High-purity semi-insulating silicon carbide single crystal for optical elements and growth process thereof

Abstract

The application relates to the technical field of silicon carbide single crystal growth, in particular to high-purity semi-insulating silicon carbide single crystal for optical elements and a growth process thereof, which comprises the following steps: S1, assembling silicon carbide powder, a graphite crucible and the like to form a thermal field device, and placing the thermal field device in an induction furnace, sequentially performing room temperature furnace washing treatment, low-temperature furnace washing treatment, and then performing thermal field impurity removal treatment; S2, assembling a silicon carbide seed crystal and the thermal field device after impurity removal, then increasing the temperature in the induction furnace and conveying high-purity argon or a mixed gas of high-purity argon and high-purity hydrogen into the induction furnace to perform crystal growth; and S3, after the crystal growth is completed, performing high-temperature and high-pressure annealing treatment, and then performing furnace cooling treatment to obtain a high-purity semi-insulating silicon carbide crystal ingot for optical elements. Through selection of specific raw materials, reasonable design of an assembly mode and combination of thermal field impurity removal, high-temperature and high-pressure annealing and the like, a silicon carbide crystal ingot with excellent light transmission performance and high resistivity is obtained.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide single crystal growth technology, and particularly to a high-purity semi-insulating silicon carbide single crystal for optical components and its growth process. Background Technology

[0002] Compared to traditional first-generation silicon-based semiconductor materials, silicon carbide single-crystal materials possess advantages such as high thermal conductivity, wide bandgap, and high breakdown electric field strength. Silicon carbide single-crystal materials have broad development prospects in the field of augmented reality (AR), such as in AR glasses. Compared to traditional waveguide materials used in AR glasses, such as glass and resin, silicon carbide single-crystal materials have a higher refractive index. Furthermore, they can achieve full-color display without the need for complex and costly double-layer waveguide materials, significantly reducing the weight and thickness of the lenses; for example, the overall weight of the Meta Orion can be controlled within 80-100 grams. In addition, using silicon carbide single-crystals as optical waveguide materials can achieve a larger field of view (FOV), thereby providing a more immersive user experience.

[0003] Currently, the silicon carbide single crystal material used in AR glasses is high-purity semi-insulating silicon carbide, and its growth method is usually physical vapor deposition (PVT). Compared with high-purity semi-insulating silicon carbide used in gallium nitride and silicon carbide microwave devices, the application of high-purity semi-insulating silicon carbide as a wafer material in optical components places higher demands on the optical performance of high-purity semi-insulating silicon carbide materials. For example, the requirements for the transmittance of high-purity semi-insulating silicon carbide materials in specific wavelength bands such as red, blue, and green light, as well as the refractive index of high-purity semi-insulating silicon carbide materials are higher. Therefore, how to improve the transmittance and refractive index of high-purity semi-insulating silicon carbide crystals has become an urgent problem to be solved.

[0004] Patent number CN201821713656.8 discloses a device for preparing high-purity silicon carbide. By ensuring that the crucible is isolated from the outside air during the growth process, nitrogen gas is prevented from entering the crucible and causing a decrease in the resistivity of the crystal, resulting in a crystal with a resistivity greater than 10. 5 A high-purity semi-insulating silicon carbide crystal with a resistivity of Ω·cm is available; however, the resistivity and transmittance of this semi-insulating silicon carbide crystal cannot meet the requirements of optical components.

[0005] Patent number CN201711189841.1 discloses a method for growing large-size semi-insulating silicon carbide single crystals using the PVT method. Although the growth method specifically includes steps such as SiC powder preparation, furnace loading and vacuuming, removal of impurity gases, rapid heating and pressurization, pressure reduction and isothermal control, crystal growth, finishing stage, and annealing, the silicon carbide single crystals obtained are undoped high-purity semi-insulating 4H-SiC. Moreover, it is used to solve the back-gate effect problem when vanadium-doped semi-insulating 4H-SiC single crystals are applied to high-power GaN / SiC HEMT devices. Its crystal quality, light transmittance, and other properties cannot meet the requirements of optical components.

[0006] This invention provides a high-purity semi-insulating silicon carbide single crystal for optical components and its growth process, in order to solve the problems of low resistivity and poor light transmittance of silicon carbide single crystals grown by existing physical vapor deposition methods. Summary of the Invention

[0007] The purpose of this invention is to provide a high-purity semi-insulating silicon carbide single crystal for optical components and its growth process, so as to solve the problems of low resistivity and poor light transmittance of silicon carbide single crystals grown by existing physical vapor deposition methods.

[0008] The technical solution of this invention is: a growth process for high-purity semi-insulating silicon carbide single crystals for optical components, comprising the following steps:

[0009] S1. Assemble silicon carbide powder, graphite crucible, graphite felt, accessories and / or raw materials to form a hot zone device, and place it in an induction furnace. Then, perform room temperature furnace cleaning, low temperature furnace cleaning, and hot zone impurity removal treatment in sequence. The silicon carbide powder includes a first silicon carbide powder with a particle size of 1-2 mm synthesized by CVD method and a second silicon carbide powder with a particle size of 0.01-0.1 mm. The second silicon carbide powder is assembled on top of the first silicon carbide powder.

[0010] S2. The silicon carbide seed crystal is assembled with the hot field device after impurity removal. Then, the temperature inside the induction furnace is raised and high-purity argon or a mixture of high-purity argon and high-purity hydrogen is introduced into the induction furnace to grow the crystal.

[0011] S3. After the crystal growth is completed, high temperature and high pressure annealing is performed first, followed by furnace cooling to obtain high purity semi-insulating silicon carbide ingots for optical components.

[0012] The high-temperature and high-pressure annealing process involves adjusting the pressure inside the induction furnace to 320-380 mbar, lowering the temperature to 1800-1900℃, and then maintaining the temperature and pressure at a constant level for several hours.

[0013] Preferably, the purity of the silicon carbide powder is not less than 99.9999%; the silicon carbide powder contains Cl element, and the N content in the silicon carbide powder does not exceed 1×10⁻⁶. 15 atoms / cm 3 Al content not exceeding 1×10 15 atoms / cm 3 ;

[0014] The accessories include porous graphite sheets and an atmosphere filtration assembly.

[0015] Preferably, in step S1, the room temperature furnace cleaning process involves raising the pressure inside the induction furnace to 450-550 mbar within 25-35 minutes at 15-35°C, maintaining the pressure for 40-80 minutes, and then reducing the pressure inside the induction furnace to the base pressure within 50-70 minutes.

[0016] The low-temperature furnace cleaning process involves raising the pressure inside the induction furnace to 450-550 mbar within 25-35 minutes at 1200-1500℃, maintaining the pressure for 40-80 minutes, and then reducing the pressure inside the induction furnace to the base pressure within 50-70 minutes.

[0017] The background pressure does not exceed 1×10 -4 pa;

[0018] The heat field impurity removal treatment is carried out at a temperature of 2000-2250℃ and a pressure of 1-3mbar for 1-10 hours.

[0019] Preferably, in step S1, the assembly operation includes the following steps: a) firstly filling the bottom of the graphite crucible with first silicon carbide powder, then placing the porous graphite sheet on top of the first silicon carbide powder, and then spreading the second silicon carbide powder on top of the porous graphite sheet.

[0020] b. Place the atmosphere filter assembly on top of the second silicon carbide powder, then assemble the components of the graphite crucible together, and wrap the graphite felt around the graphite crucible.

[0021] Preferably, the purity of both the high-purity argon and the high-purity hydrogen is not less than 99.9999%; the ratio of high-purity argon to high-purity hydrogen in the mixed gas is (10-5):1.

[0022] Preferably, the graphite crucible is made of isostatically pressed graphite material; the ash content of the graphite crucible is less than 5 ppm.

[0023] Preferably, the outer surface of the graphite crucible is coated with a metal compound coating; the metal compound coating is any one or more of silicon carbide, aluminum nitride, and tantalum carbide.

[0024] Preferably, in step S3, the furnace cooling process involves reducing the heating power of the induction furnace to 0 kW and then allowing the thermal field device to cool naturally to room temperature.

[0025] The present invention also provides a high-purity semi-insulating silicon carbide single crystal for optical components, which is grown using the above-described growth process.

[0026] Compared with the prior art, the advantages of the present invention are:

[0027] (1) The present invention provides a high-purity semi-insulating silicon carbide single crystal for optical components and its growth process. The growth process is achieved by selecting specific raw materials and auxiliary parts and / or raw materials, rationally designing the assembly method, and combining processes such as hot field impurity removal and high temperature and high pressure annealing, so that the raw materials and process steps work together to grow silicon carbide ingots with excellent light transmittance and high resistivity. Specifically, high-purity semi-insulating silicon carbide powder synthesized by CVD method is used as the raw material for crystal growth. With the help of the small amount of Cl element in the high-purity semi-insulating silicon carbide powder, the impurity content in the hot field can be further reduced during the hot field impurity removal process. In particular, the content of metallic impurities is reduced, thereby effectively improving the quality of silicon carbide ingots, avoiding the appearance of absorption peaks caused by metallic impurities, and improving the light transmittance of silicon carbide ingots. At the same time, high-temperature and high-pressure annealing further eliminates carbon and silicon vacancies in silicon carbide ingots, significantly reducing the number of deep-level defects inside the ingot, avoiding light absorption phenomena caused by ultraviolet photons, and thus greatly improving the light transmittance and resistivity of silicon carbide ingots. This solves the problems of low resistivity and poor light transmittance of silicon carbide single crystals grown by existing physical vapor deposition methods.

[0028] (2) The present invention provides a high-purity semi-insulating silicon carbide single crystal for optical components and its growth process. In this growth process, a second silicon carbide powder with a finer particle size and a denser packing is spread on top of a first silicon carbide powder with a larger particle size. The second silicon carbide powder can be used as a filter layer to filter the atmosphere generated by the sublimation of the first silicon carbide powder, filter out carbon particles in the atmosphere and pack them in the second silicon carbide powder layer, thereby reducing the carbon particle content in the atmosphere. At the same time, an atmosphere filter component is set above the second silicon carbide powder to filter the atmosphere generated by sublimation again, further reducing the carbon particle content in the atmosphere, thereby effectively reducing or avoiding carbon inclusions in the silicon carbide single crystal and improving the quality of the silicon carbide single crystal. Meanwhile, the growth process uses a graphite crucible with a metal compound coating on its outer surface. The metal compound coating can increase the density of the graphite part, thereby blocking the contamination brought by the graphite soft felt outside the graphite crucible, improving the quality of the silicon carbide ingot, and thus helping to improve its light transmittance. Attached Figure Description

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0030] Figure 1 This is a flow chart of the growth process of high-purity semi-insulating silicon carbide single crystal for optical components described in this invention.

[0031] Figure 2 This is a schematic diagram of the structure of the thermal field device described in this invention;

[0032] The components include: 1. Graphite crucible body; 2. Crucible lid; 3. Silicon carbide seed crystal; 4. First silicon carbide powder; 5. Second silicon carbide powder; 6. Porous graphite sheet; 7. Atmosphere filter assembly. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to specific embodiments:

[0034] A growth process for high-purity semi-insulating silicon carbide single crystals for optical components, such as... Figure 1 As shown, it includes the following steps:

[0035] S1. Assembly and Hot Zone Purification: The hot zone device includes graphite felt as insulation material and a graphite crucible. The graphite crucible includes a crucible body 1 and a crucible lid 2. Silicon carbide powder and silicon carbide seed crystals 3 are placed inside the graphite crucible. Furthermore, auxiliary components required for crystal growth, such as an atmosphere filtration device, can also be placed inside the graphite crucible. Raw and auxiliary materials required for crystal growth can also be placed inside the graphite crucible. The silicon carbide powder used is high-purity semi-insulating silicon carbide powder synthesized by CVD, with a particle size of 1-2 mm selected as the first silicon carbide powder 4, and a particle size of 0.01-0.1 mm selected as the second silicon carbide powder 5. Auxiliary components required for crystal growth include porous graphite sheets 6 and an atmosphere filtration assembly 7. Figure 2As shown, silicon carbide powder, a graphite crucible, graphite felt, accessories, and / or raw materials are assembled to form a thermal field device, which is then placed in an induction furnace. Afterward, a room temperature furnace cleaning process, a low temperature furnace cleaning process, and a thermal field impurity removal process are performed sequentially. The assembly process specifically includes the following steps: a) First, fill the graphite crucible body with first silicon carbide powder and spread it evenly at the bottom of the graphite crucible body. Then, place a porous graphite sheet on top of the first silicon carbide powder. Next, spread second silicon carbide powder evenly on top of the porous graphite sheet. b) Place an atmosphere filter assembly on top of the second silicon carbide powder, with a distance of 2-10 mm between them. Then, fasten the crucible lid onto the graphite crucible and cover the periphery of the graphite crucible with graphite felt to form the thermal field device. The room temperature furnace cleaning process involves raising the internal pressure of the induction furnace to 450–550 mbar within 25–35 minutes at 15–35°C and then holding the pressure for 40–80 minutes, followed by reducing the pressure to the base pressure within 50–70 minutes. Similarly, the low temperature furnace cleaning process involves raising the internal pressure of the induction furnace to 450–550 mbar within 25–35 minutes at 1200–1500°C and then holding the pressure for 40–80 minutes, followed by reducing the pressure to the base pressure within 50–70 minutes. The base pressure refers to the remaining gas pressure inside the induction furnace after vacuuming. In this application, the base pressure is no greater than 1 × 10⁻⁶ mbar. -4 pa. The hot field impurity removal treatment is carried out at a temperature of 2000~2250℃ and a pressure of 1~3mbar for 1~10h to remove impurities from graphite soft felt, graphite crucible, silicon carbide powder, etc.

[0036] In existing technologies, the growth methods for high-purity semi-insulating silicon carbide single crystals typically employ silicon carbide powder synthesized via a self-propagating method. However, silicon carbide powder synthesized via this method is usually doped with carbon, boron, and other metallic elements. These elements are difficult to remove during the impurity removal process, ultimately leading to defects such as microtubes and dislocations in the grown silicon carbide single crystal, affecting its quality and light transmittance. In this application, the high-purity semi-insulating silicon carbide powder synthesized via CVD achieves a purity of 99.9999% or higher; furthermore, the nitrogen content in this high-purity semi-insulating silicon carbide powder does not exceed 1×10⁻⁶. 15 atoms / cm 3 The Al content should not exceed 1×10 15 atoms / cm 3This makes it better suited for the growth of high-purity semi-insulating silicon carbide single crystals. Simultaneously, since chlorine or chlorine-containing gases need to be introduced into the deposition chamber during the synthesis of high-purity semi-insulating silicon carbide powder using the CVD method, the CVD-synthesized high-purity semi-insulating silicon carbide powder typically contains a small amount of chlorine (Cl). During the hot zone impurity removal process, these chlorine elements can react with the metallic impurities inherent in the graphite crucible to form low-boiling-point metal chlorides, which are then sublimated and removed at high temperatures. This helps to further reduce the impurity content in the hot zone during the hot zone impurity removal process, improve the purity of the raw materials, and thus contribute to improving the quality of the silicon carbide single crystals. It effectively avoids the absorption peaks of metallic impurities, resulting in higher light transmittance of the silicon carbide single crystals. The purpose of spreading a second silicon carbide powder with a finer particle size and a denser packing on top of a first silicon carbide powder with a larger particle size is to use the second silicon carbide powder as a filter layer to filter out carbon particles trapped in the atmosphere generated by the sublimation of the first silicon carbide powder and accumulate them in the second silicon carbide powder layer, thereby reducing carbon particles in the atmosphere and ultimately helping to reduce carbon inclusions in silicon carbide single crystals and improve the quality of silicon carbide single crystals. A porous graphite sheet is placed between the first silicon carbide powder and the second silicon carbide powder to prevent the finer second silicon carbide powder from falling into the gaps between the larger first silicon carbide powder particles. In existing methods for growing high-purity semi-insulating silicon carbide single crystals, the crucibles used are typically ordinary graphite crucibles. However, in this application, the graphite crucible is made of isostatically pressed graphite, resulting in higher thermal conductivity. The gray content of the graphite crucible is less than 5 ppm, effectively preventing metal impurities from contaminating the silicon carbide powder and single crystal. Furthermore, a metal compound coating is applied to the outer surface of the graphite crucible. This coating effectively improves the density of the graphite crucible, preventing contamination from the external graphite felt, thereby improving the growth quality and light transmittance of the silicon carbide single crystal. The metal compound coating is one or more of silicon carbide, aluminum nitride, and tantalum carbide.

[0037] S2. Crystal Growth: First, open the graphite crucible in the purified thermal field device and bond the silicon carbide seed crystal to the inside of the crucible lid. Then, fasten the crucible lid onto the graphite crucible body, completing the assembly between the silicon carbide seed crystal and the purified thermal field device. After the thermal field device is purified, the silicon carbide seed crystal is fixedly bonded to the top inside the graphite crucible. This prevents the silicon carbide seed crystal from sublimating during the purification process, thus helping to maintain the stability of the silicon carbide single crystal growth interface, reducing the internal stress of the silicon carbide single crystal, and improving the growth quality of the silicon carbide single crystal. Finally, place the assembled thermal field device into the induction furnace. The temperature inside the induction furnace is raised to 2000–2300°C, and the atmosphere required for crystal growth is supplied to the furnace for crystal growth. During the heating and crystal growth process, the pressure inside the induction furnace needs to be adjusted to 1.5–15 mbar. The atmosphere required for crystal growth is high-purity argon or a mixture of high-purity argon and high-purity hydrogen, and the purity of both high-purity argon and high-purity hydrogen is not less than 99.9999%. When the atmosphere required for crystal growth supplied to the induction furnace is a mixture of high-purity argon and high-purity hydrogen, the preferred flow rate ratio of high-purity argon to high-purity hydrogen is (10–5):1.

[0038] S3. High-temperature and high-pressure annealing followed by furnace cooling yields high-purity semi-insulating silicon carbide ingots for optical components: After crystal growth is complete, high-temperature and high-pressure annealing is performed first, followed by furnace cooling. After cooling to room temperature, high-purity semi-insulating silicon carbide ingots for optical components are obtained. The high-temperature and high-pressure annealing process involves first adjusting the pressure inside the induction furnace to 320-380 mbar, while simultaneously lowering the temperature inside the induction furnace to 1800-1900℃ to inhibit or terminate crystal growth. Then, the temperature inside the induction furnace is maintained within the range of 1800-1900℃, and the pressure is maintained within the range of 320-380 mbar for several hours; preferably, constant temperature and pressure is maintained for 5-12 hours. High-temperature and high-pressure annealing further eliminates carbon and silicon vacancies in the high-purity semi-insulating silicon carbide ingots for optical components, reduces deep-level defects, and improves light transmittance and resistivity. The furnace cooling process involves reducing the heating power of the induction furnace to 0 kW, allowing the furnace and its internal thermal field devices to cool naturally to room temperature.

[0039] The optical components obtained above are processed using high-purity semi-insulating silicon carbide ingots through orientation, grinding, rounding, and cutting to prepare wafers suitable for optical components. Existing high-purity silicon carbide single crystals are mostly used in military radar and radio frequency devices, with limited applications in optical components. However, this application improves the growth process of silicon carbide single crystals, significantly enhancing the light transmittance of the wafers, enabling their application in optical components such as AR glasses, optoelectronic displays, and optical waveguides. Example 1

[0040] S1. Assembly and Hot Zone Purification: First, fill the graphite crucible body with 1.5mm particle size silicon carbide powder and spread it evenly at the bottom of the graphite crucible body. Then, place the porous graphite sheet on top of the first silicon carbide powder. Next, spread the 0.05mm particle size second silicon carbide powder evenly on top of the porous graphite sheet. Then, place the atmosphere filter assembly on top of the second silicon carbide powder, with a 3mm gap between them. After that, close the crucible lid on the graphite crucible and cover the periphery of the graphite crucible with graphite felt to complete the assembly of the hot zone device. Place the assembled hot zone device in the induction furnace. Then, first, at 25°C, for 30 minutes... The pressure inside the induction furnace is increased to 500 mbar and held for 60 minutes. Then, the pressure is reduced to its baseline within 60 minutes to complete the room temperature furnace cleaning process. Next, the temperature inside the induction furnace is increased to 1300℃, and under constant temperature conditions at 1300℃, the pressure is increased to 500 mbar and held for 60 minutes. Then, the pressure is reduced to its baseline within 60 minutes to complete the low temperature furnace cleaning process. Finally, the temperature inside the induction furnace is increased to 2100℃, while the pressure is adjusted to 1.5 mbar. Under these conditions, the temperature and pressure are maintained for 50 minutes to remove impurities from the thermal field device. Both the first and second silicon carbide powders are high-purity semi-insulating silicon carbide powders synthesized by CVD, with a purity ≥99.9999% and an N content ≤1×10⁻⁶. 15 atoms / cm 3 Al content ≤ 1×10 15 atoms / cm 3 .

[0041] S2. Crystal Growth: First, open the graphite crucible in the purified hot zone device and attach the silicon carbide seed crystal to the inside of the crucible lid. Then, fasten the crucible lid onto the graphite crucible body to complete the assembly between the silicon carbide seed crystal and the purified hot zone device. After that, place the assembled hot zone device into the induction furnace, adjust the pressure inside the induction furnace to 3 mbar, and supply a mixture of high-purity argon and pure hydrogen with a flow ratio of 9:1 into the induction furnace. Raise the temperature inside the induction furnace to 2000-2300℃ to carry out crystal growth. The purity of both high-purity argon and high-purity hydrogen is not less than 99.9999%.

[0042] S3. High-temperature and high-pressure annealing and furnace cooling: After the crystal growth process is completed, the pressure inside the induction furnace is increased to 350 mbar and the temperature is decreased to 1850℃, and maintained at this temperature and pressure for 10 hours. Then, the heating power of the induction furnace is reduced to 0 kW, allowing the furnace and its internal thermal field device to cool naturally to room temperature, yielding a high-purity semi-insulating silicon carbide ingot, A1, for optical components. The obtained high-purity semi-insulating silicon carbide ingot A1 is then processed through orientation, grinding, rounding, and cutting to produce high-purity semi-insulating silicon carbide wafers with thicknesses of 5 mm and 10 mm for optical components. Example 2

[0043] The difference between this embodiment and Embodiment 1 is as follows: In step S2, during crystal growth, the gas supplied to the induction furnace is high-purity argon, and the purity of the high-purity argon is not less than 99.99995%; In step S3, the high-temperature and high-pressure annealing process involves raising the pressure inside the induction furnace to 150 mbar and lowering the temperature to 1900°C, maintaining this temperature and pressure condition for 10 hours; Finally, high-purity semi-insulating silicon carbide ingot A2 for optical components is obtained by crystal growth. The obtained high-purity semi-insulating silicon carbide ingot A2 for optical components is processed into high-purity semi-insulating silicon carbide wafers with thicknesses of 5 mm and 10 mm through processes such as orientation, grinding, rounding, and cutting. Example 3

[0044] The difference between this embodiment and Embodiment 1 is that: in step S1, the silicon carbide powder used is high-purity semi-insulating silicon carbide powder synthesized by a high-temperature self-propagating method; and the particle size of the silicon carbide powder is 1.5mm. The assembly process of the hot field device is as follows: first, the silicon carbide powder with a particle size of 1.5mm is filled into the graphite crucible body and spread flat; then, the atmosphere filter component is placed on top of the silicon carbide powder, with a distance of 3mm between it and the silicon carbide powder; then, the crucible lid is fastened onto the graphite crucible, and the graphite soft felt is wrapped around the periphery of the graphite crucible to complete the assembly of the hot field device. Finally, high-purity semi-insulating silicon carbide ingot A3 for optical components is obtained by crystal growth. The obtained high-purity semi-insulating silicon carbide ingot A3 for optical components is processed into high-purity semi-insulating silicon carbide wafers with thicknesses of 5mm and 10mm through processes such as orientation, flat grinding, rounding, and cutting. Example 4

[0045] The difference between this embodiment and Embodiment 1 is as follows: In step S1, the silicon carbide powder used is high-purity semi-insulating silicon carbide powder synthesized by high-temperature self-propagating method; and the particle size of the silicon carbide powder is 1mm; the assembly process of the hot field device is as follows: first, fill the graphite crucible body with silicon carbide powder with a particle size of 1mm and spread it flat, then place the atmosphere filter component on top of the silicon carbide powder, with a distance of 3mm between it and the silicon carbide powder, then, fasten the crucible lid on the graphite crucible, and cover the periphery of the graphite crucible with graphite soft felt to complete the assembly of the hot field device; in step S3, after the crystal growth is completed, the pressure in the induction furnace is increased to 350mbar to suppress the crystal growth, and at the same time, the heating power of the induction furnace is reduced to 0kw, and the furnace is naturally cooled to room temperature; finally, the crystal is grown to obtain a high-purity semi-insulating silicon carbide ingot for optical components, A4. The high-purity semi-insulating silicon carbide ingot A4 for optical components is processed into high-purity semi-insulating silicon carbide wafers with thicknesses of 5mm and 10mm through processes such as orientation, flat grinding, rounding, and cutting.

[0046] The resistivity and transmittance of high-purity semi-insulating silicon carbide wafers for optical elements obtained in Examples 1-4 were tested respectively. The test results are shown in Table 1.

[0047] Table 1. Test results of the performance of high-purity semi-insulating silicon carbide wafers for optical components obtained in Examples 1-4

[0048]

[0049] As shown in Table 1, the resistivity of the high-purity semi-insulating silicon carbide wafers for optical components with thicknesses of 5 mm and 10 mm obtained in Examples 1 and 2 is significantly higher than that of the high-purity semi-insulating silicon carbide wafers for optical components with thicknesses of 5 mm and 10 mm obtained in Examples 3 and 4. Furthermore, the transmittance of the 550-1800 nm wavelength band and the 440 nm wavelength band is also significantly higher than that of the high-purity semi-insulating silicon carbide wafers for optical components with thicknesses of 5 mm and 10 mm obtained in Examples 3 and 4. This indicates that the use of CVD to synthesize high-purity semi-insulating silicon carbide powder for crystal growth, and the use of silicon carbide powder with smaller particle size as a filter layer to filter the atmosphere generated by sublimation, can significantly improve the growth quality of silicon carbide single crystals and increase their resistivity and transmittance. Comparing the high-purity semi-insulating silicon carbide wafers with thicknesses of 5mm and 10mm processed in Example 1 with those processed in Example 2, it can be seen that the resistivity and light transmittance of the high-purity semi-insulating silicon carbide wafers with thicknesses of 5mm and 10mm processed in Example 1 are superior. This indicates that high-temperature and high-pressure annealing can eliminate carbon and silicon vacancies in the high-purity semi-insulating silicon carbide ingots for optical components, significantly reducing the number of deep-level defects inside the ingot. In particular, it has a significant suppressive effect on light absorption phenomena induced by photons in the ultraviolet band, thereby improving the crystal quality and light transmittance of the ingot.

[0050] The above embodiments are merely illustrative of the technical concept and features of the present invention, intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and should not be construed as limiting the scope of protection of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects. The scope of the present invention is defined by the appended claims rather than the foregoing description, and thus all changes falling within the meaning and scope of the equivalents of the claims are intended to be included within the present invention.

Claims

1. A process for growing a high-purity semi-insulating silicon carbide single crystal for optical elements, characterized by, It comprises the following steps: S1. Assemble silicon carbide powder, graphite crucible, graphite felt, accessories and / or raw materials to form a hot zone device, and place it in an induction furnace. Then, perform room temperature furnace cleaning, low temperature furnace cleaning, and hot zone impurity removal treatment sequentially. The silicon carbide powder includes a first silicon carbide powder with a particle size of 1-2 mm synthesized by CVD and a second silicon carbide powder with a particle size of 0.01-0.1 mm. The second silicon carbide powder is assembled on top of the first silicon carbide powder. The purity of the silicon carbide powder is not less than 99.9999%. The silicon carbide powder contains Cl element, and the N content in the silicon carbide powder does not exceed 1×10⁻⁶. 15 atoms / cm 3 Al content not exceeding 1×10 15 atoms / cm 3 ; S2, the silicon carbide seed crystal is assembled with the hot field device after impurity removal, then the temperature in the induction furnace is raised, and high-purity argon or a mixed gas of high-purity argon and high-purity hydrogen is delivered into the induction furnace for crystal growth; The hot field impurity removal treatment is performed at a temperature of 2000-2250℃ and a pressure of 1-3mbar for 1-10h; S3, after the crystal growth is completed, high-temperature and high-pressure annealing treatment is performed first, and then furnace cooling treatment is performed to obtain a high-purity semi-insulating silicon carbide crystal ingot for optical elements; The high-temperature and high-pressure annealing treatment is to adjust the pressure in the induction furnace to 320-380mbar, reduce the temperature to 1800-1900℃, and then keep the temperature and pressure constant for several hours.

2. The process for growing a high-purity semi-insulating silicon carbide single crystal for optical elements according to claim 1, characterized by: The auxiliary component comprises a porous graphite sheet and an atmosphere filtering assembly.

3. The process for growing a high-purity semi-insulating silicon carbide single crystal for optical elements according to claim 2, wherein: In step S1, the room temperature furnace washing treatment is to raise the pressure in the induction furnace to 450-550mbar within 25-35min under the condition of 15-35℃, keep the pressure for 40-80min, and then reduce the pressure in the induction furnace to the background pressure within 50-70min; The low-temperature furnace washing treatment is to raise the pressure in the induction furnace to 450-550mbar within 25-35min under the condition of 1200-1500℃, keep the pressure for 40-80min, and then reduce the pressure in the induction furnace to the background pressure within 50-70min; The background pressure is not more than 1 x 10 -4 Pa.

4. The process for growing a high-purity semi-insulating silicon carbide single crystal for optical elements according to claim 2, wherein: In step S1, the assembly operation comprises the following steps: a, first fill the first silicon carbide powder in the bottom of the graphite crucible, then place the porous graphite sheet above the first silicon carbide powder, and then lay the second silicon carbide powder on the porous graphite sheet; b, set the atmosphere filtering assembly above the second silicon carbide powder, then assemble all components of the graphite crucible together, and wrap the graphite soft felt around the circumferential side of the graphite crucible.

5. The process for growing a high-purity semi-insulating silicon carbide single crystal for optical elements according to claim 2, wherein: The purity of the high-purity argon and the high-purity hydrogen is not less than 99.9999%; in the mixed gas, the ratio of high-purity argon to high-purity hydrogen is (10-5):

1.

6. The process for growing a high-purity semi-insulating silicon carbide single crystal for optical elements according to claim 2, wherein: The graphite crucible is made of isostatic pressing graphite material; the ash content of the graphite crucible is less than 5ppm.

7. The process for growing a high-purity semi-insulating silicon carbide single crystal for optical elements according to claim 6, wherein: A metal compound coating is coated on the outer side of the graphite crucible; the metal compound coating is any one or more of silicon carbide, aluminum nitride, and tantalum carbide.

8. The process for growing a high-purity semi-insulating silicon carbide single crystal for optical elements according to claim 2, wherein: In step S3, the furnace cooling treatment is to reduce the heating power of the induction furnace to 0kw, and then naturally cool the hot field device to room temperature.

9. A high-purity semi-insulating silicon carbide single crystal for optical elements, characterized by, The high-purity semi-insulating silicon carbide crystal ingot for optical elements is grown by the growth process in any one of claims 1-8.

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