An apparatus and method for annealing silicon carbide

Abstract

The present application relates to the technical field of silicon carbide crystal preparation, and particularly relates to a silicon carbide annealing device and method. The present application provides a silicon carbide annealing device, which comprises a crucible and a cage wheel cover. The cage wheel cover is arranged in the crucible, and the cage wheel cover is in a barrel shape, comprising an upper turntable, a lower turntable and flexible blades. The axis of the upper turntable and the lower turntable is in the same straight line. The blades are in a strip shape, and the two ends of a plurality of blades are connected to the outer end of the upper turntable and the outer end of the lower turntable respectively to form a cage structure. A plurality of axially distributed silicon carbide wafers are arranged in the cage wheel cover. The upper turntable and the lower turntable are connected to an external rotary lifting device through an upper transmission rod and a lower transmission rod respectively. The present application provides a silicon carbide annealing device and method, which can ensure that the silicon carbide in the annealing device is in a temperature uniform temperature field during the annealing process.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide crystal preparation technology, and particularly to an annealing apparatus and method for silicon carbide. Background Technology

[0002] Silicon carbide, as a typical representative of wide bandgap semiconductors, has excellent properties such as large bandgap, high breakdown field strength, high saturated electron mobility, high thermal conductivity, and good thermal and chemical stability. It is an ideal substrate material for fabricating high-frequency, high-voltage, high-efficiency, radiation-resistant, and high-temperature-resistant high-power devices and blue light-emitting diodes. This makes it a promising material for applications in new energy vehicles, high-speed rail, aerospace, high-voltage smart grids, and clean energy, and has therefore attracted widespread attention from the academic community and governments around the world.

[0003] Currently, the crystal quality and manufacturing cost of silicon carbide wafers remain among the main factors limiting their large-scale application. Improving the crystal quality and increasing the wafer size are key to further enhancing the overall cost-effectiveness of silicon carbide single-crystal substrates. During crystal growth, the larger the crystal size, the more difficult it is to control the uniformity of the thermal field, the greater the thermal stress in the crystal, and the more difficult it is to control the quality of the wafer, leading to a significant increase in the wafer defect density.

[0004] High-temperature secondary annealing of silicon carbide crystals and wafers is an important way to effectively improve the quality of silicon carbide wafers and is of great significance for further improving silicon carbide wafer quality. The uniformity of temperature distribution during annealing is a crucial indicator of the annealing effect, especially important for the annealing of large-size silicon carbide crystals and wafers (6-12 inches). Existing annealing techniques mostly use sidewall heating, and the heat transfer within the annealing crucible is limited to thermal radiation and natural convection. This heat transfer efficiency is low, making it difficult to achieve good radial and axial temperature uniformity during the annealing of large-size wafers, thus hindering the achievement of ideal annealing results. Therefore, there is an urgent need to develop an efficient crystal annealing method to solve the problem of uneven radial temperature distribution during crystal annealing, in order to improve the quality of silicon carbide wafers and ultimately enhance device performance. Summary of the Invention

[0005] In view of one or more technical problems of the prior art, the present invention provides an annealing apparatus and method for silicon carbide, which can ensure that the silicon carbide in the annealing apparatus is in a uniform temperature field during the annealing process.

[0006] The present invention provides an annealing apparatus for silicon carbide, comprising a crucible and a cage-type wheel cover; The cage-like wheel cover is disposed inside the crucible. The cage-like wheel cover is barrel-shaped and includes an upper turntable, a lower turntable, and blades. The axes of the upper turntable and the lower turntable are located on the same straight line. The blades are strip-shaped, and the two ends of multiple blades are respectively connected to the outer ends of the upper turntable and the outer ends of the lower turntable to form a cage structure. Multiple axially distributed silicon carbide wafers are disposed in the cage-like wheel cover. The upper turntable and the lower turntable are respectively connected to an external rotating lifting device through an upper transmission rod and a lower transmission rod. In the first operating condition, the relative angle between the upper turntable and the lower turntable is adjusted so that multiple blades tilt and the upper turntable and the lower turntable rotate synchronously to drive the airflow using the blades; In the second operating condition, the relative angle between the upper and lower turntables is adjusted, and the distance between the upper and lower turntables is simultaneously compressed along the axial direction, causing multiple blades to tilt and spirally bend, and the upper and lower turntables are rotated synchronously to drive the airflow using the blades.

[0007] Optionally, in the first operating condition, after the upper turntable and the lower turntable rotate relative to each other, the angle between the blade and the axis of the upper turntable is 5~15°. In the second operating condition, the torsion angle of the upper turntable and the lower turntable is 15~20°, and the axial compression distance is 3~5% of the projected length on the axis after the blade torsion angle.

[0008] Optionally, the rotary lifting device includes a passive mode and an active mode. In the active mode, the rotary lifting device drives the upper turntable or the lower turntable to move axially by a preset distance. In the passive mode, the rotary lifting device is passively displaced axially when subjected to axial force.

[0009] Optionally, the blade comprises tungsten alloy, carbon fiber strip, or tungsten alloy tantalum carbide composite material, wherein the two ends of the tungsten alloy tantalum carbide composite material are tantalum carbide phases and the middle is a tungsten alloy phase.

[0010] Optionally, the two ends of the blade are rotatably connected to the upper and lower turntables via a pin structure.

[0011] Optionally, the rotating shaft of the rotary lifting device is connected to the upper and lower turntables via radial connectors to form a hollow structure.

[0012] Optionally, the lower turntable or the lower turntable is detachably connected to the connector.

[0013] Optionally, the drive shaft of the rotary lifting device connected to the lower turntable is a sleeve rod including an inner rod and an outer rod, one end of the outer rod is connected to the lower turntable, and one end of the inner rod is used to place stacked silicon carbide wafers.

[0014] This invention provides an annealing method for silicon carbide, based on any of the annealing apparatuses described above, the annealing method comprising: Phase 1: Heating up; Phase 2: Simultaneous rotation of the upper and lower turntables at a speed of 30-180 rpm for 6-18 hours. Phase Two, Constant Temperature: The upper and lower turntables are rotated synchronously under the first working condition. The rotation is a continuous periodic rotation, that is, after rotating at the maximum speed for a stable time t1, the speed is uniformly reduced to 0 over time t2 and then accelerated back to the maximum speed, and then rotated at the maximum speed for a stable time t1. This cycle repeats for a total time t. The maximum speed is ±60~120 rpm, t1 is 20~60 min, t2 is 5~15 min, and t is 10~20 h; Phase 3, cooling: In the second operating condition, the upper and lower turntables rotate synchronously at a speed of -30 to -180 rpm for a duration of 30 to 60 hours.

[0015] Optionally, the annealing crucible is a closed physical space, and the airflow inside the crucible circulates in a convective manner under the drive of the blades; the air pressure in the crucible is 30~150 kPa.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects: By rotating the bladed disk between the upper and lower turntables, gas flow near the silicon carbide crystal wafer within the cage-like shroud is promoted, thereby achieving a uniform temperature field near the silicon carbide crystal wafer. Specifically, promoting gas flow involves two operating conditions. First, in the first operating condition, the upper and lower turntables rotate relative to each other, causing the blades connecting them to tilt. The relative angle of rotation is controlled to be small, keeping the blade surface relatively flat with low bending and twisting, primarily with the blades tilting as a whole. At this time, the upper and lower turntables rotate synchronously. In this case, the airflow formed by multiple blades is mainly axial along the cage-like shroud, promoting axial airflow heat exchange near the silicon carbide wafer. Secondly, in the second operating condition, the upper and lower turntables are first twisted at a large angle, causing the blades to form a more pronounced helical bend. Further, the axial distance between the upper and lower turntables is compressed, causing the blades to bend even more. Thus, multiple blades form turbine blades. At this point, synchronous rotation of the upper and lower turntables creates radial airflow near the silicon carbide wafer, increasing radial airflow heat exchange. It should be noted that the blade shape can be flexibly switched in situ between the first and second operating conditions using a rotating lifting device. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the structure of a silicon carbide annealing apparatus according to the present invention; Figure 2 This is a schematic diagram of the assembly process of a silicon carbide annealing apparatus according to the present invention; Figure 3 These are schematic diagrams of the blade morphology of the cage-type enclosure under different working conditions of the present invention. Figure 4 This is a schematic diagram of the structure of a connector and an upper turntable threaded connection provided by the present invention; Figure 5 This is a schematic diagram of a sleeve structure provided by the present invention.

[0019] In the diagram: 1-Crucible; 2-Upper turntable; 3-Lower turntable; 4-Blade; 5-Silicon carbide wafer; 6-Rotating lifting device; 7-Connector; 8-Outer rod; 9-Inner rod. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] In the description of the embodiments of the present invention, unless otherwise expressly specified and limited, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance; unless otherwise specified or explained, the term "multiple sets" refers to two or more sets; the terms "connection," "fixed," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, an integral connection, or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0022] In this specification, it should be understood that the directional terms such as "upper" and "lower" used in the description of the embodiments of the present invention are used to describe the angles shown in the accompanying drawings and should not be construed as limiting the embodiments of the present invention. Furthermore, in the context, it should also be understood that when it is mentioned that one element is connected "upper" or "lower" to another element, it can be directly connected to the other element "upper" or "lower," or indirectly connected to the other element "upper" or "lower" through an intermediate element.

[0023] Please refer to Figure 1 , Figure 2 and Figure 3 The present invention provides an annealing apparatus for silicon carbide, comprising a crucible 1 and a cage-type wheel cover; The cage-like wheel cover is disposed inside the crucible 1. The cage-like wheel cover is barrel-shaped and includes an upper rotating disk 2, a lower rotating disk 3, and blades 4. The axes of the upper rotating disk 2 and the lower rotating disk 3 are located on the same straight line. The blades 4 are strip-shaped, and the two ends of multiple blades 4 are respectively connected to the outer ends of the upper rotating disk 2 and the lower rotating disk 3 to form a cage structure. Multiple axially distributed silicon carbide wafers 5 are disposed in the cage-like wheel cover. The upper rotating disk 2 and the lower rotating disk 3 are respectively connected to an external rotating lifting device 6 through an upper transmission rod and a lower transmission rod. In the first operating condition, the relative angle between the upper turntable 2 and the lower turntable 3 is adjusted so that multiple blades 4 are tilted and the upper turntable 2 and the lower turntable 3 are rotated synchronously to drive the airflow using the blades 4; In the second operating condition, the relative angle between the upper turntable 2 and the lower turntable 3 is adjusted, and the distance between the upper turntable 2 and the lower turntable 3 is compressed axially at the same time, so that multiple blades 4 are tilted and spirally bent, and the upper turntable 2 and the lower turntable 3 are rotated synchronously to drive the airflow using the blades 4.

[0024] By rotating the impeller between the upper turntable 2 and the lower turntable 3, gas flow near the silicon carbide crystal wafer within the cage-like shroud is promoted, thereby achieving a uniform temperature field near the silicon carbide crystal wafer. Specifically, promoting gas flow involves two operating conditions. First, in the first operating condition, the upper turntable 2 and the lower turntable 3 rotate relative to each other, causing the blades 4 connected between the upper turntable 2 and the lower turntable 3 to tilt. The relative angle of rotation is controlled to be small, keeping the surface of the blades 4 relatively flat with low bending and twisting, with the blades 4 tilting as the main feature. At this time, the upper turntable 2 and the lower turntable 3 rotate synchronously. In this case, the airflow formed by the multiple blades 4 is mainly axial along the cage-like shroud, promoting axial airflow heat exchange near the silicon carbide wafer 5. Secondly, in the second operating condition, the upper turntable 2 and the lower turntable 3 are first twisted at a large angle, causing the blade 4 to form a more pronounced helical bend. Further, the axial distance between the upper turntable 2 and the lower turntable 3 is compressed, causing the blade 4 to bend further. Thus, multiple blades 4 form turbine blades 4. At this time, synchronous rotation of the upper turntable 2 and the lower turntable 3 creates radial airflow near the silicon carbide wafer 5, increasing radial airflow heat exchange around the silicon carbide wafer 5. It should be noted that the shape of the blade 4 in the first and second operating conditions can be switched using the rotating lifting device 6.

[0025] In this embodiment, graphite pads are placed between different silicon carbide wafers 5 to promote axial and radial airflow.

[0026] In some embodiments of the present invention, in the first working condition, after the upper turntable 2 and the lower turntable 3 rotate relative to each other, the angle between the blade 4 and the axis of the upper turntable 2 is 5~15°. In the second operating condition, the torsion angle of the upper turntable 2 and the lower turntable 3 is 15~20°, and the axial compression distance is 3~5% of the projected length on the axis after the blade 4 is torsion angled.

[0027] In this embodiment, rotating blade 4 at a relatively small angle of 5-15° is beneficial for generating an airflow with the axial direction as the main direction. With a twist angle of 15-20° and axial compression of 3-5%, rotating blade 4 can generate an airflow with the radial direction as the main direction.

[0028] In some embodiments of the present invention, the rotary lifting device 6 includes a passive mode and an active mode. In the active mode, the rotary lifting device 6 drives the upper turntable 2 or the lower turntable 3 to move axially at a preset distance. In the passive mode, when the rotary lifting device 6 is subjected to axial force, it undergoes passive axial displacement.

[0029] In this embodiment, when the upper turntable 2 and the lower turntable 3 are rotated, the axial distance of the blade 4 will decrease. To prevent the blade 4 from breaking, a rotary lifting device 6 with a passive mode is provided, which can adapt to the change in axial distance caused by the rotation of the blade 4. When precise compression is required, it is adjusted to the active mode to precisely compress the blade 4 axially to the target displacement.

[0030] In this embodiment, the rotary lifting device 6 can be a servo electric cylinder or electric push rod with position feedback. When the servo motor is enabled and off or the system is set to "passive mode," its internal ball screw pair can reverse the transmission, allowing the push rod head to slide axially by external force. At this time, the servo motor will rotate and record the position. In active working mode, the servo motor receives the control signal and precisely pushes the push rod to perform quantitative extension and retraction through the screw, with a positioning accuracy of ±0.01mm. The rotary lifting device 6 can also be a combination of a linear slide and a linear actuator. The passive sliding part is supported by a linear bearing / linear guide slide. It is mounted on the base and is responsible for providing low-friction, high-precision linear guidance, allowing the shaft to be easily pulled and displaced by external force. The active driving part has the end of an electric push rod, cylinder, or hydraulic cylinder mounted on the slide. The actuator itself provides active, quantitative push and pull force, while the entire actuator-slide assembly can be passively pulled by external force as a whole.

[0031] In some embodiments of the present invention, the blade 4 comprises a tungsten alloy or carbon fiber strip or a tungsten alloy tantalum carbide composite material, wherein the two ends of the tungsten alloy tantalum carbide composite material are tantalum carbide phases and the middle is a tungsten alloy phase.

[0032] In this embodiment, tungsten alloy has high temperature resistance and low brittleness, and can deform under stress, thus adapting to changes in operating conditions. When tungsten alloy-tantalum carbide composite material is selected as blade 4, the middle part deforms under stress, while the sides remain relatively straight, making it easier to control blade 4 to form a better helical bending turbine.

[0033] Tungsten alloy and tantalum carbide composite materials can be directly bonded together by vacuum diffusion welding, or they can be prepared by sintering tungsten alloy and tantalum carbide powders with a composition gradient design.

[0034] In addition, the material of blade 4 can also be the 1800 type new ceramic aerogel sheet purchased from Suzhou Elmer Technology Co., Ltd. This material has the properties of ultra-high temperature resistance and good elasticity, and can adapt to the deformation of blade 4 under different working conditions.

[0035] In some embodiments of the present invention, the two ends of the blade 4 are rotatably connected to the upper turntable 2 and the lower turntable 3 by a pin structure.

[0036] In this application, the pin structure makes it easier for the surface of the blade 4 to be flatter when the upper turntable 2 and the lower turntable 3 rotate at a small angle relative to each other, which is beneficial for forming axial airflow drive.

[0037] In some embodiments of the present invention, the rotating shaft of the rotating lifting device 6 is connected to the upper turntable 2 and the lower turntable 3 via a radially connected member 7 to form a hollow structure.

[0038] In this embodiment, the airflow can flow through the perforated structure, which is more conducive to airflow heat exchange.

[0039] In some embodiments of the present invention, the lower turntable 3 or the lower turntable 3 is detachably connected to the connector 7.

[0040] In this embodiment, as Figure 4 As shown, the detachable connection can be a threaded connection. The detachable connection facilitates the insertion and removal of the silicon carbide wafer 5 from the cage-like cover.

[0041] Please refer to Figure 5 In some embodiments of the present invention, the drive shaft of the rotary lifting device 6 connected to the lower turntable 3 is a sleeve rod including an inner rod 9 and an outer rod 8. One end of the outer rod 8 is connected to the lower turntable 3, and one end of the inner rod 9 is used to place the stacked silicon carbide wafers 5.

[0042] In this application, the sleeve rod design enables the cage-like wheel cover to rotate, while the internal silicon carbide wafer 5 remains stationary or rotates at a low speed.

[0043] This invention provides an annealing method for silicon carbide, based on any of the annealing apparatuses described above, the annealing method comprising: Phase 1: Heating up; Phase 2: Simultaneous rotation of the upper and lower turntables at a speed of 30-180 rpm for 6-18 hours. Phase Two, Constant Temperature: The upper and lower turntables are rotated synchronously under the first working condition. The rotation is a continuous periodic rotation, that is, after rotating at the maximum speed for a stable time t1, the speed is uniformly reduced to 0 over time t2 and then accelerated back to the maximum speed, and then rotated at the maximum speed for a stable time t1. This cycle repeats for a total time t. The maximum speed is ±60~120 rpm, t1 is 20~60 min, t2 is 5~15 min, and t is 10~20 h; Phase 3, cooling: In the second operating condition, the upper and lower turntables rotate synchronously at a speed of -30 to -180 rpm for a duration of 30 to 60 hours.

[0044] In some embodiments of the present invention, the annealing crucible is a closed physical space, and the airflow inside the crucible circulates in a convective manner under the drive of the blades; the air pressure in the crucible is 30~150 kPa.

[0045] To more clearly illustrate the technical solution and advantages of the present invention, the following describes the solution of this application in detail through several embodiments.

[0046] Example 1 This example uses the silicon carbide single crystal annealing apparatus provided by the present invention ( Figure 1 Annealing of 6-inch silicon carbide wafers using the specified process and methods includes the following steps: (1) Prepare an annealing crucible. The crucible is a cylindrical open crucible with an inner diameter 30 mm larger than the diameter of the crystal to be annealed. (2) Place the cage wheel cover into the crucible, and connect the lower wheel drive shaft of the cage wheel cover to the drive device at the bottom of the equipment. (3) Place the crystal tray inside the cage-type wheel cover, and place the wafers to be annealed concentrically on the crystal tray inside the cage-type wheel cover from bottom to top. Separate the wafers with graphite blocks and control the spacing between the wafers to be 10mm. (4) Connect the upper wheel disc of the cage-type wheel cover to the upper wheel disc drive shaft; (5) Place the upper insulation material above the crucible. The diameter of the opening in the center of the upper insulation felt is just equal to the diameter of the lifting rod that controls the rotation of the cage turbine cover, so that the lifting rod can just pass through the insulation material. (6) Connect the rotating lifting rod of the control cage turbine cover to the rotating lifting mechanism at the top of the equipment; (7) Close the furnace chamber and evacuate the furnace chamber. When the furnace chamber pressure is less than or equal to 1E-4 Pa, fill the furnace chamber with protective gas. The pressure of the protective atmosphere is 100 kPa. (8) The heating and annealing process includes the following three main stages: Phase 1, heating up: switch the cage wheel cover to the second working condition, and rotate the upper and lower turntables synchronously in the second working condition at a speed of 120 rpm. The heating process lasts for 8 hours, and the target temperature is 1800 ℃. Phase Two, Temperature Control: Once the temperature reaches 1800 ℃, maintain a constant heating power and switch the cage-type wheel cover to the first operating condition. In the first operating condition, the upper and lower turntables rotate synchronously in a continuous periodic manner. That is, after rotating at the maximum speed for a stable time t1, the speed is uniformly reduced to 0 over a time t2 and then accelerated back to the maximum speed, and then rotated at the maximum speed for a stable time t1. This cycle repeats for a total time t. The maximum speed is ±120 rpm, t1 is 30 min, t2 is 10 min, and t is 15 h. Phase 3, cooling down: switch the cage wheel cover back to the second working condition, and rotate the upper and lower turntables synchronously at a speed of -120 rpm for 50 hours.

[0047] (9) After the annealing furnace temperature drops to room temperature, restore the furnace chamber pressure to one atmosphere, open the furnace cover, take out the top insulation material and the cage turbine cover in sequence, and then take out the annealed wafers in sequence.

[0048] In this embodiment, three annealed crystals were randomly selected for comparison of their crystal quality before and after annealing, as shown in Table 1. The comparison results in Table 1 clearly show that the half-width at half-maximum (WHM) of the X-ray diffraction rocking curve of the crystals decreased significantly after annealing, with a maximum reduction of approximately 80%. This indicates a significant improvement in the crystal quality of the crystals after annealing, proving that the apparatus and method provided by this invention can greatly improve crystal quality.

[0049] Table 1: Comparison of crystal quality before and after wafer annealing in Example 1 Example 2 This embodiment uses the silicon carbide single crystal annealing apparatus provided by the present invention. Figure 1 Annealing of 6-inch silicon carbide ingots using the following methods and processes includes the following steps: (1) Prepare an annealing crucible. The crucible is a cylindrical open crucible with an inner diameter 30 mm larger than the diameter of the crystal to be annealed. (2) Place the cage wheel cover into the crucible, and connect the lower wheel drive shaft of the cage wheel cover to the drive device at the bottom of the equipment. (3) Place the crystal tray inside the cage-type wheel cover, and place the wafers to be annealed concentrically on the crystal tray inside the cage-type wheel cover from bottom to top. Separate the wafers with graphite blocks and control the spacing between the wafers to be 30mm. (4) Connect the upper wheel disc of the cage-type wheel cover to the upper wheel disc drive shaft; (5) Place the upper insulation material above the crucible. The diameter of the opening in the center of the upper insulation felt is just equal to the diameter of the lifting rod that controls the rotation of the cage turbine cover, so that the lifting rod can just pass through the insulation material. (6) Connect the rotating lifting rod of the control cage turbine cover to the rotating lifting mechanism at the top of the equipment; (7) Close the furnace chamber and evacuate the furnace chamber. When the furnace chamber pressure is less than or equal to 1E-4 Pa, fill the furnace chamber with protective gas. The pressure of the protective atmosphere is 100 kPa. (8) The heating and annealing process includes the following three main stages: Phase 1, heating up: switch the cage wheel cover to the second working condition, and rotate the upper and lower turntables synchronously in the second working condition at a speed of 120 rpm. The heating process lasts for 8 hours, and the target temperature is 1800 ℃. Phase Two, Temperature Control: Once the temperature reaches 1800 ℃, maintain a constant heating power and switch the cage-type wheel cover to the first operating condition. In the first operating condition, the upper and lower turntables rotate synchronously in a continuous periodic manner. That is, after rotating at the maximum speed for a stable time t1, the speed is uniformly reduced to 0 over a time t2 and then accelerated back to the maximum speed, and then rotated at the maximum speed for a stable time t1. This cycle repeats for a total time t. The maximum speed is ±120 rpm, t1 is 30 min, t2 is 10 min, and t is 15 h. Phase 3, cooling down: switch the cage wheel cover back to the second working condition, and rotate the upper and lower turntables synchronously at a speed of -120 rpm for 50 hours.

[0050] (9) After the annealing furnace temperature drops to room temperature, restore the furnace chamber pressure to one atmosphere, open the furnace cover, take out the top insulation material and the cage turbine cover in sequence, and then take out the annealed wafers in sequence.

[0051] In this embodiment, the average half-width at half-maximum (FWHM) of the X-ray rocking curve of the annealed ingot was reduced by 60%, and the crystallization quality of the crystal was significantly improved, fully demonstrating the beneficial effects of the apparatus and method provided by the present invention.

[0052] Comparative Example 1 The only difference between this comparative example and Example 1 is that the cage-type wheel cover is not set; the other wafer annealing processes are completely the same as in Example 1.

[0053] Test results of the annealed wafer before and after annealing show that the average half-width at half-maximum (FWHM) of the X-ray rocking curve of the wafer after annealing is reduced by only about 10%, which is far less effective than in Example 1. This indicates that the ideal annealing effect cannot be obtained without the cage-type wheel cover provided by the present invention.

[0054] Comparative Example 2 The only difference between this comparative example and Example 1 is that all the second operating conditions in Example 1 are replaced with the first operating condition, that is, only the forced airflow dominated by axial convection.

[0055] Test results of the annealed wafer before and after annealing showed that the average half-width at half-maximum (FWHM) of the X-ray rocking curve of the wafer decreased by only about 25% after annealing. Although the annealing effect was better than that of Comparative Example 1, it was still far inferior to Example 1. This is because there is a large radial temperature difference in the crystal during the high-temperature annealing process. This indicates that even with the cage-type shield provided by the present invention, the ideal annealing effect cannot be obtained by using only the first working condition.

[0056] Comparative Example 3 The only difference between this comparative example and Example 1 is that all the first operating conditions in Example 1 are replaced with the second operating conditions, that is, only forced airflow dominated by radial convection.

[0057] Test results of the annealed wafer before and after annealing showed that the average half-width at half-maximum (FWHM) of the X-ray rocking curve of the wafer decreased by only about 30% after annealing. Although the annealing effect was better than that of Comparative Example 1, it was still far inferior to Example 1. This is because there is a large axial temperature difference in the crystal during the high-temperature annealing process. This indicates that even with the cage-type shield provided by the present invention, the ideal annealing effect cannot be obtained by using only the second working condition.

[0058] Comparative Example 4 The only difference between this comparative example and Example 1 is that the annealing pressure in Example 1 is reduced to 1000 Pa, while the other processes remain the same.

[0059] Test results of the annealed wafer before and after annealing showed that the average half-height of the X-ray rocking curve of the wafer decreased by only about 15% after annealing, and the annealing effect was far inferior to that of Example 1. This is because the gas convection intensity generated by the blade rotation is very limited under low gas pressure, resulting in very low convective heat transfer efficiency and a large axial and radial temperature difference during crystal annealing. Therefore, in the apparatus and method provided by this invention, high gas pressure is essential for improving the annealing effect.

[0060] Comparative Example 5 The only difference between this comparative example and Example 1 is that the diameter of the central opening of the upper layer of the crucible insulation felt is larger than the diameter of the rotating lifting rod of the wheel on the cage turbine cover, with a diameter difference of 60mm. Test results of the annealed wafers before and after annealing showed that the average half-width at half-maximum (FWHM) of the X-ray rocking curve of the wafers increased by about 50% after annealing, and the crystal quality actually deteriorated. This is because when the diameter of the central opening of the upper layer of insulation felt in the crucible is larger than the diameter of the rotating lifting rod of the wheel on the cage turbine cover, a large airflow channel is formed above the crucible leading to the outside of the crucible. This breaks the seal of the crucible's interior. The rotation of the cage turbine cover further accelerates the convective heat transfer between the high-temperature airflow inside the crucible and the low-temperature airflow outside the crucible. The large influx of cold airflow into the crucible severely disrupts the thermal balance inside the crucible, exacerbating the temperature non-uniformity during the wafer annealing process, thus leading to a deterioration in crystal quality. Therefore, in the apparatus and method provided by this invention, forming a relatively enclosed space in the crucible is essential for improving the annealing effect.

[0061] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An annealing apparatus for silicon carbide, characterized in that, Includes a crucible (1) and a cage-type wheel cover; The cage-like wheel cover is set inside the crucible (1). The cage-like wheel cover is barrel-shaped and includes an upper turntable (2), a lower turntable (3), and flexible blades (4). The axes of the upper turntable (2) and the lower turntable (3) are on the same straight line. The blades (4) are strip-shaped. The two ends of multiple blades (4) are respectively connected to the outer ends of the upper turntable (2) and the outer ends of the lower turntable (3) to form a cage structure. Multiple axially distributed silicon carbide wafers (5) are set in the cage-like wheel cover. The upper turntable (2) and the lower turntable (3) are respectively connected to an external rotating lifting device (6) through an upper transmission rod and a lower transmission rod. In the first working condition, the relative angle between the upper turntable (2) and the lower turntable (3) is adjusted so that multiple blades (4) are tilted and the upper turntable (2) and the lower turntable (3) are rotated synchronously to drive the airflow using the blades (4); In the second working condition, the relative angle between the upper turntable (2) and the lower turntable (3) is adjusted, and the distance between the upper turntable (2) and the lower turntable (3) is compressed axially at the same time, so that multiple blades (4) are tilted and spirally bent, and the upper turntable (2) and the lower turntable (3) are rotated at the same time, so as to drive the airflow using the blades (4).

2. The annealing apparatus according to claim 1, characterized in that, In the first working condition, after the upper turntable (2) and the lower turntable (3) rotate relative to each other, the angle between the blade (4) and the axis of the upper turntable (2) is 5~15°. In the second working condition, the torsion angle of the upper turntable (2) and the lower turntable (3) is 15~20°, and the axial compression distance is 3~5% of the projected length on the axis after the blade (4) torsion angle.

3. The annealing apparatus according to claim 1, characterized in that, The rotary lifting device (6) includes a passive mode and an active mode. In the active mode, the rotary lifting device (6) drives the upper turntable (2) or the lower turntable (3) to move axially at a preset distance. In the passive mode, the rotary lifting device (6) is passively displaced axially when subjected to axial force.

4. The annealing apparatus according to claim 1, characterized in that, The blade (4) comprises tungsten alloy or carbon fiber strip or tungsten alloy tantalum carbide composite material, wherein the two ends of the tungsten alloy tantalum carbide composite material are tantalum carbide phase and the middle is tungsten alloy phase.

5. The annealing apparatus according to claim 1, characterized in that, The two ends of the blade (4) are rotatably connected to the upper turntable (2) and the lower turntable (3) through a shaft pin structure.

6. The annealing apparatus according to claim 1, characterized in that, The rotating shaft of the rotating lifting device (6) is connected to the upper turntable (2) and the lower turntable (3) through a radial connector (7) to form a hollow structure.

7. The annealing apparatus according to claim 6, characterized in that, The lower turntable (3) or the lower turntable (3) is detachably connected to the connector (7).

8. The annealing apparatus according to claim 1, characterized in that, The drive shaft of the rotary lifting device (6) connected to the lower turntable (3) is a sleeve rod including an inner rod (9) and an outer rod (8). One end of the outer rod (8) is connected to the lower turntable (3), and one end of the inner rod (9) is used to place stacked silicon carbide wafers (5).

9. An annealing method for silicon carbide, characterized in that, Based on the annealing apparatus according to any one of claims 1-8, the annealing method includes: Phase 1: Heating up; Phase 2: Simultaneous rotation of the upper and lower turntables at a speed of 30-180 rpm for 6-18 hours. Phase Two, Constant Temperature: The upper and lower turntables are rotated synchronously under the first working condition. The rotation is a continuous periodic rotation, that is, after rotating at the maximum speed for a stable time t1, the speed is uniformly reduced to 0 over time t2 and then accelerated back to the maximum speed, and then rotated at the maximum speed for a stable time t1. This cycle repeats for a total time t. The maximum speed is ±60~120 rpm, t1 is 20~60 min, t2 is 5~15 min, and t is 10~20 h; Phase 3, cooling: In the second operating condition, the upper and lower turntables rotate synchronously at a speed of -30 to -180 rpm for a duration of 30 to 60 hours.

10. The annealing method according to claim 9, characterized in that, The annealing crucible is a closed physical space. Driven by the blades, the airflow inside the crucible circulates through convection. The air pressure inside the crucible is 30~150 kPa.

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