High-purity semi-insulating silicon carbide single crystal for optical element and growth process of high-purity semi-insulating silicon carbide single crystal

Abstract

The invention relates to the technical field of silicon carbide single crystal growth, in particular to a high-purity semi-insulating silicon carbide single crystal for an optical element and a growth process thereof.The growth process includes the steps that S1, silicon carbide powder, a graphite crucible and the like are assembled to form a thermal field device, the thermal field device is placed in an induction furnace, room-temperature furnace washing treatment and low-temperature furnace washing treatment are sequentially carried out, and the silicon carbide powder is obtained; carrying out thermal field impurity removal treatment; s2, assembling the silicon carbide seed crystal and the impurity-removed thermal field device, raising the temperature in the induction furnace, conveying high-purity argon or mixed gas of high-purity argon and high-purity hydrogen into the induction furnace, and performing crystal growth; s3, after crystal growth is finished, high-temperature and high-pressure annealing treatment is carried out firstly, then furnace cooling treatment is carried out, and the high-purity semi-insulating silicon carbide crystal ingot for the optical element is obtained. The silicon carbide crystal ingot with excellent light transmission performance and high resistivity is obtained by selecting specific raw materials, reasonably designing an assembly mode and combining processes of thermal field impurity removal, high-temperature and high-pressure annealing and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon carbide single crystal growth, and particularly relates to a high-purity semi-insulating silicon carbide single crystal for optical elements and a growth process thereof. Background Art

[0002] Compared with the traditional first-generation silicon-based semiconductor materials, silicon carbide single crystal materials have 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 the field of AR glasses; compared with the traditional waveguide materials used in AR glasses, such as glass, resin, etc., silicon carbide single crystal materials have a higher refractive index; moreover, full-color display can be achieved without using double-layer waveguide materials with complex processes and high costs, greatly reducing the weight and thickness of the lenses. For example, the overall weight of Meta Orion can be controlled within 80-100 grams. In addition, using silicon carbide single crystal as the optical waveguide material can obtain a larger field of view (FOV), and thus can provide a more immersive user experience.

[0003] Currently, the silicon carbide single crystal materials applied in AR glasses are all high-purity semi-insulating silicon carbide, and their growth methods are usually physical vapor deposition (PVT); compared with high-purity semi-insulating silicon carbide applied in scenarios such as gallium nitride and silicon carbide microwave devices, when using high-purity semi-insulating silicon carbide as the wafer material for optical elements, higher requirements are put forward for the optical properties of high-purity semi-insulating silicon carbide materials, such as the transmittance of high-purity semi-insulating silicon carbide materials in specific wavelength bands such as red light, blue light, green light, etc., and the refractive index of high-purity semi-insulating silicon carbide materials. Therefore, how to improve the light transmittance and refractive index of high-purity semi-insulating silicon carbide crystals has become an urgent problem to be solved.

[0004] The patent number is CN201821713656.8, which discloses a preparation device for high-purity silicon carbide. By ensuring that the crucible is isolated from the outside air during the growth process, nitrogen is prevented from entering the crucible, which may cause the resistivity of the crystal to decrease, and a high-purity semi-insulating silicon carbide crystal with a crystal resistivity greater than 10 5 Ω·cm is obtained; however, the resistivity and light transmittance of this semi-insulating silicon carbide crystal cannot meet the requirements of optical elements.

[0005] The patent number is CN201711189841.1, which discloses a growth method for growing large-sized semi-insulating silicon carbide single crystals by the PVT method. Although this growth method specifically includes steps such as SiC powder preparation, furnace loading and evacuation, impurity gas removal, rapid heating and pressurization, pressure reduction and constant temperature, crystal growth, the finishing stage, and annealing, etc.; however, the grown silicon carbide single crystals are undoped high-purity semi-insulating 4H-SiC, and are used to solve the problem of the back-gate effect when doped-vanadium semi-insulating 4H-SiC single crystals are applied to high-power GaN / SiC HEMT devices, and their performance in terms of crystal quality, light transmittance, etc. cannot meet the requirements of optical components.

[0006] The present invention provides a high-purity semi-insulating silicon carbide single crystal for optical components and its growth process to solve the problems such as low resistivity and poor light transmission performance of silicon carbide single crystals obtained by the existing physical vapor deposition method in the prior art. Summary of the Invention

[0007] The object of the present invention is to provide a high-purity semi-insulating silicon carbide single crystal for optical components and its growth process to solve the problems such as low resistivity and poor light transmission performance of silicon carbide single crystals obtained by the existing physical vapor deposition method in the prior art.

[0008] The technical solution of the present invention is: A growth process for a high-purity semi-insulating silicon carbide single crystal for optical components, comprising the following steps: S1. Assemble the silicon carbide powder, graphite crucible, graphite soft felt, accessories, and / or raw and auxiliary materials to form a hot field device, and place it in an induction furnace. Then, first perform a room-temperature furnace cleaning treatment and a low-temperature furnace cleaning treatment in sequence, and then perform a hot field impurity removal treatment; the silicon carbide powder includes a first silicon carbide powder with a particle size of 1 - 2 mm and a second silicon carbide powder with a particle size of 0.01 - 0.1 mm, both synthesized by the CVD method; the second silicon carbide powder is assembled above the first silicon carbide powder. S2. Assemble the silicon carbide seed crystal with the impurity-removed hot field device. Then, raise the temperature in the induction furnace and introduce high-purity argon gas or a mixed gas of high-purity argon gas and high-purity hydrogen gas into the induction furnace for crystal growth. S3. After the crystal growth is completed, first perform a high-temperature and high-pressure annealing treatment, and then perform a furnace cooling treatment to obtain a high-purity semi-insulating silicon carbide ingot for optical components. The high-temperature and high-pressure annealing treatment is to adjust the pressure in the induction furnace to 320 - 380 mbar, lower the temperature to 1800 - 1900 °C, and then maintain a constant temperature and pressure for several hours.

[0009] 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 15 atoms / cm 3 , the Al content does not exceed 1×10 15 atoms / cm 3 ; The auxiliary components include a porous graphite sheet and an atmosphere filtration component.

[0010] Preferably, in step S1, the room temperature furnace washing treatment is to raise the pressure inside the induction furnace to 450-550 mbar within 25-35 min under the condition of 15-35 °C, keep the pressure for 40-80 min, and then reduce the pressure inside the induction furnace to the background pressure within 50-70 min; The low-temperature furnace washing treatment is to raise the pressure inside the induction furnace to 450-550 mbar within 25-35 min under the condition of 1200-1500 °C, keep the pressure for 40-80 min, and then reduce the pressure inside the induction furnace to the background pressure within 50-70 min; The background pressure does not exceed 1×10 -4 pa; The heat field impurity removal treatment is carried out at a temperature of 2000-2250 °C and a pressure of 1-3 mbar for 1-10 h.

[0011] Preferably, in step S1, the assembly operation includes the following steps: a. First, fill the bottom of the graphite crucible with the first silicon carbide powder, then place the porous graphite sheet above the first silicon carbide powder, and then spread the second silicon carbide powder flat above the porous graphite sheet; b. Set the atmosphere filtration component above the second silicon carbide powder, then assemble the components of the graphite crucible together, and wrap the graphite soft felt around the circumference of the graphite crucible.

[0012] Preferably, 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.

[0013] Preferably, the graphite crucible is made of isostatic graphite material; the ash content of the graphite crucible is less than 5 ppm.

[0014] Preferably, the outer side 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.

[0015] Preferably, in step S3, the furnace cooling treatment is to reduce the heating power of the induction furnace to 0 kw and then let the thermal field device cool naturally to room temperature.

[0016] The present invention also provides a high-purity semi-insulating silicon carbide single crystal for optical elements, which is grown by the above growth process.

[0017] Compared with the prior art, the advantages of the present invention are: (1) A high-purity semi-insulating silicon carbide single crystal for optical elements and its growth process provided by the present invention. This growth process is to make the raw materials and process steps cooperate with each other by selecting specific raw materials and accessories and / or raw and auxiliary materials, reasonably designing the assembly method, and combining processes such as thermal field impurity removal and high-temperature and high-pressure annealing, so as to grow a silicon carbide ingot with excellent light transmission performance 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 a small amount of Cl element in the high-purity semi-insulating silicon carbide powder, the impurity content in the thermal field can be further reduced during the thermal field impurity removal process, especially the content of metal impurities, thereby effectively improving the quality of the silicon carbide ingot, avoiding the appearance of metal impurity absorption peaks, and improving the light transmission performance of the silicon carbide ingot. At the same time, through high-temperature and high-pressure annealing treatment, carbon vacancies and silicon vacancies in the silicon carbide ingot are further eliminated, the number of deep-level defects inside the ingot is significantly reduced, and the light absorption phenomenon caused by ultraviolet band photons is avoided, thereby greatly improving the light transmission performance of the silicon carbide ingot and the resistivity of the silicon carbide ingot. It solves the problems of low resistivity and poor light transmission performance of silicon carbide single crystals grown by the existing physical vapor deposition method in the prior art.

[0018] (2) A high-purity semi-insulating silicon carbide single crystal for optical elements and its growth process provided by the present invention. In this growth process, the second silicon carbide powder with smaller particle size and closer packing is laid flat above the first silicon carbide powder with 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 the carbon particles mixed in the atmosphere and accumulate them in the second silicon carbide powder layer, reducing the carbon particle content in the atmosphere. At the same time, an atmosphere filtering component is arranged above the second silicon carbide powder to filter the sublimated atmosphere 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. At the same time, this growth process selects a graphite crucible with a metal compound coating on the outer surface. The metal compound coating can increase the compactness of the graphite part, thereby blocking the pollution 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be further described below in conjunction with the drawings and embodiments: Figure 1 Process flow chart for growing high-purity semi-insulating silicon carbide single crystal for the optical element of the present invention; Figure 2 Structural schematic diagram of the thermal field device of the present invention; Wherein: 1, graphite crucible body; 2, crucible cover; 3, silicon carbide seed crystal; 4, first silicon carbide powder; 5, second silicon carbide powder; 6, porous graphite sheet; 7, atmosphere filtering component. Specific embodiments

[0020] The following combines specific embodiments to further elaborate on the content of the present invention: A growth process for high-purity semi-insulating silicon carbide single crystal for an optical element, as Figure 1 shown, includes the following steps: S1. Assembly and thermal field impurity removal: The thermal field device includes graphite soft felt and a graphite crucible as heat insulation materials. The graphite crucible includes a graphite crucible body 1 and a crucible cover 2. Silicon carbide powder and a silicon carbide seed crystal 3 are arranged in the graphite crucible; moreover, accessories required for crystal growth, such as an atmosphere filtering device, etc., can also be arranged in the graphite crucible; raw and auxiliary materials required for crystal growth can also be arranged in the graphite crucible; wherein, the silicon carbide powder is selected to be high-purity semi-insulating silicon carbide powder synthesized by the CVD method, and high-purity semi-insulating silicon carbide powder with a particle size of 1 - 2 mm is selected as the first silicon carbide powder 4, and high-purity semi-insulating silicon carbide powder with a particle size of 0.01 - 0.1 mm is selected as the second silicon carbide powder 5; accessories required for crystal growth include a porous graphite sheet 6, an atmosphere filtering component 7, etc. As Figure 2As shown, the silicon carbide powder, graphite crucible, graphite soft felt, accessories and / or raw and auxiliary materials are assembled to form a hot field device, which is placed in an induction furnace; then, a room temperature furnace washing treatment and a low temperature furnace washing treatment are carried out in sequence, and then a hot field impurity removal treatment is carried out. The assembly operation specifically includes the following steps: a. First, fill the first silicon carbide powder in the graphite crucible body and spread it on the bottom of the graphite crucible body, then place the porous graphite sheet above the first silicon carbide powder, and then spread the second silicon carbide powder above the porous graphite sheet; b. Set the atmosphere filtering component above the second silicon carbide powder, and keep a distance of 2-10 mm from the second silicon carbide powder. Then, buckle the crucible cover on the graphite crucible and wrap the graphite soft felt around the circumference of the graphite crucible to form a hot field device. The room temperature furnace washing treatment is carried out at 15-35 °C. The pressure inside the induction furnace is increased to 450-550 mbar within 25-35 minutes and then the pressure is kept constant; after keeping the pressure constant for 40-80 minutes, the pressure inside the induction furnace is reduced to the background pressure within 50-70 minutes; similarly, the low temperature furnace washing treatment is carried out at 1200-1500 °C. The pressure inside the induction furnace is increased to 450-550 mbar within 25-35 minutes and then the pressure is kept constant. After keeping the pressure constant for 40-80 minutes, the pressure inside the induction furnace is reduced to the background pressure within 50-70 minutes; where the background pressure refers to the remaining gas pressure inside the induction furnace after the induction furnace is evacuated; in this application, the background pressure is not greater than 1×10 -4 pa. The hot field impurity removal treatment is carried out at a temperature of 2000-2250 °C and a pressure of 1-3 mbar for 1-10 h to remove impurities from the graphite soft felt, graphite crucible, silicon carbide powder, etc.

[0021] In the existing methods for growing high-purity semi-insulating silicon carbide single crystals disclosed in the prior art, usually, the silicon carbide powder synthesized by the self-propagating high-temperature synthesis method is used for single crystal growth; and the silicon carbide powder synthesized by the self-propagating high-temperature synthesis method is usually doped with carbon elements, boron elements, metal elements, etc. These elements are difficult to remove during the impurity removal process, and finally, defects such as microtubes and dislocations will appear in the grown silicon carbide single crystal, affecting the quality and light transmittance of the silicon carbide single crystal. In this application, the high-purity semi-insulating silicon carbide powder synthesized by the CVD method has a purity of 99.9999% or more; and the N content in the high-purity semi-insulating silicon carbide powder does not exceed 1×10 15 atoms / cm 3 、The Al content can also not exceed 1×10 15 atoms / cm 3, making it better suitable for the growth of high-purity semi-insulating silicon carbide single crystals; at the same time, since chlorine gas or chlorine-containing gas needs to be introduced into the deposition chamber during the process of synthesizing high-purity semi-insulating silicon carbide powder by CVD method, the high-purity semi-insulating silicon carbide powder synthesized by CVD method usually contains a small amount of Cl element; in the process of hot field impurity removal, these Cl elements can react with the metal impurities on the graphite crucible to form metal chlorides with low boiling points, and sublimate and remove under high temperature conditions; it helps to further reduce the impurity content in the hot field during the hot field impurity removal process, improve the purity of the raw materials, and then help to improve the quality of the silicon carbide single crystal, can effectively avoid the absorption peak of the metal impurities, and make the silicon carbide single crystal more transparent. The second silicon carbide powder with finer particle size and more dense stacking is spread flat on top of the first silicon carbide powder with larger particle size. The purpose is to use the second silicon carbide powder as a filter layer to filter the carbon particles contained 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 the carbon particles in the atmosphere, and ultimately helping to reduce the carbon inclusions in the silicon carbide single crystal and improve the quality of the silicon carbide single crystal; a porous graphite sheet is set between the first silicon carbide powder and the second silicon carbide powder to prevent the second silicon carbide powder with finer particle size from falling into the gap of the first silicon carbide powder with larger particle size. In the growth method of high-purity semi-insulating silicon carbide single crystal disclosed in the prior art, the crucible used is usually an ordinary graphite crucible, while in the present application, the graphite crucible is made of isostatically pressed graphite material, which makes the thermal conductivity of the graphite crucible higher; the grayscale of the graphite crucible is less than 5ppm, which can effectively avoid the contamination of silicon carbide powder and silicon carbide single crystal by metal impurities; and a layer of metal compound coating is coated on the outer surface of the graphite crucible, which can effectively improve the density of the graphite crucible and block the pollution caused by the graphite soft felt outside the graphite crucible, thereby improving the growth quality of the silicon carbide single crystal and improving its light transmittance; the metal compound coating is one or more of silicon carbide, aluminum nitride, tantalum carbide, etc.

[0022] S2. Crystal growth: First, open the graphite crucible in the thermal field device after impurity removal, bond the silicon carbide seed crystal to the inner side 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 thermal field device after impurity removal; after performing thermal field impurity removal on the thermal field device, fix and bond the silicon carbide seed crystal to the top inside the graphite crucible, which can prevent the sublimation of the silicon carbide seed crystal during the thermal field impurity removal process, thereby helping to maintain the stability of the silicon carbide single crystal growth interface, reducing the stress inside the silicon carbide single crystal, and improving the growth quality of the silicon carbide single crystal; then, place the assembled thermal field device into the induction furnace, raise the temperature inside the induction furnace to 2000 - 2300 °C, and supply the atmosphere required for crystal growth into the induction furnace to carry out crystal growth; during the heating-up and crystal growth processes, the pressure inside the induction furnace needs to be adjusted to 1.5 - 15 mbar; among them, the atmosphere required for crystal growth is high-purity argon or a mixed gas of high-purity argon and high-purity hydrogen, and the purities of high-purity argon and high-purity hydrogen are both not less than 99.9999%; when the atmosphere required for crystal growth supplied into the induction furnace is a mixed gas 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.

[0023] S3. High-temperature and high-pressure annealing and furnace cooling to obtain a high-purity semi-insulating silicon carbide ingot for optical components: After the crystal growth is completed, first perform high-temperature and high-pressure annealing treatment, and then perform furnace cooling treatment. After cooling to room temperature, a high-purity semi-insulating silicon carbide ingot for optical components is obtained; among them, the high-temperature and high-pressure annealing treatment is to first adjust the pressure inside the induction furnace to 320 - 380 mbar, and at the same time lower the temperature inside the induction furnace to 1800 - 1900 °C to inhibit or end the crystal growth; then, maintain the temperature inside the induction furnace within the range of 1800 - 1900 °C and the pressure within the range of 320 - 380 mbar and hold for several hours; preferably, keep the temperature and pressure constant for 5 - 12 h; annealing in a high-temperature and high-pressure manner can further eliminate carbon vacancies and silicon vacancies in the high-purity semi-insulating silicon carbide ingot for optical components, reduce the deep-level defects inside it, and improve the light transmittance and resistivity. The furnace cooling treatment is to reduce the heating power of the induction furnace to 0 kw and then let the induction furnace and the thermal field device inside it cool naturally to room temperature.

[0024] After processing the obtained high-purity semi-insulating silicon carbide ingot for optical components through processing procedures such as orientation, surface grinding, rounding, and cutting, wafers suitable for optical components are prepared. In the prior art, the prepared high-purity silicon carbide single crystals are mostly used in scenarios such as military radars and radio frequency devices, and there are few applications for optical components; while in this application, by improving the growth process of the silicon carbide single crystal, the light transmittance of the wafer is significantly improved, enabling it to be applied in optical components such as AR glasses, optoelectronic displays, and optical waveguides. Example 1

[0025] S1. Assembly and impurity removal in the thermal field: First, fill the inside of the graphite crucible body with the first silicon carbide powder with a particle size of 1.5 mm and spread it flat on the bottom of the graphite crucible body. Then, place the porous graphite sheet above the first silicon carbide powder. Immediately afterwards, spread the second silicon carbide powder with a particle size of 0.05 mm flat above the porous graphite sheet. Then, place the atmosphere filtration component above the second silicon carbide powder, with a distance of 3 mm between them. After that, buckle the crucible lid on the graphite crucible and wrap the graphite soft felt around the circumference of the graphite crucible to complete the assembly of the thermal field device. Then, place the assembled thermal field device in the induction furnace. After that, first, at 25 °C, raise the pressure in the induction furnace to 500 mbar within 30 min and hold the pressure. After holding the pressure for 60 min, lower the chamber pressure to the background within 60 min to complete the furnace washing treatment at room temperature. Immediately afterwards, raise the temperature in the induction furnace to 1300 °C, and under the constant temperature condition of 1300 °C, raise the pressure in the induction furnace to 500 mbar within 30 min and hold the pressure. After holding the pressure for 60 min, lower the chamber pressure to the background within 60 min to complete the furnace washing treatment at low temperature. Finally, raise the temperature in the induction furnace to 2100 °C, and at the same time adjust the pressure in the induction furnace to 1.5 mbar, and under this condition, keep the temperature and pressure for 50 min to remove impurities from the thermal field device. Among them, both the first silicon carbide powder and the second silicon carbide powder are synthesized into high-purity semi-insulating silicon carbide powder by the CVD method, and the purity of the powder is ≥99.9999%, the N content is ≤1×10 15 atoms / cm 3 and the Al content is ≤1×10 15 atoms / cm 3 .

[0026] S2. Crystal growth: First, open the graphite crucible in the thermal field device after impurity removal, bond the silicon carbide seed crystal to the inside of the crucible lid, and then buckle the crucible lid on the graphite crucible body to complete the assembly between the silicon carbide seed crystal and the thermal field device after impurity removal. After that, place the assembled thermal field device in the induction furnace, adjust the pressure inside the induction furnace to 3 mbar, convey a mixed gas of high-purity argon and pure hydrogen with a flow ratio of 9:1 into the induction furnace, and raise the temperature in the induction furnace to 2000 - 2300 °C for crystal growth. Among them, the purity of both high-purity argon and high-purity hydrogen is not less than 99.9999%.

[0027] S3. High-temperature and high-pressure annealing, furnace cooling: After the crystal growth process is completed, increase the pressure in the induction furnace to 350 mbar and lower the temperature to 1850 °C, and maintain for 10 h under these temperature and pressure conditions; then, reduce the heating power of the induction furnace to 0 kW, and let the induction furnace and the internal thermal field device cool naturally to room temperature to obtain a high-purity semi-insulating silicon carbide ingot, A1, for optical elements. Process the obtained high-purity semi-insulating silicon carbide ingot A1 for optical elements through processing procedures such as orientation, surface grinding, rounding, and cutting to obtain high-purity semi-insulating silicon carbide wafers for optical elements with a thickness of 5 mm and 10 mm. Example 2

[0028] The difference between this example and Example 1 is as follows: In step S2, during the crystal growth process, the gas transported into 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 treatment is to increase the pressure in the induction furnace to 150 mbar and lower the temperature to 1900 °C, and maintain for 10 h under these temperature and pressure conditions; finally, a high-purity semi-insulating silicon carbide ingot, A2, for optical elements is obtained by crystal growth. Process the obtained high-purity semi-insulating silicon carbide ingot A2 for optical elements through processing procedures such as orientation, surface grinding, rounding, and cutting to obtain high-purity semi-insulating silicon carbide wafers for optical elements with a thickness of 5 mm and 10 mm. Example 3

[0029] The difference between this example and Example 1 is as follows: In step S1, the silicon carbide powder used is synthesized into high-purity semi-insulating silicon carbide powder by the high-temperature self-propagating method; and the particle size of the silicon carbide powder is 1.5 mm; the assembly process of the thermal field device is as follows: First, fill the inside of the graphite crucible body with silicon carbide powder with a particle size of 1.5 mm and spread it flat, then set the atmosphere filtration component above the silicon carbide powder with a distance of 3 mm between them, and then, buckle the crucible lid on the graphite crucible and wrap the graphite soft felt around the circumference of the graphite crucible to complete the assembly of the thermal field device. Finally, a high-purity semi-insulating silicon carbide ingot, A3, for optical elements is obtained by crystal growth. Process the obtained high-purity semi-insulating silicon carbide ingot A3 for optical elements through processing procedures such as orientation, surface grinding, rounding, and cutting to obtain high-purity semi-insulating silicon carbide wafers for optical elements with a thickness of 5 mm and 10 mm. Example 4

[0030] The differences between this embodiment and Embodiment 1 are as follows: In step S1, the silicon carbide powder used is high-purity semi-insulating silicon carbide powder synthesized by the high-temperature self-propagating method; and the particle size of the silicon carbide powder is 1 mm. The assembly process of the thermal field device is as follows: First, fill the inside of the graphite crucible with silicon carbide powder with a particle size of 1 mm and spread it flat. Then, place the gas filtration component above the silicon carbide powder with a distance of 3 mm between them. After that, cover the graphite crucible with the crucible lid and wrap the graphite soft felt around the circumference of the graphite crucible to complete the assembly of the thermal field device. In step S3, after the crystal growth is completed, increase the pressure in the induction furnace to 350 mbar to inhibit the crystal growth. At the same time, reduce the heating power of the induction furnace to 0 kW and cool it naturally to room temperature with the furnace. Finally, grow a high-purity semi-insulating silicon carbide ingot A4 for optical components. Process the obtained high-purity semi-insulating silicon carbide ingot A4 for optical components through processing procedures such as orientation, surface grinding, rounding, and cutting into high-purity semi-insulating silicon carbide wafers for optical components with thicknesses of 5 mm and 10 mm.

[0031] Detect the resistivity, light transmittance in bands such as 550 - 1800 nm and 440 nm, etc. of the high-purity semi-insulating silicon carbide wafers for optical components obtained in Embodiments 1 - 4 respectively. The detection results are shown in Table 1.

[0032] Table 1. Detection results of the properties of high-purity semi-insulating silicon carbide wafers for optical components obtained in Embodiments 1 - 4

[0033] As can be seen from Table 1, the resistivity of the high-purity semi-insulating silicon carbide wafers with thicknesses of 5 mm and 10 mm processed in Example 1 and Example 2 for optical elements is significantly higher than that of the high-purity semi-insulating silicon carbide wafers with thicknesses of 5 mm and 10 mm processed in Example 3 and Example 4 for optical elements; moreover, the light transmittance of the high-purity semi-insulating silicon carbide wafers with thicknesses of 5 mm and 10 mm processed in Example 1 and Example 2 for optical elements in 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 with thicknesses of 5 mm and 10 mm processed in Example 3 and Example 4 for optical elements; further indicating that the silicon carbide powder used for crystal growth is selected to synthesize high-purity semi-insulating silicon carbide powder by CVD method, and the silicon carbide powder with smaller particle size is used as the filter layer to filter the atmosphere generated by sublimation; can significantly improve the growth quality of silicon carbide single crystal, and improve its resistivity and light transmittance. Comparing the high-purity semi-insulating silicon carbide wafers with thicknesses of 5 mm and 10 mm processed in Example 1 for optical elements with the high-purity semi-insulating silicon carbide wafers with thicknesses of 5 mm and 10 mm processed in Example 2 for optical elements, it can be seen that the resistivity and light transmittance performance of the high-purity semi-insulating silicon carbide wafers with thicknesses of 5 mm and 10 mm processed in Example 1 for optical elements are more excellent, indicating that through high-temperature and high-pressure annealing treatment, carbon vacancies and silicon vacancies in the high-purity semi-insulating silicon carbide ingot for optical elements can be eliminated, and the number of deep-level defects inside the ingot can be significantly reduced, especially having an obvious inhibitory effect on the light absorption phenomenon caused by ultraviolet band photons, thereby improving the crystal quality and light transmittance of the ingot.

[0034] The above embodiments are only for illustrating the technical concept and characteristics of the present invention, and the purpose is to enable those who are familiar with this technology to understand the content of the present invention and implement it accordingly, and it cannot be used to limit the protection scope of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to include all changes falling within the meaning and scope of the equivalent elements of the claims in the present invention.

Claims

1. A growth process of high-purity semi-insulating silicon carbide single crystal for optical elements, characterized in that: The following steps are involved: S1. Assemble silicon carbide powder, graphite crucible, graphite soft felt, accessories and / or raw materials to form a thermal field device, and place it in an induction furnace. Then, perform room temperature furnace cleaning treatment, low temperature furnace cleaning treatment, and then perform thermal field impurity removal treatment. The silicon carbide powder includes a first silicon carbide powder with a particle size of 1 to 2 mm and a second silicon carbide powder with a particle size of 0.01 to 0.1 mm, both of which are synthesized by CVD method; the second silicon carbide powder is assembled above the first silicon carbide powder; S2, assembling the silicon carbide seed crystal and the impurity-removed thermal field device, then raising 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 grow the crystal; S3, after the crystal growth is completed, firstly perform a high temperature and high pressure annealing treatment, and then perform a furnace cooling treatment to obtain a high-purity semi-insulating silicon carbide ingot for optical elements; The high temperature and high pressure annealing treatment is to first adjust the pressure in the induction furnace to 320-380 mbar, then reduce the temperature to 1800-1900° C., and then maintain the constant temperature and pressure for several hours.

2. The growth process of a high-purity semi-insulating silicon carbide single crystal for optical elements according to claim 1, characterized in that: 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 15 atoms / cm 3 , Al content does not exceed 1×10 15 atoms / cm 3 ; The auxiliary parts include porous graphite sheets and atmosphere filter components.

3. The growth process of a high-purity semi-insulating silicon carbide single crystal for optical elements according to claim 2, characterized in that: In step S1, the room temperature furnace cleaning treatment is to increase the pressure inside the induction furnace to 450-550 mbar within 25-35 minutes at 15-35°C, maintain the pressure for 40-80 minutes, and then reduce the pressure inside the induction furnace to the background pressure within 50-70 minutes; The low-temperature furnace cleaning treatment is to increase the pressure in the induction furnace to 450-550 mbar within 25-35 minutes under the condition of 1200-1500°C, maintain the pressure for 40-80 minutes, and then reduce the pressure in the induction furnace to the background pressure within 50-70 minutes; The background pressure does not exceed 1×10 -4 pa; The thermal field impurity removal treatment is carried out at a temperature of 2000-2250° C. and a pressure of 1-3 mbar for 1-10 hours.

4. The growth process of a high-purity semi-insulating silicon carbide single crystal for optical elements according to claim 2, characterized in that: In step S1, the assembly operation includes the following steps: a. firstly filling the bottom of the graphite crucible with the first silicon carbide powder, then placing the porous graphite sheet on top of the first silicon carbide powder, and then, flattening the second silicon carbide powder on top of the porous graphite sheet; b. Place the atmosphere filter assembly on the second silicon carbide powder, then assemble the components of the graphite crucible together, and wrap the graphite soft felt around the graphite crucible.

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

1.

6. The growth process of a high-purity semi-insulating silicon carbide single crystal for optical elements according to claim 2, characterized in that: The graphite crucible is made of isostatically pressed graphite material; the ash content of the graphite crucible is less than 5 ppm.

7. The growth process of a high-purity semi-insulating silicon carbide single crystal for optical elements according to claim 6, characterized in that: 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.

8. The growth process of a high-purity semi-insulating silicon carbide single crystal for optical elements according to claim 2, characterized in that: In step S3, the furnace cooling process is to reduce the heating power of the induction furnace to 0 kW and then allow the thermal field device to cool naturally to room temperature.

9. A high-purity semi-insulating silicon carbide single crystal for optical elements, characterized in that: The growth process is adopted to obtain the above-mentioned product.

Images