Silicon carbide powder and its synthesis method, semiconductor devices

Abstract

This invention discloses silicon carbide powder, its synthesis method, and semiconductor devices, relating to the field of semiconductor technology. Pre-treated raw materials and pre-treated carrier gas are mixed in a specific ratio and then atomized to obtain an atomized product. The atomized product reacts in a multi-frequency region, and a multi-stage gas curtain is applied to isolate the reaction product, thus obtaining silicon carbide powder. Through the synergistic effect of the multi-frequency region, the mismatch between the generation and consumption of active particles on the time scale is fundamentally solved, achieving precise control from molecules to crystals. The multi-stage gas curtain isolation structure constructs an active oxygen barrier from both physical and chemical dimensions, allowing for precise control of the oxygen content in the product. This achieves the goal of obtaining ultra-high purity powder without any post-treatment acid washing process, fundamentally solving the pollution problem and having significant strategic importance for promoting the development of downstream high-end devices.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and more specifically, to silicon carbide powder and its synthesis method, and semiconductor devices. Background Technology

[0002] Silicon carbide (SiC), as a core representative of third-generation wide-bandgap semiconductor materials, holds an irreplaceable strategic position in aerospace, new energy vehicles, 5G communications, high-power power electronic devices, and precision ceramics due to its excellent high-temperature stability, high hardness, high thermal conductivity, and superior radiation resistance. Among them, β-SiC (cubic crystal system) has more uniform isotropy, a lower sintering temperature window, and better densification behavior compared to α-SiC (hexagonal or polymorphic crystal system), and has become a core precursor for high-end ceramic substrates, microelectromechanical system (MEMS) structural components, and semiconductor substrate polishing slurries.

[0003] In the traditional synthesis methods of silicon carbide powder, the Acheson method uses quartz sand and petroleum coke as raw materials, with a solid-state reaction temperature of about 2500℃ and a reaction time of 48h-72h. The resulting product has a wide particle size distribution and α / β mixed crystal forms; the product has low purity and high oxygen content, and mechanical ball milling introduces new impurities, requiring subsequent acid washing for impurity removal; the preparation process generates fluorine-containing waste liquid, has high energy consumption, and the intermittent production cycle is long, making continuous production impossible.

[0004] In recent years, plasma technology, such as DC arc plasma and radio frequency inductively coupled plasma, has been introduced into the preparation of silicon carbide powder. High-temperature plasma (>10000K) can instantaneously dissociate and react precursors (such as SiCl4 and CH4), theoretically enabling continuous, high-purity silicon carbide powder synthesis. However, existing plasma technology still faces two major bottlenecks: Firstly, single-frequency plasma systems cannot achieve continuous feeding and online powder output. Secondly, while high-frequency (RF) plasma can efficiently dissociate gas molecules, the generated active particles (such as SiCl4, CH4, etc.) can lead to the formation of reactive particles. 2+ Chlorine (·CH3) has an extremely short lifetime and is prone to ineffective recombination or premature nucleation before reaching the reaction zone, resulting in uneven product particle size and low yield. While low-frequency (LF) plasma can provide a longer particle residence time to promote crystal growth, its weak ionization ability makes it difficult to fully activate stable precursor molecules (such as SiCl4), leading to incomplete reactions and a large amount of unreacted chlorine remaining in the product. Plasma reactors typically require an inert atmosphere, but gas exchange between the high-temperature reaction zone and the external environment is difficult to completely eliminate. The infiltration of trace amounts of oxygen preferentially reacts with active silicon species to form SiO2, which coats the surface of SiC grains, not only reducing product purity but also severely inhibiting subsequent sintering activity.

[0005] Therefore, developing a silicon carbide powder preparation technology that can simultaneously meet the requirements of ultra-high purity, ultra-fine particle size, narrow distribution, low energy consumption, no pollution, and large-scale continuous production is of great strategic significance for promoting the development of downstream high-end devices.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide silicon carbide powder and its synthesis method, as well as semiconductor devices, to solve or improve the above-mentioned technical problems.

[0008] This invention is implemented as follows: In a first aspect, the present invention provides a method for synthesizing silicon carbide powder, comprising the following steps: The pretreatment raw materials and pretreatment carrier gas are mixed in proportion and then atomized to obtain atomized products. The atomized products react in the multi-frequency region, and the reaction products are isolated by a multi-stage gas curtain to obtain silicon carbide powder. The multi-frequency region includes the dissociation reaction region and the synthesis reaction region; The multi-stage gas curtain includes a primary gas curtain and a secondary gas curtain, wherein the primary gas curtain is located between the secondary gas curtain and the synthesis product carried by the carrier gas curtain.

[0009] In an optional embodiment, the frequency of the dissociation reaction zone is 10MHz-15MHz and the power is 15kW-25kW; the frequency of the synthesis reaction zone is 1.5MHz-3.5MHz and the power is 45kW-55kW.

[0010] In an optional implementation, the flow rate of the primary air curtain is 4 L / min-10 L / min; the flow rate of the secondary air curtain is 12 L / min-21 L / min; and the flow rate of the carrier gas is 9 L / min-11 L / min. And / or, the gas composition of the multi-stage gas curtain is selected from at least one of argon, hydrogen, helium and nitrogen.

[0011] In an optional embodiment, the pretreated raw material has at least one of the following characteristics: Feature 1: The pretreatment raw materials include a silicon source and a carbon source in a molar ratio of 1:(3-6); wherein the silicon source is selected from at least one of SiCl4, HSiCl3 and SiH4; and the carbon source is selected from at least one of CH4, C2H2 and C2H4. Feature 2: The pretreatment of the silicon source includes the following steps: the silicon source is dehydrated by passing it through an adsorption tower filled with 3Å molecular sieves at a temperature of 95℃-115℃, and the moisture content of the output silicon source is controlled to be ≤1ppm. Feature 3: The pretreatment of the carbon source includes the following steps: passing the carbon source through a Pd / Al2O3 catalyst at a temperature of 180℃-220℃ and a pressure of 0.7MPa-1.0MPa for deoxygenation treatment, and controlling the oxygen content of the output carbon source to be ≤5ppm.

[0012] In an optional embodiment, the pretreated carrier gas has at least one of the following characteristics: Feature 1: The molar ratio of pretreatment raw material to pretreatment carrier gas is 1:(1.5-2.5). Feature 2: The pretreatment of the carrier gas includes the following steps: passing the carrier gas through a ceramic filter with a filtration accuracy of 0.1μm-5μm for dust removal; Feature 3: The carrier gas is selected from at least one of argon, hydrogen, helium and nitrogen.

[0013] In an optional embodiment, the atomization frequency is 1.2MHz-2.4MHz; the average particle size of the atomized product is 2μm-4μm.

[0014] In an optional embodiment, the synthesis method further includes post-processing, which includes cooling, dust removal, sieving and cutting, wherein the cooling process includes: cooling the isolated product in a liquid helium environment at a temperature of -180°C to -150°C. Dust removal treatment includes: using a 28kV-35kV DC electric field to remove dust from the cooled products; The screening and cutting process includes screening and cutting the product after dust removal; wherein the mesh size of the screen used for screening is 350-450 mesh, and the D90 of the product after cutting is <1.1μm.

[0015] In an optional embodiment, the obtained silicon carbide powder has at least one of the following characteristics: Feature 1: The yield of silicon carbide powder is ≥99.5%; Feature 2: The content of β-phase silicon carbide in the silicon carbide powder is ≥97%; Feature 3: The purity of silicon carbide powder is ≥99.99%; Feature 4: The average particle size CV value of silicon carbide powder is <5%.

[0016] Secondly, the present invention provides a silicon carbide powder, which is prepared by the synthesis method described in any of the foregoing embodiments.

[0017] Thirdly, the present invention provides a semiconductor device, wherein the raw materials for preparing the semiconductor device include silicon carbide powder as described in the foregoing embodiments.

[0018] The present invention has the following beneficial effects: The silicon carbide powder synthesis method provided by this invention decouples the reaction process into two independent functional regions: a dissociation reaction region and a synthesis reaction region. Through the synergistic effect of multiple frequency regions, it fundamentally solves the problem of mismatch between the generation and consumption of active particles on the time scale, realizes precise control from molecules to crystals, and finally obtains nanoscale silicon carbide powder with narrow particle size distribution (CV value <5%) and single crystal form (β phase silicon carbide >99.5%).

[0019] The multi-stage gas curtain isolation structure constructs an active oxygen barrier from both physical and chemical dimensions. The outer, high-speed secondary gas curtain forms a strong physical barrier, isolating the outside air from the reaction core area. The middle, primary gas curtain acts as a chemical capture layer, utilizing the rapid reaction between the introduced gas and the permeated trace oxygen at low temperatures to convert oxygen impurities into harmless products and expel them before they contact the reaction zone. The inner carrier gas curtain is responsible for the stable transport of the synthesis products and the suppression of turbulence. This dual protection of "physical isolation + chemical reduction" keeps the oxygen content in the reaction core area at a low level (<5ppm), and the oxygen content in the products is efficiently controlled. This achieves the goal of obtaining ultra-high purity powder without any post-processing acid washing steps, fundamentally solving the contamination problem and having significant strategic importance for promoting the development of downstream high-end devices. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the spatial location of a multi-level air curtain.

[0022] Icons: 10 - Carrier air curtain; 20 - Primary air curtain; 30 - Secondary air curtain. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0024] In a first aspect, the present invention provides a method for synthesizing silicon carbide powder, comprising the following steps: The pretreatment raw materials and pretreatment carrier gas are mixed in proportion and then atomized to obtain atomized products. The atomized products react in the multi-frequency region, and the reaction products are isolated by a multi-stage gas curtain to obtain silicon carbide powder. The multi-frequency region includes the dissociation reaction region and the synthesis reaction region; The multi-stage gas curtain includes a primary gas curtain 20 and a secondary gas curtain 30. The primary gas curtain 20 is located between the secondary gas curtain 30 and the synthesis product carried by the carrier gas curtain 10. A schematic diagram of the spatial position of the multi-stage gas curtain is shown below. Figure 1 .

[0025] It should be noted that existing single-frequency plasma technology cannot simultaneously achieve both "efficient dissociation" and "sufficient growth". High-frequency plasma has strong dissociation capabilities, but the active particles have short lifespans and are prone to ineffective recombination before the reaction, resulting in dispersed product particle size and low yield. Low-frequency plasma can extend the particle residence time, but its dissociation efficiency is insufficient, resulting in low raw material conversion and more residual impurities in the product.

[0026] The multi-frequency region provided by this invention belongs to a dual-frequency radio frequency field. By introducing the synergistic effect of the dual-frequency radio frequency fields, the dissociation reaction region and the synthesis reaction region are spatially decoupled into two independent functional regions: First, in the dissociation reaction region, high-energy electrons (>5eV) are used to efficiently and uniformly dissociate silicon and carbon source molecules into highly active plasma seeds; subsequently, under the electromagnetic field constraint of the synthesis reaction region, these plasma seeds obtain a longer residence time and a more uniform temperature field, thereby completing directional nucleation and crystal growth under controlled conditions. This "high-frequency dissociation-low-frequency synthesis" partitioning design fundamentally solves the problem of mismatch between the generation and consumption of active particles on the time scale, realizes precise control from molecules to crystals, and ultimately obtains nanoscale powders with extremely narrow particle size distribution (CV value <5%) and single crystal form (β phase >99.5%).

[0027] In the reactions of the dissociation reaction zone and the synthesis reaction zone, SiCl4 is used as an example of silicon source and CH4 is used as an example of carbon source. The reaction equation of the dissociation reaction zone is as follows: SiCl4 + 2e － → Si 2+ + 4Cl － CH4→·CH3+·H; The reaction equation for the synthesis reaction zone is as follows: Si 2+ + 2Cl － +·CH3+·H → SiC + H2+ 2HCl.

[0028] Oxygen contamination is the primary factor limiting the purity of silicon carbide powder. Traditional methods rely on subsequent acid washing to remove oxides, but this process is complex, costly, and pollutes the environment. Although existing plasma processes are carried out in an inert atmosphere, oxygen exchange between the high-temperature reaction zone and the external environment is difficult to completely eliminate.

[0029] This invention innovatively designs a multi-level gas curtain isolation structure, constructing an active oxygen barrier from both physical and chemical dimensions: the outer high-speed secondary gas curtain 30 forms a strong physical barrier, isolating the outside air from the reaction core area; the middle primary gas curtain 20 acts as a chemical capture layer, utilizing the characteristic that the introduced gas and the permeated trace oxygen can react rapidly at low temperatures, converting oxygen impurities into harmless products and expelling them before they come into contact with the reaction zone; the inner carrier gas is responsible for the stable transport of the synthesis product and the suppression of turbulence. This dual protection of "physical isolation + chemical reduction" allows the oxygen content in the reaction core area to be controlled at an extremely low level (<5ppm), and the oxygen content in the product is efficiently controlled, achieving the goal of obtaining ultra-high purity powder without any post-processing acid washing steps, fundamentally solving the pollution problem, and having important strategic significance for promoting the development of downstream high-end devices.

[0030] Furthermore, the embodiments of the present invention employ a process of continuous feeding of the gasified precursor, continuous plasma reaction, and continuous product collection, which shortens the reaction time from 48 hours by 0.5 seconds and improves production efficiency by several orders of magnitude.

[0031] In an optional embodiment, the frequency of the dissociation reaction zone is 10MHz-15MHz and the power is 15kW-25kW; the frequency of the synthesis reaction zone is 1.5MHz-3.5MHz and the power is 45kW-55kW.

[0032] It should be noted that the dissociation reaction zone and the synthesis reaction zone are two spatially independent functional zones. The high-frequency zone focuses on dissociation, while the low-frequency zone dominates synthesis, thus improving energy efficiency through zoning. Through the synergistic effect of multiple frequency zones, the mismatch between the generation and consumption of active particles on the time scale is fundamentally solved, achieving precise control from molecules to crystals.

[0033] Relatively speaking, the dissociation reaction region belongs to the high-frequency region, where the electron temperature is maintained at 5eV-6eV, approximately 58,000K. Electrons gain sufficient energy in the high-frequency region, while ions, due to their large mass and inertia, hardly respond to the frequency oscillations in this region. The high-frequency skin effect in the high-frequency region concentrates the plasma at the center of the reactor, forming a high-density ionization region; moreover, the plasma impedance is low at high frequencies, resulting in high energy coupling efficiency (>90%). The higher the power in the dissociation reaction region, the greater the electron density, and the more complete the gas dissociation; increasing the power slightly raises the electron temperature, but it is more significantly affected by the frequency. If the power is <15 kW, the power is insufficient, the silicon source dissociates incompletely, and the residual Cl in the product increases; if the power is >25 kW, the power is too high, and excessive ionization leads to side reactions, such as C2 formation, and a decrease in the purity of β-SiC.

[0034] For example, the frequency of the dissociation reaction region can be selected from any one of 10MHz, 12MHz, 13MHz and 15MHz, or other values ​​in the range of 10MHz-15MHz; the power of the dissociation reaction region can be selected from any one of 15kW, 18kW, 20kW and 25kW, or other values ​​in the range of 15kW-25kW.

[0035] The synthesis reaction zone is located in the low-frequency region. In the low-frequency electric field, ions oscillate with the field, gaining higher kinetic energy, which promotes collisions between ions and neutral particles, thus accelerating silicon carbide formation. In this region, low-frequency power is primarily converted into thermal energy for heavy particles (ions and neutral atoms), maintaining the reaction zone temperature at approximately 2800℃. Furthermore, the low-frequency magnetic field (0.1T-0.3T) creates a magnetic mirror effect, confining charged particles along their axial direction and reducing diffusion losses. The temperature in the low-frequency region is controlled at 2800±30℃, with a residence time of 0.3-0.5 seconds. Low-frequency power can directly heat the heavy particles, directly affecting the temperature of the synthesis reaction zone, which is limited by the feed rate. If the power is less than 40 kW, the power is insufficient. At this time, the temperature of the synthesis reaction zone is below 2700℃, the crystallinity of β-SiC is poor, and the specific surface area increases. If the power is greater than 60 kW, the power is too high. At this time, the temperature of the synthesis reaction zone exceeds 2900℃, the grains coarsen, D50>1.5μm, and free carbon is easily generated.

[0036] For example, the frequency of the synthesis reaction zone can be selected from any one of 1.5MHz, 2.0MHz, 2.5MHz and 3.5MHz, or other values ​​in the range of 1.5MHz to 3.5MHz; the power of the synthesis reaction zone can be selected from any one of 45kW, 48kW, 50kW and 55kW, or other values ​​in the range of 45kW to 55kW.

[0037] In the optimal implementation, the frequency of the dissociation reaction zone is 13MHz and the power is 20kW, at which point the ionization efficiency is >95% and the energy consumption is the lowest.

[0038] In an optional implementation, the flow rate of the primary air curtain 20 is 4 L / min-10 L / min; the flow rate of the secondary air curtain 30 is 12 L / min-21 L / min; and the carrier gas flow rate is 9 L / min-11 L / min. And / or, the gas composition of the multi-stage gas curtain is selected from at least one of argon, hydrogen, helium and nitrogen.

[0039] Furthermore, the gas composition of the secondary gas curtain 30 is argon, the gas composition of the primary gas curtain 20 is hydrogen, and the carrier gas composition is argon. In other embodiments of the present invention, the gas composition of different gas curtains can be reasonably selected as needed.

[0040] In the traditional silicon carbide powder synthesis process, insufficient air tightness of the system allows air to seep in, inducing the oxidation of active silicon species to form a SiO2 coating layer, with the system oxygen concentration >200ppm. At the same time, the turbulence effect at the boundary of the reaction zone is significant, which disrupts the uniform distribution of the temperature and concentration fields, resulting in the random dispersion of nucleation sites. In addition, the high raw material escape rate severely restricts the purity and particle size uniformity of the powder.

[0041] The multi-stage gas curtain isolation structure provided by this invention utilizes a laminar flow gas curtain to stabilize the concentration field of the raw materials. The hydrogen introduced by the first-stage gas curtain 20 converts residual oxygen in the equipment cavity into water, which is then discharged, reducing the oxygen concentration and facilitating active purification of the reaction cavity. The design of the carrier gas carrying the raw materials increases the utilization rate of the raw materials and significantly reduces the rate of raw material escape. It constructs an active oxygen barrier from both physical and chemical dimensions, as detailed below: The high-speed secondary gas curtain 30 is ejected in a ring shape and located outside the primary gas curtain 20, forming a strong physical barrier to isolate the outside air from the reaction core area. The ejected secondary gas curtain 30 is also ring-shaped and located outside the carrier gas curtain 10, providing efficient protection and isolation for the inner carrier gas curtain 10 and the synthesis products carried by the carrier gas curtain 10.

[0042] The primary gas curtain 20 in the intermediate layer serves as a chemical capture layer. The hydrogen gas curtain (H2) introduced in it utilizes the characteristic that H2 and the trace amount of O2 that permeate can react rapidly at low temperature (300K) (H2+1 / 2O2→H2O) to convert oxygen impurities into harmless water vapor and discharge them before the products enter the gas curtain.

[0043] The innermost layer is the carrier gas curtain 10, which is responsible for the stable delivery of the synthesis product and the suppression of turbulence. This helps to reduce the premixing of raw materials and prevent premature reaction.

[0044] The embodiments of the present invention, through the dual protection of "physical isolation + chemical reduction" as described above, control the oxygen content in the core reaction area to a low level (<5ppm), and the oxygen content in the product drops sharply from 5000ppm-12000ppm in traditional processes to 180ppm-300ppm. For the first time, the goal of obtaining ultra-high purity powder without any post-processing acid washing process has been achieved, fundamentally solving the pollution problem.

[0045] For example, the flow rate of the primary gas curtain 20 can be selected from any one of 4 L / min, 6 L / min, 8 L / min, and 10 L / min, or other values ​​within the range of 4 L / min to 10 L / min; if the flow rate is too high, hydrogen will come in, causing the carbon source to crack and produce free carbon. In actual production, a fluctuation of 0.2 L / min in the flow rate of the primary gas curtain 20 is acceptable.

[0046] The flow rate of the secondary air curtain 30 can be selected from any one of 12 L / min, 15 L / min, 18 L / min, and 21 L / min, or other values ​​within the range of 12 L / min to 21 L / min; if the flow rate is too high, it will cause Ar turbulence, leading to increased particle scattering. A fluctuation of 0.5 L / min in the flow rate of the secondary air curtain 30 is within the allowable range.

[0047] The carrier gas flow rate can be selected from any one of 9 L / min, 9.5 L / min, 10 L / min, 10.5 L / min, and 11 L / min, or other values ​​within the range of 9 L / min to 11 L / min. A fluctuation of 0.3 L / min above or below the carrier gas flow rate is permissible.

[0048] In the optimal implementation, when the flow rate of the primary air curtain 20 is 6 L / min, the oxygen conversion rate is >99% and there is no carbon deposition. When the flow rate of the secondary air curtain 30 is 18 L / min, the balance point between oxygen control and particle loss is achieved.

[0049] In an optional embodiment, the pretreated raw material has at least one of the following characteristics: Feature 1: The pretreatment raw materials include a silicon source and a carbon source in a molar ratio of 1:(3-6); wherein the silicon source is selected from at least one of SiCl4, HSiCl3 and SiH4; and the carbon source is selected from at least one of CH4, C2H2 and C2H4. The amount of carbon source used is higher than that of silicon source to ensure the complete conversion of silicon source and avoid the introduction of more oxygen impurities by free silicon. When the carbon source content is 20% higher than that of silicon source, it will lead to an increase in the particle size of silicon carbide powder, resulting in carbon encapsulation growth and a decrease in the purity of β phase silicon carbide.

[0050] For example, the molar ratio of silicon source to carbon source can be selected from any one of 1:3, 1:4, 1:5 and 1:6, or other values ​​in the range of 1:(3-6).

[0051] Feature 2: The pretreatment of the silicon source includes the following steps: the silicon source is dehydrated by passing it through an adsorption tower filled with 3Å molecular sieves at a temperature of 95℃-115℃, and the moisture content of the output silicon source is controlled to be ≤1ppm. Feature 3: The pretreatment of the carbon source includes the following steps: passing the carbon source through a Pd / Al2O3 catalyst at a temperature of 180℃-220℃ and a pressure of 0.7MPa-1.0MPa for deoxygenation treatment, and controlling the oxygen content of the output carbon source to be ≤5ppm.

[0052] By pretreating raw materials or carrier gas in different ways, ultrapure feed can be achieved.

[0053] In other embodiments of the present invention, the dehydration treatment of the silicon source and the deoxygenation treatment of the carbon source can be carried out in other reasonable ways according to actual needs.

[0054] In an optional embodiment, the pretreated carrier gas has at least one of the following characteristics: Feature 1: The molar ratio of pretreatment raw material to pretreatment carrier gas is 1:(1.5-2.5). Feature 2: The pretreatment of the carrier gas includes the following steps: passing the carrier gas through a ceramic filter with a filtration accuracy of 0.1μm-5μm for dust removal; Feature 3: The carrier gas is selected from at least one of argon, hydrogen, helium and nitrogen.

[0055] For example, the molar ratio of pretreatment feedstock to pretreatment carrier gas can be selected from any one of 1:1.5, 1:1.8, 1:2.0, 1:2.3 and 1:2.5, or other values ​​in the range of 1:(1.5-2.5).

[0056] In an optional embodiment, the atomization frequency is 1.2MHz-2.4MHz; the average particle size of the atomized product is 2μm-4μm.

[0057] It should be noted that, in this embodiment of the invention, the pre-treated raw materials and pre-treated carrier gas are pre-mixed in a static mixing container to obtain a pre-mixed gas; the pre-mixed gas is then conveyed to a piezoelectric ultrasonic atomizer for atomization to generate uniform droplets with an average particle size of 2μm-4μm. In other embodiments of the invention, the atomization equipment can be selected reasonably according to actual needs.

[0058] For example, the frequency of the atomization process can be selected from any one of 1.2MHz, 1.5MHz, 1.7MHz, and 2.4MHz, or other values ​​within the range of 1.2MHz to 2.4MHz. If the frequency is too high, the average particle size of the atomized droplets will be too small, making them easily dispersed by the air curtain.

[0059] In the preferred embodiment, the atomization frequency is 1.7 MHz, at which the average droplet size matches the particle size of the reaction zone.

[0060] In an optional embodiment, the atomized droplets are preheated to prevent condensation of the atomized liquid. Specifically, in an embodiment of the present invention, the droplets generated by the atomization process are transported to a preheating chamber at a temperature of 130°C-180°C.

[0061] In an optional embodiment, the synthesis method further includes post-processing, which includes cooling, dust removal, sieving and cutting, wherein the cooling process includes: cooling the isolated product in a liquid helium environment at a temperature of -180°C to -150°C. Dust removal treatment includes: using a 28kV-35kV DC electric field to remove dust from the cooled products; The screening and cutting process includes screening and cutting the product after dust removal; wherein the mesh size of the screen used for screening is 350-450 mesh, and the D90 of the product after cutting is <1.1μm.

[0062] In an embodiment of the present invention, liquid helium is injected through a pore injection ring (pore diameter 0.1mm-0.4mm) to achieve 2×10 5 With a cooling rate of K / s, the product temperature is reduced from 2800℃ to 300℃ in 0.01 seconds, locking the nanocrystalline structure in milliseconds. This avoids the traditional 48-hour natural cooling process and significantly shortens the production cycle.

[0063] In an optional embodiment, the obtained silicon carbide powder has at least one of the following characteristics: Feature 1: The yield of silicon carbide powder is ≥99.5%; Feature 2: The content of β-phase silicon carbide in the silicon carbide powder is ≥97%; Feature 3: The purity of silicon carbide powder is ≥99.99%; Feature 4: The average particle size CV value of silicon carbide powder is <5%.

[0064] In an optional embodiment, the reaction byproduct HCl can be recovered for the regeneration of SiCl4 in silane, and the cooled helium can be recycled.

[0065] The silicon carbide powder synthesis process provided by this invention has no wastewater or waste acid discharge; and the oxygen content is efficiently controlled. In summary, the silicon carbide powder synthesis method provided by this invention includes the following steps: (1) Pretreatment of raw materials and carrier gas The pretreatment of the silicon source includes the following steps: the silicon source is dehydrated by passing it through an adsorption tower filled with 3Å molecular sieves at a temperature of 95℃-115℃, and the moisture content of the output silicon source is controlled to be ≤1ppm; the silicon source is selected from at least one of SiCl4, HSiCl3 and SiH4.

[0066] The pretreatment of the carbon source includes the following steps: passing the carbon source through a Pd / Al2O3 catalyst at a temperature of 180℃-220℃ and a pressure of 0.7MPa-1.0MPa for deoxygenation treatment, and controlling the oxygen content of the output carbon source to be ≤5ppm; the carbon source is selected from at least one of CH4, C2H2 and C2H4.

[0067] The pretreatment of the carrier gas includes the following steps: passing the carrier gas through a ceramic filter with a filtration accuracy of 0.1μm-5μm for dust removal; the carrier gas is selected from at least one of argon, hydrogen, helium and nitrogen.

[0068] The molar ratio of pretreatment raw material to pretreatment carrier gas is 1:(1.5-2.5).

[0069] (2) Atomization treatment After mixing the pretreatment raw materials and pretreatment carrier gas in step (1) in proportion, the mixture is atomized to obtain the atomized product.

[0070] The pretreatment raw materials include silicon and carbon sources in a molar ratio of 1:(3-6); the atomization frequency is 1.2MHz-2.4MHz; and the average particle size of the atomized products is 2μm-4μm.

[0071] (3) Multi-frequency response and air curtain isolation The atomized product from step (2) is reacted in a multi-frequency zone, and the reaction product is isolated by applying a multi-stage gas curtain to obtain an isolated product.

[0072] The multi-frequency region includes a dissociation reaction region and a synthesis reaction region; the frequency of the dissociation reaction region is 10MHz-15MHz, and the power is 15kW-25kW; the frequency of the synthesis reaction region is 1.5MHz-3.5MHz, and the power is 45kW-55kW.

[0073] The multi-stage gas curtain includes a primary gas curtain 20 and a secondary gas curtain 30. The primary gas curtain 20 is located between the secondary gas curtain 30 and the synthesis product carried by the carrier gas curtain 10. The flow rate of the primary gas curtain 20 is 4 L / min-10 L / min; the flow rate of the secondary gas curtain 30 is 12 L / min-21 L / min; and the carrier gas flow rate is 9 L / min-11 L / min.

[0074] (4) Post-processing Post-processing includes cooling, dust removal, sieving, and cutting. After post-processing, silicon carbide powder is obtained.

[0075] The cooling process includes: cooling the isolated product in a liquid helium environment at a temperature of -180°C to -150°C. Dust removal treatment includes: using a 28kV-35kV DC electric field to remove dust from the cooled products; The screening and cutting process includes screening and cutting the product after dust removal; wherein the mesh size of the screen used for screening is 350-450 mesh, and the D90 of the product after cutting is <1.1μm.

[0076] The yield of the obtained silicon carbide powder is ≥99.5%; the content of β-phase silicon carbide in the silicon carbide powder is ≥97%; the purity of the silicon carbide powder is 99.99%; and the average particle size CV value of the silicon carbide powder is <5%.

[0077] It should be noted that the equipment for synthesizing silicon carbide powder in the embodiments of the present invention is a vertical multi-stage temperature control structure, wherein the temperature of the dissociation reaction zone is 8000K-10000K, the temperature of the synthesis reaction zone is 2500K-2800K, and the cooling treatment zone uses liquid helium for spray cooling, with a temperature <500K.

[0078] Secondly, the present invention provides a silicon carbide powder, which is prepared by the synthesis method described in any of the foregoing embodiments.

[0079] Thirdly, the present invention provides a semiconductor device, wherein the raw materials for preparing the semiconductor device include silicon carbide powder as described in the foregoing embodiments.

[0080] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0081] Example 1 This embodiment provides a silicon carbide powder, which is prepared using the following steps: (1) Pretreatment of raw materials and carrier gas The pretreatment of the silicon source includes the following steps: the silicon source is dehydrated by passing it through an adsorption tower filled with 3Å molecular sieves at a temperature of 110℃, and the moisture content of the output silicon source is controlled to be ≤1ppm; the silicon source is SiCl4.

[0082] The pretreatment of the carbon source includes the following steps: passing the carbon source through a Pd / Al2O3 catalyst at a temperature of 200℃ and a pressure of 0.8MPa for deoxygenation treatment, and controlling the oxygen content of the output carbon source to be ≤5ppm; the carbon source is CH4.

[0083] The pretreatment of the carrier gas includes the following steps: passing the carrier gas through a ceramic filter with a filtration accuracy of 0.1 μm for dust removal; the carrier gas is argon.

[0084] The molar ratio of the pretreated silicon source, pretreated carbon source, and pretreated carrier gas is 1:4:10.

[0085] (2) Atomization treatment After mixing the pretreatment raw materials and pretreatment carrier gas in step (1) in proportion, the mixture is atomized to obtain the atomized product.

[0086] The pretreatment raw materials include silicon and carbon sources in a molar ratio of 1:4; the atomization frequency is 1.7MHz; and the average particle size of the atomized products is 3μm.

[0087] (3) Multi-frequency response and air curtain isolation The atomized product from step (2) is reacted in a multi-frequency zone, and the reaction product is isolated by applying a multi-stage gas curtain to obtain an isolated product.

[0088] The multi-frequency region includes a dissociation reaction region and a synthesis reaction region; the frequency of the dissociation reaction region is 13MHz and the power is 20kW; the frequency of the synthesis reaction region is 2MHz and the power is 50kW.

[0089] The multi-stage gas curtain includes a primary gas curtain 20 and a secondary gas curtain 30. The primary gas curtain 20 is located between the secondary gas curtain 30 and the synthesis product carried by the carrier gas curtain 10. The flow rate of the primary gas curtain 20 is 6 L / min; the flow rate of the secondary gas curtain 30 is 18 L / min; and the flow rate of the carrier gas is 10 L / min.

[0090] (4) Post-processing Post-processing includes cooling, dust removal, sieving, and cutting. After post-processing, silicon carbide powder is obtained.

[0091] The cooling process includes: cooling the isolated product in a liquid helium environment at a temperature of -180°C to -150°C. Dust removal treatment includes: using a 28kV-35kV DC electric field to remove dust from the cooled products; The screening and cutting process includes screening and cutting the product after dust removal; wherein the mesh size of the screen used for screening is 400 mesh, and the D90 of the product after cutting is <1.1μm.

[0092] The yield of the obtained silicon carbide powder is ≥99.5%; the content of β-phase silicon carbide in the silicon carbide powder is ≥97%; the purity of the silicon carbide powder is 99.99%; and the average particle size CV value of the silicon carbide powder is <5%.

[0093] Comparative Example 1 This comparative example provides a silicon carbide powder, which is prepared using a conventional process, specifically including the following steps: (1) Raw material preparation and pretreatment Natural quartz sand (SiO2≥99.2%) is coarsely crushed to a particle size of <5mm using a crusher; Petroleum coke (fixed carbon ≥95%) is crushed to <3mm using a hammer crusher; Weigh the SiO2:C ratio at 1:1.5 (mass ratio) and put it into a twin-screw mixer. Add 3wt% sawdust as a pore-forming agent and dry mix for 2 hours until uniform. The moisture content of the mixture should be controlled at 5-8%, and water mist should be sprayed to adjust if the moisture content is insufficient.

[0094] (2) Charging of the resistance furnace A 20cm thick layer of coke is laid at the bottom of the rectangular graphite furnace body as a conductive bed; A graphite electrode with a diameter of 30 cm was inserted vertically. The mixture is filled in layers and compacted every 30cm of filling, with a 50cm diameter cavity reserved in the center as the reaction core area. The top layer is covered with a 20cm coke insulation layer, and the sides of the furnace are sealed with refractory clay.

[0095] (3) High-temperature synthesis reaction The electrodes were subjected to 10kV / 50kA AC current and heated to 1400℃ at a rate of 50℃ / h (taking 28 hours). When maintained in the temperature range of 1400℃-2000℃ for 12 hours, the following reaction occurs: SiO2 + 3C → SiC + 2CO↑; Continue to increase the temperature to 2500℃ at a rate of 30℃ / h and maintain it for 48 hours to ensure the reaction is complete; The total power consumption is approximately 6500 kWh / ton of product.

[0096] (4) Cooling and furnace opening After power failure, allow the furnace to cool naturally for 72 hours until the furnace body temperature is <50℃; The silicon carbide crystal block in the central reaction zone is manually chiseled out.

[0097] (5) Crushing and grading The crystalline blocks are coarsely crushed into particles <2cm by a crusher; It is crushed to <5mm in a double roll crusher; Wet grinding in a ball mill (water-to-material ratio 2:1) for 24 hours until D50≈5μm; Hydrocyclones are used to remove coarse particles >10μm in size.

[0098] (6) Chemical purification The slurry was transferred to an acid-resistant reactor, and a mixture of 20 wt% hydrofluoric acid (HF) and 15 wt% nitric acid (HNO3) was added. Dissolve metal oxides and free silicon by stirring and acid washing at 80℃ for 6 hours: SiO2 + 6HF → H2SiF6 + 2H2O.

[0099] After dehydration in a filter press, the filtrate is washed with deionized water until the conductivity of the filtrate is <50 μS / cm.

[0100] (7) Drying and sieving The filter cake enters a spray drying tower (inlet air temperature 250℃) to produce powder with a moisture content of <0.5%; Hard agglomerates are removed using an ultrasonic vibrating screen (400 mesh). Magnetic separator removes iron impurities (magnetic field strength is 1.2T).

[0101] (8) Quality inspection and packaging X-ray diffraction (XRD) was used to detect the β-SiC phase content (92%-95%). Laser particle size analyzer analysis of particle size distribution (D90 / D10>4); The carbon-sulfur analyzer determined the oxygen content to be 180ppm-300ppm; Nitrogen-filled and sealed in double-layer aluminum foil bags.

[0102] Experimental Example 1 This experiment was conducted to investigate the effect of the molar ratio of silicon source to carbon source on silicon carbide powder. The preparation steps were the same as in Example 1, except that the molar ratio of silicon source to carbon source was different. The D50, silicon carbide particle size range, β-SiC content, oxygen content and specific surface area were summarized and analyzed. The relevant results are shown in Table 1.

[0103] Among them, the particle size D50 was tested using a Malvern laser particle size analyzer; the β-SiC content and phase type were tested using an X-ray diffractometer; the oxygen content was tested using an oxygen, nitrogen, and hydrogen analyzer; and the specific surface area was tested using a fully automated specific surface area analyzer.

[0104] Table 1. Effect of the molar ratio of silicon source to carbon source

[0105] As can be seen from the data in Table 1, the optimal ratio of silicon source to carbon source is 1:4; an excess of carbon >20% leads to an increase in the particle size of silicon carbide powder, resulting in carbon encapsulation growth and a decrease in the purity of the β phase.

[0106] Experimental Example 2 This experiment was used to investigate the effect of atomization frequency on silicon carbide powder. The preparation steps were the same as in Example 1, except that the atomization frequency was different. The diameter of the atomized product, the CV value of silicon carbide particle size, the silicon carbide yield, and the carbon deposition rate in the reactor were summarized and analyzed. The relevant results are shown in Table 2.

[0107] The yield is calculated as: (mass of collected SiC powder / theoretical mass of generated SiC) × 100%.

[0108] Table 2 Effect of atomization frequency

[0109] As can be seen from the data in Table 2, the optimal atomization frequency is 1.7MHz; excessively high frequencies result in atomized products that are too small and easily dispersed by the air curtain.

[0110] Experimental Example 3 This experiment was used to investigate the effects of the frequency and power of the dissociation reaction zone on silicon carbide powder. The preparation steps were the same as in Example 1, except that the frequency and power of the dissociation reaction zone were different. The ionization efficiency of the raw materials, the synthesis rate, the unit energy consumption, and the residual Cl were summarized and analyzed. The relevant results are shown in Table 3.

[0111] Chlorine residue (ppm) was tested using ion chromatography; free carbon content (at%) was tested using thermogravimetric-mass spectrometry; reaction zone temperature (°C) was tested using infrared thermal imager; the ionization efficiency η (%) was calculated using the formula: η = actual number of dissociated SiCl4 moles / completely dissociated SiCl4 moles × 100%; and the concentration of unreacted SiCl4 in the tail gas was tested using gas chromatography-mass spectrometry (GC-MS).

[0112] Table 3. Effects of frequency and power in the dissociation reaction zone

[0113] As shown in Table 3, the optimal dissociation reaction frequency is 13MHz and the power is 20kW, resulting in an ionization efficiency >95% and the lowest energy consumption. Insufficient power leads to incomplete dissociation of SiCl4 and an increase in Cl residue.

[0114] Test Example 4 This experiment was used to investigate the effects of the frequency and power of the synthesis reaction zone on silicon carbide powder. The preparation steps were the same as in Example 1, except that the frequency and power of the synthesis reaction zone were different. The synthesis rate, β-SiC content, D50, oxygen content and free carbon content were summarized and analyzed. The relevant results are shown in Table 4.

[0115] The particle size was measured using a Malvern laser particle size analyzer; the β-SiC content and phase type were measured using an X-ray diffractometer; the oxygen content was measured using an oxygen, nitrogen, and hydrogen analyzer; and the free carbon content was measured using a thermogravimetric-mass spectrometer.

[0116] Table 4. Effects of frequency and power in the synthesis reaction zone

[0117] As shown in Table 4, the optimal frequency for the synthesis reaction zone is 2.0 MHz. At the same power, 2.0 MHz yields the highest β-SiC content (99.7%) and the lowest energy consumption per unit (3.8 kWh / kg). At frequencies too low (1.5 MHz), the ion energy is too high, leading to grain coarsening (increased D50) and an increase in free carbon. At frequencies too high (2.5 MHz), the ion energy is insufficient, resulting in incomplete synthesis and a decrease in β-SiC purity.

[0118] The optimal power for the synthesis reaction zone was 50 kW. At a frequency of 2.0 MHz, this power resulted in the highest β-SiC content (99.7%), a moderate particle size (0.82 μm), and the lowest oxygen content (0.18 at%). Insufficient power (40 kW) led to a lower reaction temperature (<2700℃), poor crystallinity, and a decrease in β-SiC content. Excessive power (60 kW) resulted in temperatures exceeding 2900℃, excessive grain growth (D50>1.0 μm), and a significant increase in free carbon content (>0.15%).

[0119] Experimental Example 5 This experiment was used to investigate the effect of the flow rate of the primary gas curtain 20 on silicon carbide powder. The preparation steps were the same as in Example 1, except that the flow rate of the primary gas curtain 20 was different. The oxygen conversion rate, free carbon content, product color and specific surface area were summarized and analyzed. The relevant results are shown in Table 5.

[0120] The free carbon content was tested using a thermogravimetric-mass spectrometer; the specific surface area was tested using a fully automated specific surface area analyzer.

[0121] Table 5. Impact of Level 1 Air Curtain Flow Rate 20

[0122] As can be seen from the data in Table 5, the optimal flow rate for the first-stage gas curtain 20 is 6 L / min, with an oxygen conversion rate >99% and no carbon deposition; excess H2 leads to methane cracking and the generation of free carbon.

[0123] Experimental Example 6 This experiment was used to investigate the effect of the flow rate of the secondary gas curtain 30 on silicon carbide powder. The preparation steps were the same as in Example 1, except that the flow rate of the secondary gas curtain 30 was different. The O2 concentration in the synthesis reaction zone, particle loss rate, amount of silicon carbide powder deposited on the wall (abbreviated as: wall deposition), and D50 fluctuation of silicon carbide powder were summarized and analyzed. The relevant results are shown in Table 6.

[0124] Among them, oxygen content was tested using an oxygen, nitrogen, and hydrogen analyzer; particle size was tested using a Malvern laser particle size analyzer; and wall deposition was measured by weighing.

[0125] Table 6. Impact of the secondary air curtain flow rate of 30

[0126] As can be seen from the data in Table 6, the optimal flow rate for the secondary air curtain is 18 L / min, which represents the balance between oxygen control and particle loss; at 21 L / min, Ar turbulence leads to increased particle scattering.

[0127] Experimental Example 7 This experimental example analyzes the differences between Example 1 and Comparative Example 1. The analysis items include particle size distribution CV value, unit energy consumption, β-SiC purity, oxygen impurity content, waste status, and reaction time. The analysis results are summarized in Table 7.

[0128] Table 7 Analysis Results

[0129] Test Example 1 In this test example, the purity of the silicon carbide powder prepared in Example 1 was analyzed. The purity analysis results of Example 1 are shown in Table 8.

[0130] Table 8 Purity analysis results of Example 1

[0131] In summary, the silicon carbide powder synthesis method of this invention fundamentally solves the mismatch between the generation and consumption of active particles on a time scale through the synergistic effect of multiple frequency zones, achieving precise control from molecules to crystals. The multi-level gas curtain isolation structure constructs an active oxygen barrier from both physical and chemical dimensions, allowing for precise control of the oxygen content in the product. This achieves the goal of obtaining ultra-high purity powder without any post-processing acid washing steps, fundamentally solving the pollution problem and having significant strategic importance for promoting the development of downstream high-end devices.

[0132] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for synthesizing silicon carbide powder, characterized in that, Includes the following steps: The pretreatment raw materials and pretreatment carrier gas are mixed in proportion and then atomized to obtain atomized products. The atomized products react in the multi-frequency region, and the reaction products are isolated by a multi-stage gas curtain to obtain silicon carbide powder. The multi-frequency region includes a dissociation reaction region and a synthesis reaction region; The multi-stage gas curtain includes a primary gas curtain and a secondary gas curtain, wherein the primary gas curtain is located between the secondary gas curtain and the synthesis product carried by the carrier gas curtain.

2. The method for synthesizing silicon carbide powder according to claim 1, characterized in that, The frequency of the dissociation reaction zone is 10MHz-15MHz, and the power is 15kW-25kW; the frequency of the synthesis reaction zone is 1.5MHz-3.5MHz, and the power is 45kW-55kW.

3. The method for synthesizing silicon carbide powder according to claim 1, characterized in that, The flow rate of the primary air curtain is 4 L / min-10 L / min; the flow rate of the secondary air curtain is 12 L / min-21 L / min; and the flow rate of the carrier gas is 9 L / min-11 L / min. And / or, the gas composition of the multi-stage gas curtain is selected from at least one of argon, hydrogen, helium and nitrogen.

4. The method for synthesizing silicon carbide powder according to claim 1, characterized in that, The pretreated raw material has at least one of the following characteristics: Feature 1: The pretreatment raw materials include a silicon source and a carbon source in a molar ratio of 1:(3-6); wherein the silicon source is selected from at least one of SiCl4, HSiCl3 and SiH4; and the carbon source is selected from at least one of CH4, C2H2 and C2H4. Feature 2: The pretreatment of the silicon source includes the following steps: the silicon source is dehydrated by passing it through an adsorption tower filled with 3Å molecular sieves at a temperature of 95℃-115℃, and the moisture content of the output silicon source is controlled to be ≤1ppm. Feature 3: The pretreatment of the carbon source includes the following steps: passing the carbon source through a Pd / Al2O3 catalyst at a temperature of 180℃-220℃ and a pressure of 0.7MPa-1.0MPa for deoxygenation treatment, and controlling the oxygen content of the output carbon source to be ≤5ppm.

5. The method for synthesizing silicon carbide powder according to claim 1, characterized in that, The pretreated carrier gas has at least one of the following characteristics: Feature 1: The molar ratio of the pretreatment raw material to the pretreatment carrier gas is 1:(1.5-2.5). Feature 2: The pretreatment of the carrier gas includes the following steps: passing the carrier gas through a ceramic filter with a filtration accuracy of 0.1μm-5μm for dust removal; Feature 3: The carrier gas is selected from at least one of argon, hydrogen, helium and nitrogen.

6. The method for synthesizing silicon carbide powder according to claim 1, characterized in that, The atomization frequency is 1.2MHz-2.4MHz; the average particle size of the atomized product is 2μm-4μm.

7. The method for synthesizing silicon carbide powder according to claim 1, characterized in that, The synthesis method further includes post-processing, which includes cooling, dust removal, sieving, and cutting. The cooling process includes: cooling the isolated product in a liquid helium environment at a temperature of -180°C to -150°C; Dust removal treatment includes: using a 28kV-35kV DC electric field to remove dust from the cooled products; The screening and cutting process includes screening and cutting the product after dust removal; wherein the mesh size of the screen used for screening is 350-450 mesh, and the D90 of the product after cutting is <1.1μm.

8. The method for synthesizing silicon carbide powder according to claim 1, characterized in that, The obtained silicon carbide powder has at least one of the following characteristics: Feature 1: The yield of silicon carbide powder is ≥99.5%; Feature 2: The content of β-phase silicon carbide in the silicon carbide powder is ≥97%; Feature 3: The purity of silicon carbide powder is ≥99.99%; Feature 4: The average particle size CV value of silicon carbide powder is <5%.

9. A silicon carbide powder, characterized in that, It is prepared by the silicon carbide powder synthesis method as described in any one of claims 1-8.

10. A semiconductor device, characterized in that, The raw materials for preparing semiconductor devices include silicon carbide powder as described in claim 9.

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