Synthesis device and synthesis method of high-purity silicon carbide powder

Abstract

The application relates to the technical field of silicon carbide, in particular to a synthesis device and a synthesis method of high-purity silicon carbide powder. By arranging a graphite inner crucible in the graphite crucible main body, carbon powder and high-purity silicon can be placed separately, nitrogen and metal impurities can be discharged under the driving of silicon vapor generated during rapid heating and the inner-outer pressure difference, and the purity of the silicon carbide powder is improved. In order to reduce corrosion, the density of through holes in the edge area of the graphite crucible cover is less than or equal to that in the central area, silicon vapor is discharged along the through holes in the central area preferentially, the transport flux and residence time of silicon vapor in the edge area are reduced, and the reaction between silicon vapor and the graphite crucible cover and the graphite crucible main body is reduced; in addition, a TaC plating layer is arranged on the outer surface of the graphite crucible cover, so that the service life of the graphite crucible cover is prolonged.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide technology, and specifically to an apparatus and method for synthesizing high-purity silicon carbide powder. Background Technology

[0002] Silicon carbide (SiC), as a third-generation wide-bandgap semiconductor material, exhibits great application potential in high-temperature, high-frequency, high-power, and radiation-resistant devices due to its excellent properties such as high thermal conductivity, high breakdown field strength, and high saturated electron drift velocity. Especially in the field of augmented reality (AR) glasses, colorless and transparent high-purity semi-insulating silicon carbide material has become an ideal alternative to traditional materials due to its ultra-thinness, high heat dissipation, wide field of view, and absence of "rainbow" interference. However, the preparation of such materials requires low nitrogen content (nitrogen concentration below 1×10⁻⁶). 16 pcs / cm 3 Based on high-purity (≥6N) silicon carbide powder, this poses an extremely high challenge to existing synthesis technologies.

[0003] Currently, silicon carbide powder is mainly prepared using the self-propagating high-temperature synthesis (SHS) method, which involves loading a mixture of high-purity carbon powder and high-purity silicon powder into a crucible and synthesizing them at high temperatures. This method is advantageous due to its simplicity, energy efficiency, and high performance; however, it suffers from the following problems: firstly, the concentration of nitrogen and metallic impurities (Al, Fe, V, W, etc.) is difficult to control; secondly, under high-temperature conditions, silicon-based gaseous substances readily react with graphite components, leading to accelerated crucible wear and a shorter service life. Summary of the Invention

[0004] To overcome the above problems, the present invention provides an apparatus and method for synthesizing high-purity silicon carbide powder.

[0005] To achieve the above technical objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides an apparatus for synthesizing high-purity silicon carbide powder, comprising a graphite crucible body, a graphite crucible cover, and a graphite inner crucible, wherein the graphite crucible cover is disposed on the top of the graphite crucible body; and the graphite inner crucible is placed inside the graphite crucible body. The graphite crucible lid is provided with multiple through holes, which are arranged in a multi-layered circular array along the radius of the graphite crucible lid. The area at a distance less than or equal to 0.5R from the axis of the graphite crucible lid is the central area, and the area at a distance greater than 0.5R from the axis of the graphite crucible lid is the edge area, where R is the radius of the graphite crucible lid. The density of through holes is designed based on the temperature field distribution inside the graphite crucible body, and the density of through holes in the edge area is less than that in the central area.

[0006] In one or more embodiments, the graphite crucible body is made of isostatic graphite.

[0007] In one or more embodiments, the height of the graphite crucible body is 250-350 mm, and the thickness of the sidewalls and bottom is 10-25 mm. By increasing the thickness of the bottom and sidewalls of the graphite crucible body, the service life of the graphite crucible body can be effectively extended.

[0008] In one or more embodiments, the thickness of the graphite crucible lid is 3 to 10 mm; In one or more embodiments, the outer surface of the graphite crucible lid is provided with a TaC coating.

[0009] Preferably, the thickness of the TaC coating is 30~40 μm.

[0010] The perforation density in the edge region is lower than that in the central region. Silicon vapor preferentially exits through the perforations in the central region, reducing the transport flux and residence time of silicon vapor in the edge region. This decreases the reaction between silicon vapor and the graphite crucible lid and body, thereby inhibiting graphite component corrosion and extending the service life of the crucible body. Furthermore, the TaC coating on the outer surface of the graphite crucible lid also enhances its service life.

[0011] In one or more embodiments, the diameter of the through hole is 0.5 to 2 mm.

[0012] In one or more embodiments, the density of through holes in the edge region is 0.1~0.3 holes / cm². 2 .

[0013] In one or more embodiments, the density of through holes in the central region is 0.3~0.9 holes / cm². 2 .

[0014] In one or more embodiments, the inner graphite crucible is made of isostatic graphite.

[0015] In one or more embodiments, the height of the graphite inner crucible is 80-130 mm, and the thickness of the sidewalls and bottom is 3-5 mm. By setting the thickness of the bottom and sidewalls of the graphite inner crucible, the temperature and time for impurity removal can be effectively controlled, and the leakage of liquid silicon can be controlled. After the graphite inner crucible is corroded through, liquid silicon and gaseous silicon can react with carbon powder in gas-solid and liquid-solid reactions, effectively increasing the reaction temperature, thereby reducing the N concentration and metal impurity concentration in the silicon carbide powder and improving the purity of the α-SiC powder.

[0016] In one or more embodiments, the apparatus for synthesizing high-purity silicon carbide powder further includes a heat preservation unit disposed outside the graphite crucible body and the graphite crucible lid. The insulation unit includes a top insulation component, a side insulation component, and a bottom insulation component; the top insulation component, the side insulation component, and the bottom insulation component form a cavity, and the graphite crucible body and the graphite crucible lid are located in the cavity.

[0017] Preferably, the top insulation component is located above the graphite crucible lid, and there is a gap between the top insulation component and the graphite crucible lid; an air vent is opened in the middle of the top insulation component; the air vent is connected to the gap.

[0018] A second aspect of the present invention provides a method for synthesizing high-purity silicon carbide powder, which is implemented using the apparatus for synthesizing high-purity silicon carbide powder described in the first aspect, and includes the following steps: The synthesis apparatus for high-purity silicon carbide powder was activated by air firing under an argon atmosphere. Spread the carbon powder evenly on the bottom of the graphite crucible body, put the high-purity silicon into the graphite inner crucible, place the graphite inner crucible on top of the carbon powder, and cover the graphite crucible body with the graphite crucible lid. The high-purity silicon carbide powder synthesis device was placed in the synthesis furnace. After the furnace chamber was evacuated, high-purity argon gas was introduced. Then, the temperature was raised to 2000-2200℃ at a heating rate of 5-10℃ / min and maintained at a constant temperature for 0.5-2 h. Argon gas was continuously introduced, and the temperature was increased to 2100-2400℃ at a heating rate of 5-10℃ / min, and maintained at a constant temperature for 2-8 hours. Argon gas is continuously introduced, and the temperature is lowered to room temperature to obtain high-purity silicon carbide powder.

[0019] In one or more embodiments, during air-firing activation, the temperature is 2000~2400℃, the argon flow rate is 100~500sccm, and the pressure is 30~200 mbar.

[0020] In one or more embodiments, the molar ratio of toner to high-purity silicon is 1:(1.15~1.3).

[0021] In one or more embodiments, when the furnace cavity is evacuated, the vacuum level reaches 10. -5 ~10 -6 mbar.

[0022] Preferably, when evacuating the furnace cavity, a mechanical vacuum pump and a molecular pump are started sequentially to perform gradient evacuation, wherein the mechanical pump pumps evacuate for 1-10 hours to reduce the furnace pressure to 10. -1 ~10 -2 mbar, then the molecular pump continues to pump for 1~10 h to achieve a furnace vacuum of 10 mbar. -5 ~10 -6 mbar.

[0023] In one or more embodiments, after the furnace cavity is evacuated, when high-purity argon is introduced, the argon flow rate is 100~500 sccm.

[0024] In one or more embodiments, when argon gas is continuously introduced, the gas flow rate is 100~300 sccm.

[0025] In one or more embodiments, when cooling to room temperature to obtain high-purity silicon carbide powder, when cooling to 1800°C, the cooling time is 5~8 hours; after cooling to 1800°C, it is naturally cooled with the furnace.

[0026] In a third aspect, the present invention provides a silicon carbide crystal, the raw material of which is high-purity silicon carbide powder synthesized by the synthesis method described in the second aspect.

[0027] The beneficial effects of this invention are as follows: (1) In this invention, by setting a graphite inner crucible inside the graphite crucible body, carbon powder and high-purity silicon can be placed separately. The silicon vapor generated during rapid heating is driven by the internal and external pressure difference to discharge nitrogen and metal impurities (Al, Fe, V, W, etc.), thereby improving the purity of silicon carbide powder. However, the discharge of silicon vapor can corrode the graphite crucible cover. In order to reduce corrosion and improve the service life of the graphite crucible body and the graphite crucible cover, this invention sets the through-hole density in the edge area of ​​the graphite crucible cover to be less than or equal to that in the central area. Silicon vapor is preferentially discharged along the through-holes in the central area, reducing the transport throughput and residence time of silicon vapor in the edge area, reducing the reaction between silicon vapor and the graphite crucible cover and the graphite crucible body, thereby inhibiting the corrosion of graphite components and extending the service life of the crucible body. In addition, the TaC coating on the outer surface of the graphite crucible cover can improve the service life of the graphite crucible cover.

[0028] (2) In this invention, by setting a graphite inner crucible inside the graphite crucible body, carbon powder and high-purity silicon can be placed separately, reducing the stacking thickness and increasing the reaction temperature, thus enabling the efficient synthesis of high-purity silicon carbide powder.

[0029] (3) The high-purity silicon carbide powder synthesis device provided by the present invention has a simple structure, and the graphite crucible body and graphite crucible cover can be fully utilized, which can meet the needs of large-scale and low-cost production. Attached Figure Description

[0030] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0031] Figure 1 This is a schematic diagram of the structure of a device for synthesizing high-purity silicon carbide powder. Figure 2This is a simulation result of the temperature field at the bottom of the high-temperature zone in Example 1; Figure 3 This is a top view of the graphite crucible lid in Example 1; Figure 4 This is a simulation result of the temperature field in the middle of the high-temperature zone in Example 2; Figure 5 This is a top view of the graphite crucible lid in Example 2; Figure 1 , Figure 3 and Figure 5 In the middle, 1-graphite crucible body, 2-graphite crucible lid, 3-graphite inner crucible, 4-side insulation component, 5-bottom insulation component, 6-top insulation component, 7-vent hole, 8-through hole and 9-TaC coating; Figure 6 This is a physical image of the SiC wafer prepared in Example 5; Figure 7 The results are from secondary ion mass spectrometry (SIMS) analysis of optical SiC wafers. Figure 8 The results are from the absorption rate test of an optical SiC wafer. Figure 9 These are the resistivity test results for optical SiC wafers, where E5 represents 10. 5 E6 represents 10 6 E7 indicates 10 7 E8 represents 10 8 E9 represents 10 9 E10 means 10 10 E11 represents 10 11 E12 represents 10 12 . Detailed Implementation

[0032] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0033] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0034] Currently, silicon carbide powder is mainly prepared using the self-propagating high-temperature synthesis (SHS) method, which involves loading a mixture of high-purity carbon powder and high-purity silicon powder into a crucible and synthesizing them at high temperatures. This method is advantageous due to its simplicity, energy efficiency, and high performance; however, it suffers from the following problems: firstly, the concentration of nitrogen and metallic impurities (Al, Fe, V, W, etc.) is difficult to control; secondly, under high-temperature conditions, silicon-based gaseous substances readily react with graphite components, leading to accelerated crucible wear and a shorter service life.

[0035] To overcome the above problems, the present invention provides an apparatus and method for synthesizing high-purity silicon carbide powder.

[0036] In this invention, by setting an inner graphite crucible inside the graphite crucible body, carbon powder and high-purity silicon can be placed separately. The silicon vapor generated during rapid heating, driven by the internal and external pressure difference, removes nitrogen and metallic impurities (Al, Fe, V, W, etc.), improving the purity of the silicon carbide powder. However, the removal of silicon vapor can corrode the graphite crucible lid. To reduce corrosion and extend the service life of the graphite crucible body and lid, this invention sets the perforation density in the edge region of the graphite crucible lid to be less than or equal to that in the central region. Silicon vapor preferentially exits along the perforations in the central region, reducing the transport throughput and residence time of silicon vapor in the edge region, and decreasing the reaction between silicon vapor and the graphite crucible lid and body. This inhibits graphite component corrosion and extends the service life of the crucible body. Furthermore, a TaC coating on the outer surface of the graphite crucible lid further enhances its service life.

[0037] The present invention limits the through-hole density based on the internal temperature field distribution of the graphite crucible body, which can facilitate the silicon vapor transport path, optimize the gas flow field distribution inside the crucible body, reduce the local high concentration of silicon vapor retention and non-uniform reaction, and improve the purity of crystalline silicon carbide powder.

[0038] By setting the thickness of the bottom and sidewalls of the graphite inner crucible, the temperature and time for impurity removal can be effectively controlled, and the leakage of liquid silicon can be made controllable. After the graphite inner crucible is corroded through, liquid silicon and gaseous silicon can react with carbon powder in gas-solid and liquid-solid reactions, effectively increasing the reaction temperature, thereby reducing the N concentration and metal impurity concentration in the silicon carbide powder and improving the purity of α-SiC powder.

[0039] In this invention, by setting a graphite inner crucible inside the graphite crucible body, carbon powder and high-purity silicon can be placed separately, reducing the stacking thickness and increasing the reaction temperature, thus enabling the efficient synthesis of high-purity silicon carbide powder.

[0040] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0041] In the following embodiments, R is the radius of the graphite crucible lid.

[0042] Example 1 like Figure 1 As shown, a device for synthesizing high-purity silicon carbide powder includes a graphite crucible body 1, a graphite crucible cover 2, and a graphite inner crucible 3. The graphite crucible cover 2 is placed on top of the graphite crucible body 1; the graphite inner crucible 3 is placed inside the graphite crucible body 1. like Figure 3 As shown, multiple through holes 8 are provided on the graphite crucible cover 2. The multiple through holes are arranged in a multi-layered circular array along the radial direction of the graphite crucible cover. The area with a distance from the axis of the graphite crucible cover 2 less than or equal to 0.5R is the central area, and the area with a distance from the axis of the graphite crucible cover greater than 0.5R is the edge area. The density of through holes is designed based on the temperature field distribution inside the graphite crucible body 1. The density of through holes in the edge area is less than that in the central area.

[0043] Figure 2 When the graphite crucible lid 2 is not designed with through holes 8 and is placed on the graphite crucible body 1, the internal temperature field distribution of the graphite crucible body 1 is as follows: Under these temperature field conditions, the high-temperature region is mainly located at the bottom of the crucible, the radial temperature difference on the melt surface is small, and the difference in Si vapor generation between the center and the edge regions is limited. However, the axial temperature gradient in the edge region is greater than that in the center region, giving the edge region a stronger driving force for gas phase buoyancy. Based on the above temperature field characteristics, this embodiment adopts a gradient lid structure with a higher opening density in the center region than in the edge region to adjust the gas phase transport path and reduce the rapid escape of gaseous substances from the edge region.

[0044] like Figure 3 As shown, the graphite crucible lid 2 has 192 through holes 8, with a through hole density of 0.2 holes / cm² in the edge area. 2 The density of through holes in the central region is 0.6 per cm³. 2 Each through hole 8 has a diameter of 0.5 mm. The density of through holes 8 in the upper edge area of ​​the graphite crucible cover 2 is less than that in the central area. More silicon vapor is discharged from the through holes in the central area, reducing the direct escape and residence of silicon vapor in the edge area, thereby improving the service life of the graphite crucible cover 2 and the graphite crucible body 1.

[0045] The main body 1 of the graphite crucible is made of isostatic graphite. This is because isostatic graphite has a series of characteristics such as high purity, high density, isotropy and excellent thermal shock resistance. These advantages can meet the stringent requirements of silicon carbide crystal growth for purity, thermal stability and service life.

[0046] The graphite crucible body 1 has a height of 300 mm and a thickness of 15 mm for the side walls and bottom. By increasing the thickness of the bottom and side walls of the graphite crucible body, the service life of the graphite crucible body can be effectively extended.

[0047] The thickness of the graphite crucible lid 2 is 5 mm. By reducing the thickness of the graphite crucible lid, the temperature difference can be effectively increased, which is more conducive to the discharge of impurities.

[0048] The outer surface of the graphite crucible lid 2 is provided with a TaC coating 9. The thickness of the TaC coating 9 is 40 μm. The TaC coating 9 is highly dense and resistant to high temperature, which can effectively inhibit the corrosion of the graphite crucible lid 2 and improve the service life of the graphite crucible lid.

[0049] The inner graphite crucible 3 is made of isostatic graphite. This is because isostatic graphite has a series of characteristics such as high purity, high density, isotropy and excellent thermal shock resistance. These advantages can meet the stringent requirements of silicon carbide crystal growth for purity, thermal stability and service life.

[0050] The graphite inner crucible 3 has a height of 100 mm and a thickness of 3 mm for its sidewalls and bottom. By setting the thickness of the bottom and sidewalls of the graphite inner crucible 3, the temperature and time for impurity removal can be effectively controlled, and the leakage of liquid silicon can be controlled. After the graphite inner crucible 3 is corroded through, liquid silicon and gaseous silicon can react with carbon powder in gas-solid and liquid-solid reactions, effectively increasing the reaction temperature, thereby reducing the N concentration and metal impurity concentration in the silicon carbide powder and improving the purity of the α-SiC powder.

[0051] The apparatus for synthesizing high-purity silicon carbide powder also includes a heat preservation unit located outside the graphite crucible body 1 and the graphite crucible cover 2. The insulation unit consists of a top insulation component 6, a side insulation component 4, and a bottom insulation component 5. These components form a cavity, within which the graphite crucible body 1 and the graphite crucible lid are located. The top insulation component 6 is positioned above the graphite crucible lid 2, and a gap exists between the top insulation component 6 and the graphite crucible lid 2. An vent 7 is opened in the center of the top insulation component 6, and the vent 7 communicates with the gap. The vent 7 can be used for the discharge of silicon vapor and for temperature measurement. The insulation unit can construct and maintain a precise, stable, and pure high-temperature environment.

[0052] Example 2 like Figure 1 As shown, a device for synthesizing high-purity silicon carbide powder includes a graphite crucible body 1, a graphite crucible cover 2, and a graphite inner crucible 3. The graphite crucible cover 2 is placed on top of the graphite crucible body 1; the graphite inner crucible 3 is placed inside the graphite crucible body 1. like Figure 5As shown, multiple through holes 8 are provided on the graphite crucible cover 2. The multiple through holes are arranged in a multi-layered circular array along the radial direction of the graphite crucible cover. The area with a distance from the axis of the graphite crucible cover 2 less than or equal to 0.5R is the central area, and the area with a distance from the axis of the graphite crucible cover greater than 0.5R is the edge area. The density of through holes is designed based on the temperature field distribution inside the graphite crucible body 1. The density of through holes in the edge area is less than that in the central area.

[0053] Figure 4 When the graphite crucible lid 2 is not designed with through holes 8 and is placed on the graphite crucible body 1, the internal temperature field distribution of the graphite crucible body 1 is as follows: Under this temperature field condition, the high-temperature region is mainly located in the middle of the crucible, the radial temperature difference on the melt surface is small, and the axial temperature gradient between the center and the edge regions is similar, resulting in a more uniform gas phase transport distribution. Based on the above temperature field characteristics, this embodiment adopts a gradient graphite crucible lid 2 structure with a small difference in opening density between the center and edge regions to achieve a match between exhaust resistance and temperature field distribution.

[0054] like Figure 5 As shown, the graphite crucible lid 2 has 96 through holes 8, and the density of through holes in the edge area is 0.2 holes / cm². 2 The density of through holes in the central region is 0.3 per cm. 2 Each through hole 8 has a diameter of 0.5 mm. The density of through holes 8 in the upper edge area of ​​the graphite crucible cover 2 is less than that in the central area. More silicon vapor is discharged from the through holes in the central area, reducing the direct escape and residence of silicon vapor in the edge area, thereby improving the service life of the graphite crucible cover 2 and the graphite crucible body 1.

[0055] The main body 1 of the graphite crucible is made of isostatic graphite. This is because isostatic graphite has a series of characteristics such as high purity, high density, isotropy and excellent thermal shock resistance. These advantages can meet the stringent requirements of silicon carbide crystal growth for purity, thermal stability and service life.

[0056] The graphite crucible body 1 has a height of 300 mm and a thickness of 15 mm for the side walls and bottom. By increasing the thickness of the bottom and side walls of the graphite crucible body, the service life of the graphite crucible body can be effectively extended.

[0057] The thickness of the graphite crucible lid 2 is 5 mm. By reducing the thickness of the graphite crucible lid, the temperature difference can be effectively increased, which is more conducive to the discharge of impurities.

[0058] The outer surface of the graphite crucible lid 2 is provided with a TaC coating 9. The thickness of the TaC coating 9 is 40 μm. The TaC coating 9 is highly dense and resistant to high temperature, which can effectively inhibit the corrosion of the graphite crucible lid 2 and improve the service life of the graphite crucible lid.

[0059] The inner graphite crucible 3 is made of isostatic graphite. This is because isostatic graphite has a series of characteristics such as high purity, high density, isotropy and excellent thermal shock resistance. These advantages can meet the stringent requirements of silicon carbide crystal growth for purity, thermal stability and service life.

[0060] The graphite inner crucible 3 has a height of 100 mm and a thickness of 3 mm for its sidewalls and bottom. By setting the thickness of the bottom and sidewalls of the graphite inner crucible 3, the temperature and time for impurity removal can be effectively controlled, and the leakage of liquid silicon can be controlled. After the graphite inner crucible 3 is corroded through, liquid silicon and gaseous silicon can react with carbon powder in gas-solid and liquid-solid reactions, effectively increasing the reaction temperature, thereby reducing the N concentration and metal impurity concentration in the silicon carbide powder and improving the purity of the α-SiC powder.

[0061] The apparatus for synthesizing high-purity silicon carbide powder also includes a heat preservation unit located outside the graphite crucible body 1 and the graphite crucible cover 2. The insulation unit consists of a top insulation component 6, a side insulation component 4, and a bottom insulation component 5. These components form a cavity, within which the graphite crucible body 1 and the graphite crucible lid are located. The top insulation component 6 is positioned above the graphite crucible lid 2, and a gap exists between the top insulation component 6 and the graphite crucible lid 2. An vent 7 is opened in the center of the top insulation component 6, and the vent 7 communicates with the gap. The vent 7 can be used for the discharge of silicon vapor and for temperature measurement. The insulation unit can construct and maintain a precise, stable, and pure high-temperature environment.

[0062] Example 3 A method for synthesizing high-purity silicon carbide powder, using the synthesis apparatus for high-purity silicon carbide powder in Example 1, includes the following steps: (1) The apparatus for synthesizing high-purity silicon carbide powder in Example 1 was placed in an induction heating furnace and activated by air burning under an argon atmosphere, and then cooled to room temperature with the furnace. During the air burning activation, the temperature was 2300℃ and the time was 5 h. The argon flow rate was 100 sccm and the pressure was 100 mbar.

[0063] (2) Spread 1200 g of carbon powder evenly on the bottom of the graphite crucible body, put 3360 g of high-purity silicon into the graphite inner crucible, place the graphite inner crucible on top of the carbon powder, and cover the graphite crucible body with the graphite crucible lid.

[0064] (3) Place the high-purity silicon carbide powder synthesis device in an induction heating furnace and evacuate the furnace cavity (vacuum degree reaches 10). -5 (mbar). When evacuating the furnace cavity, the mechanical vacuum pump and the molecular pump are started sequentially to perform gradient evacuation, with the mechanical pump pumping for 1 hour to reduce the furnace pressure to 10. -1mbar, then the molecular pump continued to pump for 3 hours to achieve a furnace vacuum of 10. -5 mbar.

[0065] High-purity argon gas (flow rate of 100 mbar) was then introduced, followed by a heating rate of 10 °C / min to 2100 °C, which was maintained at a constant temperature for 1 h. Rapid heating to 2100 °C causes silicon to melt, forming silicon melt and silicon vapor. Due to the high pressure of silicon vapor at high temperatures, impurities can be expelled using the internal and external pressure difference.

[0066] (4) Argon gas was continuously introduced (gas flow rate of 100 mbar), and the temperature was raised to 2200℃ at a heating rate of 10℃ / min and kept constant for 8 h. As the silicon melt continuously corroded the thin-walled graphite crucible, it was eventually corroded through, allowing the gaseous and liquid phase silicon to react with carbon. During the synthesis process, impurities were continuously removed, reducing the concentration of N and metal impurities in the silicon carbide powder. (5) Argon gas is continuously introduced (gas flow rate is 100 mbar) and cooled to room temperature to obtain high-purity silicon carbide powder. When cooling to room temperature to obtain high-purity silicon carbide powder, the cooling time from the highest temperature (2200℃) to 1800℃ is 6 h; after cooling to 1800℃, it is naturally cooled with the furnace.

[0067] Example 4 A method for synthesizing high-purity silicon carbide powder, using the synthesis apparatus for high-purity silicon carbide powder in Example 2, includes the following steps: (1) The apparatus for synthesizing high-purity silicon carbide powder in Example 1 was placed in an induction heating furnace and activated by air burning under an argon atmosphere, and then cooled to room temperature with the furnace. During the air burning activation, the temperature was 2300℃ and the time was 5 h. The argon flow rate was 100 sccm and the pressure was 100 mbar.

[0068] (2) Spread 1200 g of carbon powder evenly on the bottom of the graphite crucible body, put 3360 g of high-purity silicon into the graphite inner crucible, place the graphite inner crucible on top of the carbon powder, and cover the graphite crucible body with the graphite crucible lid.

[0069] (3) Place the high-purity silicon carbide powder synthesis device in an induction heating furnace and evacuate the furnace cavity (vacuum degree reaches 10). -5 (mbar). When evacuating the furnace cavity, the mechanical vacuum pump and the molecular pump group are started sequentially to perform gradient evacuation, with the mechanical pump pumping for 1 hour to reduce the furnace pressure to 10. -1 mbar, then the molecular pump continued to pump for 3 hours to achieve a furnace vacuum of 10. -5 mbar.

[0070] High-purity argon gas (flow rate of 100 mbar) was then introduced, followed by a heating rate of 10 °C / min to 2100 °C, which was maintained at a constant temperature for 1 h. Rapid heating to 2100 °C causes silicon to melt, forming silicon melt and silicon vapor. Due to the high pressure of silicon vapor at high temperatures, impurities can be expelled using the internal and external pressure difference.

[0071] (4) Argon gas was continuously introduced (gas flow rate of 100 mbar), and the temperature was raised to 2200℃ at a heating rate of 10℃ / min and kept constant for 8 h. As the silicon melt continuously corroded the thin-walled graphite crucible, it was eventually corroded through, allowing the gaseous and liquid phase silicon to react with carbon. During the synthesis process, impurities were continuously removed, reducing the concentration of N and metal impurities in the silicon carbide powder. (5) Argon gas is continuously introduced (gas flow rate is 100 mbar) and cooled to room temperature to obtain high-purity silicon carbide powder. When cooling to room temperature to obtain high-purity silicon carbide powder, the cooling time from the highest temperature (2200℃) to 1800℃ is 6 h; after cooling to 1800℃, it is naturally cooled with the furnace.

[0072] Example 5 A method for synthesizing high-purity silicon carbide powder, using the synthesis apparatus for high-purity silicon carbide powder in Example 1, includes the following steps: (1) The apparatus for synthesizing high-purity silicon carbide powder in Example 1 was placed in an induction heating furnace and activated under an argon atmosphere. Then it was cooled to room temperature with the furnace. During the activation, the temperature was 2200℃, the time was 10 h, the argon flow rate was 300 sccm, and the pressure was 50 mbar.

[0073] (2) Spread 900 g of carbon powder evenly on the bottom of the graphite crucible body, put 2520 g of high-purity silicon into the graphite inner crucible, place the graphite inner crucible on top of the carbon powder, and cover the graphite crucible body with the graphite crucible lid.

[0074] (3) Place the high-purity silicon carbide powder synthesis device in an induction heating furnace and evacuate the furnace cavity (vacuum degree reaches 5×10). -6 (mbar). When evacuating the furnace cavity, the mechanical vacuum pump and the molecular pump group are started sequentially to perform gradient evacuation, with the mechanical pump pumping for 2 hours to reduce the furnace pressure to 10. -1 ~10 -2 mbar, then the molecular pump continued to pump for 8 hours to achieve a furnace vacuum of 5 × 10 mbar. - 6 mbar.

[0075] High-purity argon gas (flow rate of 300 mbar) was then introduced, followed by a heating rate of 10 °C / min to 2100 °C, which was maintained at a constant temperature for 1 h. Rapid heating to 2100 °C causes silicon to melt, forming silicon melt and silicon vapor. Due to the high pressure of silicon vapor at high temperatures, impurities can be expelled using the internal and external pressure difference.

[0076] (4) Argon gas was continuously introduced (gas flow rate of 300 mbar, crucible pressure adjusted to 100 mbar), and the temperature was raised to 2200℃ at a heating rate of 10℃ / min and kept constant for 4 h. As the silicon melt continuously corroded the thin-walled graphite crucible, it was eventually corroded through, allowing the gas phase and liquid phase silicon to come into contact with carbon and react. During the synthesis process, impurities were continuously removed, reducing the concentration of N and metal impurities in the silicon carbide powder. (5) Argon gas is continuously introduced (gas flow rate is 300 mbar) and cooled to room temperature to obtain high-purity silicon carbide powder. When cooling to room temperature to obtain high-purity silicon carbide powder, the cooling time from the highest temperature (2200℃) to 1800℃ is 5 h; after cooling to 1800℃, it is naturally cooled with the furnace.

[0077] Example 6 A method for synthesizing high-purity silicon carbide powder, using the synthesis apparatus for high-purity silicon carbide powder in Example 1, includes the following steps: (1) The synthesis apparatus for high-purity silicon carbide powder in Example 1 was placed in an induction heating furnace and activated by air burning under an argon atmosphere, and then cooled to room temperature with the furnace. During the air burning activation, the temperature was 2400℃, the time was 5 h, the argon flow rate was 500 sccm, and the pressure was 30 mbar.

[0078] (2) Spread 1500 g of carbon powder evenly on the bottom of the graphite crucible body, put 4200 g of high-purity silicon into the graphite inner crucible, place the graphite inner crucible on top of the carbon powder, and cover the graphite crucible body with the graphite crucible lid.

[0079] (3) Place the high-purity silicon carbide powder synthesis device in an induction heating furnace and evacuate the furnace cavity (vacuum degree reaches 10). -6 (mbar). When evacuating the furnace cavity, the mechanical vacuum pump and the molecular pump group are started sequentially to perform gradient evacuation, with the mechanical pump pumping for 5 hours to reduce the furnace pressure to 10. -1 ~10 -2 mbar, then the molecular pump continued to pump for 10 h to achieve a furnace vacuum of 5 × 10 mbar. - 6 mbar.

[0080] High-purity argon gas (flow rate of 300 mbar) was then introduced, followed by a heating rate of 10 °C / min to 2150 °C, which was maintained at a constant temperature for 1 h. The temperature was then rapidly increased to 2100 °C, at which point silicon melted to form silicon melt and silicon vapor. Due to the high pressure of silicon vapor at high temperatures, impurities could be expelled using the internal and external pressure difference.

[0081] (4) Argon gas was continuously introduced (gas flow rate of 300 mbar, crucible pressure adjusted to 100 mbar), and the temperature was raised to 2300℃ at a heating rate of 10℃ / min and kept constant for 3 h. As the silicon melt continuously corroded the thin-walled graphite crucible, it was eventually corroded through, allowing the gas phase and liquid phase silicon to react with carbon. During the synthesis process, impurities were continuously removed, reducing the concentration of N and metal impurities in the silicon carbide powder. (5) Argon gas is continuously introduced (gas flow rate is 300 mbar) and cooled to room temperature to obtain high-purity silicon carbide powder. When cooling to room temperature to obtain high-purity silicon carbide powder, the cooling time from the highest temperature (2300℃) to 1800℃ is 5 h; after cooling to 1800℃, it is naturally cooled with the furnace.

[0082] The impurity element content in the high-purity silicon carbide powder prepared in Examples 3 to 6 was tested by glow discharge mass spectrometry (GDMS). The results are shown in Table 1. It can be seen from Table 1 that the content of Al, Fe, W and N impurities in the silicon carbide powder is low, the purity of SiC powder is high, and it can be used to prepare optical grade SiC crystals.

[0083] Table 1. Impurity element content in high-purity silicon carbide powder

[0084] Example 7 Preparation of SiC crystals using the high-purity silicon carbide powder prepared in Example 3: The high-purity silicon carbide powder and seed crystal prepared in Example 3 were loaded into a SiC crystal growth crucible and subjected to vacuum treatment to achieve a vacuum degree of 10. -5 mbar; high-purity argon gas was introduced for crystal growth at 2150℃ for 90 hours. After growth, the temperature was lowered to room temperature. The resulting 500 μm thick optical SiC wafer is shown in the image. Figure 6 As shown.

[0085] Secondary ion mass spectrometry (SIMS) test results of optical SiC wafers are as follows: Figure 7 As shown, from Figure 7 It can be seen that the N concentration of the prepared crystals is 10 16 The following results reflect good control of nitrogen source pollution and high crystal purity.

[0086] The absorption rate test results of optical SiC wafers are as follows: Figure 8 As shown, from Figure 8 It can be seen that the visible light absorption rate of the 500-micrometer-thick optical SiC wafer is as low as 0.2%, and due to the low impurity concentration in the wafer, no corresponding impurity absorption peaks were observed.

[0087] The resistivity test results of optical SiC wafers are as follows: Figure 9 As shown, from Figure 9 As can be seen, the resistivity of a 500-micrometer-thick optical SiC wafer has reached approximately 1×10⁻⁶. 12 (1E12) and above, and because the impurity concentration in the optical SiC wafer is low, no region with corresponding low resistivity was observed.

[0088] Comparative Example 1 Compared with Example 1, the apparatus for synthesizing silicon carbide powder does not include a graphite inner crucible. The carbon powder and high-purity silicon are mixed and placed inside the graphite crucible body. The other synthesis processes are the same as in Example 3.

[0089] In step (3) the silicon melting stage, the carbon powder reacts with the silicon in advance, resulting in the formation of β-SiC; in step (4) the high temperature synthesis stage, β-SiC is transformed into α-SiC. However, due to the short reaction time, the transformation of β-SiC is incomplete, affecting the purity of the powder. At the same time, due to the consumption of silicon, the vapor pressure is low, the effect of removing impurities is poor, and the N concentration and metal impurity concentration of the synthesized SiC powder are still high.

[0090] The impurity element content in the silicon carbide powder prepared in Comparative Example 1 was tested by glow discharge mass spectrometry (GDMS). The results are shown in Table 2. It can be seen from Table 2 that the silicon carbide powder has high contents of impurities such as Al, Fe, and N, and the SiC powder has low purity, which is not conducive to the preparation of SiC optical crystals.

[0091] Comparative Example 2 Compared with Example 1, the graphite crucible lid in the silicon carbide powder synthesis apparatus was not provided with a through hole, while the other synthesis processes were the same as in Example 3.

[0092] In step (4) the high-temperature synthesis stage, the silicon melt vaporizes into silicon vapor. Since the graphite crucible lid has no pores, the silicon vapor cannot escape, and N and metal impurities still exist.

[0093] The impurity element content in the silicon carbide powder prepared in Comparative Example 2 was determined using glow discharge mass spectrometry (GDMS). Table 2 shows that the silicon carbide powder contains high levels of impurities such as Al, Fe, and N, which is detrimental to the preparation of optical SiC crystals. Furthermore, excess silicon vapor cannot be consumed and will deposit in the SiC powder, resulting in Si-rich SiC powder. Due to the imbalance in the C / Si ratio, the prepared SiC optical crystals exhibit defects such as microtubes.

[0094] Comparative Example 3 Compared to Example 1, the graphite crucible lid in the silicon carbide powder synthesis apparatus has 192 through holes, with a through hole density of 0.2 holes / cm² in the edge region. 2 The density of through holes in the central region is 0.6 per cm³. 2 Each through-hole has a diameter of 3 mm; the outer surface of the graphite crucible lid is not coated with TaC. Other synthesis processes are the same as in Example 3.

[0095] The impurity element content in the silicon carbide powder prepared in Comparative Example 3 was tested by glow discharge mass spectrometry (GDMS). The results are shown in Table 2. It can be seen from Table 2 that the impurity content of Al, Fe, W and N in the silicon carbide powder is low and the purity of SiC powder is high. However, in the silicon melting stage in step (3) and the high temperature synthesis stage in step (4), due to the large through hole of the graphite crucible cover, the silicon vapor leakage will be large. In addition, the silicon vapor will continue to react with the graphite crucible cover, corroding the graphite crucible cover and affecting the service life of the crucible. In fact, during use, the graphite crucible cover will be corroded into large diameter holes, causing silicon vapor leakage and posing a production safety hazard.

[0096] Comparative Example 4 Compared to Example 1, the graphite crucible lid in the silicon carbide powder synthesis apparatus has 48 through holes, with a through hole density of 0.1 holes / cm² in the edge region. 2 The density of through holes in the central region is 0.1 per cm³. 2 The diameter of each through hole is 0.5 mm, and the other synthesis process is the same as in Example 3.

[0097] In steps (3) silicon melting stage and (4) high temperature synthesis stage, due to the low density of through holes in the graphite crucible lid, the gas flow resistance in the cavity increases, which leads to a decrease in the efficiency of nitrogen impurity discharge and a longer residence time of impurities in the reaction area, which is not conducive to the preparation of high-purity silicon carbide powder.

[0098] The impurity element content in the silicon carbide powder prepared in Comparative Example 4 was tested by glow discharge mass spectrometry (GDMS). The results are shown in Table 2. It can be seen from Table 2 that the silicon carbide powder has high contents of Al, Fe, W and N impurities, and the purity of SiC powder is low.

[0099] Table 2. Impurity element content in silicon carbide powders of Comparative Examples 1-4

[0100] 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. An apparatus for synthesizing high-purity silicon carbide powder, characterized in that, It includes a graphite crucible body, a graphite crucible lid, and a graphite inner crucible, wherein the graphite crucible lid is located on top of the graphite crucible body; and the graphite inner crucible is placed inside the graphite crucible body. The graphite crucible lid is provided with multiple through holes, which are arranged in a multi-layered circular array along the radius of the graphite crucible lid. The area at a distance less than or equal to 0.5R from the axis of the graphite crucible lid is the central area, and the area at a distance greater than 0.5R from the axis of the graphite crucible lid is the edge area, where R is the radius of the graphite crucible lid. The density of through holes is designed based on the temperature field distribution inside the graphite crucible body, and the density of through holes in the edge area is less than that in the central area.

2. The apparatus for synthesizing high-purity silicon carbide powder as described in claim 1, characterized in that, The main body of the graphite crucible is made of isostatic graphite; The height of the graphite crucible body is 250-350 mm, and the thickness of the side walls and bottom is 10-25 mm.

3. The apparatus for synthesizing high-purity silicon carbide powder as described in claim 1, characterized in that, The thickness of the graphite crucible lid is 3~10 mm; The outer surface of the graphite crucible lid is coated with a TaC layer; the thickness of the TaC coating layer is 30~40 μm.

4. The apparatus for synthesizing high-purity silicon carbide powder as described in claim 1, characterized in that, The diameter of the through hole is 0.5~2 mm; The density of through holes in the edge region is 0.1~0.3 per cm³. 2 The density of through holes in the central region is 0.3~0.9 per cm³. 2 ; The inner crucible is made of isostatically pressed graphite. The height of the graphite inner crucible is 80~130 mm, and the thickness of the side walls and bottom is 3~5 mm.

5. The apparatus for synthesizing high-purity silicon carbide powder as described in claim 1, characterized in that, The apparatus for synthesizing high-purity silicon carbide powder also includes a heat preservation unit located outside the graphite crucible body and the graphite crucible lid; The insulation unit includes a top insulation component, a side insulation component, and a bottom insulation component; The top insulation component, the side insulation component, and the bottom insulation component form a cavity, and the graphite crucible body and the graphite crucible lid are located inside the cavity; The top insulation component is located above the graphite crucible lid, and there is a gap between the top insulation component and the graphite crucible lid; an air vent is opened in the middle of the top insulation component; the air vent is connected to the gap.

6. A method for synthesizing high-purity silicon carbide powder, characterized in that, The synthesis of high-purity silicon carbide powder using the apparatus described in any one of claims 1 to 5 includes the following steps: The synthesis apparatus for high-purity silicon carbide powder was activated by air firing under an argon atmosphere. Spread the carbon powder evenly on the bottom of the graphite crucible body, put the high-purity silicon into the graphite inner crucible, place the graphite inner crucible on top of the carbon powder, and cover the graphite crucible body with the graphite crucible lid. The high-purity silicon carbide powder synthesis device was placed in the synthesis furnace. After the furnace chamber was evacuated, high-purity argon gas was introduced. Then, the temperature was raised to 2000-2200℃ at a heating rate of 5-10℃ / min and maintained at a constant temperature for 0.5-2 h. Argon gas was continuously introduced, and the temperature was increased to 2100-2400℃ at a heating rate of 5-10℃ / min, and maintained at a constant temperature for 2-8 hours. Argon gas is continuously introduced, and the temperature is lowered to room temperature to obtain high-purity silicon carbide powder.

7. The synthesis method according to claim 6, characterized in that, During dry firing activation, the temperature is 2000~2400℃, the argon flow rate is 100~500 sccm, and the pressure is 30~200 mbar; The molar ratio of toner to high-purity silicon is 1:(1.15~1.3). When the furnace cavity is evacuated, the vacuum level reaches 10. -5 ~10 -6 mbar.

8. The synthesis method as described in claim 6, characterized in that, After evacuating the furnace cavity, when introducing high-purity argon gas, the argon gas flow rate is 100~500 sccm; When argon gas is continuously introduced, the gas flow rate is 100~300 sccm.

9. The synthesis method according to claim 6, characterized in that, When obtaining high-purity silicon carbide powder by cooling to room temperature, the cooling time is 5-8 hours when the temperature is reduced to 1800℃; after cooling to 1800℃, the powder is allowed to cool naturally with the furnace.

10. A silicon carbide crystal, characterized in that, The raw material is high-purity silicon carbide powder synthesized by the synthesis method described in any one of claims 6 to 9.

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