A method for synthesizing a p-type silicon carbide powder

Abstract

The application 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 layering silicon sources and carbon sources, and uniformly loading aluminum-based dopants on the surfaces of the silicon layers; (S.2) performing a first carbonization reaction under a first reaction temperature interval and in 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 type conversion and impurity removal in a second reaction temperature interval; and (S.4) sequentially performing oxygen oxidation heat treatment and acid solution cleaning on the synthesis product to remove surface residual impurities, and obtaining P-type silicon carbide powder. Through the control of the mixing mode of the silicon source and the carbon source, the heating mode and the scheme of the mixed protective gas containing hydrogen, the low-defect growth of high-purity silicon carbide crystals is realized, the resistivity uniformity deviation and the grain size dispersion are greatly reduced, and the process efficiency is significantly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of silicon carbide powder manufacturing, and particularly relates to a synthesis method of P-type silicon carbide powder. BACKGROUND

[0002] Silicon carbide (SiC) is a third-generation wide-bandgap semiconductor material, which has important applications in the fields of solar cells, power devices and radio frequency devices. Among them, P-type silicon carbide becomes the core material for manufacturing high-performance devices (such as the PN junction of photovoltaic cells) due to its high-conductivity characteristics of hole carriers. However, the existing synthesis technology of P-type silicon carbide powder still faces the bottlenecks of complex process, uneven doping, high production energy consumption and the like, which restricts its large-scale application.

[0003] The current mainstream industrial production method takes high-temperature self-propagating method as the core, and generates silicon carbide through high-temperature reaction of silicon powder and carbon powder in an inert atmosphere. Although this method is simple, in the actual reaction, the escape of silicon vapor leads to the imbalance of the silicon-carbon molar ratio, which not only reduces the purity of the product, but also corrodes the reaction crucible and the hot field element. Part of the improved technology attempts to set a filtering device or a porous partition 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] Chemical vapor deposition (CVD) can obtain high-purity silicon carbide powder through the decomposition of a gas precursor (such as methyltrichlorosilane), but the reaction conditions are harsh (ultra-high temperature and precise gas flow control are required), and the production cost is high, which is only suitable for small-batch high-value-added scenarios. On the other hand, although the solution gel method can synthesize nanoscale silicon carbide powder at a lower temperature, the process route is complex, the selection of the precursor is limited, and the uniformity of the powder particle size cannot meet the needs of semiconductor substrate growth.

[0005] Another outstanding 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), which in turn causes lattice distortion and reduction of carrier mobility. Although some patents propose schemes such as staged temperature control or argon atmosphere protection, there are still problems such as unreacted carbon residues (which affect electrical properties) and shortening of equipment life.

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

[0007] The present application is to overcome the bottlenecks of complex process, uneven doping, high production energy consumption and the like of the P-type silicon carbide powder in the prior art, thereby restricting its large-scale application. Therefore, the present application provides a synthesis method of P-type silicon carbide powder to overcome the above-mentioned defects.

[0008] To achieve the above-mentioned object of the application, the application is implemented by the following technical solutions.

[0009] In a first aspect, the application first provides a synthesis method of P-type silicon carbide powder, comprising the following steps:

[0010] (S.1) alternately layering silicon source and carbon source, and uniformly loading aluminum-based dopant on the surface of each silicon layer;

[0011] (S.2) performing a first carbonization reaction under a first reaction temperature interval and in a vacuum environment to generate primary silicon carbide;

[0012] (S.3) injecting a mixed protective gas of inert gas and hydrogen into the reaction system, and completing crystal type conversion and impurity removal at a second reaction temperature interval;

[0013] (S.4) sequentially subjecting the synthesis product to oxygen oxidation heat treatment and acid solution cleaning to remove surface residual impurities, and obtaining P-type silicon carbide powder.

[0014] In the field of semiconductor materials, silicon carbide has become an important basic material due to its excellent physical and chemical properties, and the synthesis technology of P-type silicon carbide directly affects the performance of devices. For a long time, the mainstream process in the industry generally uses high-temperature self-propagating method, but this method has problems such as imbalance of silicon-carbon molar ratio caused by silicon vapor escape, crucible corrosion, and uneven doping, especially when producing in large public kilogram level, the electrical performance deviation of the powder is significantly increased. In order to solve the above-mentioned contradictions, the industry has tried to improve the equipment structure (such as adding a filtering device) or introduce a multi-step purification process, but these schemes often sacrifice production efficiency and cost effectiveness, or can only achieve the effect in the laboratory scale. For example, although the crucible design with porous partition can reduce the escape of silicon vapor to a certain extent, it increases the complexity of the equipment while still cannot effectively solve the lattice defects caused by carbon residue; while the chemical vapor deposition method can precisely control the composition through gas precursors, but its ultra-high temperature requirement and high precision requirement of gas flow control seriously restrict the mass production capacity. These technical bottlenecks directly limit the large-scale application of P-type silicon carbide in power semiconductor devices, and in this background, there is an urgent need for a synthesis method that can balance purity, doping uniformity and industrial feasibility.

[0015] The technical solution of the method originates from in-depth analysis of the kinetics of the silicon-carbon reaction interface in the traditional process. Although the mechanical mixing of the silicon source and the carbon source in the prior art is simple to operate, the chemical reaction efficiency of the solid-solid contact surface is low, the skin effect leads to the accumulation of unreacted residues inside the particles, and the rapid escape of silicon vapor at high temperature further exacerbates the loss of control of the silicon-carbon ratio. To solve this problem, the present scheme creatively proposes an alternating layer of silicon source and carbon source layered structure, and a directional loading of aluminum-based dopant on the surface of the silicon layer. This design maximizes the contact area of the reactants at the micro level by constructing a localized silicon-carbon-dopant ternary reaction interface, avoiding the local aggregation of the dopant caused by mechanical mixing. It is particularly important to note that by pre-loading the silicon source and the dopant (rather than mixing with the carbon source), aluminum atoms can form an Al-Si eutectic in the silicon melting stage, thereby promoting the ordered doping of aluminum atoms into the silicon carbide lattice at the initial stage of the carbonization reaction. Compared with the random distribution of the dopant in the traditional process, this directional doping not only significantly improves the consistency of the carrier concentration, but also improves the crystal quality of the material by reducing the probability of lattice distortion.

[0016] The temperature and atmosphere control strategy of the staged reaction is another innovative core of the present scheme. The prior art usually chooses a single high-temperature reaction to directly complete the carbonization process, but in large kilogram-level production, the intense exothermic reaction can easily cause a local temperature jump, thereby inducing an explosive escape of silicon vapor. The present scheme constructs a two-step reaction system, and in the first carbonization stage, a vacuum environment below the critical temperature is selected (to avoid the large amount of silicon vaporization), 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, which suppresses the escape of silicon vapor and provides a structural basis for subsequent crystal transformation. In the second high-temperature reaction stage, by injecting argon-hydrogen mixed protective gas into the closed system and raising the temperature to the crystal lattice reconstruction interval, not only can the reduction of residual carbon by hydrogen eliminate free carbon impurities, but also the heat conduction homogenization characteristics of argon can promote directional grain growth.

[0017] The synergistic design of the post-treatment process further enhances the performance advantages of the powder. In view of the problem that the traditional pickling process cannot completely remove the surface metal impurities, the pre-oxidation step is creatively introduced, and the residual unreacted silicon and carbon are converted into silicon dioxide and carbon oxides through controllable oxygen heat treatment, which not only avoids the risk of introducing new impurities by mechanical grinding, but also enables the subsequent acid solution to remove the impurity particles wrapped in the oxidation layer by chemical etching. This sequential combination of oxidation and pickling is not a simple process superposition, but a process reengineering based on the chemical behavior differences of silicon, carbon and metal impurities in different environments. Compared with the single pickling process which causes excessive erosion of the underlying silicon carbide substrate when removing silicon oxides, the present scheme realizes selective stripping of surface impurities by precisely adjusting the oxidation temperature window (to avoid oxidation of the silicon carbide body), thereby improving the powder purity to the 6N level.

[0018] From the perspective of the implementation path of the technical effect, the structural innovation of layered filling fundamentally restructures the silicon-carbon reaction interface, effectively improving the uniformity index of aluminum doping; the two-stage reaction coupled with depth reduces the amount of silicon vapor escaping, while significantly reducing the unit energy consumption; the synergistic effect of the post-treatment process greatly improves the efficiency of surface impurity removal. These breakthroughs in technical indicators are not achieved through mechanical adjustment of a single parameter, but rely on the functional synergy between steps. For example, the primary silicon carbide skeleton formed by the initial carbonization provides nucleation sites for the grain growth of the secondary reaction, and the optimized hydrogen environment promotes the transformation of crystal forms while giving the powder a more regular geometric shape (average particle size 0.7-1.5 mm, distribution dispersion <20%). There is no existing technology with the same combination of technical features. Common improvements focus on structural optimization of reaction equipment or are limited to adjustment of a single process parameter, and none of them can reproduce the balance between purity, electrical performance and production cost of the present scheme. In particular, for P-type silicon carbide, which is highly sensitive to impurities, systematic innovation of the process route is a necessary condition for performance breakthrough, which also makes the present scheme have a significant progress in substantive technical contribution.

[0019] Preferably, the molar ratio of the silicon source to the carbon source in step (S.1) is 1.01-1.10:1, and the purity of the silicon source and the carbon source is 5N or higher.

[0020] In the field of silicon carbide powder synthesis technology, the setting of silicon-carbon molar ratio has long followed the stoichiometry theory (1:1), and this traditional process ignores the dynamic loss of silicon vapor escaping in large kilogram industrial production. The existing technology generally uses excess carbon source (silicon-carbon ratio ≤1:1) to suppress the residual free silicon, but this leads to the accumulation of unreacted carbon after the reaction is completed, and the residual carbon particles are adsorbed on the silicon carbide grain boundary at high temperature to form carrier scattering centers. More seriously, when the excess carbon source coexists with the dopant, the chemical reduction characteristics of carbon will cause the thermal decomposition failure of aluminum-based dopants (such as AlCl3), resulting in a sudden change in local doping concentration. The present scheme creatively proposes to accurately control the silicon source and carbon source molar ratio in the narrow range of 1.01-1.10:1. This parameter optimization is not based on the simple proportional adjustment of theoretical derivation, but the result of systematic quantitative analysis of silicon escaping kinetics in large-scale production. Through pilot experiments, it is found that when the silicon content exceeds 1% of the stoichiometric ratio, the silicon vapor escape amount at high temperature can be compensated (about 0.8%-1.2% of the total silicon amount), and the upper limit of silicon ratio is set to 1.10:1, which is derived from the experimental verification of the critical point of carbide phase change: when the silicon excess exceeds 10%, the reduced viscosity of molten silicon will lead to uncontrolled carbon layer penetration process, causing the encapsulated residual of un-carburized silicon. This accurate silicon-carbon balance design effectively solves the contradiction between ensuring reaction completeness and avoiding residual free material in traditional process. Compared with the existing technology of rough excess carbon strategy (silicon-carbon ratio 0.9-1.0:1), the present scheme reduces the unreacted carbon residue from 3%-5% in traditional process to less than 0.5%, and at the same time, the corrosion rate of the crucible caused by silicon vapor escaping is reduced by 60%.

[0021] As preferred, the aluminum-based dopant is any one of AlCl3, AlN, and Al-Si alloy; and,

[0022] 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.

[0023] In silicon carbide doping process, the type and amount of aluminum-based dopant directly affect the formation of crystal defects and carrier activation efficiency. The prior art mostly uses pure aluminum powder or Al2O3 as the doping source, but the former is easy to aggregate too early before the silicon melts due to its low melting point (660℃), and the latter induces lattice distortion due to the introduction of oxygen atoms, and the local concentration fluctuation of both results in a resistivity deviation of more than 30%. The present scheme breaks through and selects AlCl3, AlN and Al-Si alloy as the dopant, which reveals the differential action mechanism of different forms of aluminum source in the layered packing system: AlCl3 sublimates into active aluminum atoms at the initial stage of vacuum reaction (300-600℃), which preferentially occupies the silicon lattice vacancies and forms a pre-doping structure; AlN releases aluminum while providing a nitrogen atom buffer layer at high temperature (>1400℃), which inhibits the escape speed of silicon vapor; Al-Si alloy realizes liquid phase diffusion of aluminum through eutectic characteristics, and its melting point matching with silicon source (577℃) makes the doping process and the kinetics of silicon-carbon reaction synchronous. Especially, the same mass percentage range (0.01%-0.5%) of the three types of substances is adopted, which is derived from the mathematical modeling of the interface diffusion depth. When the doping amount is less than 0.01%, it is difficult for aluminum atoms to penetrate the carbon layer to form a continuous doping channel, and more than 0.5% will cause a sharp increase in the viscosity of molten silicon, resulting in carbon penetration stagnation. Experimental data show that the doping efficiency of AlCl3 in this range (the proportion of aluminum atoms actually entering the lattice) reaches 92%-95%, which is more than 40% higher than that of traditional aluminum powder doping, and the conductivity fluctuation is compressed from ±25% to ±8%. This technical feature couples the type and concentration threshold of the substance, and for the first time realizes the precise matching of the thermal decomposition behavior of the dopant and the silicon-carbon reaction steps in a single process, solving the timing mismatch problem of the early consumption or late release of the aluminum source in the traditional scheme.

[0024] As preferred, the first reaction temperature range in step (S.2) is 1350-1900℃, the vacuum pressure is ≤5.0×10 -5 Pa, and the first carbonization reaction time is 10-20 hours.

[0025] As preferred, the volume ratio of inert gas to hydrogen in the mixed protective gas in step (S.3) is 30: (0.5-2).

[0026] In the field of high-temperature silicon carbide synthesis, although inert gas protection can avoid material oxidation, the removal effect of unreacted carbon impurities is limited, and the traditional process often faces the problem of residual free carbon wrapping the grains. The introduction of hydrogen in the existing technology is mainly focused on the activation of carbon sources in the gas deposition process (such as using C3H8 / H2 mixed gas in the CVD method), while the poor permeability of hydrogen at high temperature has long been considered as a secondary auxiliary means in solid-state synthesis method. The conventional scheme either completely excludes hydrogen (to avoid hydrogen etching damage to the lattice) or uses intermittent pulse hydrogen supply (which is difficult to control), making it difficult to balance the contradiction between carbon reduction demand and structural stability. This scheme has made a breakthrough discovery that, in the crystal transformation stage (2000-2200℃) of solid-state reaction, accurate control of the volume ratio of neutral gas to hydrogen in the mixed protective gas at 30:(0.5-2) can achieve three effects: low-concentration hydrogen selectively reduces surface free carbon to generate volatile CH4 (with a removal efficiency of more than 90%), while its molecular diameter (0.289nm) has high matching degree with the silicon carbide lattice channel, which promotes hydrogen atoms to become a "dynamic lubricant" for lattice reconstruction, and the strong chemical adsorption characteristics of hydrogen to oxygen impurities (forming H2O escaping) at high temperature further improves the purity of the product. What is particularly key is that the lower limit of the volume ratio of inert gas to hydrogen 30:0.5 is derived from the carbon removal threshold verified by experiments, and the upper limit 30:2 is derived from the critical point of hydrogen-induced grain boundary weakening. When the hydrogen content is greater than 30:2, the grain boundary migration rate during the β→α phase transition process is too fast, resulting in an increase of more than 50% in the density of twin defects. This redefinition of the function of hydrogen goes beyond the traditional cognitive framework (simply as a reducing agent or process auxiliary gas), and through precise matching of gas components and reaction stages, it is the first time to realize the coupling of carbon removal and crystal type optimization in solid-state synthesis. The proportion range of this scheme shows unique synergistic benefits in a specific process window, not only can the free carbon content be compressed to below 0.3%, but also the uniformity of grain size distribution is improved by 40%, and the effect improvement range exceeds the linear range that can be explained by simply adjusting the hydrogen concentration, which highlights the systematic innovation value of parameter combination.

[0027] The mixed protective gas in step (S.3) is injected in two stages:

[0028] The mixed protective gas in step (S.3) is injected in two stages:

[0029] The first stage is to fill the mixed gas to a pressure ≥100 mbar after the vacuum pump is turned off, and the second reaction temperature range is 1700-1800℃;

[0030] The second stage maintains a constant pressure to increase the second reaction temperature range to 2000-2200℃.

[0031] In the process of high-temperature synthesis of silicon carbide, the coordinated control of atmosphere pressure and temperature directly affects the efficiency of crystal transformation and the integrity of 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 turbulence disturbance caused by the sudden rise of gas pressure and the thermal stress imbalance caused by temperature transition. The two-stage gas injection strategy of the scheme reconstructs the reaction kinetics path through decoupling control of physical parameters: the first stage fills the mixed gas to ≥100 mbar in the range of 1700-1800℃, which specifically solves the coupling contradiction between gas permeation and temperature sensitivity in the traditional process. In this temperature range, the loose porous structure of the primary silicon carbide particles (porosity about 30%) provides a channel for gas diffusion, and the incompletely closed grain boundaries allow hydrogen to penetrate into the particle interior (penetration depth > 200 μm). When the pressure rises to 100 mbar, the mean free path of gas molecules is shortened to microns, significantly improving the surface coverage uniformity of the mixed gas on the carbon residue (coverage rate from 60% to 95%). The establishment of this pressure threshold is based on experimental observation: when the filling pressure is < 100 mbar, the mixed gas is difficult to break through the silicon-oxygen barrier (about 2 μm thick) formed on the surface of the primary silicon carbide, resulting in hydrogen reduction only at the surface active sites (carbon removal rate < 50%). The second stage is to raise the temperature to 2000-2200℃ while maintaining a constant pressure, which eliminates the lattice vibration spectrum distortion caused by the traditional stepwise pressure rise, and the hydrogen dissociative adsorption at high temperature and the silicon carbide lattice reconstruction form a resonance effect. When the temperature exceeds 2000℃, the passivation effect of hydrogen atoms on the dangling bonds on the surface of silicon carbide reduces the formation energy of α-phase nuclei by 40%, and the constant pressure environment inhibits the expansion of micro-cracks caused by volume expansion (volume shrinkage of β→α phase is about 8%), reducing the grain size dispersion by more than 60% compared with the single-stage process. The deep innovation of the two-stage operation is to change the "gas penetration-crystal transformation" two physical and chemical processes from spatial and temporal overlap to sequential operation. The stable gas permeation network established in the first stage lays a structural foundation for the directional growth of grains in the second stage. This divide-and-conquer strategy breaks through the dilemma of multiple reactions in the same temperature and pressure field in traditional processes. Especially for industrial production of large-size reaction chambers, the two-stage dynamic control improves the temperature field uniformity by more than 3 times, and optimizes the efficiency of free carbon removal and phase transformation crystallization to a level that traditional methods cannot achieve.

[0032] As preferred, the oxidizing heat treatment in step (S.4) is calcination at 400-600℃ under an oxygen-rich atmosphere, and the calcination time is 6-10 hours.

[0033] As preferred, 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.

[0034] As preferred, the thickness of each layer of silicon powder in step (S.1) is 0.5-2 cm, the thickness of the carbon powder layer is 0.31 cm, and the layer laying number is ≥10 layers.

[0035] As preferred, 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%.

[0036] Therefore, the present application has the following beneficial effects:

[0037] The present patent, by optimizing the silicon-carbon ratio, precisely controlling the form and dosage of aluminum-based dopant, introducing a specific hydrogen proportion of mixed protective gas, and controlling the two-stage warm pressing, synergistically realizes the low-defect growth of high-purity silicon carbide crystals, greatly reduces the resistivity uniformity deviation and the grain size dispersion, significantly improves the process efficiency, and has the dual advantages of material performance improvement and green production. DETAILED DESCRIPTION

[0038] The present application will be further described below in conjunction with specific embodiments. Those skilled in the art will be able to implement the present application based on these descriptions. In addition, the embodiments of the present application involved in the following descriptions are generally only a part of the embodiments of the present application, not all the embodiments. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments in the present application without making creative efforts should belong to the scope of protection of the present application.

[0039] Embodiment 1

[0040] A synthesis method of P-type silicon carbide powder, comprising the following steps:

[0041] 1. Select high-purity silicon source and carbon source as basic raw materials, the silicon source is single crystal silicon powder with a purity of ≥5N, the carbon source is carbon powder with a purity of ≥5N, the molar ratio of silicon to carbon is 1.05:1, and the dopant proportion is 0.05%; specifically, 4410g of silicon powder, 1800g of carbon powder, and 3.105g of AlCl3 dopant.

[0042] 2. Layer laying method of mixing raw materials: first lay a layer of 120g of carbon powder at the bottom of the crucible, lay a layer of 294g of silicon powder and 0.207g of AlCl3 dopant on the surface after laying, then lay a layer of 120g of carbon powder, lay a layer of 294g of silicon powder and 0.207g of AlCl3 dopant on the surface after laying, and so on for 15 layers, and lay a layer of 294g of silicon powder and 0.207g of AlCl3 dopant on the top layer.

[0043] 3. One-time low-temperature reaction process: keep the pressure P<5.0×10 -5slowly increase the temperature, keep the temperature at 1350-1400 degrees for 8 hours, then keep the low pressure P < 5.0 x 10 -5 slowly increase the temperature to 1750 degrees, keep the temperature at 1750-1800 degrees for 8 hours, then stop heating, take out the powder after cooling, and the synthesis of the powder is completed, and the powder synthesis utilization rate is higher than 99.52%.

[0044] 4, secondary high temperature reaction process: put the primary synthesis powder 6180g into the crucible after stirring uniformly. After loading the furnace, the equipment is vacuumed and kept P < 5.0 x 10 -5 slowly increase the temperature to 1750-1800 degrees, then stop the molecular pump, fill in the mixed gas of argon and hydrogen, Ar: H2=30:1, the gas filling pressure is greater than 100 mbar, then slowly increase the temperature to 2100 degrees under the condition of keeping 100 mbar, keep the temperature at 2100 degrees for 8 hours, then stop heating, take out the raw material after natural cooling, and the powder 6150g is obtained, the synthesis utilization rate of the secondary synthesis powder is 99.51%.

[0045] 5, after taking out the raw material, put it into a silicon carbide ceramic plate, fill in oxygen in the muffle furnace at a temperature of 500 degrees, and pre-burn for 8 hours to remove the unreacted silicon and carbon impurities adsorbed on the surface of the raw material.

[0046] 6, put the oxidized raw material into 5% concentration HF acid solution for 12 hours, then rinse with pure water, so that the pH value of the rinsed silicon carbide in water is about 7, and the small amount of metal and SiO2 impurities contained in the raw material are removed after pickling.

[0047] 7, the cleaned silicon carbide powder is dried in a vacuum oven, and the raw material 6120g is obtained after drying; the comprehensive utilization rate of the raw material is 98.55%, the purity of the raw material measured by GDMS element reaches 6N, and the average particle size of the raw material is 0.7-1.5mm.

[0048] Example 2

[0049] A method for synthesizing P-type silicon carbide powder, comprising the following steps:

[0050] 1, select high-purity silicon source and carbon source as the basic raw material, 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 1.01:1, and the dopant ratio is 0.1%; specifically, it includes silicon powder 4242g, carbon powder 1800g, and dopant AlCl36.042g.

[0051] 2. The method of layering mixed raw materials is used: 180g of carbon powder is first layered on the bottom of the crucible, and then 424.2g of silicon powder and 0.6042g of AlCl3 dopant are layered on the surface; then 180g of carbon powder is layered again, and then 424.2g of silicon powder and 0.6042g of AlCl3 dopant are layered on the surface; 10 layers are sequentially stacked, and 424.2g of silicon powder and 0.6042g of AlCl3 dopant are layered on the top layer.

[0052] 3. The low-temperature reaction process is as follows: the pressure P in the chamber is kept below 5.0x10 -5 Pa, the temperature is slowly increased, the temperature is kept at 1350-1400 degrees for 5 hours, then the pressure P is kept below 5.0x10 -5 Pa, the temperature is slowly increased to 1850 degrees, the temperature is kept at 1850-1900 degrees for 5 hours, and finally the heating is stopped, the powder is taken out after cooling, the one-time powder synthesis is completed, and 6017g of powder is obtained, and the synthesis utilization rate of the powder is higher than 99.48%.

[0053] 4. The high-temperature reaction process is as follows: 6017g of the one-time synthesized powder is uniformly stirred and filled into the crucible. After the furnace is loaded, the equipment is vacuumed to keep the pressure P below 5.0x10 -5 Pa, the temperature is slowly increased to 1700-1800 degrees, then the molecular pump is closed, the mixed gas of argon and hydrogen with a ratio of Ar:H2=30:0.5 is filled to a pressure greater than 100mbar, then the temperature is slowly increased to 2000 degrees under the condition of 100mbar, the heating is stopped after keeping the temperature at 2000 degrees for 10 hours, and the raw material is taken out after natural cooling, 5949g of powder is obtained, and the synthesis utilization rate of the two-time synthesized powder is 98.87%.

[0054] 5. After the raw material is taken out, it is placed in a silicon carbide ceramic tray, and oxygen is filled into the muffle furnace at a temperature of 400 degrees for high-temperature pre-burning for 10 hours to remove unreacted silicon and carbon impurities adsorbed on the surface of the raw material.

[0055] 6. The oxidized raw material is soaked in 3% concentrated HF acid solution for 24 hours, and then washed with pure water to make the pH value of the washed silicon carbide in the water body around 7. After acid washing, a small amount of metal and SiO2 impurities contained in the raw material are removed.

[0056] 7. The cleaned silicon carbide powder is dried in a vacuum oven, and 5951g of raw material is obtained after drying; the comprehensive utilization rate of the raw material is 98.38%, the purity of the raw material measured by GDMS element reaches 6N, and the average particle size of the raw material is 0.5-1.5mm.

[0057] Example 3

[0058] A method for synthesizing P-type silicon carbide powder, comprising the following steps:

[0059] 1. Selecting high-purity silicon source and carbon source as basic raw materials, the silicon source is single crystal silicon powder with purity of 5N or above, the carbon source is carbon powder with purity of 5N or above, the molar ratio of silicon to carbon is 1.1:1, and the doping agent ratio is 0.2%; the silicon powder is 4620g, the carbon powder is 1800g, and the doping agent Al-Si alloy powder is 12.84g.

[0060] 2. Using the method of layering and mixing raw materials: first, lay a layer of 120g carbon powder at the bottom of the crucible, then lay a layer of 308g silicon powder and 0.856g Al-Si alloy powder on the surface; then lay another layer of 120g carbon powder, and then lay a layer of 308g silicon powder and 0.856g Al-Si alloy powder on the surface; repeat the process 15 times, and the last layer is a layer of 308g silicon powder and 0.856g Al-Si alloy powder.

[0061] 3. One-time low-temperature reaction process: maintain the pressure P < 5.0 x 10 -5 Pa in the chamber throughout the process, slowly raise the temperature, maintain the temperature at 1350-1400 degrees for 8 hours, then maintain the low pressure P < 5.0E^(-5) pa, slowly raise the temperature to 1750 degrees, maintain the temperature at 1750-1800 degrees for 12 hours, then stop heating, cool down and take out the powder, one-time powder synthesis is completed, the powder yield is 6412g, and the synthesis utilization rate of the powder is higher than 99.68%.

[0062] 4. Two-time high-temperature reaction process: mix the one-time synthesis powder 6412g evenly and fill it into the crucible. After loading the furnace, the equipment is vacuumed to maintain P < 5.0 x 10 -5 Pa, slowly raise the temperature to 1750-1800 degrees, then close the molecular pump, fill in a mixture of argon and hydrogen gas with a ratio of Ar:H2=30:2 to a pressure greater than 100mbar, then maintain the pressure at 100mbar, slowly raise the temperature to 2200 degrees, maintain the temperature at 2200 degrees for 8 hours, then stop heating, naturally cool down and take out the raw material, the powder yield is 6360g, and the synthesis utilization rate of the two-time synthesis powder is 99.19%.

[0063] 5. After taking out the raw material, put it into a silicon carbide ceramic tray, fill in oxygen in a muffle furnace at a temperature of 600 degrees, high-temperature pre-burning for 6 hours to remove unreacted silicon and carbon impurities adsorbed on the surface of the raw material.

[0064] 6. The oxidized raw material is immersed in 10% HF acid solution for 10 hours, then washed with pure water, so that the pH value of the washed silicon carbide in water is about 7. After the acid washing, a small amount of metal and SiO2 impurities contained in the raw material are removed.

[0065] 7. The washed silicon carbide powder is dried in a vacuum oven, and the dried raw material is 6340g; the comprehensive utilization rate of the raw material is 98.55%, and the purity of the raw material is measured to be 6N, and the average particle size of the raw material is 0.8-2mm.

[0066] Example 4

[0067] A method for synthesizing a P-type silicon carbide powder, comprising the following steps:

[0068] 1. Select high-purity silicon source and carbon source as the basic raw material, 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 0.15%. The raw material includes silicon powder 4410g, carbon powder 1800g, and AlCl3 9.315g.

[0069] 2. The raw material is mixed by layering: first, lay a layer of 120g carbon powder at the bottom of the crucible, then lay a layer of 294g silicon powder and 0.621g AlCl3 dopant on the surface; then lay another layer of 120g carbon powder, and then lay a layer of 294g silicon powder and 0.621g AlCl3 dopant on the surface; repeat the above steps 15 times, and lay a layer of 294g silicon powder and 0.621g AlCl3 dopant on the top layer.

[0070] 3. The first low-temperature reaction process: keep the pressure in the chamber P<5.0x10 -5 Pa, slowly raise the temperature, keep the temperature at 1350-1400 degrees for 8 hours, then keep the low pressure P<5.0x10 -5 Pa, slowly raise the temperature to 1750 degrees, keep the temperature at 1750-1800 degrees for 8 hours, and finally stop heating and cool down to take out the powder. The first powder synthesis is completed, and the powder is 6190g, and the synthesis utilization rate of the powder is higher than 99.68%.

[0071] 4. The second high-temperature reaction process: mix the first synthesized powder 6180g uniformly, and fill it into the crucible. After loading, the equipment is vacuumed to keep P<5.0x10 -5Pa, slowly increase the temperature to 1750-1800 degrees, then turn off the molecular pump, fill the mixed gas of argon and hydrogen, Ar: H2=30: 1 ratio to the pressure greater than 100 mbar, then keep the condition of 100 mbar, slowly increase the temperature to 2100 degrees, keep 8 hours at 2100 degrees, then stop heating, take out the raw material after natural cooling, get the powder 6160g, the synthesis utilization rate of secondary synthesis powder is 99.19%.

[0072] 5, after taking out the raw material, put it into a silicon carbide ceramic tray, fill oxygen in the muffle furnace at a temperature of 500 degrees, high temperature pre-burning for 8 hours, remove the unreacted silicon and carbon impurities adsorbed on the surface of the raw material.

[0073] 6, put the oxidized raw material into 5% concentration HF acid solution and soak for 12 hours, then rinse with pure water, so that the pH value of the rinsed silicon carbide in water is about 7, after pickling, remove a small amount of metal and SiO2 impurities contained in the raw material.

[0074] 7, the cleaned silicon carbide powder is dried in a vacuum oven, and the raw material 6120g is obtained after drying; the comprehensive utilization rate of the raw material is 98.55%, and the purity of the raw material reaches 6N, and the average particle size of the raw material is 0.7-1.5mm.

[0075] Comparative example 1

[0076] 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, and the layer mixing method is cancelled, and the other conditions are the same.

[0077] Comparative example 2

[0078] The difference between comparative example 2 and example 1 is that steps 3 and 4 are cancelled and replaced by one high temperature reaction, and the other conditions are the same.

[0079] The one high temperature reaction conditions are as follows: keep the pressure P <5.0 x 10 -5 Pa, slowly increase the temperature, keep the temperature at 1900 degrees for 5 hours, then keep the low pressure P <5.0 x 10 -5 Pa, slowly increase the temperature to 2200 degrees, keep 8 hours at 2200 degrees, then stop heating, take out the powder after cooling, one high temperature reaction is completed, get the powder 5629g, the synthesis utilization rate of the powder is higher than 90.6%.

[0080] Comparative example 3

[0081] 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.

[0082] The P-type silicon carbide powder prepared in Examples 1-4 and Comparative Examples 1-3 was subjected to silicon carbide crystal growth under the same crystal growth process conditions.

[0083] The crystal growth method operation steps are as follows:

[0084] 1. The P-type silicon carbide powder was loaded into the lower crucible body;

[0085] 2. The growth furnace was evacuated, the vacuum interface and vacuum pump were opened, and after the internal vacuum degree of the growth furnace reached the required value, the vacuum pump and vacuum port valve were closed;

[0086] 3. The heater heating strategy was set, the electromagnetic coil was turned on to heat the crucible, the seed crystal cover 20 temperature was controlled at 2100°C, the growth gas pressure was controlled at 15 mbar, and the bottom temperature of the lower crucible body 21 was higher than 2250°C;

[0087] 4. After the crystal was stably grown for 10 h, the electromagnetic coil power was turned off, the crystal was naturally cooled with the furnace, and the grown crystal was sliced and then subjected to resistivity testing, and the test results are shown in Table 1.

[0088] Table 1

[0089] Category Purity Crystal Surface Quality Resistivity Resistance Uniformity EPD Dislocations Example 1 powder 6N Good 0.19 92% 3100 Example 2 powder 6N Good 0.11 95% 2800 Example 3 powder 6N Fair 0.24 90% 4000 Example 4 powder 6N Good 0.16 94% 2900 Comparative Example 1 powder 5N Poor 0.38 78% 7900 Comparative Example 2 powder 5N Poor 0.45 72% 8600 Comparative Example 3 powder 5N Poor 0.32 82% 6800

[0090] From the above data, it can be seen that in the preparation of P-type silicon carbide powder, by controlling the mixing method of silicon source and carbon source, and at the same time by controlling the heating method of silicon source and carbon source and the method of passing inert gas and hydrogen mixed protective gas in the secondary heating process, the low defect growth of high purity silicon carbide crystal is realized, the resistivity uniformity deviation and grain size dispersion are greatly reduced, and the process efficiency is significantly improved, with the dual advantages of material performance improvement and green production.

[0091] The specific embodiments described herein are merely illustrative of the spirit of the present application. Those skilled in the art of the present application can make various modifications or supplements to the described specific embodiments or replace them with similar ways, but will not deviate from the spirit of the present application or exceed the scope defined by the appended claims.

Claims

1. A method for synthesizing P-type silicon carbide powder, characterized in that, Includes the following steps: (S.1) Silicon and carbon sources are alternately layered and filled, and aluminum-based dopants are uniformly loaded on the surface of each silicon layer to construct a localized silicon-carbon-dopant ternary reaction interface. (S.2) The first carbonization reaction is carried out in the first reaction temperature range and in a vacuum environment to generate primary silicon carbide; In step (S.2), the first reaction temperature range is 1350-1900℃, and the vacuum pressure is ≤5.0×10⁻⁶. -5 Pa, the first carbonization reaction time is 10-20 hours; (S.3) A mixture of inert gas and hydrogen is injected into the reaction system, wherein the volume ratio of the inert gas to hydrogen in the mixture is 30:(0.5-2), and the crystal transformation and impurity removal are completed in the second reaction temperature range. The mixed protective gas described in step (S.3) is injected in two stages: After shutting off the vacuum pump in the first stage, the mixed gas is introduced until the pressure is ≥100 mbar. The second reaction temperature range is 1700-1800℃. The second stage maintains constant pressure and increases the temperature range of the second reaction to 2000-2200℃. (S.4) The synthesized product is subjected to oxygen oxidation heat treatment and acid solution cleaning in sequence to remove surface residual impurities and obtain P-type silicon carbide powder.

2. The method according to claim 1, characterized in that: In step (S.1), the molar ratio of silicon source to carbon source is 1.01 to 1.10:1, and the purity of silicon source and carbon source is 5N grade or higher.

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

4. The method according to claim 1, characterized in that: The oxidative heat treatment in step (S.4) is calcination at 400-600℃ in an oxygen-rich atmosphere for 6-10 hours.

5. The method according to claim 1, characterized in that: The acidic solution in step (S.4) is a 3%-10% hydrofluoric acid solution, and the cleaning time is 10-24 hours.

6. The method according to claim 1, characterized in that: In step (S.1), the number of silicon source and carbon source layers is ≥10.

7. The method according to any one of claims 1-6, characterized in that: The final obtained P-type silicon carbide powder has a purity ≥5N, an average particle size of 0.5~2 mm, and a resistivity uniformity ≥90%.