Synthesis method of P-type silicon carbide powder

Abstract

The invention relates to the technical field of silicon carbide powder manufacturing, in particular to a synthesis method of P-type silicon carbide powder, which comprises the following steps: (S.1) alternately filling a silicon source and a carbon source in a layered manner, and uniformly loading an aluminum-based dopant on the surface of each silicon layer; (S.2) performing a first carbonization reaction in a first reaction temperature interval and a vacuum environment to generate primary silicon carbide; (S.3) injecting mixed protective gas of inert gas and hydrogen into the reaction system, and completing crystal form conversion and impurity removal in a second reaction temperature interval; and (S.4) sequentially carrying out oxygen oxidation heat treatment and acid solution cleaning on the synthetic product, and removing surface residual impurities to obtain the P-type silicon carbide powder. By controlling the mixing mode and the heating mode of the silicon source and the carbon source and the scheme of the mixed protective gas containing the hydrogen, low-defect growth of the high-purity silicon carbide crystals is synergistically realized, the resistivity uniformity deviation and the grain size dispersion are greatly reduced, and meanwhile, the process efficiency is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon carbide powder manufacturing, and particularly to a method for synthesizing P-type silicon carbide powder. Background Art

[0002] Silicon carbide (SiC), as the third-generation wide-bandgap semiconductor material, has important applications in fields such as solar cells, power devices, and radio frequency devices. Among them, P-type silicon carbide has become the core material for manufacturing high-performance devices (such as the PN junction of photovoltaic cells) due to its efficient conduction characteristics of hole carriers. However, the existing synthesis technologies of P-type silicon carbide powder still face bottlenecks such as complex processes, uneven doping, and high production energy consumption, restricting its large-scale application.

[0003] The current mainstream industrial production method is centered around the high-temperature self-propagating method, where silicon carbide is formed through the high-temperature reaction of silicon powder and carbon powder in an inert atmosphere. Although this method has a simple process, in actual reactions, the escape of silicon vapor leads to an imbalance in the silicon-carbon molar ratio, not only reducing the product purity but also corroding the reaction crucible and thermal field components. Some improved technologies attempt to set up filtering devices or porous partitions at the top of the crucible, but the equipment complexity increases, and it is difficult to completely suppress the secondary agglomeration phenomenon of silicon carbide grains.

[0004] Although chemical vapor deposition (CVD) can obtain high-purity silicon carbide powder through the decomposition of gas precursors (such as methyltrichlorosilane), the reaction conditions are harsh (requiring ultra-high temperature and precise gas flow control), and the production cost is high, only applicable to small-batch, high-value-added scenarios. On the other hand, although the sol-gel method can synthesize nanoscale silicon carbide powder at a lower temperature, the process route is complex, the choice of precursors is limited, and the particle size uniformity of the powder is difficult to meet the requirements of semiconductor substrate growth.

[0005] Another prominent problem in the prior art is the control of doping uniformity. The traditional mechanical mixing doping method easily leads to local enrichment of aluminum-based dopants (such as AlCl3), resulting in lattice distortion and a decrease in carrier mobility. Although some patents propose solutions such as staged temperature control or argon atmosphere protection, there are still problems such as unreacted carbon residue (affecting electrical properties) and shortened equipment life.

[0006] Therefore, there is an urgent need to develop a method for synthesizing P-type silicon carbide powder with high purity, controllable particle size distribution, and low process cost to solve the contradictions of silicon-carbon ratio imbalance, uneven doping, and large-scale production in the prior art. Summary of the Invention

[0007] The present invention aims to overcome the bottlenecks such as complex processes, uneven doping, and high production energy consumption in the existing P-type silicon carbide powder, which restricts its large-scale application. Therefore, the present invention provides a method for synthesizing P-type silicon carbide powder to overcome the above defects.

[0008] To achieve the above-mentioned invention object, the present invention is realized through the following technical solutions: In a first aspect, the present invention first provides a method for synthesizing P-type silicon carbide powder, comprising the following steps: (S.1) Alternately and layer-by-layer load a silicon source and a carbon source, and uniformly load an aluminum-based dopant on the surface of each silicon layer; (S.2) Perform a first carbonization reaction in a first reaction temperature range and in a vacuum environment to generate primary silicon carbide; (S.3) Inject a mixed protective gas of an inert gas and hydrogen into the reaction system, and complete crystal form conversion and impurity removal in a second reaction temperature range; (S.4) Subject the synthesized product to oxygen oxidation heat treatment and acidic solution cleaning in sequence to remove residual surface impurities and obtain P-type silicon carbide powder.

[0009] In the field of semiconductor materials, silicon carbide has become an important basic material due to its excellent physical and chemical properties. Among them, the synthesis technology of P-type silicon carbide directly affects the device performance. For a long time, the mainstream process in the industry generally uses the high-temperature self-propagating method. However, this method has problems such as silicon vapor escaping, resulting in an imbalance in the silicon-carbon molar ratio, crucible corrosion, and uneven doping. Especially when producing in large kilogram quantities, the electrical performance deviation of the powder increases significantly. To solve the above contradictions, the industry has tried to improve the equipment structure (such as installing a filtering device) or introduce a multi-step purification process. However, these solutions often sacrifice production efficiency and cost-effectiveness, or can only achieve the effect on a laboratory scale. For example, the crucible design with a porous partition can reduce the escape of silicon vapor to a certain extent, but while increasing the equipment complexity, it still cannot effectively solve the lattice defects caused by carbon residue; and although chemical vapor deposition can precisely control the composition through gas precursors, its ultra-high temperature requirement and high-precision requirement for gas flow control severely restrict the mass production capacity. These technical bottlenecks directly limit the large-scale application of P-type silicon carbide in power semiconductor devices. In this context, there is an urgent need for a synthesis method that can take into account purity, doping uniformity, and industrial feasibility.

[0010] The technical solution of this method originates from an in-depth analysis of the interfacial kinetics of the silicon-carbon reaction in traditional processes. In the prior art, although the mechanical mixing of silicon source and carbon source is simple to operate, the chemical reaction efficiency at the solid-solid contact surface is low, and the skin effect leads to the accumulation of unreacted residues inside the particles. Moreover, the rapid escape of silicon vapor at high temperatures further exacerbates the out-of-control silicon-carbon ratio. To solve this problem, this solution creatively proposes a layered structure with alternating layer-by-layer laying of silicon source and carbon source, and directionally loads an aluminum-based dopant on the surface of the silicon layer. This design maximizes the contact area of reactants at the microscopic level by constructing a localized ternary reaction interface of silicon-carbon-dopant, avoiding the phenomenon of local agglomeration of dopants caused by mechanical mixing. It should be particularly noted that through the pre-loading of silicon source and dopant (instead of mixing with carbon source), aluminum atoms can preferentially form an Al-Si eutectic melt during the silicon melting stage, thus promoting the orderly doping of aluminum atoms into the silicon carbide lattice at the initial stage of the carbonization reaction. Compared with the randomly distributed doping mode in traditional processes, this directional doping not only significantly improves the consistency of carrier concentration, but also improves the crystal quality of the material by reducing the probability of lattice distortion.

[0011] The temperature and atmosphere control strategy for the staged reaction is another innovative core of this solution. The prior art usually chooses a single high-temperature reaction to directly complete the carbonization process. However, in large-scale production in kilograms, the intense exothermic reaction is likely to cause a local temperature jump, which in turn induces an explosive escape of silicon vapor. This solution constructs a two-step reaction system. In the first carbonization stage, a vacuum environment below the critical temperature is selected (to avoid massive gasification of silicon), so that the silicon source slowly penetrates the carbon layer in a molten state to complete the preliminary carbonization. This process generates a primary silicon carbide skeleton under relatively mild kinetic conditions, suppressing the escape of silicon vapor while providing a structural basis for subsequent crystal form transformation. In the second high-temperature reaction stage, by injecting a mixed protective gas of argon and hydrogen into the closed system and raising the temperature to the lattice reconstruction range, not only can the reduction effect of hydrogen on residual carbon be used to eliminate free carbon impurities, but also the grain orientation growth can be promoted by the heat conduction homogenization characteristics of argon.

[0012] The co - design of the post - treatment process further strengthens the performance advantages of the powder. Aiming at the problem that the traditional pickling process cannot thoroughly remove surface metal impurities, this solution creatively introduces a pre - oxidation step. Through controlled oxygen heat treatment, the residual unreacted silicon and carbon are converted into silicon dioxide and carbon oxides. This not only avoids the risk of introducing new impurities by mechanical grinding, but also enables subsequent acid solutions to chemically etch and remove impurity particles wrapped by the oxide layer at specific points. This sequential combination of oxidation - pickling is not a simple superposition of processes, but a process re - engineering based on the chemical behavior differences of silicon, carbon, and metal impurities in different environments. Compared with the excessive erosion of the underlying silicon carbide matrix during the removal of silicon oxides by a single pickling process, this solution realizes the selective stripping of surface impurities by precisely adjusting the oxidation temperature window (avoiding the oxidation of the silicon carbide body itself), thereby improving the powder purity to the 6N level.

[0013] From the perspective of the implementation path of technical effects, the structural innovation of layered loading fundamentally reconstructs the silicon - carbon reaction interface, effectively improving the uniformity index of aluminum doping; the deeply coupled two - stage reaction significantly reduces the amount of silicon vapor escaping and greatly reduces the unit energy consumption through the dynamic adjustment of temperature and atmosphere; the synergistic effect of the post - treatment process greatly improves the surface impurity removal efficiency. These breakthroughs in technical indicators are not achieved through the mechanical adjustment of a single parameter, but rely on the functional synergy between steps. For example, the primary silicon carbide skeleton formed during the first carbonization provides nucleation sites for the grain growth of the secondary reaction, and the optimized hydrogen environment promotes crystal form transformation while endowing the powder with a more regular geometric morphology (average particle size 0.7 - 1.5 mm, distribution dispersion < 20%). No solution with the same combination of technical features has been found in the prior art. Common improvement directions either focus on the structural optimization of reaction equipment or are limited to the adjustment of a single process parameter, and none of them can reproduce the balance ability of this solution among purity, electrical properties, and production cost. Especially for the P - type silicon carbide system, which is extremely sensitive to impurities, systematic innovation of the process route is a necessary condition for achieving performance leapfrogging, which also makes this solution have significant progressiveness at the level of substantial technical contributions.

[0014] Preferably, in step (S.1), the molar ratio of the silicon source to the carbon source is 1.01 - 1.10:1, and the purity of the silicon source and the carbon source is above 5N level.

[0015] In the field of silicon carbide powder synthesis technology, the setting of the silicon-carbon molar ratio has long followed the stoichiometry theory (1:1). This traditional process ignores the dynamic loss of silicon vapor escape in large-scale industrial production in kilograms. Existing technologies generally use an excessive carbon source (silicon-carbon ratio ≤ 1:1) to inhibit the residual free silicon. However, this leads to the accumulation of unreacted carbon after the reaction. The residual carbon particles adsorb on the silicon carbide grain boundaries at high temperatures to form carrier scattering centers. More seriously, when the excessive carbon source coexists with the dopant, the chemical reduction property of carbon will cause the thermal decomposition failure of the aluminum-based dopant (such as AlCl3), resulting in a sudden change in the local doping concentration. This solution creatively proposes to precisely control the molar ratio of the silicon source to the carbon source within a narrow range of 1.01 - 1.10:1. This parameter optimization is not a simple ratio adjustment based on theoretical derivation, but the result of a systematic quantitative analysis of the silicon escape kinetics under large-scale production. Through pilot experiments, it is found that when the silicon content exceeds the stoichiometric ratio by 1%, it can compensate for the silicon vapor escape amount in the high-temperature stage (about 0.8% - 1.2% of the total silicon amount), and the upper limit of the silicon ratio is set to 1.10:1 from the experimental verification of the carbide phase transition critical point: when the silicon excess exceeds 10%, the viscosity reduction of the molten silicon will lead to the out-of-control carbon layer penetration process, causing the encapsulated residue of uncarbided silicon. This precise silicon-carbon balance design effectively overcomes the contradiction in the traditional process of ensuring both the completeness of the reaction and avoiding the residue of free substances. Compared with the rough excessive carbon strategy (silicon-carbon ratio 0.9 - 1.0:1) in the existing technology, this solution reduces the residual amount of unreacted carbon from 3% - 5% in the traditional process to less than 0.5%, and at the same time reduces the crucible corrosion rate caused by silicon vapor escape by 60%.

[0016] Preferably, the aluminum-based dopant is any one of AlCl3, AlN, and Al-Si alloy; and, The addition amount of the aluminum-based dopant is 0.05% - 0.2% of the total mass of the silicon source and the carbon source.

[0017] In the silicon carbide doping process, the type and addition amount of aluminum-based dopants directly affect the formation of crystal defects and the carrier activation efficiency. In the prior art, pure aluminum powder or Al2O3 is mostly used as the doping source. However, the former is prone to premature aggregation before the silicon melts due to its low melting point (660°C), and the latter induces lattice distortion due to the incorporation of oxygen atoms. The local concentration fluctuations of both lead to a resistivity deviation often exceeding 30%. This solution breakthroughly selects three types of compounds, namely AlCl3, AlN, and Al-Si alloy, as dopants. This choice reveals the differential action mechanism of different forms of aluminum sources in the layered loading system: AlCl3 sublimates and decomposes into active aluminum atoms at the initial stage of the vacuum reaction (300 - 600°C), preferentially occupying the silicon lattice vacancies to form a pre-doped structure; AlN dissociates at high temperatures (>1400°C) to release aluminum and simultaneously provides a nitrogen atom buffer layer to inhibit the escape rate of silicon vapor; the Al-Si alloy realizes the liquid-phase diffusion of aluminum through its eutectic characteristics, and its melting point matching with the silicon source (577°C) enables the doping process to be synchronized with the kinetics of the silicon-carbon reaction. Particularly crucial is that the three substances adopt the same mass percentage range (0.01% - 0.5%). This parameter design is derived from the mathematical modeling of the interface diffusion depth. When the doping amount is less than 0.01%, aluminum atoms are difficult to penetrate the carbon layer to form a continuous doping channel, while exceeding 0.5% will cause a sharp increase in the viscosity of molten silicon, resulting in the stagnation of carbon penetration. Experimental data show that the doping efficiency (the proportion of aluminum atoms actually entering the lattice) of AlCl3 within this range reaches 92% - 95%, which is more than 40% higher than that of traditional aluminum powder doping. At the same time, the conductivity fluctuation is compressed from ±25% to ±8%. This technical feature realizes the precise matching of the thermal decomposition behavior of the dopant and the silicon-carbon reaction steps in a single process for the first time through the coupled design of the substance type and concentration threshold, solving the problem of timing mismatch of premature consumption or delayed release of the aluminum source in the traditional solution.

[0018] Preferably, in step (S.2), the first reaction temperature range is 1350 - 1900°C, the vacuum pressure ≤ 5.0×10 -5 Pa, and the first carbonization reaction time is 10 - 20 hours.

[0019] Preferably, in step (S.3), the volume ratio of the inert gas to hydrogen in the mixed protective gas is 30:(0.5 - 2).

[0020] In the field of high-temperature silicon carbide synthesis, although inert gas protection can avoid material oxidation, its effect on removing unreacted carbon impurities is limited. Traditional processes often face the problem of residual free carbon wrapping grains. In existing technologies, the introduction of hydrogen mostly focuses on the activation of carbon sources in the gas-phase deposition process (such as using a C3H8 / H2 mixture in the CVD method). Due to the difference in high-temperature permeability of hydrogen, the solid-state synthesis method has long been regarded as a secondary auxiliary means. Conventional solutions either completely exclude hydrogen (to avoid lattice damage caused by hydrogen etching) or use intermittent pulsed hydrogen supply (with high control difficulty), making it difficult to balance the contradiction between carbon reduction requirements and structural stability. This solution has a breakthrough discovery that in the crystal form transformation stage (2000 - 2200 °C) of the solid-state reaction, precisely controlling the volume ratio of the neutral gas to hydrogen in the mixed protective gas to 30:(0.5 - 2) can synergistically achieve three effects: low-concentration hydrogen selectively reduces surface free carbon to form volatile CH4 (with a removal efficiency of over 90%). At the same time, its molecular diameter (0.289 nm) has a high degree of matching with the silicon carbide lattice channels, promoting hydrogen atoms to become the "dynamic lubricant" for lattice reconstruction. Moreover, the strong chemisorption property of hydrogen to oxygen impurities at high temperatures (forming H2O and escaping) further improves the product purity. Particularly crucial is that the lower limit of the volume ratio of inert gas to hydrogen, 30:0.5, is derived from the experimentally verified carbon removal threshold, and the upper limit of 30:2 is derived from the critical point of grain boundary weakening caused by hydrogen penetration. When the hydrogen content is greater than 30:2, the grain boundary migration rate is too fast during the β→α phase transformation process, resulting in an increase in the twin defect density of over 50%. This redefinition of the function of hydrogen goes beyond the traditional cognitive framework (simply as a reducing agent or process auxiliary gas). Through the precise matching of gas components and reaction stages, the coupling of carbon removal and crystal form optimization is achieved for the first time in solid-state synthesis. The proportional range of this solution exhibits unique synergistic benefits within a specific process window. It can not only compress the free carbon content to below 0.3%, but also improve the uniformity of grain size distribution by 40%. The improvement effect exceeds the linear range that can be explained by simply adjusting the hydrogen concentration, demonstrating the systematic innovation value of the parameter combination.

[0021] The mixed protective gas described in step (S.3) is injected in two-stage operation: The mixed protective gas described in step (S.3) is injected in two-stage operation: In the first stage, after closing the vacuum pump, the mixed gas is filled until the pressure ≥ 100 mbar, and the second reaction temperature range is 1700 - 1800 °C; In the second stage, the pressure is maintained constant while the second reaction temperature range is raised to 2000 - 2200 °C.

[0022] During the high-temperature synthesis of silicon carbide, the coordinated control of the atmosphere pressure and temperature directly affects the crystal form transformation efficiency and the integrity of the crystal structure. The existing technology usually adopts a single-stage operation mode of "vacuum heating - direct constant pressure", but this mode is difficult to overcome the turbulent disturbance caused by the sudden increase in air pressure and the thermal stress imbalance caused by the temperature jump. The two-stage gas injection strategy of this solution reconstructs the reaction kinetic path through the decoupled control of physical parameters: in the first stage, a mixed gas is filled in the temperature range of 1700 - 1800 °C to a design of ≥100 mbar, specifically solving the coupling contradiction between gas penetration and temperature sensitivity in the traditional process - within this temperature range, the loose and porous structure of primary silicon carbide particles (porosity of about 30%) provides a channel for gas diffusion, and at the same time, the incompletely closed grain boundaries allow hydrogen to penetrate into the particle interior (penetration depth > 200 μm). When the pressure is increased to 100 mbar, the mean free path of gas molecules is shortened to the micron level, significantly improving the surface coverage uniformity of the mixed gas on carbon residues (coverage rate increased from the conventional 60% to 95%). The establishment of the pressure threshold in this stage is based on experimental observations: when the inflation pressure < 100 mbar, the mixed gas is difficult to break through the silicon-oxygen barrier layer (about 2 μm thick) formed on the surface of primary silicon carbide, resulting in hydrogen reduction only staying at the surface active sites (carbon removal rate < 50%). In the second stage, the temperature is raised to 2000 - 2200 °C while maintaining the pressure stable. In this process, the lattice vibration spectrum distortion caused by the traditional stepwise pressure increase is eliminated by the constant pressure, and at the same time, the dissociation adsorption of hydrogen in the high-temperature section and the lattice reconstruction of silicon carbide can form a resonance effect - when the temperature exceeds 2000 °C, the passivation effect of hydrogen atoms on the dangling bonds on the surface of silicon carbide reduces the formation energy of α-phase crystal nuclei by 40%, and the constant pressure environment inhibits the microcrack propagation caused by volume expansion (β→α phase transformation volume shrinkage of about 8%), and the grain size dispersion is reduced by more than 60% compared with the single-stage process. The deep innovation of the two-stage operation is to transform the two physicochemical processes of "gas infiltration - crystal form transformation" from spatio-temporal overlap to serialized operation. The stable gas infiltration network established in the first stage lays a structural foundation for the directional growth of grains in the second stage. This strategy of dividing and conquering breaks through the dilemma of mutual constraints of multiple reactions in the same temperature and pressure field in the traditional process. Especially for the industrial production of large-scale reaction chambers, the two-stage dynamic control improves the temperature field uniformity by more than 3 times, and synergistically optimizes the efficiency of free carbon removal and phase change crystallization to a level that cannot be achieved by traditional methods Preferably, the oxidation heat treatment in step (S.4) is calcination at 400 - 600 °C in an oxygen-rich atmosphere for 6 - 10 hours.

[0023] Preferably, the acidic solution in step (S.4) is a hydrofluoric acid solution with a concentration of 3% - 10%, and the cleaning time is 10 - 24 hours.

[0024] Preferably, in step (S.1), the thickness of each layer of silicon powder is 0.5 - 2 cm, the thickness of the carbon powder layer is 0.31 cm, and the number of layer paving times ≥ 10 layers.

[0025] Preferably, the purity of the finally obtained P-type silicon carbide powder is ≥ 5N, the average particle size is 0.5 - 2 mm, and the resistivity uniformity is ≥ 90%.

[0026] Therefore, the present application has the following beneficial effects: This patent realizes the low-defect growth of high-purity silicon carbide crystals through optimizing the silicon-carbon ratio, precisely controlling the morphology and dosage of aluminum-based dopants, introducing a mixed protective gas with a specific hydrogen ratio, and two-stage temperature and pressure control, significantly reducing the deviation of resistivity uniformity and the dispersion of grain size. At the same time, the process efficiency is significantly improved, with the dual advantages of material property improvement and green production. Detailed implementation manners

[0027] The following further describes the present invention with reference to specific embodiments. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. In addition, the embodiments of the present invention involved in the following description are usually only a part of the embodiments of the present invention, rather than all of the embodiments. Therefore, all other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments of the present invention shall fall within the scope of protection of the present invention.

[0028] Example 1 A method for synthesizing P-type silicon carbide powder, comprising the following steps: 1. Select high-purity silicon source and carbon source as the basic raw materials. The silicon source is single-crystal silicon powder with a purity of more than 5N, the carbon source is carbon powder with a purity of more than 5N, the molar ratio of silicon to carbon is 1.05:1, and the dopant ratio is 0.05%; specifically, 4410 g of silicon powder, 1800 g of carbon powder, and the dopant is 3.105 g of AlCl3.

[0029] 2. Adopt the method of layer-by-layer paving of mixed raw materials: First, lay a layer of 120 g of carbon powder at the bottom of the crucible. After leveling, lay a layer of 294 g of silicon powder and 0.207 g of AlCl3 dopant on the surface; then lay another layer of 120 g of carbon powder, and after leveling, lay a layer of 294 g of silicon powder and 0.207 g of AlCl3 dopant on the surface; stack 15 layers in sequence, and lay a layer of 294 g of silicon powder and 0.207 g of AlCl3 dopant on the topmost layer.

[0030] 3. The first low-temperature reaction process: While maintaining the pressure P < 5.0×10 -5 pa in the whole process chamber, slowly raise the temperature, keep the reaction time at 8 hours at a temperature of 1350 - 1400 degrees, and then keep the low pressure P < 5.0×10-5 Under the condition of -5 Pa, slowly raise the temperature to 1750 °C, maintain it at 1750 - 1800 °C for 8 hours, finally stop heating, take out the powder after cooling, and the synthesis of the primary powder is completed. Obtain 6180 g of powder, and the synthesis utilization rate of the powder is higher than 99.52%.

[0031] 4. Secondary high-temperature reaction process: Mix 6180 g of the primary synthesized powder evenly and fill it into the crucible. After loading into the furnace, the equipment evacuates to maintain a pressure of P < 5.0×10 -5 Pa or less, slowly raise the temperature to 1750 - 1800 °C, then close the molecular pump, and fill in a mixed gas of argon and hydrogen. Fill it with a ratio of Ar:H2 = 30:1 to a pressure greater than 100 mbar, and then maintain it at 100 mbar. Slowly raise the temperature to 2100 °C, stop heating after maintaining it at 2100 °C for 8 hours, and take out the raw materials after natural cooling. Obtain 6150 g of powder, and the synthesis utilization rate of the secondary synthesized powder is 99.51%.

[0032] 5. After taking out the raw materials, put them into a silicon carbide ceramic plate, and charge oxygen in a muffle furnace at a temperature of 500 °C for high-temperature pre-burning for 8 hours to remove impurities such as unreacted silicon and carbon adsorbed on the surface of the raw materials.

[0033] 6. Immerse the oxidized raw materials in a 5% concentration of HF acid solution for 12 hours, then rinse with pure water to make the pH value of the rinsed silicon carbide in water around 7. After pickling, remove a small amount of metals and impurities such as SiO2 contained in the raw materials.

[0034] 7. Dry the rinsed silicon carbide powder in a vacuum oven. After drying, obtain 6120 g of raw materials; the comprehensive utilization rate of the raw materials is 98.55%. The purity of the raw materials reaches 6N by GDMS element measurement, and the average particle size of the raw materials is 0.7 - 1.5 mm.

[0035] Example 2 A method for synthesizing P-type silicon carbide powder, comprising the following steps: 1. Select high-purity silicon source and carbon source as the basic raw materials. The silicon source is single-crystal silicon powder with a purity of more than 5N, and the carbon source is carbon powder with a purity of more than 5N. The molar ratio of silicon to carbon is 1.01:1, and the doping agent ratio is 0.1%; specifically, it includes 4242 g of silicon powder, 1800 g of carbon powder, and 6.042 g of doping agent AlCl3.

[0036] 2. Method of laying mixed raw materials: First, lay a layer of 180 g of carbon powder at the bottom of the crucible. After leveling, lay a layer of 424.2 g of silicon powder and 0.6042 g of AlCl3 dopant on the surface; then lay another layer of 180 g of carbon powder, and after leveling, lay a layer of 424.2 g of silicon powder and 0.6042 g of AlCl3 dopant on the surface; stack 10 layers in sequence, and lay a layer of 424.2 g of silicon powder and 0.6042 g of AlCl3 dopant on the topmost layer.

[0037] 3. One-time low-temperature reaction process: Under the condition that the pressure P in the whole process chamber is maintained at P < 5.0×10 -5 Pa, slowly raise the temperature. Keep the reaction time for 5 hours at a temperature of 1350 - 1400 degrees, and then under the condition of maintaining a low pressure of P < 5.0×10 -5 Pa, slowly raise the temperature to 1850 degrees, keep it at 1850 - 1900 degrees for 5 hours, finally stop heating, take out the powder after cooling, and the one-time powder synthesis is completed. Obtain 6017 g of powder, and the synthesis utilization rate of the powder is higher than 99.48%.

[0038] 4. Two-time high-temperature reaction process: Mix 6017 g of the one-time synthesized powder evenly and fill it into the crucible. After loading into the furnace, the equipment evacuates to maintain a pressure of P < 5.0×10 -5 Pa or less, slowly raise the temperature to 1700 - 1800 degrees, then turn off the molecular pump, and fill in a mixed gas of argon and hydrogen. Fill it with gas at a ratio of Ar:H2 = 30:0.5 to a pressure greater than 100 mbar, and then under the condition of maintaining 100 mbar, slowly raise the temperature to 2000 degrees. After maintaining for 10 hours at 2000 degrees, stop heating, and take out the raw material after natural cooling. Obtain 5949 g of powder, and the synthesis utilization rate of the two-time synthesized powder is 98.87%.

[0039] 5. After taking out the raw material, put it into a silicon carbide ceramic dish, and charge oxygen in a muffle furnace at a temperature of 400 degrees for high-temperature pre-burning for 10 hours to remove impurities such as unreacted silicon and carbon adsorbed on the surface of the raw material.

[0040] 6. Immerse the oxidized raw material in 3% concentrated HF acid solution for 24 hours, and then rinse it with pure water to make the pH value of the rinsed silicon carbide in water around 7. After pickling, remove a small amount of metals and impurities such as SiO2 contained in the raw material.

[0041] 7. The washed silicon carbide powder is dried in a vacuum oven, and 5951 g of raw material is obtained after drying; the comprehensive utilization rate of the raw material is 98.38%. The purity of the raw material reaches 6N by GDMS element measurement, and the average particle size of the raw material is 0.5 - 1.5 mm.

[0042] Example 3 A method for synthesizing P-type silicon carbide powder, comprising the following steps: 1. Select high-purity silicon source and carbon source as the basic raw materials. The silicon source is single-crystalline silicon powder with a purity of more than 5N, and the carbon source is carbon powder with a purity of more than 5N. The molar ratio of silicon to carbon is 1.1:1, and the doping agent ratio is 0.2%. 4620 g of silicon powder, 1800 g of carbon powder, and 12.84 g of Al-Si alloy powder as the doping agent.

[0043] 2. Adopt the method of laying and mixing raw materials in layers: First, lay a layer of 120 g of carbon powder at the bottom of the crucible. After paving it flat, lay a layer of 308 g of silicon powder and 0.856 g of Al-Si alloy powder on the surface. Then lay another layer of 120 g of carbon powder, and after paving it flat, lay a layer of 308 g of silicon powder and 0.856 g of Al-Si alloy powder on the surface. Stack 15 layers in sequence, and the top layer is a layer of 308 g of silicon powder and 0.856 g of Al-Si alloy powder.

[0044] 3. The first low-temperature reaction process: Under the condition of maintaining the pressure P of the whole process chamber < 5.0×10 -5 Pa, slowly raise the temperature. Keep the reaction time for 8 hours at a temperature of 1350 - 1400 degrees, and then under the condition of maintaining a low pressure P < 5.0E^(-5) pa, slowly raise the temperature to 1750 degrees, and keep it at 1750 - 1800 degrees for 12 hours. Finally, stop heating, take out the powder after cooling, and the first powder synthesis is completed. 6412 g of powder is obtained, and the synthesis utilization rate of the powder is higher than 99.68%.

[0045] 4. The second high-temperature reaction process: Stir 6412 g of the first synthesized powder evenly and then fill it into the crucible. After loading it into the furnace, the equipment evacuates to maintain P < 5.0×10 -5 Pa or less, slowly raise the temperature to 1750 - 1800 degrees, then turn off the molecular pump, and fill in a mixed gas of argon and hydrogen. Inflate it to a pressure greater than 100 mbar at a ratio of Ar:H2 = 30:2, and then under the condition of maintaining 100 mbar, slowly raise the temperature to 2200 degrees. After maintaining it at 2200 degrees for 8 hours, stop heating, and take out the raw material after natural cooling. 6360 g of powder is obtained, and the synthesis utilization rate of the second synthesized powder is 99.19%. 5. After taking out the raw material, put it into a silicon carbide ceramic plate, and charge oxygen in a muffle furnace at a temperature of 600 degrees for high-temperature pre-burning for 6 hours to remove impurities such as unreacted silicon and carbon adsorbed on the surface of the raw material.

[0046] 6. Immerse the oxidized raw material in 10% concentrated HF acid solution for 10 hours, and then rinse it with pure water to make the pH value of the rinsed silicon carbide in water around 7. After pickling, remove a small amount of metals and impurities such as SiO2 contained in the raw material.

[0047] 7. The silicon carbide powder after cleaning is dried in a vacuum oven, and 6340 g of raw material is obtained after drying; the comprehensive utilization rate of the raw material is 98.55%. After measurement, the purity of the raw material reaches 6N, and the average particle size of the raw material is 0.8 - 2 mm.

[0048] Example 4 A method for synthesizing P-type silicon carbide powder includes the following steps: 1. Select high-purity silicon source and carbon source as the basic raw materials. The silicon source is single-crystalline silicon powder with a purity of more than 5N, and the carbon source is carbon powder with a purity of more than 5N. The molar ratio of silicon to carbon is 1.05:1, and the doping agent ratio is 0.15%. The materials include 4410 g of silicon powder, 1800 g of carbon powder, and 9.315 g of AlCl3.

[0049] 2. Adopt the method of laying and mixing raw materials layer by layer: First, lay a layer of 120 g of carbon powder at the bottom of the crucible. After leveling, lay a layer of 294 g of silicon powder and 0.621 g of AlCl3 doping agent on the surface; then lay another layer of 120 g of carbon powder, and after leveling, lay a layer of 294 g of silicon powder and 0.621 g of AlCl3 doping agent on the surface; stack 15 layers in sequence, and lay a layer of 294 g of silicon powder and 0.621 g of AlCl3 doping agent on the top layer.

[0050] 3. The first low-temperature reaction process: Under the condition of maintaining the pressure P < 5.0×10 -5 Pa in the whole process chamber, slowly raise the temperature. Keep the reaction time for 8 hours at a temperature of 1350 - 1400 degrees, and then keep the low pressure P < 5.0×10 -5 Pa. Slowly raise the temperature to 1750 degrees, and keep it for 8 hours at 1750 - 1800 degrees. Finally, stop heating, cool it down, and take out the powder. The synthesis of the first powder is completed, and 6190 g of powder is obtained. The synthesis utilization rate of the powder is higher than 99.68%.

[0051] 4. The second high-temperature reaction process: Mix 6180 g of the first synthesized powder evenly and then fill it into the crucible. After loading into the furnace, the equipment is evacuated to maintain P < 5.0×10 -5 Pa or less, and slowly raise the temperature to 1750 - 1800 degrees. Then turn off the molecular pump and fill in a mixed gas of argon and hydrogen. Fill it with gas at a ratio of Ar:H2 = 30:1 to a pressure greater than 100 mbar, and then keep it at 100 mbar. Slowly raise the temperature to 2100 degrees, and keep it for 8 hours at 2100 degrees. Then stop heating, and take out the raw material after natural cooling. 6160 g of powder is obtained. The synthesis utilization rate of the second synthesized powder is 99.19%.

[0052] 5. After taking out the raw materials, place them in a silicon carbide ceramic dish, and charge oxygen in a muffle furnace at a temperature of 500 °C for 8 hours of high-temperature pre-burning to remove impurities such as unreacted silicon and carbon adsorbed on the surface of the raw materials.

[0053] 6. Immerse the oxidized raw materials in a 5% concentration HF acid solution for 12 hours, and then rinse with pure water to make the pH value of the rinsed silicon carbide in water around 7. After pickling, remove a small amount of metals and impurities such as SiO2 contained in the raw materials.

[0054] 7. The washed silicon carbide powder is dried in a vacuum oven, and 6120 g of raw materials are obtained after drying; the comprehensive utilization rate of the raw materials is 98.55%, the purity of the raw materials reaches 6N after measurement, and the average particle size of the raw materials is 0.7 - 1.5 mm.

[0055] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that in Step 2, the single-crystal silicon powder, carbon powder, and dopant AlCl3 are directly mixed evenly, and the method of layer-by-layer mixing is cancelled, and the other conditions are the same.

[0056] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that Steps 3 and 4 are cancelled and replaced with a single high-temperature reaction, and the other conditions are the same.

[0057] The conditions for the single high-temperature reaction are as follows: Under the condition that the pressure P in the whole process chamber < 5.0×10 -5 pa, slowly raise the temperature, keep the reaction time for 5 hours at a temperature of 1900 °C, and then keep the low pressure P < 5.0×10 -5 pa, slowly raise the temperature to 2200 °C, keep it at 2200 °C for 8 hours, finally stop heating, take out the powder after cooling, and the single high-temperature reaction is completed. 5629 g of powder is obtained, and the synthesis utilization rate of the powder is higher than 90.6%.

[0058] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the mixed protective gas in Step 4 is cancelled, and the other conditions are the same.

[0059] Under the same crystal growth process conditions, the P-type silicon carbide powders prepared in Examples 1 - 4 and Comparative Examples 1 - 3 are used for silicon carbide crystal growth.

[0060] The operating steps of the crystal growth method are as follows: 1. Load the P-type silicon carbide powder into the lower crucible body; 2. Evacuate the inside of the growth furnace, open the vacuum interface and the vacuum pump, and close the vacuum pump and the vacuum port valve after the vacuum degree inside the growth furnace reaches the requirement; 3 Set the heating strategy of the heater, turn on the electromagnetic coil to heat the crucible, control the temperature of the upper seed crystal cover 20 at 2100 °C, control the growth pressure at 15 mbar, and the bottom temperature of the lower crucible body 21 is higher than 2250 °C; 4 After the crystal grows stably for 10 h, turn off the power supply of the electromagnetic coil, let the crystal cool naturally with the furnace, and after slicing the grown crystal, perform resistivity tests respectively. The test results are shown in Table 1 below.

[0061] Table 1 Category Purity Crystal surface quality Resistivity Resistance uniformity EPD dislocation Powder of Example 1 6N Better 0.19 92% 3100 Powder of Example 2 6N Better 0.11 95% 2800 Powder of Example 3 6N Average 0.24 90% 4000 Powder of Example 4 6N Better 0.16 94% 2900 Powder of Comparative Example 1 5N Worse 0.38 78% 7900 Powder of Comparative Example 2 5N Worse 0.45 72% 8600 Powder of Comparative Example 3 5N Worse 0.32 82% 6800 It can be seen from the data in the above table that in the process of preparing P-type silicon carbide powder in this patent, by controlling the mixing method of the silicon source and the carbon source, and at the same time by controlling the heating methods of the silicon source and the carbon source and introducing a mixed protective gas of inert gas and hydrogen during the secondary heating process, the low-defect growth of high-purity silicon carbide crystals is synergistically achieved, the deviation of resistivity uniformity and the dispersion of grain size are greatly reduced, and at the same time the process efficiency is significantly improved, with the dual advantages of improving material performance and green production.

[0062] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Those skilled in the art to which the present invention pertains can make various modifications or supplements to the described specific embodiments or use similar methods to replace them, but will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A method for synthesizing P-type silicon carbide powder, characterized in that It includes the following steps: (S.1) Alternately and layer by layer load a silicon source and a carbon source, and evenly load an aluminum-based dopant on the surface of each silicon layer; (S.2) Conduct a first carbonization reaction under a first reaction temperature range and in a vacuum environment to generate primary silicon carbide; (S.3) Inject a mixed protective gas of an inert gas and hydrogen into the reaction system, and complete crystal form transformation and impurity removal in a second reaction temperature range; (S.4) Subject the synthesized product to oxygen oxidation heat treatment and acid solution cleaning in sequence to remove residual impurities on the surface and obtain P-type silicon carbide powder.

2. The method according to claim 1, wherein: In step (S.1), the molar ratio of the silicon source to the carbon source is 1.01 - 1.10:1, and the purity of the silicon source and the carbon source is above 5N grade.

3. The method according to claim 1, wherein: The aluminum-based dopant is any one of AlCl3, AlN, and Al-Si alloy; and, The addition amount of the aluminum-based dopant is 0.05% - 0.2% of the total mass of the silicon source and the carbon source.

4. The method according to claim 1, wherein: The first reaction temperature range described in step (S.2) is 1350 - 1900 °C, the vacuum pressure ≤ 5.0×10 -5 Pa, and the first carbonization reaction time is 10 - 20 hours.

5. The method according to claim 1, wherein: In step (S.3), the volume ratio of the neutral gas to hydrogen in the mixed protective gas is 30:(0.5 - 2).

6. The method according to claim 5, wherein: In step (S.3), the injection of the mixed protective gas is operated in two stages: In the first stage, after closing the vacuum pump, fill the mixed gas until the pressure ≥ 100 mbar, and the second reaction temperature range is 1700 - 1800 °C; In the second stage, maintain a constant pressure and raise the second reaction temperature range to 2000 - 2200 °C.

7. The method according to claim 1, wherein: The oxidation heat treatment in step (S.4) is calcination at 400 - 600 °C in an oxygen-rich atmosphere, and the calcination time is 6 - 10 hours.

8. The method according to claim 1, wherein: The acid solution in step (S.4) is a hydrofluoric acid solution with a concentration of 3% - 10%, and the cleaning time is 10 - 24 hours.

9. The method according to claim 1, wherein: In step (S.1), the number of layer paving times of the silicon source and the carbon source ≥ 10 layers.

10. The method according to any one of claims 1 - 9, wherein: The finally obtained P-type silicon carbide powder has a purity ≥ 5N, an average particle size of 0.5 - 2 mm, and a resistivity uniformity ≥ 90%.