A method for improving the surface quality of large size silicon carbide wafers

Abstract

The present application relates to the technical field of silicon carbide crystal, and particularly relates to a method for improving the surface shape and quality of a large-size silicon carbide wafer. The present application provides a method for improving the surface shape and quality of a large-size silicon carbide wafer, which comprises: stacking a plurality of hollow heat pressing discs in which wafers are placed to form a columnar stacking unit; wherein the hollow heat pressing disc comprises two disc bodies, the two disc bodies are respectively provided with a groove and a protrusion, the length of the protrusion is less than the depth of the groove, and the groove and the protrusion are matched to combine the two disc bodies to press the wafer; one end of the stacking unit is placed at the bottom of a crucible, and the other end is fixedly connected to a transmission shaft that is transmitted into the crucible; the crucible is heated to a preset temperature, and the transmission shaft applies pressure to the stacking unit. The present application provides a method for improving the surface shape and quality of a large-size silicon carbide wafer, and can improve the surface shape and quality of the large-size silicon carbide wafer.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide crystal technology, and in particular to a method for improving the surface shape and quality of large-size silicon carbide wafers. Background Technology

[0002] Silicon carbide, as a third-generation wide-bandgap semiconductor material, possesses outstanding properties such as a large bandgap, high breakdown electric field strength, excellent thermal conductivity, fast saturated electron drift velocity, and strong chemical stability. It can significantly improve the working efficiency, high temperature resistance, and voltage withstand level of semiconductor devices. It has irreplaceable application value in fields such as new energy vehicle on-board power supply and electric drive systems, photovoltaic and wind power generation inverter equipment, rail transit traction converters, 5G communication radio frequency devices, and high-end power electronic equipment. It is a key basic material for promoting efficient energy conversion, upgrading the semiconductor industry structure, and localization of core components for high-end equipment.

[0003] With the rapid scaling up of the global new energy and power semiconductor industries, higher demands are being placed on the fabrication cost, production efficiency, and device integration of silicon carbide substrates. Large-size silicon carbide substrates (diameter ≥ 6 inches) have become an urgent need for industry development. Using large-size substrates can effectively increase the number of effective chips per wafer, significantly reduce the overall cost of device manufacturing, and align with the trend of mass production and standardization of automotive-grade semiconductor devices. It also aligns with the upgrading direction of advanced epitaxial growth and device manufacturing processes. It is a crucial prerequisite for realizing the large-scale application of silicon carbide devices and overcoming industry capacity and cost constraints, and has become a key research and development focus for domestic and international silicon carbide material and device manufacturers.

[0004] Currently, the industrial-scale fabrication of large-size silicon carbide substrates (diameter ≥ 6 inches) still faces technical challenges, including poor crystal quality, low overall yield, substrate warpage, and high internal defect density. The main causes of these problems are: during the growth of large-size silicon carbide crystals, the temperature field distribution and material transport field uniformity under high-temperature growth conditions are difficult to precisely control. Thermal and interfacial stresses generated during the crystal growth cycle easily induce intrinsic crystal defects such as dislocations, microtubes, and stacking faults. Simultaneously, silicon carbide itself possesses high hardness and brittleness, making it prone to stress accumulation and surface damage during subsequent processing steps such as slicing, grinding, and chemical mechanical polishing. This further hinders the substrate's planarity and parallelism from meeting the requirements of high-end device fabrication processes, severely limiting the stable mass production and engineering applications of large-size silicon carbide substrates.

[0005] Therefore, there is an urgent need for a method to further improve the surface profile and crystal quality of large-size silicon carbide single crystal substrates in order to promote the rapid development of the industry. Summary of the Invention

[0006] This invention provides a method for improving the surface shape and quality of large-size silicon carbide wafers, which can enhance the surface shape and quality of large-size silicon carbide wafers.

[0007] This invention provides a method for improving the surface shape and quality of large-size silicon carbide wafers, comprising: Multiple hollow heat-spreading pressure plates containing wafers are stacked to form a columnar stacking unit; wherein, the hollow heat-spreading pressure plate includes two plates, each plate having a groove and a protrusion respectively, the length of the protrusion being less than the depth of the groove, the groove and the protrusion cooperating to combine the two plates to press the wafer. One end of the stacking unit is placed at the bottom of the crucible, and the other end is fixedly connected to the drive shaft that feeds into the crucible. The crucible is heated to a preset temperature, and the drive shaft applies pressure to the stacking unit.

[0008] Optionally, multiple heat-spreading blades are arranged between the hollow heat-spreading pressure plates, and the multiple heat-spreading blades are inclined to the radial direction of the plate to form an impeller; Heating the crucible to a preset temperature and applying pressure to the stacking unit by the drive shaft include: After heating begins, the first operating condition is executed: the stacking unit is driven to rotate by the drive shaft, so that the airflow flows along the heat-spreading blades into the space between the hollow heat-spreading pressure plates; After heating for a preset time, pressure is applied to 1.8~2.2MPa using the drive shaft, and the pressure is maintained until the temperature rises to the preset temperature.

[0009] Optionally, after reaching the preset temperature, the following steps are also included: Perform the second operating condition: maintain the temperature and pressure, and continue to rotate the stacking unit using the drive shaft so that the airflow flows along the heat-spreading blades into the space between the hollow heat-spreading pressure plates.

[0010] Optionally, after completing the second working condition, a third working condition is also included: Maintain pressure and reduce temperature to room temperature. During this process, the stacking unit is rotated in the opposite direction using the drive shaft to allow airflow to flow outward from the space between the hollow heat-spreading pressure plates along the heat-spreading blades.

[0011] Optionally, when the temperature inside the crucible is within a preset range, a vibration with a frequency of 10-70 Hz, a micrometer-level amplitude, and a direction axial to the drive shaft is applied using the drive shaft.

[0012] Optionally, the input amplitude of the drive shaft is determined in the following manner: A three-dimensional finite element model was established, including the drive shaft, the sheet, the wafer, and the heat dissipation blades; the silicon carbide wafer, the graphite sheet, and the heat dissipation blades were given realistic material properties. The bottom of the three-dimensional finite element model is constrained, and a sinusoidal micron-level displacement excitation is applied to the top. A frequency sweep analysis was performed in the range of 10~70Hz to output the axial displacement response amplitude of the center point on the upper surface of each wafer layer. Plot the frequency-response amplitude orientation, determine the resonance peaks of each order, read the amplitude decay curve of each wafer layer, change the number of wafer layers, repeat the analysis, and obtain a database of the number of layers and the amplitude distribution of each layer. The natural frequencies of the system at each order are obtained through modal analysis, and the fitting formula A is obtained by mathematically fitting the amplitude decay curve. out(i) = A in exp(-β sim · i); Among them: A out(i) : Output amplitude at the i-th wafer layer; A in : Input amplitude of the drive shaft; β sim : Amplitude attenuation coefficient; exp: Exponential function; After adding or subtracting 20% ​​from the inherent frequencies, the avoidance range is obtained. After removing the avoidance range from 10 to 70 Hz, the safe range is determined. Any frequency in the safe range is then selected as the operating frequency. The number of wafers is determined to be N. The fitting formula corresponding to the working frequency is determined. Within the input amplitude range of Nμm to 2Nμm, all input amplitudes are traversed with a step size of 0.5μm, and multiple sets of wafer amplitude groups are output. From the multiple sets of wafer amplitude groups, the wafer amplitude group in which each wafer amplitude is within the amplitude range and the difference between the maximum and minimum amplitude is the smallest is selected. The input amplitude corresponding to the wafer amplitude group is used as the input amplitude of the experiment. If there is no wafer amplitude group that meets the selection criteria, the working frequency is changed and the step is repeated.

[0013] Optionally, the amplitude range includes 1~10μm or 2~5μm.

[0014] Optionally, the preset time is 3 hours, the drive shaft speed under the first working condition is 160 rpm, the heating efficiency is controlled so that the time to reach the preset temperature is 10 hours, and the preset temperature is 1800℃.

[0015] Optionally, the second operating condition lasts for 10 hours and the drive shaft rotates at 80 rpm.

[0016] Optionally, the cooling time for the third operating condition is 40 hours, and the drive shaft speed is -160 rpm.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: The crucible is heated to a high temperature, and multiple hollow homogenizing pressure plates are stacked inside to form a stacking unit, in which wafers are placed. The top of the stacking unit is connected to a drive shaft, and the bottom abuts against the bottom of the crucible. The drive shaft applies axial pressure to press the wafers, which have a certain degree of plasticity at high temperatures, to be flatter. Attached Figure Description

[0018] 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.

[0019] Figure 1 This is a schematic diagram of a device structure for improving the surface shape and quality of large-size silicon carbide wafers according to an embodiment of the present invention; Figure 2 This is a test report diagram of wafer #1 after surface correction in Example 1; Figure 3 This is the test report after the surface correction of wafer #8 in Example 2; Figure 4 This is the test report after the surface correction of wafer #15 in Example 3.

[0020] In the picture: 1-Stacking unit; 11-Wafer; 12-Dish body; 13-Heating blade; 2-Crucible; 3-Drive shaft; 4-Controller; 5-Support platform. Detailed Implementation

[0021] 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.

[0022] Please refer to Figure 1 This invention provides a method for improving the surface profile and quality of large-size silicon carbide wafers, comprising: Multiple hollow heat-spreading pressure plates containing wafers 11 are stacked to form a columnar stacking unit 1; wherein, the hollow heat-spreading pressure plate includes two sheet bodies 12, each sheet body 12 is provided with a groove and a protrusion, the length of the protrusion is less than the depth of the groove, the groove and the protrusion cooperate to combine the two sheet bodies 12 to press the wafers 11. One end of the stacking unit 1 is placed at the bottom of the crucible 2, and the other end is fixedly connected to the drive shaft 3 that feeds into the crucible 2; The crucible 2 is heated to a preset temperature, and the drive shaft 3 applies pressure to the stacking unit 1.

[0023] The crucible 2 is heated to a high temperature, and multiple hollow homogenizing pressure plates are stacked inside the crucible 2 to form a stacking unit 1, in which a wafer 11 is placed. The top of the stacking unit 1 is connected to a drive shaft 3, and the bottom abuts against the bottom of the crucible 2. The drive shaft 3 applies axial pressure to make the wafer 11, which has a certain plasticity at high temperature, more flat.

[0024] In some embodiments of the present invention, a plurality of heat-spreading blades 13 are provided between the hollow heat-spreading pressure plates, and the plurality of heat-spreading blades 13 are inclined to the radial direction of the plate body 12 to form an impeller; Heating the crucible 2 to a preset temperature and applying pressure to the stacking unit 1 by the drive shaft 3 include: After heating begins, the first working condition is executed: the drive shaft 3 drives the stacking unit 1 to rotate, so that the airflow flows along the heat-spreading blades into the space between the hollow heat-spreading pressure plates; After heating for a preset time, pressure is applied to 1.8~2.2MPa using the drive shaft 3, and the pressure is maintained until the temperature rises to the preset temperature.

[0025] In this embodiment, to further increase the thermal conductivity within the crucible 2, multiple heat-spreading blades 13 are arranged between different hollow heat-spreading pressure plates, forming impellers at an oblique radial angle. The stacking unit 1 can be rotated as a whole via the drive shaft 3, causing the airflow to move radially. In the first operating condition, to allow heat to be quickly conducted to the wafer 11, the stacking unit 1 is rotated to guide the hot airflow near the crucible 2 into the space between the wafers 12 via the heat-spreading blades 13, thereby rapidly heating the wafer 11 by heating the wafers 12. After a preset heating time, the pressure is gradually increased, causing the heated wafer 11 to be under pressure and undergo plastic deformation to form a relatively flat crystal surface.

[0026] In some embodiments of the present invention, after reaching the preset temperature, the method further includes: Execute the second working condition: maintain the temperature and pressure, and continue to rotate the stacking unit 1 using the drive shaft 3 so that the airflow flows along the heat-spreading blades into the space between the hollow heat-spreading pressure plates.

[0027] In this embodiment, continuous heat and pressure are maintained to further flatten the crystal surface, and the heat-equalizing blades 13 are continuously rotated to maintain the temperature.

[0028] In some embodiments of the present invention, after the second working condition is completed, a third working condition is further included: Maintain pressure and reduce temperature to room temperature. During this process, the stacking unit 1 is rotated in the opposite direction using the drive shaft 3 so that airflow flows outward from the space between the hollow heat-spreading pressure plates along the heat-spreading blades.

[0029] In this embodiment, after the second working condition of heat preservation and pressure holding, the flattening of the wafer 11 is basically completed, and it is gradually cooled down and annealed. During this period, it rotates in the opposite direction to discharge the hot air between the hollow heat-spreading pressure plates and continuously promote air flow.

[0030] It should be noted that the rotation and pressurization of the drive shaft 3 are achieved by the controller 4 controlling the drive device, and the output end of the drive device is connected to the drive shaft 3.

[0031] It should also be noted that, in order to facilitate the overall rotation of the stacking unit 1, a cone with its tip pointing downwards is fixedly connected to the bottom of the stacking unit 1, and a concave hole is provided at the bottom of the crucible 2 to match the cone and support platform 5.

[0032] In some embodiments of the present invention, when the temperature inside the crucible 2 is within a preset range, a vibration with a frequency of 10-70 Hz, a micrometer-level amplitude, and a direction axial to the drive shaft 3 is applied using the drive shaft 3.

[0033] In this embodiment, to further enhance the effect and efficiency of crystal surface flatness, micro-vibration is added after reaching the preset range (1200~1800℃). Oscillating force-assisted hot pressing can effectively improve the surface shape of the SiC wafer 11, correcting surface defects such as warping, undulations, and local unevenness; however, parameter mismatch can exacerbate deformation and introduce new damage. During hot pressing, SiC wafer 11 is prone to internal thermal stress, clamping stress, and residual lattice stress, which are the main causes of warping and excessive bow height. Periodic oscillation force can break the stress lock-in state, allowing the wafer 11 to gradually release internal stress within the high-temperature plastic range, resulting in a more flat macroscopic surface shape. Static hot pressing is prone to uneven local contact and micro-gaps, leading to inconsistent force / heat and inducing surface shape deviations. Small-amplitude oscillation can improve the contact uniformity between the wafer 11 and the fixture / pad, resulting in a more balanced distribution of pressure and temperature fields and suppressing differential deformation. At high temperatures, the SiC surface layer has slight plasticity. Oscillating shear force will cause controllable slippage in the 11 micro-regions of the wafer, correcting micron-level surface undulations and edge warping.

[0034] It should be noted that high-frequency, large-amplitude vibrations can generate significant impact forces, leading to alternating fatigue stress and causing microcracks, dislocation proliferation, surface scratches, and surface deterioration in wafer 11. If vibration begins at a lower temperature, SiC, with its high hardness and extremely poor plasticity, cannot be leveled by external forces, which will only exacerbate localized stress concentration. Furthermore, if the oscillation frequency matches the natural frequency of the fixture / wafer 11, resonance will occur, significantly aggravating warping and jitter deformation.

[0035] It should also be noted that piezoelectric ceramics can be installed on the drive shaft 3 to provide axially controllable micro-vibration force.

[0036] In some embodiments of the present invention, the input amplitude of the transmission shaft 3 is determined in the following manner: A three-dimensional finite element model is established, including the drive shaft 3, the sheet 12, the wafer 11, and the heat dissipation blade 13; wherein, the silicon carbide wafer 11, the graphite sheet 12, and the heat dissipation blade 13 are given realistic material properties; The bottom of the three-dimensional finite element model is constrained, and a sinusoidal micron-level displacement excitation is applied to the top. A frequency sweep analysis was performed in the range of 10~70Hz to output the axial displacement response amplitude of the center point on the upper surface of each wafer 11. Plot the frequency-response amplitude orientation, determine the resonance peaks of each order, read out the amplitude decay curve of each layer of wafer 11, change the number of wafer 11 layers, repeat the analysis, and obtain a database of layer number-amplitude distribution of each layer. The natural frequencies of the system at each order are obtained through modal analysis, and the fitting formula A is obtained by mathematically fitting the amplitude decay curve. out(i) = A in exp(-β sim · i); Among them: A out(i) : Output amplitude at position 11 of the i-th layer wafer; A in : Input amplitude of drive shaft 3; β sim : Amplitude attenuation coefficient; exp: Exponential function; After adding or subtracting 20% ​​from the inherent frequencies, the avoidance range is obtained. After removing the avoidance range from 10 to 70 Hz, the safe range is determined. Any frequency in the safe range is then selected as the operating frequency. The number of wafers 11 is determined to be N. The fitting formula corresponding to the working frequency point is determined. Within the input amplitude range of Nμm to 2Nμm, all input amplitudes are traversed with a step size of 0.5μm, and multiple sets of wafer 11 amplitude groups are output. From the multiple sets of wafer 11 amplitude groups, the wafer 11 amplitude group in which each wafer 11 amplitude is within the amplitude range and the difference between the maximum and minimum amplitude is the smallest is selected. The input amplitude corresponding to the wafer 11 amplitude group is used as the input amplitude of the experiment. If there is no wafer 11 amplitude group that meets the selection criteria, the working frequency point is changed and the step is repeated.

[0037] In this embodiment, to ensure that each wafer 11 can be leveled more quickly through vibration, each wafer 11 needs to be located within a favorable amplitude range. However, the amplitude gradually decreases along the drive shaft 3. If the input amplitude of the drive shaft 3 is too large, the upper wafer 11 may experience excessive amplitude; if the input amplitude is too small, the bottom wafer 11 may experience insufficient amplitude. Furthermore, since the wafers 11 are stacked, it is difficult to determine the amplitude of each wafer 11 experimentally. Therefore, this application provides a method for determining the input amplitude. First, a model and constraints are established to simulate the experimental state. Then, based on the analysis results, the resonant frequency is avoided, and the operating frequency is determined. Based on the simulation data, a fitting formula is derived. After determining the operating frequency point, the amplitude of each wafer 11 under any number of wafers 11 and any input amplitude can be determined using the fitting formula. After determining the number of wafers 11 according to the actual situation, multiple sets of wafer 11 amplitude data can be obtained by traversing a suitable amplitude range. After filtering according to requirements, an input amplitude suitable for each wafer 11 can be obtained.

[0038] In some embodiments of the present invention, the amplitude range includes 1~10μm or 2~5μm.

[0039] In some embodiments of the present invention, the preset time is 3 hours, the speed of the drive shaft 3 under the first working condition is 160 rpm, the heating efficiency is controlled so that the time to reach the preset temperature is 10 hours, and the preset temperature is 1800°C.

[0040] In some embodiments of the present invention, the duration of the second working condition is 10 hours, and the rotational speed of the drive shaft 3 is 80 rpm.

[0041] In some embodiments of the present invention, the cooling time of the third working condition is 40 hours, and the rotational speed of the drive shaft 3 is -160 rpm.

[0042] To more clearly illustrate the technology and effects of this application, the following embodiments are also provided: Example 1 Prepare a heating crucible with an inner diameter 100 mm larger than the wafer diameter; Place a bottom pad and a bottom conical hollow homogenizing tray in the crucible from bottom to top; Six silicon carbide wafers to be corrected and five middle-layer hollow heat exchange plates are placed alternately on top of the bottom conical hollow heat exchange tray. A top hollow homogenizing pressure plate is placed above the sixth silicon carbide wafer to be corrected at the top. The pressure and torque transmission shaft is connected to the top hollow heat-spreading platen; Place insulation material on top of the crucible and connect the pressure and torque transmission shaft to the equipment's multi-functional drive; The furnace chamber is closed and evacuated. When the furnace chamber pressure is less than or equal to 1E-4 Pa, protective gas is introduced into the furnace chamber. The pressure of the protective atmosphere is 100 kPa. The heating annealing process includes the following three main stages: The first operating condition is heating. The heating power is turned on to heat the crucible. The heating process lasts for 10 hours, and the target temperature is 1800 ℃.

[0043] After heating for 3 hours, the control driver applies downward pressure to the tower-type homogenizing spinneret in situ. The pressure increases uniformly with heating time, from 0 to 2 MPa. The second operating condition is constant temperature. After the temperature rises to 1800 ℃, the heating power is kept constant, and the downward pressure on the tower-type heat exchanger is kept constant for 10 hours.

[0044] The third operating condition is cooling. The heating power supply is controlled to make the crucible temperature drop evenly and slowly to room temperature. The cooling time is 40 hours. During the cooling process, the downward pressure on the tower-type homogenizing spunbonder is kept constant at 2 MPa.

[0045] After the annealing furnace temperature drops to room temperature, the furnace chamber pressure is restored to one atmosphere. The furnace cover is opened, and the top insulation material, the tower-type homogenizing spinneret, and the wafer are taken out in sequence. Then, the surface parameters of the wafer are tested and characterized.

[0046] |BOW| and Warp values ​​are important indicators reflecting the surface quality of wafers. Smaller values ​​indicate better wafer flatness, less wafer deformation, and higher quality. Table 1 summarizes the surface data comparison of wafers #1 to #6 in Example 1 before and after correction. Figure 2 This is the test report after wafer #1 has undergone surface correction. It can be seen that the device and method provided by this invention can effectively reduce the |BOW| and Warp values ​​of the wafer, with an average reduction of 156.092 μm.

[0047] Table 1: Comparison of wafer shape indicators before and after correction in Example 1 Example 2 Example 2 is basically the same as Example 1, except that the following rotation method is added to the three working conditions: The first operating condition is heating. The heating power is turned on to heat the crucible. The heating process lasts for 10 hours, and the target temperature is 1800 ℃.

[0048] While heating, the driver is controlled to rotate the tower-type heat spreader clockwise at 160 rpm. After heating for 3 hours, the driver applies downward pressure to the tower-type heat spreader in place, and the pressure increases uniformly from 0 to 2 MPa over the heating time. The second operating condition is constant temperature. After the temperature rises to 1800 ℃, the heating power is kept constant, and the downward pressure on the tower-type heat exchanger is kept constant. The driver is controlled to reduce the clockwise rotation speed of the tower-type heat exchanger to 80 rpm and maintain this for 10 hours.

[0049] The third working condition is cooling. The heating power supply is controlled to make the crucible temperature drop evenly and slowly to room temperature. The cooling time is 40 hours. During the cooling process, the driver is controlled to make the tower-type heat exchanger rotate counterclockwise at a speed of -160 rpm. During the cooling process, the downward pressure on the tower-type heat exchanger is kept constant at 2 MPa.

[0050] Table 2 summarizes the surface profile data of wafers #7 to #12 in Example 2 before and after correction. Figure 3 This is the test report for wafer #8 after surface correction. It can be seen that the device and method provided by this invention can effectively reduce the |BOW| and Warp values ​​of the wafer, with an average reduction of 178.238 μm. When the surface correction values ​​of the wafer are similar, Example 2 is more effective than Example 1, with the corrected surface correction values ​​all reduced to within 20 μm, and the average reduction increased by approximately 20 μm. This is attributed to the fact that in-situ rotation of the device according to the process provided by this invention can significantly improve the uniformity of the in-plane temperature distribution during wafer hot pressing. Therefore, this embodiment fully demonstrates the effectiveness and necessity of the device and process provided by this invention.

[0051] Table 2: Comparison of wafer shape indicators before and after correction in Example 2 Example 3 Example 3 is basically the same as Example 2, except that a method of applying vibration to the drive shaft using a piezoelectric ceramic vibrator is added. The vibration frequency is 20Hz and the input amplitude is 6.3μm. The amplitude is determined by using a fitting formula obtained by establishing a finite element model and combining it with the vibration frequency. In this formula, β = 0.15 / layer, the number of wafers is 6, and to ensure that the bottom layer has a 3μm amplitude, the input amplitude needs to be set to approximately 6.3μm.

[0052] Table 3 summarizes the surface profile data of wafers #13 to #18 in Example 3 before and after correction. Figure 4 This is a test report for wafer #15 after surface correction. It can be seen that the device and method provided by this invention can effectively reduce the |BOW| and Warp values ​​of the wafer, with an average reduction of 192.676 μm. When the surface correction values ​​are similar, Example 3 shows the best effect compared to Examples 1 and 2. The corrected surface values ​​are all reduced to within 5 μm, and the average reduction is about 40 μm greater than that of Example 1. This is attributed to the fact that applying periodic oscillation force to the wafer in situ according to the process provided by this invention can break the stress lock-in state in the wafer, allowing the wafer to gradually release internal stress within the high-temperature plastic range. Simultaneously, it can improve the contact uniformity between the wafer and the pressure plate, making the pressure and temperature field distribution more balanced, thereby improving the wafer surface shape. Therefore, this embodiment fully demonstrates the effectiveness and necessity of the device and process provided by this invention.

[0053] Table 3: Comparison of wafer shape indicators before and after correction in Example 3 Finally, it should be noted that the above embodiments and comparative examples 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 and comparative examples, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments and comparative examples, or equivalent substitutions can be made to some of the technical features. Such 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 and comparative examples of the present invention.

Claims

1. A method for improving the surface shape and quality of large-size silicon carbide wafers, characterized in that, include: Multiple hollow heat-spreading pressure plates containing wafers (11) are stacked to form a columnar stacking unit (1); wherein, the hollow heat-spreading pressure plate includes two plates (12), each plate (12) is provided with a groove and a protrusion, the length of the protrusion is less than the depth of the groove, and the groove and the protrusion cooperate to combine the two plates (12) to press the wafer (11). One end of the stacking unit (1) is placed at the bottom of the crucible (2), and the other end is fixedly connected to the drive shaft (3) that feeds into the crucible (2); The crucible (2) is heated to a preset temperature, and the drive shaft (3) applies pressure to the stacking unit (1).

2. The method for improving the surface shape and quality of large-size silicon carbide wafers according to claim 1, characterized in that, Multiple heat-spreading blades (13) are arranged between the hollow heat-spreading pressure plates. The multiple heat-spreading blades (13) are inclined to the radial direction of the plate body (12) to form an impeller. Heating the crucible (2) to a preset temperature and applying pressure to the stacking unit (1) by the drive shaft (3) include: After heating begins, the first working condition is executed: the stacking unit (1) is driven to rotate by the drive shaft (3) so that the airflow flows along the heat-spreading blades into the space between the hollow heat-spreading pressure plates; After heating for a preset time, pressure is applied to 1.8~2.2MPa using the drive shaft (3), and the pressure is maintained until the temperature rises to the preset temperature.

3. The method for improving the surface shape and quality of large-size silicon carbide wafers according to claim 2, characterized in that, After reaching the preset temperature, it also includes: Perform the second working condition: maintain the temperature and pressure, and continue to rotate the stacking unit (1) using the drive shaft (3) so that the airflow flows along the heat-spreading blades into the space between the hollow heat-spreading pressure plates.

4. The method for improving the surface shape and quality of large-size silicon carbide wafers according to claim 3, characterized in that, After completing the second working condition, the third working condition is also included: Maintain pressure and reduce temperature to room temperature. During this process, the stacking unit (1) is rotated in the opposite direction using the drive shaft (3) so that airflow flows outward from the space between the hollow heat-spreading pressure plates along the heat-spreading blades.

5. The method for improving the surface shape and quality of large-size silicon carbide wafers according to claim 1, characterized in that, When the temperature inside the crucible (2) is within a preset range, a vibration with a frequency of 10~70Hz, a micrometer-level amplitude, and a direction in the axial direction of the transmission shaft (3) is applied by the transmission shaft (3).

6. The method for improving the surface shape and quality of large-size silicon carbide wafers according to claim 5, characterized in that, The input amplitude of the drive shaft (3) is determined in the following manner: A three-dimensional finite element model is established, including the drive shaft (3), the sheet (12), the wafer (11), and the heat dissipation blade (13); wherein, the silicon carbide wafer (11), the graphite sheet (12), and the heat dissipation blade (13) are given real material properties; The bottom of the three-dimensional finite element model is constrained, and a sinusoidal micron-level displacement excitation is applied to the top. A frequency sweep analysis was performed in the range of 10~70Hz to output the axial displacement response amplitude of the center point on the upper surface of each wafer (11). Plot the frequency-response amplitude orientation, determine the resonance peaks of each order, read the amplitude decay curve of each layer of the wafer (11), change the number of layers of the wafer (11), repeat the analysis, and obtain a database of the number of layers and the amplitude distribution of each layer. The natural frequencies of the system at each order are obtained through modal analysis, and the fitting formula A is obtained by mathematically fitting the amplitude decay curve. out(i) = A in exp(-β sim · i); Among them: A out(i) : Output amplitude at the i-th layer wafer (11); A in : Input amplitude of drive shaft (3); β sim : Amplitude attenuation coefficient; exp: Exponential function; After adding or subtracting 20% ​​from the inherent frequencies, the avoidance range is obtained. After removing the avoidance range from 10 to 70 Hz, the safe range is determined. Any frequency in the safe range is then selected as the operating frequency. The number of wafers (11) is determined to be N. The fitting formula corresponding to the working frequency point is determined. In the input amplitude range of Nμm to 2Nμmm, all input amplitudes are traversed with a step size of 0.5μm. Multiple sets of wafer (11) amplitude groups are output. From the multiple sets of wafer (11) amplitude groups, the wafer (11) amplitude group in which each wafer (11) amplitude is within the amplitude range and the difference between the maximum and minimum amplitude is the smallest is selected. The input amplitude corresponding to the wafer (11) amplitude group is used as the input amplitude of the experiment. If there is no wafer (11) amplitude group that meets the selection criteria, the working frequency point is changed and the step is repeated.

7. The method for improving the surface shape and quality of large-size silicon carbide wafers according to claim 6, characterized in that, The amplitude range includes 1~10μm or 2~5μm.

8. The method for improving the surface shape and quality of large-size silicon carbide wafers according to claim 2, characterized in that, The preset time is 3 hours, the speed of the drive shaft (3) under the first working condition is 160 rpm, the heating efficiency is controlled so that the time to reach the preset temperature is 10 hours, and the preset temperature is 1800℃.

9. A method for improving the surface shape and quality of large-size silicon carbide wafers according to claim 3, characterized in that, The second working condition lasts for 10 hours, and the rotational speed of the drive shaft (3) is 80 rpm.

10. A method for improving the surface shape and quality of large-size silicon carbide wafers according to claim 4, characterized in that, The cooling time for the third working condition is 40 hours, and the rotation speed of the drive shaft (3) is -160 rpm.

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