Device and method for preparing large-size silicon carbide single crystal

Abstract

The invention relates to the field of crystal material preparation, in particular to a device and a method for preparing large-size silicon carbide single crystals. The device for preparing the large-size silicon carbide single crystals comprises a crucible, a seed crystal support, a heating mechanism, a heat preservation mechanism and the like, a partition piece is arranged in the crucible to divide the crucible into a raw material cavity, a growth cavity and the like, and the device is further provided with structures such as an acceleration guide ring and the like; the invention also discloses a method for preparing the large-size silicon carbide single crystal by using the device. The method comprises the following steps: selecting seed crystals for pretreatment, adding raw materials, arranging a flow guide structure, filling inert gas for pressurizing and heating, vacuumizing, expanding, filling gas again for cooling, post-treating and the like. The large-size silicon carbide single crystal can be efficiently prepared, directional flow and temperature gradient control of a silicon carbide gas phase source are guaranteed through a reasonable device structure and process steps, and the preparation efficiency and the single crystal quality are improved.

Description

Technical Field

[0001] This application relates to the technical field of crystal material preparation, and in particular to an apparatus and method for preparing large-size silicon carbide single crystals. Background Technology

[0002] Silicon carbide, as a wide bandgap semiconductor material, possesses excellent properties such as high thermal conductivity, high breakdown electric field, and high electron saturation drift velocity. Large-size silicon carbide single crystals (≥8 inches) are key raw materials for preparing large-size silicon carbide substrates. However, due to the significant difficulty in expanding the diameter of large-size silicon carbide single crystals, the entire industry suffers from a shortage of large-size seed crystals, resulting in high prices and severely restricting the development of the silicon carbide industry.

[0003] There are two main traditional methods for expanding the diameter of silicon carbide single crystals. One method uses optimized thermal field conditions to grow a small-diameter silicon carbide seed crystal laterally to a large-diameter silicon carbide single crystal. However, this method has the problem of a long expansion cycle, resulting in low production efficiency and high cost. The other method uses a planarization method to combine multiple small wafers into a seed crystal of the target diameter, and then grows the crystal to obtain a large-diameter silicon carbide single crystal. However, due to the presence of seams, the seed crystal at the splicing point is damaged, inevitably producing microtube cracks. Although some microtubes can be healed by repeated growth, the iteration cycle is long, and the dislocation density caused by lattice distortion at the seam is difficult to eliminate, which cannot meet the quality requirements of commercial substrates. Summary of the Invention

[0004] In order to improve the expansion efficiency of silicon carbide single crystals while ensuring their quality, this application provides an apparatus and method for preparing large-size silicon carbide single crystals.

[0005] On the one hand, this application provides an apparatus for preparing large-size silicon carbide single crystals, which adopts the following technical solution: An apparatus for preparing large-size silicon carbide single crystals, comprising: A crucible includes a crucible body with one end open and a partition plate disposed inside the crucible body. The crucible body has one end open, and the partition plate divides the interior of the crucible body into a raw material chamber and a growth chamber. A discharge hole is provided at the edge of the partition plate, and a material separator is provided on the partition plate. The material separator is located inside the growth chamber. A seed crystal holder is disposed at the opening of the crucible body and closes the opening of the crucible body; Heating mechanism, used to heat the crucible.

[0006] By adopting the above technical solution, during operation, silicon carbide raw material is placed in the raw material chamber. After the heating mechanism is activated, the raw material sublimates upon heating, generating a silicon carbide vapor source. Due to the obstruction of the partition plate, the silicon carbide vapor source cannot diffuse directly upwards, but is forced to enter the area between the outer wall of the partition cylinder and the inner wall of the growth chamber through the discharge hole at the edge of the partition plate, and finally reaches the edge of the seed crystal fixed on the seed crystal holder, completing the directional transport process of the silicon carbide vapor source. By optimizing the silicon carbide vapor source transport path, the silicon carbide vapor source is preferentially supplied to the edge of the seed crystal, thus efficiently expanding the seed crystal diameter.

[0007] Optionally, it also includes a heat preservation mechanism, which includes an insulating heat preservation cylinder, a bottom heat preservation base and a top heat preservation plate. The bottom heat preservation base is disposed at the bottom of the crucible body and the insulating heat preservation cylinder is sleeved on the outside of the crucible body. The top surface of the seed crystal support is provided with a heat insulation area and a heat dissipation area surrounding the heat insulation area, and the top insulation plate covers the heat insulation area.

[0008] By adopting the above technical solution, the insulation mechanism reduces the overall heat loss of the system. In particular, the insulation base enhances the insulation effect on the bottom of the crucible body, preventing crystallization caused by excessive cooling at the bottom of the crucible. The top insulation plate covers the heat-insulating area, reducing heat loss from the seed crystal center; while the exposed heat dissipation area promotes cooling at the seed crystal edge. This temperature difference creates a radial temperature field that decreases from the seed crystal center to the edge, guiding the rising silicon carbide vapor source from below to condense and grow more tending to condense and grow at the cooler, more supersaturated seed crystal edge.

[0009] Optionally, the heating mechanism includes an induction coil wound around the crucible body along its height direction, and the partition plate and the material separating cylinder are made of graphite.

[0010] By adopting the above technical solutions, the induction coil heating method has high thermal efficiency and avoids external pollution; while the graphite partition plate can not only withstand extreme high temperatures, but its good thermal conductivity and thermal expansion coefficient similar to that of silicon carbide raw materials ensure the stability of the thermal field.

[0011] Optionally, an acceleration guide ring is provided on the inner sidewall of the growth chamber, and a heating element is provided inside the acceleration guide ring; A speed-increasing flow channel is formed between the inner wall of the speed-increasing guide ring and the outer wall of the material separator cylinder. The speed-increasing flow channel includes a flow-dispersing channel, a flow-guiding channel, and an inlet channel connected sequentially from top to bottom. The cross-sectional area enclosed by the inlet channel gradually increases in the direction away from the flow-guiding channel.

[0012] By adopting the above technical solution, the silicon carbide vapor source flowing out of the outlet first enters the gradually narrowing inlet channel, where the flow velocity initially increases. It then enters a narrower guide channel, where the flow velocity further accelerates, and finally, the high-speed airflow is directed to the edge region of the seed crystal through a diffuser channel. This accelerates, rectifyes, and guides the silicon carbide vapor source. Through changes in the channel cross-section, the diffused silicon carbide vapor source is converged and accelerated into a concentrated, directional airflow, significantly improving the efficiency and directionality of the silicon carbide vapor source's transport to the seed crystal edge.

[0013] Optionally, the crucible body is provided with a material collection chamber, which is located between the seed crystal holder and the speed-increasing flow channel; the inner sidewall of the material collection chamber is provided with a discharge port and a feed port, and the discharge port is located above the feed port; The end of the material separator cylinder away from the partition plate is fitted with a support ring. The support ring is located in the flow channel, and a flow guiding slope is provided on the outer wall of the support ring. The flow guiding slope is used to guide the silicon carbide vapor source to the feed inlet.

[0014] By adopting the above technical solution, the silicon carbide vapor source discharged from the diffuser channel is divided into two paths. The first path flows directly to the outer edge of the lower half of the seed crystal to participate in growth. The second path, under the guidance of the inclined surface of the supporting ring, is guided to the inlet of the collecting chamber and collects in the collecting chamber. Subsequently, the silicon carbide vapor source in the collecting chamber mainly flows out from the higher outlet and is preferentially transported to the outer edge of the upper half of the seed crystal for deposition. This compensates for the concentration attenuation of the silicon carbide vapor source during its ascent along the edge of the seed crystal due to deposition, ensuring that both the upper and lower parts of the seed crystal receive a sufficient supply of silicon carbide vapor source, thus improving the axial uniformity of crystal growth.

[0015] Optionally, a first temperature measuring element and a second temperature measuring element are provided at intervals on the seed crystal holder. The first temperature measuring element is used to detect the temperature in the middle of the seed crystal, and the second temperature measuring element is used to detect the temperature at the edge of the seed crystal. An edge temperature controller is also embedded in one end of the seed crystal holder, and the first and second temperature measuring elements are both electrically connected to the edge temperature controller.

[0016] By employing the above technical solution, a first temperature sensor monitors the temperature at the center of the seed crystal, while a second temperature sensor monitors the temperature at the edge of the seed crystal. By comparing the two readings, if the edge temperature is too high, which is detrimental to deposition, the edge temperature controller is de-energized or shut down; if the edge temperature is too low, the heating power is increased, thereby dynamically maintaining the optimal radial temperature difference. Through real-time, precise monitoring and active control of the seed crystal edge and center temperatures, the radial temperature gradient is fine-tuned, effectively compensating for temperature field fluctuations caused by the growth process or external disturbances. This ensures the continuous stability of edge-preferred growth conditions, thereby guaranteeing the uniformity and high quality of crystal diameter expansion.

[0017] Optionally, the edge temperature controller includes an annular heating tube, on which a heat exchange inlet pipe and a heat exchange outlet pipe are connected, and one end of the heat exchange inlet pipe and the heat exchange outlet pipe are both located outside the crucible body; The heat exchange tube is provided with a first flow control element, and the heat exchange inlet tube is provided with a second flow control element.

[0018] By adopting the above technical solution, the flow rate of the cooling medium flowing into the annular electric heating tube can be controlled by adjusting the first and second flow control devices on the heat exchange inlet pipe and heat exchange outlet pipe. This can control the temperature of the seed crystal edge region. When the cooling medium flow rate is small, the electric heating tube loses less heat and the cooling effect on the seed crystal edge is weak. When the cooling medium flow rate is large, the electric heating tube loses more heat and the cooling effect on the seed crystal edge is strong.

[0019] On the other hand, this application provides a method for preparing large-size silicon carbide single crystals, comprising the following steps: S1. Select a seed crystal of appropriate size, pre-treat the surface of the seed crystal to reduce the roughness of the seed crystal edge, and remove impurities and contaminants from the side surface of the seed crystal. S2. Add silicon carbide raw material to the raw material cavity of the crucible body, and arrange a flow guiding structure in the crucible body so that the silicon carbide gas source produced after the silicon carbide raw material is heated flows in a direction to the outer circumferential sidewall of the seed crystal; fix the pretreated seed crystal on the seed crystal holder, and then move the seed crystal into the growth cavity of the crucible. S3. Inert gas is introduced into the crucible to pressurize it to 10-100 kPa; the crucible is then heated to 2000-2500°C and maintained for 1-10 hours; the crucible is then evacuated to reduce the internal pressure to 100-5000 Pa and maintained for 1-5 hours; the crucible is then evacuated again to reduce the internal pressure to 100-1000 Pa; subsequently, the crucible is lifted or the induction coil is moved downward at a speed of 0.1-1 mm / h, and the growth time is controlled at 20-200 hours to complete the diameter expansion of the seed crystal. S4. Inert gas is introduced into the crucible again to increase the internal pressure to 20-80 kPa. The crucible is then cooled to obtain silicon carbide single crystals of the target size. S5. Post-process the silicon carbide single crystal of the target size to obtain silicon carbide single crystal of the required size.

[0020] By adopting the above technical solution, the pressure and temperature are first increased and then the pressure is reduced in stages. The pressure-temperature curve is optimized and combined with the operation of lifting the crucible or moving the coil, the crystal expansion temperature is controlled within a reasonable range as the crystal diameter increases. This ensures that the crystal can grow at the edge diameter under stable and optimal thermodynamic conditions, and ultimately achieves a balance between high efficiency and high quality when expanding the seed crystal.

[0021] Optionally, step S3 further includes controlling the axial temperature gradient at 3-15℃ / cm and the radial temperature gradient at 0.3-12℃ / cm during the heating of the crucible.

[0022] By adopting the above technical solutions, controlling the axial temperature gradient at 3-15°C / cm ensures sufficient growth driving force and interface stability; controlling the radial temperature gradient at 0.3-12°C / cm ensures the effectiveness and uniformity of edge-preferred growth.

[0023] Optionally, the inert gas is argon, and when filling the crucible with inert gas, the gas flow rate is controlled at 50-1000 sccm.

[0024] By adopting the above technical solution, high-purity argon gas of a specific flow rate is introduced into the crucible as needed during the pressurization, growth and cooling stages, providing a stable inert environment for the expansion growth of the seed crystal, which helps the seed crystal to expand and improves the expansion efficiency.

[0025] In summary, this application includes at least one of the following beneficial effects: 1. This application provides a partition plate with a discharge hole on the edge of the crucible body, so that the silicon carbide vapor source flows directionally along the discharge hole to the outer circumferential sidewall of the seed crystal, which solves the problem of long diameter expansion cycle in traditional methods, and efficiently prepares large-size seed crystals. It can quickly prepare large-size seed crystals. 2. The process described in this application is simple and easy to operate, which is conducive to large-scale production by enterprises, reduces production difficulty and costs, and achieves cost reduction and efficiency improvement.

[0026] 3. This application plays a positive role in alleviating the current shortage of large-size seed crystals; 4. The growth chamber in this application has an acceleration guide ring with heating element on the inner sidewall, which forms an acceleration flow channel, accelerates the transport of silicon carbide vapor source, and further improves the seed crystal diameter expansion efficiency. Attached Figure Description

[0027] Figure 1 This is a cross-sectional view of an apparatus for preparing large-size silicon carbide single crystals according to Embodiment 1 of this application; Figure 2 This is a cross-sectional view of an apparatus for preparing large-size silicon carbide single crystals according to Embodiment 2 of this application; Figure 3 This is a partial cross-sectional view of an apparatus for preparing large-size silicon carbide single crystals according to Embodiment 2 of this application; Explanation of reference numerals in the attached drawings: 1. Crucible; 11. Crucible body; 111. Collection chamber; 1111. Discharge port; 1112. Inlet; 12. Divider plate; 121. Discharge hole; 13. Raw material chamber; 14. Growth chamber; 15. Separator cylinder; 16. Speed-increasing guide ring; 17. Speed-increasing flow channel; 171. Dispersing channel; 172. Guide channel; 173. Flow channel; 18. Support ring; 181. Guide slope; 19. Receiving block; 2. Seed crystal holder; 3. Heating mechanism; 31. Induction coil; 32. Heating element; 33. Annular electric heating tube; 34. Heat exchange inlet pipe; 341. First flow control element; 35. Heat exchange tube array; 351. Second flow control element; 4. Insulation mechanism; 41. Insulating insulation cylinder; 42. Bottom insulation base; 43. Top insulation board; 5. First temperature measuring element; 6. Second temperature measuring element; 7. Seed crystal. Detailed Implementation

[0028] The following is in conjunction with the appendix Figure 1 -Appendix Figure 3 This application will be described in further detail.

[0029] Example 1 Reference Figure 1 This application provides an apparatus for preparing large-size silicon carbide single crystals, including a crucible 1, a seed crystal holder 2, a heating mechanism 3, and a heat preservation mechanism 4. The crucible 1 includes a crucible body 11 with one open end and a partition plate 12 disposed within the crucible body 11. The partition plate 12 divides the interior of the crucible body 11 into a raw material chamber 13 and a growth chamber 14, which are distributed vertically. In this embodiment, the crucible body 11 is specifically cylindrical, and a receiving block 19 is fixed on the inner wall of the crucible body. Multiple receiving blocks 19 are fixed at intervals around the axis of the crucible 1. The partition plate 12 is placed on the receiving block 19, enabling the partition plate 12 to be detachably installed within the crucible body 11, facilitating the addition of silicon carbide raw material into the raw material chamber 13 during operation. The partition plate 12 is circular, and multiple discharge holes 121 are opened at the edge of the partition plate 12. A material separator 15 is fixed on the partition plate 12, and the material separator 15 is located within the growth chamber 14. The seed crystal holder 2 is snapped into the opening of the crucible body 11 and seals the opening of the crucible body 11. During operation, a seed crystal 7 of appropriate size can be bonded to the bottom of the seed crystal holder 2, and then the seed crystal holder 2 can be used to seal the opening of the crucible body 11; at this time, one end of the separator cylinder 15 abuts against the bottom end of the seed crystal 7 in the growth chamber 14.

[0030] The crucible body 11 is generally made of graphite, and its open-end design facilitates the placement and removal of the seed crystal 7 and raw materials. The partition plate 12 can also be made of graphite. The partition plate 12 effectively separates the raw material chamber 13 from the growth chamber 14. Silicon carbide raw materials are placed in the raw material chamber 13 and heated to generate a silicon carbide vapor source, which flows to the growth chamber 14 through the outlet hole 121. The outlet hole 121 is located at the edge of the partition plate 12, allowing the silicon carbide vapor source to preferentially flow to the edge of the seed crystal 7, promoting the growth of the seed crystal 7 edge and achieving diameter expansion. The separator cylinder 15 is also made of graphite, which further guides the flow direction of the silicon carbide vapor source, preventing it from becoming too dispersed within the growth chamber 14. The seed crystal holder 2 can also be made of graphite, and its shape is adapted to the opening of the crucible body 11, serving to seal the opening.

[0031] Reference Figure 1 The insulation mechanism 4 includes an insulating insulation cylinder 41, a bottom insulation seat 42, and a top insulation plate 43. The bottom insulation seat 42 is fixed to the bottom of the crucible body 11, and the insulating insulation cylinder 41 is fitted over the crucible body 11. A connecting groove is provided on the bottom insulation seat 42, and the bottom of the insulating insulation cylinder 41 is engaged with the connecting groove. Specifically, the insulating insulation cylinder 41 is cylindrical, the bottom insulation seat is frustum-shaped, and the seed crystal holder 2 is also frustum-shaped. The top surface of the seed crystal holder 2 is divided into a circular heat insulation area and an annular heat dissipation area surrounding the heat insulation area. The top insulation plate 43 covers and is fixed to the heat insulation area.

[0032] Reference Figure 1 An insulating heat-insulating cylinder 41 is fitted over the crucible body 11 to reduce heat loss and improve energy efficiency. The insulating heat-insulating cylinder 41, the bottom heat-insulating base 42, and the top heat-insulating plate 43 are all made of graphite and are positioned at the bottom of the crucible body 11 to enhance heat insulation and prevent overcooling that could lead to crystallization. The top heat-insulating plate 43 covers the heat-insulating area of ​​the seed crystal holder 2. The thickness of the top heat-insulating plate 43 is controlled between 1-10 mm, and its diameter between 50-200 mm. In this embodiment, the thickness of the top heat-insulating plate 43 is 2 mm, and its diameter is 180 mm. The top heat-insulating plate 43 can adjust the temperature distribution within the crucible body 11; after adjustment, the radial temperature gradient within the crucible body 11 decreases from the center to the edge, forming a radial temperature gradient. Such a temperature gradient is conducive to the deposition and growth of silicon carbide vapor source at the edge of seed crystal 7, and promotes the expansion of the diameter of seed crystal 7.

[0033] Reference Figure 1The heating mechanism 3 includes an induction coil 31, which is wound around the outside of the crucible body 11 along its height. The induction coil 31 provides heat to the crucible 1 through electromagnetic induction, raising the silicon carbide material inside the crucible 1 to a suitable temperature to generate a silicon carbide vapor source. The number of turns and the winding density of the induction coil 31 are adjusted according to actual needs to meet different heating requirements. When the induction coil 31 is working, the temperature distribution inside the crucible body 11 is adjusted by controlling the vertical relative position of the induction coil 31 and the crucible body 11. After adjustment, the axial temperature gradient inside the crucible body 11 decreases from the lower end to the upper end, forming an axial temperature gradient to ensure sufficient driving force for the expansion of the seed crystal 7 and the interface stability of the material in the material cavity 13.

[0034] In other embodiments, the induction coil 31 may be replaced by other heating elements 32, such as a resistance heating wire.

[0035] The implementation principle of this embodiment is as follows: the interior of the crucible body 11 is divided into a raw material chamber 13 and a growth chamber 14 by a partition plate 12. The discharge hole 121 and the separator cylinder 15 at the edge of the partition plate 12 guide the silicon carbide vapor source preferentially to the edge of the seed crystal 7. Simultaneously, the heating mechanism 3 and the heat preservation mechanism 4 cooperate to achieve axial and radial temperature gradient control during the heating process, creating favorable conditions for the diameter expansion growth of the seed crystal 7. Compared with traditional devices, this method improves the utilization efficiency of the silicon carbide vapor source, promotes the growth of the seed crystal 7 at its edge, effectively expands the diameter of the seed crystal 7, improves the efficiency of seed crystal diameter expansion, and reduces production costs.

[0036] Example 2 This application provides an apparatus for preparing large-size silicon carbide single crystals. The difference between this embodiment and the above embodiments is that: Reference Figure 2 An acceleration guide ring 16 is fixed on the inner wall of the growth chamber 14. The heating mechanism 3 also includes a heating element 32, which is fixed inside the acceleration guide ring 16. An acceleration flow channel 17 is formed between the inner wall of the acceleration guide ring 16 and the outer wall of the separator cylinder 15. The acceleration flow channel 17 includes a diffuser channel 171, a guide channel 172, and an inlet channel 173 connected sequentially from top to bottom. The cross-sectional area enclosed by the inlet channel 173 gradually increases in the direction away from the guide channel 172, and the cross-sectional area enclosed by the diffuser channel 171 also gradually increases in the direction away from the guide channel 172. The acceleration guide ring 16 can be made of graphite, and the heating element 32 can be a resistance heating wire. The acceleration guide ring 16 can accelerate the flow rate of the silicon carbide vapor source in the growth chamber 14, allowing it to flow more quickly towards the edge of the seed crystal 7. During operation, the heating element 32 is activated to heat the speed-increasing guide ring 16, which prevents the silicon carbide vapor source from depositing on the inner wall of the speed-increasing channel 17 during the process of hindering the flow of the speed-increasing channel.

[0037] The design of the speed-increasing guide ring 16 and the speed-increasing flow channel 17 can effectively improve the speed and efficiency of silicon carbide vapor source to the edge of seed crystal 7, enabling the silicon carbide vapor source to reach the edge of seed crystal 7 more quickly and accurately, and promoting the growth of the edge of seed crystal 7.

[0038] Reference Figure 2 and Figure 3 The crucible body 11 has an annular collecting cavity 111 located between the seed crystal holder 2 and the speed-increasing flow channel 17. The inner wall of the collecting cavity 111 has a discharge port 1111 and a feed port 1112, with multiple discharge ports 1111 and feed ports 1112 spaced around the axis of the crucible body 11, and the discharge port 1111 located above the feed port 1112. A support ring 18 is fitted and fixedly connected to the end of the separator cylinder 15 away from the separator plate 12. The support ring 18 is made of the same material as the separator cylinder 15. The support ring 18 is located within the diffusion channel 171, and a guide slope 181 is provided on the outer wall of the support ring 18; specifically, the support ring 18 has an inverted frustum-shaped annular structure. When the silicon carbide vapor source flows from the guide channel 172 to the diffuser channel 171, the outflowing silicon carbide vapor source splits into two streams. One stream directly acts on the outer edge of the lower half of the seed crystal 7; the other stream is fed into the collection chamber 111 through the inlet 1112 of the guide slope 181. The silicon carbide vapor source in the collection chamber 111 is preferentially transported to the outer edge of the upper half of the seed crystal 7 for deposition. This compensates for the concentration attenuation caused by deposition during the ascent of the silicon carbide vapor source along the edge of the seed crystal 7, significantly improving the axial uniformity of crystal growth, thereby obtaining large-size silicon carbide single crystals with equal height and thickness.

[0039] Reference Figure 2 A first temperature measuring element 5 and a second temperature measuring element 6 are spaced apart on one end of the seed crystal holder 2, both embedded and fixed to it. The first temperature measuring element 5 is located in the middle of the seed crystal holder 2, and the second temperature measuring element 6 is located near the edge of the seed crystal holder 2. When the seed crystal 7 is connected to the seed crystal holder 2, the first temperature measuring element 5 can detect the temperature in the middle of the seed crystal 7, and the second temperature measuring element 6 can detect the temperature at the edge of the seed crystal 7. Both the first temperature measuring element 5 and the second temperature measuring element 6 can be temperature sensors such as thermocouples, which can accurately detect the temperature of the edge and the middle of the seed crystal 7 in real time.

[0040] The heating mechanism 3 also includes an edge temperature controller, specifically a ring-shaped heating element 33 embedded in the end face of the seed crystal holder 2. The first temperature measuring element 5 and the second temperature measuring element 6 are both electrically connected to the edge temperature controller. The ring-shaped heating element 33 can be made of a high-temperature resistant alloy material, providing additional heat to the edge of the seed crystal 7 through an electrothermal effect. A heat exchange inlet pipe 34 and a heat exchange outlet pipe 35 are connected to the ring-shaped heating element 33. One end of both the heat exchange inlet pipe 34 and the heat exchange outlet pipe 35 is located outside the crucible body 11. A first flow control element 341 is installed at the end of the heat exchange outlet pipe 35 outside the crucible body 11, and a second flow control element 351 is installed at the end of the heat exchange inlet pipe 34 outside the crucible body 11. The heat exchange inlet pipe 34 and the heat exchange outlet pipe 35 can work with the ring-shaped heating element 33 to circulate a cooling medium, thereby regulating the temperature of the ring-shaped heating element 33. The first flow control element 341 and the second flow control element 351 can be flow regulating valves, which can accurately control the flow rate of the cooling medium.

[0041] The temperature of the edge and center of the seed crystal 7 is monitored in real time by the first temperature measuring element 5 and the second temperature measuring element 6, and the temperature signal is transmitted to the edge temperature controller. Based on the temperature difference data, cooling or heating treatment is selected for the edge of the seed crystal 7. During cooling treatment, cooling medium is introduced into the annular electric heating tube 33 through the heat exchange inlet pipe 34, and the flow rate of the cooling medium is adjusted by the first flow control element 341 and the second flow control element 351, thereby controlling the cooling power of the annular electric heating tube 33. During heating treatment, the operating power of the annular electric heating tube 33 is controlled, thereby controlling the heating power of the annular electric heating tube 33. This keeps the temperature difference between the edge and center of the seed crystal 7 within a suitable range, optimizes the temperature environment for seed crystal 7 growth, further promotes the diameter expansion growth of the seed crystal 7, and improves the quality and stability of the diameter expansion of the seed crystal 7.

[0042] Example 3 This application provides a method for preparing large-size silicon carbide single crystals, which uses the apparatus for preparing large-size silicon carbide single crystals from Example 1 or Example 2, and includes the following steps: S1. Select a seed crystal 7 of suitable size; a 6-inch seed crystal 7 is selected. Pre-treat the surface of the seed crystal 7. Pre-treatment includes rough rolling of the outer diameter, fine rolling of the outer diameter, polishing, cleaning, and drying to reduce the roughness of the seed crystal 7's edges, ensuring that the roughness Ra of the seed crystal 7's edges is ≤0.5nm, and to remove impurities and contaminants from the side surfaces of the seed crystal 7. In this embodiment, during the pre-treatment of the seed crystal 7, the roughness of the seed crystal 7's edges needs to be controlled to be 0.2nm.

[0043] For rough rolling of the outer diameter, a coarse-grained grinding wheel can be used to pre-process the seed crystal 7, removing most of the excess material from the surface. Fine rolling of the outer diameter uses a fine-grained grinding wheel to further improve the accuracy of the outer diameter. Polishing can be performed using chemical mechanical polishing to make the surface of the seed crystal 7 smoother. Cleaning can be done using deionized water and a specialized cleaning agent to remove impurities, and drying can be done using hot air drying or vacuum drying.

[0044] S2. Silicon carbide raw material is added to the raw material cavity 13 of the crucible body 11. A flow guiding structure is arranged inside the crucible body 11 so that the silicon carbide vapor source produced after the silicon carbide raw material is heated flows directionally to the outer circumferential sidewall of the seed crystal 7. After the pretreated seed crystal 7 is fixed to the seed crystal holder 2 by bonding or physical fixing, the seed crystal 7 is then moved into the growth cavity 14 of the crucible 1. In this embodiment, the flow guiding structure is specifically a partition plate 12 and a material separator 15.

[0045] S3. Inert gas is introduced into crucible 1 to pressurize it to 10-100 kPa. Then, the crucible 1 is heated by heating mechanism 3, such as induction coil 31, to 2000-2500°C and maintained for 1-10 hours. The crucible 1 is then evacuated to reduce the internal pressure to 100-5000 Pa and maintained for 1-5 hours. The crucible 1 is then evacuated again to reduce the internal pressure to 100-1000 Pa. Subsequently, the crucible 1 is lifted or the induction coil 31 is moved downwards, and the moving speed of the crucible 1 or the induction coil 31 is controlled at 0.1-1 mm / h. The growth time is controlled at 20-200 hours to complete the diameter expansion of the seed crystal 7.

[0046] During the heating process, the axial temperature gradient is controlled at 3-15℃ / cm, and the radial temperature gradient is controlled at 0.3-12℃ / cm. Argon is used as the inert gas, and the gas flow rate is controlled at 50-1000 sccm.

[0047] S4. Inert gas is introduced into crucible 1 again to increase the internal pressure of crucible 1 to 20-80 kPa. Crucible 1 is then cooled down, either by natural cooling or forced air cooling, to obtain silicon carbide single crystals of the target size.

[0048] S5. Post-processing of silicon carbide single crystals of the target size, including crystal cutting, grinding and polishing, to obtain high-quality silicon carbide single crystals that meet the required size.

[0049] The implementation principle of this embodiment is as follows: By pre-treating the seed crystal 7, the cleanliness and integrity of the seed crystal 7 surface are ensured, providing a good foundation for diameter expansion growth. A flow guiding structure is arranged within the crucible body 11 to direct the silicon carbide vapor source towards the edge of the seed crystal 7, improving the utilization efficiency of the silicon carbide vapor source. By precisely controlling parameters such as pressure, temperature gradient, and gas flow rate, an environment conducive to the diameter expansion growth of the seed crystal 7 is created. The post-processing steps further improve the quality and dimensional accuracy of the silicon carbide single crystal. Compared with traditional methods, this method solves the problems of long diameter expansion cycle and low efficiency of the seed crystal 7. The process is simple, easy to operate, and can efficiently and cost-effectively prepare large-size silicon carbide single crystals.

[0050] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. An apparatus for preparing large-size silicon carbide single crystals, characterized in that, include: The crucible (1) includes a crucible body (11) with one end open and a partition plate (12) disposed inside the crucible body (11). The crucible body (11) has one end open, and the partition plate (12) divides the interior of the crucible body (11) into a raw material chamber (13) and a growth chamber (14). A discharge hole (121) is provided at the edge of the partition plate (12), and a material separator (15) is provided on the partition plate (12). The material separator (15) is located inside the growth chamber (14). Seed crystal holder (2) is disposed at the opening of the crucible body (11) and closes the opening of the crucible body (11); Heating mechanism (3) is used to heat crucible (1).

2. The apparatus for preparing large-size silicon carbide single crystals according to claim 1, characterized in that, It also includes a heat preservation mechanism (4), which includes an insulating heat preservation cylinder (41), a bottom heat preservation seat (42) and a top heat preservation plate (43). The bottom heat preservation seat (42) is located at the bottom of the crucible body (11), and the insulating heat preservation cylinder (41) is sleeved on the outside of the crucible body (11). The top surface of the seed crystal holder (2) is provided with a heat insulation area and a heat dissipation area surrounding the heat insulation area, and the top insulation plate (43) covers the heat insulation area.

3. The apparatus for preparing large-size silicon carbide single crystals according to claim 1, characterized in that, The heating mechanism (3) includes an induction coil (31), which is wound around the outside of the crucible body (11) along the height direction of the crucible body (11). The partition plate (12) and the material separator (15) are made of graphite.

4. The apparatus for preparing large-size silicon carbide single crystals according to claim 1, characterized in that, An acceleration guide ring (16) is provided on the inner wall of the growth chamber (14), and a heating element (32) is provided inside the acceleration guide ring. A speed-increasing flow channel (17) is formed between the inner wall of the speed-increasing guide ring (16) and the outer wall of the material separator (15). The speed-increasing flow channel (17) includes a flow-dispersing channel (171), a flow-guiding channel (172), and an inlet channel (173) connected sequentially from top to bottom. The cross-sectional area enclosed by the inlet channel (173) gradually increases in the direction away from the flow-guiding channel (172).

5. The apparatus for preparing large-size silicon carbide single crystals according to claim 4, characterized in that, The crucible body (11) is provided with a material collection chamber (111), which is located between the seed crystal holder (2) and the speed-increasing flow channel (17); the inner side wall of the material collection chamber (111) is provided with a discharge port (1111) and a feed port (1112), and the discharge port (1111) is located above the feed port (1112); The end of the material separator (15) away from the partition plate (12) is fitted with a support ring (18). The support ring (18) is located inside the diffuser channel (171), and a guide slope (181) is provided on the outer wall of the support ring (18). The guide slope (181) is used to guide the silicon carbide vapor source to the feed inlet (1112).

6. The apparatus for preparing large-size silicon carbide single crystals according to claim 5, characterized in that, The seed crystal holder (2) is provided with a first temperature measuring element (5) and a second temperature measuring element (6) at intervals. The first temperature measuring element (5) is used to detect the temperature in the middle of the seed crystal (7), and the second temperature measuring element (6) is used to detect the temperature at the edge of the seed crystal (7). One end of the seed crystal holder (2) is also embedded with an edge temperature controller, and the first temperature measuring element (5) and the second temperature measuring element (6) are both electrically connected to the edge temperature controller.

7. The apparatus for preparing large-size silicon carbide single crystals according to claim 6, characterized in that, The edge temperature controller includes an annular heating tube (33), and the annular heating tube (33) is connected to a heat exchange inlet tube (34) and a heat exchange outlet tube (35). One end of the heat exchange inlet tube (34) and the heat exchange outlet tube (35) are located outside the crucible body (11). The heat exchange pipe (35) is provided with a first flow control element (341), and the heat exchange inlet pipe (34) is provided with a second flow control element (351).

8. A method for preparing large-size silicon carbide single crystals, characterized in that, The preparation of large-size silicon carbide single crystals using the apparatus for preparing large-size silicon carbide single crystals as described in any one of claims 1-7 includes the following steps: S1. Select a seed crystal (7) of appropriate size, pre-treat the surface of the seed crystal (7) to reduce the roughness of the edge of the seed crystal (7) and remove impurities and contaminants from the side surface of the seed crystal (7); S2. Add silicon carbide raw material to the raw material cavity (13) of the crucible body (11), and arrange a flow guiding structure in the crucible body (11) so that the silicon carbide gas source produced after the silicon carbide raw material is heated flows in a direction to the outer circumferential sidewall of the seed crystal (7); fix the pretreated seed crystal (7) on the seed crystal holder (2), and then move the seed crystal (7) into the growth cavity (14) of the crucible (1); S3. Inert gas is introduced into the crucible (1) to pressurize the crucible (1) to 10-100 kPa; the crucible (1) is then heated to 2000-2500°C and maintained for 1-10 hours; the crucible (1) is evacuated to reduce the internal pressure to 100-5000 Pa and maintained for 1-5 hours; the crucible (1) is evacuated again to reduce the internal pressure to 100-1000 Pa; then the crucible (1) is lifted or the induction coil (31) is moved downward at a speed of 0.1-1 mm / h, and the growth time is controlled at 20-200 hours to complete the diameter expansion of the seed crystal (7); S4. Inert gas is introduced into the crucible (1) again to raise the internal pressure of the crucible (1) to 20-80 kPa. The crucible (1) is then cooled to obtain silicon carbide single crystal of the target size. S5. Post-process the silicon carbide single crystal of the target size to obtain silicon carbide single crystal of the required size.

9. The method for preparing large-size silicon carbide single crystals according to claim 8, characterized in that, Step S3 further includes controlling the axial temperature gradient at 3-15℃ / cm and the radial temperature gradient at 0.3-12℃ / cm during the heating of the crucible (1).

10. The method for preparing large-size silicon carbide single crystals according to claim 9, characterized in that, Argon is used as the inert gas. When filling the crucible (1) with inert gas, the gas flow rate is controlled at 50-1000 sccm.

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