and carbon atoms, and the molar ratio of silicon atoms to carbon atoms is controlled at (1~1.05):(1~1.5).
[0041] Furthermore, the amount of hydrogen in the reaction gas described in step three (4) accounts for 40% to 90% of the total volume of the reaction gas.
[0042] Furthermore, when argon is used as a dilution gas in step three (4), the volume ratio of argon to hydrogen is 1:(5~10).
[0043] This invention employs a catalytic-free suspension polymerization method to prepare a precursor resin, which serves as a nucleation seed crystal and binder. A high-intensity granulation process is used to prepare pre-sintered spheres with a particle size of 1-25 mm that do not break during a free fall from a height of 1 m. These pre-sintered spheres, with a certain degree of bonding, are then used in a high-temperature crystallization furnace with a specific heating curve to achieve solidification, a self-propagating synergistic carbothermal reduction reaction, and crystal growth around the in-situ seed crystal, resulting in silicon carbide polycrystalline grains. A densification reaction is then performed to increase the particle density. Finally, rapid cooling breaks down the adhesion between the grains, yielding large-size, high-density, semiconductor-grade, high-purity silicon carbide polycrystalline grains grown in situ.
[0044] The silicon carbide polycrystalline grains prepared by this invention have a particle size of 0.8~20mm, a purity of 6N, and a density of 1.6~2.5g / cm³. 3 .
[0045] The method of this invention achieves a silicon carbide polycrystalline yield of 85% to 90%, allows for continuous feeding and discharging, has high single-unit output, can achieve automation, reduces human intervention, and provides stable quality. It is suitable for the growth of large-size single crystals and can be used in the field of silicon carbide preparation. Detailed Implementation
[0046] The beneficial effects of the present invention will be verified using the following examples.
[0047] Example 1: The preparation method of in-situ large-size high-density semiconductor-grade high-purity silicon carbide polycrystalline grains in this example is carried out according to the following steps:
[0048] I. The precursor resin obtained by catalytic-free suspension polymerization is used as a nucleation seed crystal and binder:
[0049] 372 kg of phenyltrimethoxysilane and 88 kg of propylmethyltriethoxysilane were added to a solvent of 800 kg of methanol and 800 kg of water. 2.3 kg of trichlorosilane was added as a hydrolysis catalyst, and hydrolysis was carried out at 40 °C. 6 kg of aminopropyltrimethoxysilane was added to the hydrolysate, and polymerization was carried out at 50 °C to obtain a liquid precursor resin, which was used as a binder. The molecular weight of the liquid precursor resin was approximately 2000.
[0050] 372 kg of phenyltrimethoxysilane and 88 kg of propylmethyltriethoxysilane were added to a solvent of 800 kg of methanol and 800 kg of water. 2.3 kg of trichlorosilane was added as a hydrolysis catalyst, and hydrolysis was carried out at 40 °C. 10 kg of aminopropyltrimethoxysilane was added to the hydrolysate, and polymerization was carried out at 100 °C to obtain a solid precursor resin, which served as a nucleation seed crystal. The molecular weight of this solid precursor resin was approximately 5500.
[0051] II. Preparation of silicon-carbon pre-sintered bodies:
[0052] 30 kg of high-purity silicon particles with a purity of 6N, 12.5 kg of high-purity graphite powder with a purity of 6N, and 4 kg of solid precursor resin were mixed at room temperature for 20 min to obtain a premixed powder. The premixed powder was then placed in a high-intensity granulator, and 2.5 kg of liquid precursor resin was added as a binder. The mixture was then mixed and granulated at a granulator rotation speed of 400 r / min and a granulation temperature of 30~40℃ to obtain pre-sintered spheres with a particle size of 1~25 mm. Moreover, the pre-sintered spheres did not break during a free fall from a height of 1 m.
[0053] III. In-situ preparation of large-size, high-density, high-purity semiconductor-grade silicon carbide polycrystalline material:
[0054] The pre-sintered spheres are added to the feeding hopper of the high-temperature crystallization furnace without contact via a high-level hopper. The feeding hopper then feeds the pre-sintered spheres into the high-temperature crystallization furnace through a quantitative feeding system. In the high-temperature crystallization furnace, the following processes are sequentially performed: solidification, self-propagating synergistic carbothermal reduction reaction, in-situ silicon carbide grain growth, in-situ silicon carbide grain densification, and cooling annealing. The operation of each process is as follows:
[0055] (1) Curing process: Evacuate the system to 10 -4 Pa, the system is heated to 110℃ at a heating rate of 8℃ / min and held at that temperature for 3 hours; then the system is heated to 230℃ at a heating rate of 10℃ / min and held at that temperature for 5 hours; this is the first stage;
[0056] (2) Self-propagating synergistic carbothermic reduction reaction process: The system vacuum is maintained at 10 -4 Pa, the system is heated to 1350℃ at a heating rate of 15℃ / min and held at that temperature for 10 hours; this is the second stage. During this process, the seed crystal precursor undergoes a pyrolysis reaction to generate silicon carbide pre-seed crystal precursor. At 1350℃, silicon and carbon undergo a self-propagating reaction. The strong exothermic process of the self-propagating reaction causes the seed crystal precursor to undergo a carbothermic reduction reaction, resulting in an in-situ silicon carbide crystallization center - silicon carbide seed crystal.
[0057] (3) In-situ silicon carbide grain growth process: The system vacuum is maintained at 10000Pa, the system is heated to 2300℃ at a heating rate of 15℃ / min and held for 20 hours to obtain in-situ large-size high-purity semiconductor-grade silicon carbide polycrystalline material; this is the third stage. In this process, the carbon and silicon in the granulated silicon-carbon pre-sintered body will react further to generate new silicon carbide. These newly generated silicon carbide will crystallize and grow around the silicon carbide seed crystal to obtain silicon carbide polycrystalline grains;
[0058] (4) In-situ silicon carbide grain densification process: Adjust the system vacuum to 10000 Pa and reduce the system temperature to 1600℃; then introduce the reaction gas from the bottom of the high-temperature crystallization furnace for densification. The partial pressure of the reaction gas in the whole system is maintained at 1000 Pa, and the densification process is controlled for 12 hours; wherein the reaction gas is a mixture of methylchlorosilane, hydrogen and argon in a volume ratio of 1:8:1.
[0059] (5) Cooling and annealing stage: High-purity low-temperature argon gas is introduced into the system to reduce the temperature of the system from 1600℃ to 1250℃ within 1 hour, and then the system is naturally cooled to room temperature to obtain large-size high-density semiconductor-grade high-purity silicon carbide polycrystalline grains; during this process, the adhesion and breakage between the grains are achieved by rapid cooling.
[0060] The large-size, high-density semiconductor-grade high-purity silicon carbide polycrystalline grains prepared in this embodiment have a particle size of 3 mm and a density of 1.8 g / cm³. 3 The yield of large-size, high-density semiconductor-grade high-purity silicon carbide polycrystalline grains prepared in this embodiment is 85%.
[0061] Elemental analysis of the large-size, high-density semiconductor-grade high-purity silicon carbide polycrystalline grains prepared in this embodiment was performed using glow discharge mass spectrometry (GDMS). The results are shown in Table 1. As can be seen from Table 1, the mass purity of the large-size, high-density semiconductor-grade high-purity silicon carbide polycrystalline grains prepared in this embodiment is 99.9999%, reaching 6.3N.
[0062] Table 1. Elemental analysis results of large-size, high-density semiconductor-grade high-purity silicon carbide polycrystalline grains prepared in Example 1
[0063]
[0064] Example 2: The preparation method of in-situ large-size high-density semiconductor-grade high-purity silicon carbide polycrystalline grains in this example is carried out according to the following steps:
[0065] I. The precursor resin obtained by catalytic-free suspension polymerization is used as a nucleation seed crystal and binder:
[0066] 372 kg of phenyltrimethoxysilane and 88 kg of propylmethyltriethoxysilane were added to a solvent of 800 kg of methanol and 800 kg of water. 2.3 kg of trichlorosilane was added as a hydrolysis catalyst, and hydrolysis was carried out at 40 °C. 6 kg of aminopropyltrimethoxysilane was added to the hydrolysate, and polymerization was carried out at 50 °C to obtain a liquid precursor resin, which was used as a binder. The molecular weight of the liquid precursor resin was approximately 2000.
[0067] 372 kg of phenyltrimethoxysilane and 88 kg of propylmethyltriethoxysilane were added to a solvent of 800 kg of methanol and 800 kg of water. 2.3 kg of trichlorosilane was added as a hydrolysis catalyst, and hydrolysis was carried out at 40 °C. 10 kg of aminopropyltrimethoxysilane was added to the hydrolysate, and polymerization was carried out at 100 °C to obtain a solid precursor resin, which served as a nucleation seed crystal. The molecular weight of this solid precursor resin was approximately 5500.
[0068] II. Preparation of silicon-carbon pre-sintered bodies:
[0069] 30 kg of high-purity silicon particles with a purity of 6N, 12.5 kg of high-purity graphite powder with a purity of 6N, and 4 kg of solid precursor resin were mixed at room temperature for 20 min to obtain a premixed powder. The premixed powder was then placed in a high-intensity granulator, and 2.5 kg of liquid precursor resin was added as a binder. The mixture was then mixed and granulated at a granulator rotation speed of 400 r / min and a granulation temperature of 30~40℃ to obtain pre-sintered spheres with a particle size of 1~25 mm. Moreover, the pre-sintered spheres did not break during a free fall from a height of 1 m.
[0070] III. In-situ preparation of large-size, high-density, high-purity semiconductor-grade silicon carbide polycrystalline material:
[0071] The pre-sintered spheres are added to the feeding hopper of the high-temperature crystallization furnace without contact via a high-level hopper. The feeding hopper then feeds the pre-sintered spheres into the high-temperature crystallization furnace through a quantitative feeding system. In the high-temperature crystallization furnace, the following processes are sequentially performed: solidification, self-propagating synergistic carbothermal reduction reaction, in-situ silicon carbide grain growth, in-situ silicon carbide grain densification, and cooling annealing. The operation of each process is as follows:
[0072] (1) Curing process: Evacuate the system to 10 -4 Pa, the system is heated to 110℃ at a heating rate of 8℃ / min and held at that temperature for 3 hours; then the system is heated to 230℃ at a heating rate of 10℃ / min and held at that temperature for 5 hours; this is the first stage;
[0073] (2) Self-propagating synergistic carbothermic reduction reaction process: The system vacuum is maintained at 10 -4 Pa, the system is heated to 1350℃ at a heating rate of 15℃ / min and held at that temperature for 10 hours; this is the second stage. During this process, the seed crystal precursor undergoes a pyrolysis reaction to generate silicon carbide pre-seed crystal precursor. At 1350℃, silicon and carbon undergo a self-propagating reaction. The strong exothermic process of the self-propagating reaction causes the seed crystal precursor to undergo a carbothermic reduction reaction, resulting in an in-situ silicon carbide crystallization center - silicon carbide seed crystal.
[0074] (3) In-situ silicon carbide grain growth process: The system vacuum is maintained at 10000Pa, the system is heated to 2300℃ at a heating rate of 15℃ / min and held for 20 hours to obtain in-situ large-size high-purity semiconductor-grade silicon carbide polycrystalline material; this is the third stage. In this process, the carbon and silicon in the granulated silicon-carbon pre-sintered body will react further to generate new silicon carbide. These newly generated silicon carbide will crystallize and grow around the silicon carbide seed crystal to obtain silicon carbide polycrystalline grains;
[0075] (4) In-situ silicon carbide grain densification process: The system vacuum is adjusted to 5000 Pa and the system temperature is reduced to 1500℃; then the reaction gas is introduced from the bottom of the high-temperature crystallization furnace for densification. The partial pressure of the reaction gas in the whole system is maintained at 1500 Pa, and the densification process is controlled for 12 hours; wherein the reaction gas is a mixture of silane, methane and hydrogen in a volume ratio of 1:1.8:7.2.
[0076] (5) Cooling and annealing stage: High-purity low-temperature argon gas is introduced into the system to reduce the temperature of the system from 1500℃ to 1200℃ within 1 hour, and then the system is naturally cooled to room temperature to obtain large-size high-density semiconductor-grade high-purity silicon carbide polycrystalline grains; during this process, the adhesion and breakage between the grains are achieved by rapid cooling.
[0077] The large-size, high-density semiconductor-grade high-purity silicon carbide polycrystalline grains prepared in this embodiment have a particle size of 3 mm and a density of 2.1 g / cm³. 3 The purity is higher than 6N. The yield of large-size, high-density semiconductor-grade high-purity silicon carbide polycrystalline grains prepared in this embodiment is 86%.
Claims
1. A method for producing large-size high-density semi-conductor grade high-purity silicon carbide polycrystalline grains in-situ, characterized by, The method is carried out according to the following steps: I. The precursor resin is prepared by a non-catalytic suspension polymerization method, which is used as a nucleation seed and an adhesive: A certain proportion of mono-aromatic ring silane and linear silane is added into a solvent mixed by methanol or ethanol and water, and a small amount of chlorosilane is added as a hydrolysis catalyst to carry out hydrolysis; then, a base silane is added as a polymerization catalyst to carry out polymerization in the hydrolyzed solution, so as to obtain solid and liquid precursor resins; II. Preparation of silicon-carbon pre-sintered body: The high-purity silicon material, high-purity graphite powder and solid precursor resin are premixed according to the mass ratio of (28-32):(12-13):(1-5) to obtain a premixed powder; the premixed powder is added into a strong granulator, and the liquid precursor resin is added as an adhesive at the same time, and the mass ratio of the premixed powder and the adhesive is 100:(3-10); the premixed powder and the adhesive are mixed and granulated under the conditions of a rotation speed of 50-500 r / min and a granulation temperature of 20-50 DEG C to obtain pre-sintered body spheres with a particle size of 1-25 mm; the pre-sintered body spheres do not break during free falling at a height of 1 m; the pre-sintered body spheres with a certain binding force are prepared through the strong granulation process; III. Preparation of in-situ large-size high-purity semiconductor-grade silicon carbide polycrystal material: The pre-sintered body spheres are added into a feeding bin of a high-temperature crystallization furnace through a high-position bin without contact; the feeding bin feeds the silicon-carbon pre-sintered body into the high-temperature crystallization furnace through a quantitative feeding system; the processes of solidification, self-propagating and carbonthermal reduction reaction, in-situ silicon carbide grain growth, in-situ silicon carbide grain densification and cooling annealing are sequentially carried out in the high-temperature crystallization furnace, and the operations of the processes are as follows: (1) Curing process: the system is vacuumed to 10 -3 Pa, the system is heated to 80~120℃ at a heating rate of 5~10℃ / min and kept for 2~4 hours; then the system is heated to 200~240℃ at a heating rate of 5~10℃ / min and kept for 4~6 hours; this is the first stage; (2) Degassing process: the system is vacuumed to 10 -5 Pa, the system is heated to 80~120℃ at a heating rate of 5~10℃ / min and kept for 2~4 hours; then the system is heated to 200~240℃ at a heating rate of 5~10℃ / min and kept for 4~6 hours; this is the second stage; (2) self-propagating synergistic carbothermal reduction reaction process: the system is kept in vacuum at 10 -3 to 10 -5 Pa, the system is raised to 1200-1400 ℃ at a temperature raising rate of 10-15 ℃ / min and kept for 8-12 hours; this is the second stage, in this process, the seed crystal precursor generates pyrolysis reaction to generate silicon carbide pre-seed crystal precursor, and silicon and carbon generate self-propagating reaction under the condition of 1200-1400 ℃, the strong exothermic process of the self-propagating reaction makes the seed crystal precursor generate carbothermal reduction reaction to obtain in-situ silicon carbide crystallization center-silicon carbide seed crystal; (3) In-situ silicon carbide grain growth process: the system is kept in vacuum at 2000-80000 Pa, the system is raised to 2200-2400 DEG C at a temperature rising rate of 10-15 DEG C / min and kept for 12-24 hours to obtain in-situ large-size high-purity semiconductor-grade silicon carbide polycrystal material; this is the third stage; in this process, the carbon and silicon in the granulated silicon-carbon pre-sintered body further react to generate new silicon carbide, and the new silicon carbide grows around the silicon carbide seed crystal to obtain silicon carbide grains with a size of 0.8-20 mm; (4) In-situ silicon carbide grain densification process: the system is adjusted to vacuum at 2000-2000 Pa, and the system temperature is reduced to 1500-2000 DEG C; then, a reaction gas is introduced from the bottom of the high-temperature crystallization furnace for densification, the partial pressure of the reaction gas in the whole system is maintained at 200-5000 Pa, and the densification process is controlled for 8-24 hours; the reaction gas is a mixture of methylchlorosilane, hydrogen and argon; or a mixture of trichlorosilane, methane, ethylene and hydrogen; or a mixture of trichlorosilane, acetylene, ethylene and hydrogen; or a mixture of silicon tetrachloride, methane, ethylene and hydrogen; or a mixture of silicon tetrachloride, acetylene, ethylene and hydrogen; or a mixture of monosilane, methane and hydrogen; or a mixture of monosilane, acetylene, ethylene and hydrogen; (5) cooling annealing stage: high purity low temperature argon is introduced into the system to make the system reduce the temperature from 1500-2000℃ to 1000-1500℃ within 30 min-2h, and then naturally cool to room temperature, to obtain large size high density semi-conductor grade high purity silicon carbide polycrystal.
2. The method according to claim 1, wherein the method is characterized by: The mono-aromatic ring silane in step one is phenyltrimethoxysilane, phenyltriethoxysilane, methylphenyldimethoxysilane, methylphenyldiethoxysilane, dimethylphenylmethoxysilane or dimethylphenylethoxysilane.
3. The method according to claim 1 or 2, wherein the method is characterized by, The linear silane in step one is trimethylmethoxysilane, trimethyltriethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, butyltrimethoxysilane, butyltriethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, dodecylsilane or hydrogen-substituted dialkoxy silane of the above silanes.
4. The method according to claim 1 or 2, wherein the method is characterized by, The chlorosilane in step one is an acidic catalytic silane monomer, which is trichlorosilane, silicon tetrachloride, dichlorosilane, methylchlorosilane or methylhydrochlorosilane.
5. The method according to claim 1 or 2, wherein the method is characterized by, The basic silane in step one is aminopropyltrimethoxysilane, aminopropyltriethoxysilane, hexamethyldisilazane, aminoethylaminopropyltrimethoxysilane or secondary amine silane.
6. The method according to claim 1 or 2, wherein the method is characterized by, The molar ratio of the mono-aromatic ring silane to the linear silane in step one is 1: (0.1-0.5).
7. The method according to claim 1 or 2, wherein the method is characterized by, The amount of the chlorosilane added in step one is 0.1%-0.5% of the total mass of the mono-aromatic ring silane and the linear silane.
8. The method according to claim 1 or 2, wherein the method is characterized by, The amount of the basic silane added in step one is 1.5%-10% of the total mass of the mono-aromatic ring silane and the linear silane.
9. The method according to claim 1 or 2, wherein the method is characterized by, The molar ratio of the silicon atom to the carbon atom in the reaction gas in step three (4) is controlled to be (1-1.05):(1-1.5).
10. The method according to claim 1 or 2, wherein the method is characterized by: The amount of hydrogen in the reaction gas in step three (4) is 40%-90% of the volume of the whole reaction gas.