Hot zone assembly and method for producing high purity optical crystals

Abstract

A thermal field assembly and method for preparing high-purity optical crystals are disclosed. The thermal field assembly comprises: a lower guide tube supported on the upper end of the inner edge of an outer annular support plate, with multiple notches uniformly formed circumferentially at its upper end; an upper guide tube fixedly supported above the lower guide tube, its upper end fitted to a cover, and its lower end coaxially connected to the upper end of the lower guide tube, forming multiple air passages in conjunction with the notches; a seed crystal bonded to the cover; an annular connecting plate fixedly connected to the lower end of the upper guide tube; and multiple arc-shaped lower baffles correspondingly distributed on the outer side of the multiple air passages, with their upper ends hinged to the lower end of the annular connecting plate. The method involves: during crystal growth, when the gas pressure in the crystal growth chamber is less than a set threshold, the arc-shaped lower baffles close the air passages; when the gas pressure is greater than or equal to the set threshold, the air passages open under the action of the pressure difference. This invention can adaptively maintain the stability of the atmosphere within the crystal growth chamber, enabling the preparation of high-purity, high-quality silicon carbide optical crystals.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology, specifically relating to a thermal field component and method for preparing high-purity optical crystals. Background Technology

[0002] Silicon carbide (SiC) optical crystals are the core substrate material for waveguide lenses in AR glasses. With their unique physicochemical properties, such as ultra-high refractive index and excellent thermal conductivity, they effectively overcome the technical bottlenecks of traditional optical materials in areas like field of view, rainbow patterns, and heat dissipation, making them the preferred material for high-performance AR waveguide devices. Regarding optical refractive index parameters, existing traditional AR lens substrate materials have significant performance limitations. Conventional resins have a refractive index of approximately 1.51, while high-refractive-index resins are only 1.74; ordinary glass has a refractive index of approximately 1.5, while high-refractive-index glass reaches a maximum of only 1.9. In contrast, silicon carbide materials can achieve a refractive index of over 2.6, demonstrating a significant performance advantage. In waveguide structure design, the refractive index of the substrate material is positively correlated with the field of view (FOV) of the AR lens; the higher the refractive index, the larger the achievable field of view and the better the optical imaging effect. Traditional glass materials require a three-layer stacked structure, which can only achieve a field of view of about 40 degrees. The stacked structure also leads to problems such as thick lenses and large image loss. However, using a single-layer silicon carbide substrate can achieve an ultra-large field of view of more than 80 degrees. While making the device thinner and lighter, it can provide a larger and clearer visual imaging effect. At the same time, it can effectively improve the rainbow pattern problem that is prone to occur in traditional lenses, and its excellent thermal conductivity can significantly improve the heat dissipation performance of the device.

[0003] However, silicon carbide optical crystals suffer from industry pain points such as high manufacturing difficulty and low yield. Crystal purity is a core indicator determining the optical performance of silicon carbide, directly affecting key optical parameters such as refractive index, haze, light absorption, and transmittance. Various impurities are easily introduced during silicon carbide crystal growth, readily inducing crystal phase transitions, inclusions, and other defects, severely reducing the optical quality of the crystal and hindering the mass production and application of high-performance silicon carbide optical crystals.

[0004] Therefore, there is an urgent need to provide a thermal field component and method for preparing high-purity optical crystals, so as to prepare high-purity, high-quality silicon carbide optical crystals by optimizing the equipment structure and growth process system, and meet the needs of large-scale application of high-end AR optical waveguide lenses. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a thermal field component and method for preparing high-purity optical crystals. This component can adaptively maintain the stability of the atmosphere within the crystal growth cavity, enabling the preparation of high-purity, high-quality silicon carbide optical crystals, which can meet the large-scale application requirements of high-end AR waveguide lenses. This method is simple to implement, low in cost, and quantifiable, and can produce high-quality, high-purity optical crystals.

[0006] To achieve the above objectives, the present invention provides a thermal field assembly for preparing high-purity optical crystals, comprising: A crucible body, the crucible body comprising a crucible and a cover disposed on the open end of the crucible; A support assembly is fixedly mounted inside the crucible and isolates the inner cavity of the crucible into a crystal growth area and a powder carrying area; the support assembly includes an outer annular support plate and an inner filter plate; the inner filter plate is encapsulated inside the outer annular support plate; The lower guide tube is coaxially supported on the upper end of the inner edge of the outer annular support plate, and its upper end is uniformly provided with multiple notches along the circumferential direction. The upper guide tube is coaxially fixed above the lower guide tube. Its upper end is fitted and connected to the cover, and its lower end is coaxially connected to the upper end of the lower guide tube. It also has multiple notches to form multiple air passages. Seed crystal, which is located inside the upper guide tube and is bonded to the cover; The flow guide support assembly includes an annular connecting plate and an arc-shaped lower baffle. The annular connecting plate is coaxially disposed on the outer side of the upper end of the lower flow guide cylinder, and its upper end is fixedly connected to the lower end of the upper flow guide cylinder. Multiple arc-shaped lower baffles are correspondingly distributed on the outer side of multiple air passages, and their upper ends are hinged to the lower end of the annular connecting plate.

[0007] Furthermore, the upper guide tube includes a vertical cylindrical section and an annular support section, with the annular support section fixedly connected to the outer side of the lower end of the vertical cylindrical section. In this technical solution, the annular support section facilitates connection to the inner wall of the crucible. Simultaneously, it provides a foundation for the installation of the guide support assembly.

[0008] Furthermore, to improve the heat insulation effect around the seed crystal, the annular felt is fitted onto the outside of the upper guide tube. In this technical solution, fitting the annular felt onto the outside of the upper guide tube can effectively improve the heat insulation performance of the crystal edge, thereby facilitating the formation of a temperature gradient to effectively increase the crystal's convexity and make the crystal surface more full.

[0009] Furthermore, to effectively alter the radial heat flow distribution on the outer side, thereby controlling the curvature of the crystal growth interface and matching the growth rates of the crystal edge and center in stages, a convexity adjustment ring is also included. The lower end of the convexity adjustment ring is supported on the upper end of the outer annular support plate and located outside the flow guide tube, with its outer circular surface closely connected to the inner wall of the crucible. Its upper end is spaced apart from the flow guide support assembly. In this technical solution, the convexity adjustment ring, in conjunction with the annular felt, better regulates the temperature gradient, ensuring uniform crystal growth and effectively preventing phase transitions, polymorphism, or other defects, thus enabling the preparation of high-quality silicon carbide crystals.

[0010] Furthermore, to precisely adjust crystal convexity and reduce growth defects, the convexity adjustment ring is a variable-diameter structure, with its inner diameter gradually decreasing from top to bottom. In this technical solution, based on the variable-diameter structure of the convexity adjustment ring, the growth rate at the crystal edge is ensured to be no greater than the growth rate at the center during the early stages of crystal growth, and simultaneously, the edge growth rate is ensured to be no less than the center growth rate during the later stages of crystal growth. This allows for convex growth in the early stages and effective control of convexity in the later stages, thus achieving effective adjustment of crystal convexity. Therefore, by setting the convexity adjustment ring, the radial heat flow distribution outside the lower guide tube can be effectively changed, thereby controlling the curvature of the crystal growth interface. By optimizing the temperature gradient, crystal defects can be effectively reduced, which is beneficial to improving growth quality. Simultaneously, based on the variable-diameter convexity adjustment ring combined with the annular insulation felt, the radial temperature field and the curvature of the growth interface can be more flexibly controlled, thereby precisely adjusting crystal convexity and more effectively reducing growth defects.

[0011] Furthermore, for ease of assembly and maintenance, the crucible includes a bottom main body section and a stacked extension section; The bottom main body section is used to form a closed powder carrying cavity; the lower end of the superimposed extension section is coaxially connected to the upper end of the bottom main body section, and its upper end serves as the upper opening end of the crucible.

[0012] Furthermore, to facilitate the introduction of mixed gas to replace impurities and extract and retain fine powder particles, while simultaneously using variable-diameter channels to guide airflow and prevent backflow, ensuring the cleanliness of the gas within the cavity, a purification cylinder is also included. This purification cylinder is located in the central region at the bottom of the powder-bearing area, with its lower end inserted into a pre-drilled hole in the center of the crucible bottom. Multiple airflow channels are evenly distributed on its body, with the outer port diameter L2 of each channel being smaller than the inner port diameter L1. In this technical solution, the purification cylinder not only allows gas introduction during the early stages of crystal growth but also absorbs excess fine carbon powder impurities from the silicon carbide powder during the middle and later stages of crystal growth, preventing these carbon powder particles from entering the crystal growth chamber and avoiding the introduction of carbon-encapsulated impurities. Therefore, the purification cylinder effectively removes nitrogen impurities from the powder and the thermal field, reducing nitrogen doping during crystal growth and effectively improving crystal purity. Simultaneously, the unidirectional controllable exhaust mechanism formed by the purification cylinder and the guiding support assembly creates an environment free of impurities in the crystal growth chamber, reducing inclusions formed during crystal growth. Furthermore, to ensure filtration effectiveness, the inner filter plate is a composite structure, comprising an upper filter plate, a lower filter plate, and a denitrifying agent layer; the upper and lower filter plates are spaced apart vertically; the denitrifying agent layer fills the gap between the upper and lower filter plates. In this technical solution, the composite filter plate structure allows tantalum metal to fully react with nitrogen gas at high temperatures to form tantalum nitride, thereby achieving highly efficient nitrogen removal and ensuring effective gas filtration.

[0013] Furthermore, to effectively improve crystal purity and growth quality, the upper guide tube, lower guide tube, guide support assembly, upper filter plate, and lower filter plate are all tantalum carbide coated parts with a graphite substrate. In this technical solution, using a graphite-based tantalum carbide coating on high-temperature contact components effectively eliminates the problem of carbon production from graphite volatilization, better adapts to high-temperature crystal growth conditions, and effectively improves the overall structural durability and crystal purity.

[0014] In this invention, a lower guide tube is installed at the upper end of the support assembly and positioned around the inner filter plate. This effectively guides the gas passing through the inner filter plate towards the seed crystal region, ensuring the crystal growth process. Multiple notches are evenly distributed circumferentially at the upper end of the lower guide tube. Simultaneously, an upper guide tube is coaxially connected to the upper end of the lower guide tube, and the upper end of the upper guide tube is fitted tightly to the cover. This creates multiple air passages between the upper and lower guide tubes. This prevents gas reaching the lower end of the cover from directly overflowing; instead, it flows downwards through the reverse flow of the upper guide tube and exits through the air passages. This effectively ensures the temperature at the seed crystal edge region, contributing to the quality of crystal growth. The annular connecting plate of the flow-guiding support assembly is fitted onto the outer side of the upper end of the lower guide tube and fixedly connected to the lower end of the upper guide tube, providing a mounting base for multiple arc-shaped lower baffles. Multiple arc-shaped lower baffles are distributed on the outer sides of multiple air passages and hinged to an annular mounting plate. Under normal conditions, the weight of the arc-shaped lower baffles keeps the multiple air passages closed. Simultaneously, when the gas pressure in the crystal growth chamber is too high, the pressure difference automatically opens the multiple air passages, ensuring that excess gas in the crystal growth chamber can escape to the outside. Thus, the flow-guiding support assembly forms a controllable exhaust mechanism, ensuring that excess gas in the crystal growth chamber is automatically released to the outside at appropriate times, while effectively preventing external gases and impurities from entering the crystal growth chamber and affecting crystal purity. This ensures crystal growth quality while effectively preventing the introduction of external impurities.

[0015] This component can adaptively maintain the stability of the atmosphere inside the crystal growth cavity, enabling the fabrication of high-purity, high-quality silicon carbide optical crystals, which can meet the needs of large-scale applications of high-end AR waveguide lenses.

[0016] This invention also provides a method for preparing high-purity optical crystals, employing a thermal field assembly for preparing high-purity optical crystals, comprising the following steps: Step 1: Fix the purification cylinder in the center of the bottom of the crucible, and fill the powder carrying area with silicon carbide powder layer by layer from bottom to top, and spread a layer of stabilizer between two adjacent layers of silicon carbide powder; complete the assembly of the thermal field components. Step 2: Transfer the hot zone components to the crystal growth furnace, first evacuate the vacuum, then heat up, and hold at 1200℃ for ventilation; The gas exchange process is as follows: First, a mixture of purified gas and inert gas is filled through the purification cylinder, and then a vacuum process is performed. This filling and vacuuming process is repeated 3 times. Step 3: Continue heating to the crystal growth temperature and reduce the crystal growth pressure. In the early stage of crystal growth, a mixture of purified gas and inert gas is continuously introduced through the purification cylinder. In the middle and late stages of crystal growth, the gas is continuously evacuated through the purification cylinder until the crystal growth is completed. During crystal growth, when the saturated vapor pressure in the crystal growth chamber is less than a set threshold, the arc-shaped lower baffle keeps the gas passage closed to prevent external gas from entering the crystal growth chamber. When the saturated vapor pressure is greater than or equal to the set threshold, the arc-shaped lower baffle is pushed to rotate and open the gas passage under the action of pressure difference, allowing some of the excess gas flow to escape to the outside.

[0017] In this invention, silicon carbide powder and stabilizer are layered and differentiated, facilitating uniform release of the stabilizer throughout the process and contributing to a more stable growth environment. During the gas exchange process, multiple vacuuming and mixed gas replacement processes effectively remove impurities from the furnace, improving crystal purity from the source. During crystal growth, the purification chamber employs a phased matching of ventilation and extraction modes with furnace pressure, replacing impurities in the early stages and retaining carbon powder impurities in the later stages, specifically addressing crystal growth issues at different stages. Simultaneously, the automatic pressure relief structure of the thermal field components enables adaptive control of the furnace pressure, ensuring the continuity and stability of the crystal growth process.

[0018] This method is simple to implement, low in cost, and quantifiable. It can not only fully displace nitrogen impurities in the powder during crystal growth using a purification cylinder with an anti-backflow structure, but also effectively remove nitrogen from the gas flow components by utilizing the denitrifying agent in the internal filter plate, greatly reducing the nitrogen content in the crystal. At the same time, with the controllable exhaust mechanism, it can adaptively maintain the stability of the atmosphere inside the crystal growth chamber, thereby producing high-quality, high-purity optical crystals. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the thermal field component in this invention; Figure 2 This is an assembly diagram of the upper guide tube, annular felt, and guide support assembly in this invention; Figure 3 This is a schematic diagram of the lower guide tube in this invention; Figure 4 for Figure 1 A schematic diagram of a partial structure; Figure 5 This is a schematic diagram of the arc-shaped lower baffle in the closed state in this invention; Figure 6 This is a schematic diagram of the arc-shaped lower baffle in the open state in this invention; Figure 7 This is a schematic diagram of the internal filter plate in this invention; Figure 8 This is a schematic diagram of the purification tube in this invention; Figure 9 for Figure 8 A partial cross-sectional view; Figure 10 This is a schematic diagram of the loading structure of the method section in this invention; Figure 11 An image of a wafer prepared using the method of this invention.

[0020] In the diagram, 1. Crucible body, 2. Crucible, 3. Cover, 4. Outer annular support plate, 5. Inner filter plate, 6. Lower guide tube, 7. Upper guide tube, 8. Convexity adjustment ring, 9. Seed crystal, 10. Annular felt, 11. Guide support assembly, 12. Annular connecting plate, 13. Arc-shaped lower baffle, 14. Gas passage, 15. Vertical cylinder section, 16. Annular support section, 17. Bottom main body section, 18. Overlapping extension section, 19. Upper filter screen plate, 20. Lower filter screen plate, 21. Nitrogen removal agent layer, 22. Purification cylinder, 23. Silicon carbide powder, 24. Stabilizer, 25. Gas flow channel, 26. Notch. Detailed Implementation

[0021] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0022] Example 1:

[0023] like Figures 1 to 10 This embodiment provides a thermal field assembly for preparing high-purity optical crystals, including: The crucible body 1 includes a crucible 2 and a cover 3 covering the open end of the crucible 2; A support assembly is fixedly mounted inside the crucible 2, separating the inner cavity of the crucible 2 into a crystal growth area and a powder carrying area. The support assembly includes an outer annular support plate 4 and an inner filter plate 5. The outer annular support plate 4 is fixedly mounted inside the crucible 2. In a preferred embodiment, an annular recess is formed in the middle of the crucible 2, and the outer edge of the outer annular support plate 4 is supported on the annular recess. The inner filter plate 5 is encapsulated inside the outer annular support plate 4. The lower guide tube 6 is coaxially supported on the upper end of the inner edge of the outer annular support plate 4, and its upper end extends to a position close to the cover 3. Multiple notches 26 are evenly opened on its upper end along the circumference. The upper guide tube 7 is coaxially fixed above the lower guide tube 6. Its upper end is fitted and connected to the cover 3, and its lower end is coaxially connected to the upper end of the lower guide tube 6. It also cooperates with multiple notches 26 to form multiple air passages 14. In this preferred embodiment, the inner diameter of the upper guide tube 7 is 206mm and the height of the upper guide tube 7 is 3mm.

[0024] An annular felt 10 is fitted onto the outside of the upper guide tube 7. The annular felt 10 forms an annular heat-insulating zone on the outside of the upper guide tube 7, which can effectively ensure the temperature of the edge area of ​​the seed crystal 9, thus helping to ensure the growth quality of the crystal. Preferably, the thickness of the annular felt 10 is 5-10 mm, most preferably 10 mm, and the height is 5-30 mm, most preferably 15 mm. The thickness and height of the annular felt 10 can be adjusted according to the crystal's surface shape requirements. If the crystal has low convexity and a concave surface, the thickness and height of the annular felt 10 can be increased to effectively improve the heat insulation performance of the crystal edge, thereby forming a larger radial temperature gradient, which in turn increases the crystal's convexity and makes the crystal surface more full. If the crystal has high convexity, the thickness and height of the annular felt 10 can be reduced to decrease the heat insulation effect of the crystal edge and reduce the radial temperature gradient, thereby achieving the effect of adjusting the crystal's convexity and surface shape. As a preferred embodiment, the height of the annular gas passage 14 is 0.5-3 mm, more preferably 1-2 mm, and most preferably 1.5 mm, mainly used to release excess saturated gas in the crystal growth chamber; A convexity adjustment ring 8 is provided, with its lower end supported on the upper end of the outer annular support plate 4 and located outside the guide tube 6. Its outer surface is in close contact with the inner wall of the crucible 2, and its upper end is spaced apart from the guide support assembly 11. Preferably, the convexity adjustment ring 8 has a variable diameter structure, with its inner diameter gradually decreasing from top to bottom.

[0025] As a preferred embodiment, the slope or inclination formed by the inner side of the convexity adjustment ring 8 and the angle α between it and the horizontal plane can be adjusted according to the crystal surface shape, wherein 90°≥α≥60°, and the most preferred is 75°; as a further preferred embodiment, the convexity adjustment ring 8 is made of graphite, which can act as a heating element during induction heating, effectively increasing the temperature of the crystal edge and enabling rapid growth of the crystal edge; the structure of the inner diameter of the convexity adjustment ring 8 gradually decreasing from top to bottom ensures that in the early stage of crystal growth, the edge growth rate is not greater than the center growth rate; in the later stage of growth, the edge growth rate is not less than the center growth rate, so that the crystal grows convexly in the early stage and the convexity can be effectively controlled in the later stage, thereby achieving effective adjustment of the crystal convexity; thus, by setting the convexity adjustment ring, the radial heat flow distribution on the outside of the lower guide tube can be effectively changed, thereby controlling the curvature of the crystal growth interface, and by optimizing the temperature gradient, crystal defects can be effectively reduced, which is beneficial to improving the growth quality.

[0026] Seed crystal 9, which is located inside the upper guide tube 7 and is bonded to the cover 3, is preferably 205mm in diameter and 0.5mm thick in thickness.

[0027] As a preferred embodiment, a certain gap is left between the upper guide tube 7 and the seed crystal 9. More preferably, the gap is 0.5 to 2 mm, and most preferably 0.5 to 1 mm. As another preferred embodiment, the lower end of the upper guide tube 7 is located below the lower end of the seed crystal 9, and the height difference between the two is 0.5 to 5 mm, and more preferably 1 to 3 mm. The flow guide support assembly 11 includes an annular connecting plate 12, an arc-shaped felt ring, and an arc-shaped lower baffle 13. The annular connecting plate 12 is coaxially disposed on the outer side of the upper end of the lower flow guide cylinder 6, and its upper end is fixedly connected to the lower end of the upper flow guide cylinder 7. Multiple arc-shaped lower baffles 13 are correspondingly distributed on the outer side of multiple air passages 14, and their upper ends are hinged to the lower end of the annular connecting plate 12. The multiple arc-shaped lower baffles 13 are used to close the multiple air passages 14 under normal conditions to block the communication between the crystal growth chamber and the outside, so as to prevent external gas from passing through the air passages 14 in the early stage of growth. When the saturated vapor pressure in the crystal growth chamber is too high, multiple air passages 14 are automatically opened by the pressure difference to ensure that some of the excess gas can escape smoothly to the outside through the air passages 14. In this way, a one-way airflow channel with no inflow is formed at the outlet of the multiple air passages 14. This can ensure that the excess gas in the crystal growth chamber can overflow to the outside at the appropriate time, and can also effectively prevent external gas from entering the crystal growth chamber and affecting the purity of the crystal. This ensures the quality of the crystal and effectively avoids the introduction of external impurities. As a preferred embodiment, the number of arc-shaped lower baffles 13 is not less than 3. As the optimal choice in this embodiment, the number of arc-shaped felt rings and the number of arc-shaped lower baffles 13 are both 4.

[0028] As a preferred embodiment, the upper guide tube 7 includes a vertical cylindrical section 15 and an annular support section 16, the annular support section 16 being fixedly connected to the outer side of the lower end of the vertical cylindrical section 15. More preferably, an annular positioning step is provided on the inner side of the top of the crucible 2, and the outer edge of the annular support section 16 is embedded in the annular positioning step.

[0029] As a preferred embodiment, the annular connecting plate 12 is fixedly connected to the lower end of the annular support section 16; As a preferred embodiment, the crucible 2 includes a bottom main body section 17 and a superimposed extension section 18; The bottom main body section 17 is used to form a closed powder carrying cavity at the bottom; the size of the superimposed extension section 18 is adapted to the size of the bottom main body section, and its lower end is coaxially connected to the upper end of the bottom main body section 17, and its upper end serves as the upper opening end of the crucible 2; as a preferred embodiment, the lower end of the superimposed extension section 18 is connected to the upper end of the bottom main body section 17 by a threaded connection.

[0030] As a preferred embodiment, a purification cylinder 22 is also included. The purification cylinder 22 is located in the central area at the bottom of the powder carrying area, and its lower end is inserted into a reserved hole in the center of the bottom of the crucible 2. Multiple airflow channels 25 are evenly opened on its cylinder body, and the diameter L2 of the outer port of the airflow channel 25 is smaller than the diameter L1 of the inner port. This structure can form a high-speed airflow by utilizing the smaller diameter of the outer port when gas is introduced, which is conducive to the purification gas penetrating into the powder more fully. At the same time, it can effectively prevent the powder from being drawn into the inner cavity of the purification cylinder by utilizing the smaller diameter of the outer port when gas is evacuated. As a preferred embodiment, the cross-section of the airflow channel is in the form of a "crescent moon" shape with the middle slightly higher than the two ends. In this way, both the inner and outer ports face downwards, which can more effectively prevent silicon carbide powder from flowing back into the purification cylinder from the outer port during the gas evacuation process in the early stage of crystal growth. At the same time, it can effectively prevent the carbon powder impurities in the powder from flowing back into the powder carrying cavity again when the fine carbon powder impurities in the powder are drawn into the purification cylinder in the middle and later stages of crystal growth.

[0031] As a preferred embodiment, the lower end of the purification cylinder 22 is threaded into a pre-drilled hole at the center of the bottom of the crucible 2; the upper end of the purification cylinder 22 is located below the upper end of the powder carrying area to ensure that its top end is below the powder surface. As a preferred embodiment, the inner filter plate 5 is a composite structure, comprising an upper filter plate 19, a lower filter plate 20, and a denitrifying agent layer 21; the upper filter plate 19 and the lower filter plate 20 are distributed vertically at intervals; the denitrifying agent layer 21 fills the gap between the upper filter plate 19 and the lower filter plate 20. Preferably, in this embodiment, the lower filter plate 20 has a diameter of 210 mm, with its mesh pore size concentrated in the range of 300–600 μm; the upper filter plate 19 has a diameter of 207 mm, with its mesh pore size concentrated in the range of 50–200 μm.

[0032] The inner filter plate 5 is mainly used to filter carbon particles and silicon droplets mixed in during silicon carbide gas transmission. It can also remove nitrogen compounds mixed in the gas using a denitrifying agent. Preferably, the upper part of the inner circular surface of the outer annular support plate 4 has an annular mounting step, where the lower filter plate 20 overlaps the annular mounting step, the denitrifying agent layer 21 is laid flat on the upper surface of the lower filter plate 20, and the upper filter plate 19 is pressed onto the upper surface of the denitrifying agent layer 21. The edge portion of the formed inner filter plate 5 is fitted and overlapped on the annular mounting step. Further preferably, the annular mounting step is a stepped step including an upper annular step and a lower annular step, wherein the inner diameter of the upper annular step is larger than the inner diameter of the lower annular step. Furthermore, the lower filter plate 20 and the denitrifying agent layer 21 are located in the lower annular step, and the upper surface of the denitrifying agent layer 21 is flush with the upper end of the lower annular step. The upper filter plate 19 is embedded in the upper annular step, and its upper end face can be flush with the upper end of the upper annular step. Thus, a stepped structure is formed instead of a straight cylindrical structure. This can effectively prevent airflow from passing directly through the joint between the filter plate and the outer annular support plate 4, ensuring that all airflow must pass through the lower filter plate 20, the denitrifying agent layer 21, and the upper filter plate 19 before entering the crystal growth cavity, avoiding the formation of inclusions. As a further preferred embodiment, the mesh size of the upper filter plate 19 is larger than the mesh size of the lower filter plate 20. As another preferred option, the denitrifying agent layer 21 is formed of elemental tantalum. Since tantalum reacts with nitrogen under high temperature conditions to form tantalum nitride, it can achieve the purpose of denitrification. As a further preferred option, the elemental tantalum is in the shape of a cylindrical rod, and the length of the cylindrical rod is 2 to 5 mm, more preferably 2 to 3 mm, and most preferably 3 mm. The diameter of the cross section of the cylindrical rod is 1 to 3 mm, more preferably 2 mm. The rod-shaped design allows irregular flow channels to be formed when a large amount of elemental tantalum is stacked, thereby effectively ensuring the smooth passage of gas. As a preferred embodiment, the upper guide tube 7, lower guide tube 6, guide support assembly 11, upper filter plate 19, and lower filter plate 20 are all tantalum carbide coated parts with a graphite substrate. In this way, the inner walls of the crystal growth chamber formed between the seed crystal 9, upper guide tube 7, lower guide tube 6, and inner filter plate 5 are all coated with tantalum carbide, eliminating exposed graphite and thus preventing the generation of carbon particles within the crystal growth chamber. Example 2:

[0033] like Figures 1 to 9 This embodiment provides a method for preparing high-purity optical crystals, employing a thermal field assembly for preparing high-purity optical crystals, including the following steps: Step 1: Fix the purification cylinder 22 in the center area of ​​the bottom of the crucible 2, and fill the powder carrying area with silicon carbide powder 23 layer by layer from bottom to top, and spread a layer of stabilizer 24 between two adjacent layers of silicon carbide powder 23; install the support assembly, lower guide cylinder 6, upper guide cylinder 7, convexity adjustment ring 8, guide support assembly 11, annular felt 10 and cover 3 in sequence to complete the assembly of the thermal field assembly; After filling each layer of silicon carbide powder, a jig is first used to level the upper surface of the powder, and then the stabilizer is applied; preferably, the stabilizer is a cerium-containing compound, such as cerium oxide or cerium silicide. Preferably, four layers of silicon carbide powder and three layers of stabilizer are laid. Specifically, first, a silicon carbide powder layer of height H1 is laid at the bottom of crucible 2, and the upper surface of the silicon carbide powder layer is leveled using a jig to ensure that the flatness difference is less than 1 mm. Then, a stabilizer layer of dosage W1 is evenly laid on the upper surface of the silicon carbide powder layer. Next, a silicon carbide powder layer of height H1 is laid on top of the stabilizer layer, and the upper surface of the silicon carbide powder layer of layer is leveled using a jig to ensure that the flatness difference is less than 1 mm. Then, a stabilizer layer of dosage W1 is evenly laid on the upper surface of the silicon carbide powder layer. The stabilizer layer 2 is evenly spread on the upper surface of the second powder layer, with a dosage of W2; then, a silicon carbide powder layer 3 with a height of H2 is spread on top of the stabilizer layer 2, and the upper surface of the silicon carbide powder layer 3 is leveled using a jig to ensure that the flatness difference is less than 1mm; then, a stabilizer layer 3 is evenly spread on the upper surface of the silicon carbide powder layer 3, with a dosage of W3; then, a silicon carbide powder layer 4 with a height of H3 is spread on top of the stabilizer layer 3, and the upper surface of the silicon carbide powder layer 4 is leveled using a jig to ensure that the flatness difference is less than 0.5mm; As a further preferred option, the particle size of silicon carbide powder is 1-5 mm, more preferably 3-5 mm; in this embodiment, the particle size of silicon carbide powder is 4-5 mm; cerium silicide is used as the crystal stabilizer, and the charging height is required to be H1 > H2 > H3. The design of gradually decreasing silicon carbide powder layer height from bottom to top is because the high-temperature zone is at the bottom of the powder during crystal growth, causing a positive temperature deviation from bottom to top. The powder at the bottom will preferentially and rapidly sublimate at a higher temperature, and the stabilizer will also be released along with the powder. The release rate of the stabilizer is slower closer to the top. Setting the charging height difference allows the stabilizer to be released evenly in the early, middle, and late stages of crystal growth, without premature or delayed release. The amount of stabilizer used is W1 > W2 > W3. The principle of this design is the same as above. Since the sublimation rate of the induction-heated powder is uneven, the powder at the bottom will preferentially and rapidly sublimate. Increasing the amount of stabilizer at the bottom is also to effectively balance the ratio of stabilizer to powder. As a further preferred option, after each layer of silicon carbide powder is laid flat on the surface, four points are selected on the surface to measure the height difference. Step 2: Transfer the hot zone components to the crystal growth furnace, first evacuate the vacuum to meet the predetermined production requirements, preferably with a pressure of less than or equal to 5E-6 mbar, then heat up and hold at 1200°C for ventilation. The gas exchange process is as follows: First, a mixture of purified gas and inert gas is filled through the purification cylinder 25, and then a vacuum process is performed. This filling and vacuuming process is repeated 3 times. As a preferred embodiment, the flow ratio of purified gas to inert gas during the gas exchange process is 2:8 to 3:7; as a further preferred embodiment, the purified gas is preferably hydrogen with a purity of 9N or higher, and the inert gas is preferably argon with a purity of 9N or higher. In this embodiment, the preferred flow rates of hydrogen and argon are 30 sccm and 70 sccm, respectively. Step 3: Continue heating to the crystal growth temperature. As a preferred method, the crystal growth temperature is 2250-2300℃. High-temperature crystal growth is beneficial to improving crystal purity. The crystal growth pressure is reduced to 10–5 mbar, more preferably to 6 mbar, to enter the early stage of crystal growth. During this stage, a mixture of purified gas and inert gas is continuously introduced through the purification chamber 25. Preferably, the flow rate ratio of purified gas to inert gas during the early stage is 1:8 to 1:9. More preferably, the flow rates of hydrogen and argon are 10 sccm and 90 sccm, respectively. The crystal growth time is 30–60 hours, preferably 50 hours. During the middle and later stages of crystal growth, the pressure is maintained at 5–3 mbar, and gas is continuously evacuated through the purification chamber 25. At the same time, inert gas is introduced through the gas inlet of the furnace cavity, but hydrogen is not introduced. The crystal growth time is 120–150 hours, preferably 150 hours, until the crystal growth is completed. This effectively suppresses rapid crystal growth. Because the temperature is set relatively high during the early stage of crystal growth, excessively rapid growth will cause impurity gases to not have time to escape and will be incorporated into the crystal, thus failing to achieve the purification effect. When a purification tube is used to introduce purification gas in the early stage of crystal growth, it can fully replace the impurity gas in the powder. In the middle and later stages of crystal growth, the entire crucible is kept in a state with fewer impurities, which can carry out rapid growth. However, due to the high temperature in the early stage, silicon sublimates preferentially, and a "carbon-rich" situation will occur in the middle and later stages. At this time, the purification tube is kept in a vacuum state, which can draw the fine carbon powder impurities in the powder into the purification tube and avoid the introduction of encapsulation. During the crystal growth process, when the saturated vapor pressure in the crystal growth chamber is less than a set threshold, the arc-shaped lower baffle 13 keeps the gas passage 14 closed to prevent external gas from entering the crystal growth chamber. When the saturated vapor pressure is greater than or equal to the set threshold, the arc-shaped lower baffle 13 is pushed to rotate and open the gas passage 14 under the action of pressure difference, so that some of the excess gas flow can escape to the outside.

[0034] After crystal growth, silicon carbide crystal A is obtained. Silicon carbide crystal A is then processed, resulting in a colorless and transparent wafer with good color. Figure 11 As shown; When testing optical parameters, wafers of different sizes were selected and named wafer 1, wafer 2, and wafer 3, respectively. The main optical parameters tested were transmittance, reflectance, and absorptivity. The test results are shown in Table 1, and all meet the requirements of leading optical customers.

[0035] Table 1: Optical Specifications The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A thermal field assembly for preparing high-purity optical crystals, characterized in that, include: The crucible body (1) includes a crucible (2) and a cover (3) covering the open end of the crucible (2). The support assembly is fixedly mounted inside the crucible (2) and isolates the inner cavity of the crucible (2) into a crystal growth area and a powder carrying area; the support assembly includes an outer annular support plate (4) and an inner filter plate (5); the inner filter plate (5) is encapsulated inside the outer annular support plate (4); The lower guide tube (6) is coaxially supported on the upper end of the inner edge of the outer annular support plate (4), and its upper end is uniformly provided with multiple notches (26) along the circumferential direction. The upper guide tube (7) is coaxially fixed above the lower guide tube (6). Its upper end is connected to the cover (3), and its lower end is coaxially connected to the upper end of the lower guide tube (6). It also forms multiple air passages (14) with multiple notches (26). Seed crystal (9), the seed crystal (9) is located inside the upper guide tube (7) and is bonded to the cover (3); The flow guide support assembly (11) includes an annular connecting plate (12) and an arc-shaped lower baffle (13). The annular connecting plate (12) is coaxially disposed on the outer side of the upper end of the lower flow guide cylinder (6), and its upper end is fixedly connected to the lower end of the upper flow guide cylinder (7). Multiple arc-shaped lower baffles (13) are correspondingly distributed on the outer side of multiple air passages (14), and their upper ends are hinged to the lower end of the annular connecting plate (12).

2. The thermal field assembly for preparing high-purity optical crystals according to claim 1, characterized in that, The upper guide tube (7) includes a vertical cylindrical section (15) and an annular support section (16), the annular support section (16) being fixedly connected to the outer side of the lower end of the vertical cylindrical section (15).

3. The thermal field assembly for preparing high-purity optical crystals according to claim 1, characterized in that, An annular felt (10) is fitted onto the outside of the upper guide tube (7).

4. The thermal field assembly for preparing high-purity optical crystals according to claim 1, characterized in that, Also includes: The lower end of the convexity adjustment ring (8) is supported on the upper end of the outer annular support plate (4) and located on the outside of the guide tube (6). Its outer circular surface is in close contact with the inner wall of the crucible (2), and its upper end is in spaced fit with the guide support assembly (11).

5. The thermal field assembly for preparing high-purity optical crystals according to claim 3, characterized in that, The convexity adjustment ring (8) is a variable diameter structure, and its inner diameter gradually decreases from top to bottom.

6. The thermal field assembly for preparing high-purity optical crystals according to claim 1, characterized in that, The crucible (2) includes a bottom main body section (17) and an overlay extension section (18); The bottom main body section (17) is used to form a bottom-closed powder carrying cavity; the lower end of the superimposed extension section (18) is coaxially connected to the upper end of the bottom main body section (17), and its upper end serves as the upper opening end of the crucible (2).

7. The thermal field assembly for preparing high-purity optical crystals according to claim 1, characterized in that, Also includes: Purification cylinder (22) is located in the center of the bottom of the powder carrying area. Its lower end is inserted into the reserved hole in the center of the bottom of the crucible (2). Multiple air flow channels (25) are evenly opened on its cylinder body, and the outer port diameter L2 of the air flow channel (25) is smaller than the inner port diameter L1.

8. The thermal field assembly for preparing high-purity optical crystals according to claim 1, characterized in that, The inner filter plate (5) is a composite structure, which includes an upper filter plate (19), a lower filter plate (20) and a denitrifying agent layer (21); the upper filter plate (19) and the lower filter plate (20) are distributed vertically at intervals; the denitrifying agent layer (21) is filled in the interval between the upper filter plate (19) and the lower filter plate (20).

9. A thermal field assembly for preparing high-purity optical crystals according to claim 7, characterized in that, The upper guide tube (7), lower guide tube (6), guide support assembly (11), upper filter screen (19) and lower filter screen (20) are all tantalum carbide coated parts with graphite substrate.

10. A method for preparing high-purity optical crystals, comprising using a thermal field assembly for preparing high-purity optical crystals as described in any one of claims 1 to 9, characterized in that, Includes the following steps: Step 1: Fix the purification cylinder (22) in the center area of ​​the bottom of the crucible (2), and load silicon carbide powder (23) layer by layer from bottom to top in the powder carrying area, and spread a layer of stabilizer (24) between two adjacent layers of silicon carbide powder (23); complete the assembly of the thermal field components; Step 2: Transfer the hot zone components to the crystal growth furnace, first evacuate the vacuum, then heat up, and hold at 1200℃ for ventilation; The gas exchange process is as follows: First, a mixture of purified gas and inert gas is filled through the purification cylinder (25), and then a vacuum process is performed. This filling and vacuuming process is repeated 3 times. Step 3: Continue heating to the crystal growth temperature and reduce the crystal growth pressure. In the early stage of crystal growth, a mixture of purified gas and inert gas is continuously introduced through the purification tube (25). In the middle and late stages of crystal growth, the gas is continuously evacuated through the purification tube (25) until the crystal growth is completed. During the crystal growth process, when the saturated vapor pressure in the crystal growth chamber is less than the set threshold, the arc-shaped lower baffle (13) keeps the gas passage (14) closed to prevent external gas from entering the crystal growth chamber. When the saturated vapor pressure is greater than or equal to the set threshold, the arc-shaped lower baffle (13) is pushed to rotate and open the gas passage (14) under the action of pressure difference, so that some of the excess gas flow can escape to the outside.

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