A method for preparing aluminum nitride single crystal substrate

Abstract

The invention discloses a method for preparing an aluminum nitride single crystal substrate, and relates to the relevant field of aluminum nitride single crystal substrates. The invention adopts a bidirectional growth method to prepare an aluminum nitride single crystal substrate, and has the advantage that it can significantly increase the crystal growth rate, which can reach 1.0-1.5 mm / h. At the same time, by controlling the upper and lower temperature gradients, the uniform growth of the crystal in two directions is achieved, thereby reducing stress concentration and defect generation. The method not only improves the production efficiency of the substrate, but also optimizes the crystal quality, ensures that it has excellent mechanical, thermal and optical properties, and is suitable for the manufacture of high-performance electronic devices.

Description

Technical Field

[0001] The present invention relates to the field related to aluminum nitride single crystal substrates, and in particular to a method for preparing an aluminum nitride single crystal substrate. Background Art

[0002] Aluminum nitride single crystal substrate is a single crystal substrate made of high-purity aluminum nitride material. It has excellent thermal conductivity, electrical insulation and high mechanical strength. It is often used in the manufacture of high-power electronic devices, optoelectronic devices and microwave devices. It can provide a stable crystal structure and help improve the performance and durability of the device, especially in extreme environments such as high temperature and high pressure. Aluminum nitride single crystal substrates are also widely used in power semiconductors and radio frequency devices because of their good compatibility with other semiconductor materials (such as gallium nitride).

[0003] The existing patent application number is: CN201780015442.5, which is a method for manufacturing an aluminum nitride single crystal substrate, comprising: a preparation step of preparing a base substrate formed of aluminum nitride single crystal; a growth step of growing an aluminum nitride single crystal layer with a thickness of more than 500 μm on the main surface of the base substrate to obtain a stacked body; a separation step of cutting the aluminum nitride single crystal layer portion of the stacked body to separate the stacked body into a base substrate of a thin film stacked with at least a portion of the aluminum nitride single crystal layer and an aluminum nitride single crystal layer portion other than the above; a regeneration grinding step of grinding the surface of the thin film of the base substrate stacked with the thin film; and a circulation step of using the regenerated base substrate formed of aluminum nitride single crystal obtained in the regeneration grinding step as a base substrate for growing aluminum nitride single crystals on its grinded surface.

[0004] The above patents and prior art have the following problems in actual use: they grow on one side with a slow growth rate, resulting in low production efficiency; at the same time, the crystal is prone to stress concentration and structural defects due to uneven temperature control, affecting the quality and performance of the substrate; and in the post-processing polishing process, it is manual or semi-automatic operation, which consumes manpower and affects work efficiency. Summary of the invention

[0005] Therefore, in order to solve the above-mentioned shortcomings, the present invention provides a method for preparing an aluminum nitride single crystal substrate.

[0006] In order to achieve the above object, the present invention adopts the following technical scheme: a method for preparing an aluminum nitride single crystal substrate, the specific steps are as follows:

[0007] S1 equipment preparation: high temperature furnace: induction heating furnace or resistance heating furnace, working temperature range is 1800℃ to 2000℃, crucible design: high purity graphite or boron nitride crucible with upper and lower symmetrical structure, temperature gradient control: set two upper and lower temperature gradients in the crystal growth area, gas control system: ensure the supply of high purity nitrogen, nitrogen purity is 99.999%, flow rate is 10-30sccm;

[0008] S2 material preparation: high-purity aluminum source: AlN powder, purity ≥ 99.999%, nitrogen source: high-purity nitrogen, used to provide reaction atmosphere;

[0009] S3 reactor design and bidirectional growth environment: adopting a double crucible structure with symmetry up and down, placing seed AlN powder on the upper and lower sides of the crucible respectively, so that aluminum nitride crystals grow in the upper and lower directions, temperature gradient: upper growth zone temperature: 1800℃ to 2000℃, lower growth zone temperature: 1700℃ to 1900℃, temperature gradient: maintain 30-50℃ / cm;

[0010] S4 crystal growth steps:

[0011] a. Initial preparation: loading raw materials - vacuum treatment - introducing nitrogen; b. Crystal growth process: heating and temperature rise - bidirectional growth; c. Cooling and finishing: slow cooling - crystal cutting;

[0012] S5 post-processing: completed with a grinding auxiliary device, rough grinding and fine polishing are used in the grinding process, combined with cerium oxide polishing liquid for mechanical polishing;

[0013] S6 quality inspection: Perform X-ray diffraction to check the crystal structure, ensure the single crystal quality of the crystal, and determine that there are no significant lattice defects.

[0014] Preferably, the crystal growth step described in S4 comprises the following specific steps:

[0015] a. Initial preparation: Loading raw materials: Place high-purity AlN powder in the middle reaction zone of the graphite crucible, place seed crystals above and below, and ensure that they are kept 10-15mm away from the gas phase reaction zone; Vacuum treatment: Evacuate the reactor to 10 -5 Up to 10 - 4 Torr to remove oxygen and moisture in the reactor; Introduce nitrogen: Through the nitrogen introduction system, maintain the nitrogen flow rate at 10-30sccm to ensure uniform nitrogen supply;

[0016] b. Crystal growth process: Heating: Heating to 1800°C at a rate of 5°C / min to ensure that aluminum reacts with nitrogen to generate AlN gas phase substances. The temperatures of the upper and lower growth zones should be controlled at 1800-2000°C and 1700-1900°C, respectively. The temperature gradient diffuses upward and downward from the crystal growth center; Bidirectional growth: The gas phase AlN is transported in the upward and downward directions respectively through the temperature gradient, deposited and grown along the surface of the seed crystal, AlN grows simultaneously in two directions, and maintains the stability of the crystal structure. The growth rate is controlled to be 0.2-0.5mm / h, which is achieved by adjusting the nitrogen flow rate and temperature gradient; Growth time: The crystal growth time is 50 to 100 hours;

[0017] c. Cooling and finishing: Slow cooling: After the growth is completed, slowly cool down to room temperature at a rate of 3-5℃ / min; Crystal cutting: Use laser cutting to cut the crystal into single crystal substrates with a thickness of 200-500 microns.

[0018] Preferably, the grinding auxiliary device includes a protective chamber for protection, a grinding belt arranged at the lower end of the protective chamber for grinding the substrate, an auxiliary adjustment mechanism arranged at the top of the grinding belt for clamping and adjusting the substrate, and an auxiliary cleaning mechanism arranged at the upper end of the protective chamber for cleaning the substrate.

[0019] Preferably, the auxiliary adjustment mechanism includes two groups of relatively arranged base plates, a fixing rod arranged between the two groups of base plates, an auxiliary rail arranged at the top of the left end base plate, a main rail installed at the top of the right end base plate, a pressing mechanism arranged on the inner sides of the main rail and the auxiliary rail, a fixing seat arranged at the right end of the top of the right end base plate, a first motor arranged on the right side of the fixing seat, a rocker arm connected to the output shaft of the first motor and placed on the left side of the fixing seat, a connecting rod connected to the other end of the rocker arm, and a slider arranged on the outside of the pressing mechanism, the inner side of the connecting rod passes through the main rail and is connected to the pressing mechanism, and the base plate is installed on the top of the grinding belt.

[0020] Preferably, the guiding rail is in an inverted T-shape, the lower end of the main rail is in an inverted T-shape, and the upper end is in an inverted Y-shape, guide grooves are provided on the inner sides of the main rail and the guiding rail, the slider is movably embedded in the guide groove inside the main rail, and is also connected to another set of pressing mechanisms inside the guiding rail through another set of sliders.

[0021] Preferably, a placement groove is opened at the front and rear positions of the lower end of the main rail, and the connecting rod is placed inside the placement groove.

[0022] Preferably, the pressing mechanism includes an outer shell for protection and connected to a slider on the outside, a pressure plate arranged on the inner side of the outer shell, a connecting block connected to the inner side of the pressure plate and placed inside the outer shell, a cam arranged inside the outer shell and abutting against the connecting block, a connecting shaft arranged in the middle of the cam, the bottom of the connecting shaft is rotatably connected to the bottom of the outer shell, and a bolt arranged at the upper end of the outer shell and connected to the cam.

[0023] Preferably, the auxiliary cleaning mechanism includes a top seat installed on the top of the protective bin, a second motor arranged at the left end of the bottom of the top seat, a rotating rod connected to the output shaft of the second motor, a pull rod hinged to the other end of the rotating rod, a sliding block hinged to the other end of the pull rod, a guide member arranged at the front end of the sliding block, a connecting member connected to the upper end of the guide member, a support plate connected to the upper end of the front end surface of the connecting member, an embedded rod arranged at the four ends of the outer side of the support plate, a support seat contacting the embedded rod and installed on the top of the protective bin, an injection port opened at the front end of the support plate, and a spray plate arranged at the bottom of the support plate.

[0024] Preferably, a slide groove is provided in the middle of the guide member, the upper end of the slide groove is connected to the connecting member, and a convex column is provided at the lower end of the connecting member, and the convex column is movably embedded in the slide groove.

[0025] Preferably, a strip groove is provided at the lower end of the top seat for the sliding block to movably embed.

[0026] Beneficial effects of the present invention:

[0027] The advantage of the present invention in preparing aluminum nitride single crystal substrate by adopting the bidirectional growth method is that it can significantly increase the crystal growth rate, which can reach 1.0-1.5 mm / h. At the same time, by controlling the upper and lower temperature gradients, the uniform growth of the crystal in two directions is achieved, thereby reducing stress concentration and defect generation. This method not only improves the production efficiency of the substrate, but also optimizes the crystal quality, ensuring that it has excellent mechanical, thermal and optical properties, and is suitable for the manufacture of high-performance electronic devices.

[0028] The present invention is completed by adopting a grinding auxiliary device in the post-processing step. An auxiliary adjustment mechanism is arranged in the device. The lower part of the auxiliary adjustment mechanism corresponds to the grinding belt. The mechanism can clamp the substrate and adjust the angle position, which is convenient for grinding the grinding belt without manual adjustment. An auxiliary cleaning mechanism corresponding to the auxiliary adjustment mechanism is installed on the upper end of the device. The auxiliary cleaning mechanism can match the adjustment process to perform efficient spray cleaning on the substrate, automatically operate, effectively improve work efficiency, and has strong applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the structure of the grinding auxiliary device of the present invention;

[0030] Figure 2 It is a schematic diagram of the structure of the auxiliary adjustment mechanism of the present invention;

[0031] Figure 3 It is a schematic diagram of the main rail structure of the present invention;

[0032] Figure 4 It is a schematic diagram of the structure of the pressing mechanism of the present invention;

[0033] Figure 5It is a schematic diagram of the main structure of the auxiliary cleaning mechanism of the present invention;

[0034] Figure 6 It is a schematic diagram of the structure of the auxiliary cleaning mechanism of the present invention;

[0035] Figure 7 It is a structural schematic diagram of the auxiliary cleaning mechanism of the present invention from another viewing angle.

[0036] Among them: protective bin-1, grinding belt-2, auxiliary adjustment mechanism-3, auxiliary cleaning mechanism-4, bottom plate-31, fixed rod-32, auxiliary rail-33, main rail-34, pressing mechanism-35, fixed seat-36, first motor-37, rocker arm-38, connecting rod-39, slider-310, outer shell-351, pressure plate-352, connecting block-353, cam-354, connecting shaft-355, bolt-356, top seat-41, second motor-42, rotating rod-43, pull rod-44, sliding block-45, guide member-46, connecting member-47, support plate-48, embedded rod-49, support seat-410, injection port-411, spray plate-412. DETAILED DESCRIPTION

[0037] In order to further explain the technical solution of the present invention, it is described in detail below through specific embodiments.

[0038] The present invention provides a method for preparing an aluminum nitride single crystal substrate, S1 equipment preparation: high temperature furnace: induction heating furnace or resistance heating furnace, the working temperature range is 1900°C, crucible design: adopting a high-purity graphite or boron nitride crucible with an upper and lower symmetrical structure, temperature gradient control: setting two upper and lower temperature gradients in the crystal growth zone, gas control system: ensuring the supply of high-purity nitrogen, the purity of nitrogen is 99.999%, and the flow rate is 20sccm; S2 material preparation: high-purity aluminum source: AlN powder, the purity is ≥99.999%, nitrogen source: high-purity nitrogen, used to provide a reaction atmosphere; S3 Reactor design and bidirectional growth environment: adopt a double crucible structure with symmetry up and down, place seed AlN powder on the upper and lower sides of the crucible respectively, so that aluminum nitride crystals grow in the upper and lower directions, temperature gradient: upper growth zone temperature: 1900℃, lower growth zone temperature: 1800℃, temperature gradient: maintain 40℃ / cm; S4 Crystal growth steps: a. Initial preparation: Loading raw materials: Place high-purity AlN powder in the middle reaction zone of the graphite crucible, place seed crystals up and down, and ensure that it is kept at a distance of 12.5mm from the gas phase reaction zone; Vacuum treatment: Evacuate the reactor to 10 -5 Up to 10 -4Torr to remove oxygen and moisture in the reactor; introduce nitrogen: through the nitrogen introduction system, maintain the nitrogen flow rate at 20sccm to ensure uniform nitrogen supply; b. Crystal growth process: heating: heat up to 1800℃ at a rate of 5℃ / min to ensure that aluminum reacts with nitrogen to generate AlN gas phase substances. The temperatures of the upper and lower growth zones should be controlled at 1900℃ and 1800℃ respectively. The temperature gradient diffuses upward and downward from the crystal growth center; bidirectional growth: through the temperature gradient, the gas phase AlN is transported in the upward and downward directions respectively, deposited and grown along the surface of the seed crystal, AlN grows simultaneously in two directions, and maintains the stability of the crystal structure, and controls The growth rate is 0.2-0.5mm / h, which is achieved by adjusting the nitrogen flow rate and temperature gradient; Growth time: The crystal growth time is 50 to 100 hours; c. Cooling and finishing: Slow cooling: After the growth is completed, slowly cool down to room temperature at a rate of 3-5℃ / min; Crystal cutting: Use laser cutting to cut the crystal into single crystal substrates with a thickness of 200-500 microns; S5 post-processing: It is completed using a grinding auxiliary device, and rough grinding and fine polishing are used during the grinding process, combined with cerium oxide polishing liquid for mechanical polishing; S6 quality inspection: Perform X-ray diffraction to check the crystal structure, ensure the single crystal quality of the crystal, and determine that there are no significant lattice defects;

[0039] To achieve an accurate temperature gradient of 40°C / cm, independent heating elements and intelligent control systems are required. High-precision temperature sensors are arranged every 1 cm in the reaction zone along the crystal growth direction to achieve real-time monitoring and control of temperature. Each heating section has an independent PID temperature controller, which can automatically adjust the power output according to the sensor data to maintain the target temperature difference. At the same time, the feedback control system controls the temperature data through the PLC or DCS system to compare it with the target gradient in real time, and sets high-frequency adjustment to ensure that the temperature gradient is stable at around 40°C / cm and maintain a temperature accuracy of ±1°C. In addition, a heat-insulating reflective barrier is added to the outside of the heating zone to reduce heat loss, and a heat-averaging zone is added between each section to make the temperature field more uniform. Through step-by-step debugging and calibration, a constant temperature gradient can be maintained in each crystal growth cycle. At the same time, an abnormal alarm system is equipped to promptly alarm and stop the operation when the temperature difference deviates from the set tolerance to ensure the stability of the preparation process and the high-quality growth of aluminum nitride single crystal substrates.

[0040] See also Figure 1 The grinding auxiliary device includes a protective bin 1, the bottom of which is installed on the top of a grinding belt 2, an auxiliary adjustment mechanism 3 is arranged above the grinding belt 2, the auxiliary adjustment mechanism 3 is used to clamp and adjust the position of the substrate to facilitate grinding, and an auxiliary cleaning mechanism 4 is arranged at the upper end of the protective bin 1, which can efficiently clean the substrate adjusted by the auxiliary adjustment mechanism 3.

[0041] See also Figure 2-Figure 4The auxiliary adjustment mechanism 3 includes two sets of bottom plates 31 arranged opposite to each other. The front and rear ends of the inner sides of the two sets of bottom plates 31 are connected by a fixing rod 32. A guide rail 33 is fixed to the left end of the top of the left bottom plate 31. The guide rail 33 is in an inverted T shape. A main guide rail 34 is locked in the middle of the top of the right bottom plate 31. Guide grooves are provided on the inner sides of the main guide rail 34 and the guide rail 33. The lower end of the main guide rail 34 is in an inverted T shape and the upper end is in an inverted Y shape. A placement groove is provided at the front and rear positions of the lower end of the main guide rail 34. A fixing seat 36 is locked in the middle of the right end of the top of the right bottom plate. The fixing seat A first motor 37 is arranged on the right side of 36, the output shaft of the first motor 37 passes through the fixing seat 36 and is connected to a swing rod 38, the other end of the swing rod 38 is connected to a connecting rod 39, the left side of the connecting rod 39 passes through the main guide rail 34 and is connected to a pressing mechanism 35, the connecting rod 39 is placed inside the placement groove, a slider 310 is arranged at the front and rear positions outside the pressing mechanism 35, the slider 310 can be movably embedded in the guide groove inside the main guide rail 34, and is also connected to another group of pressing mechanisms 35 through another group of sliders 310 inside the auxiliary guide rail 33, and the bottom plate 31 is installed on the top of the grinding belt 2;

[0042] The pressing mechanism 35 includes a shell 351 for protection, a contact pressure plate 352 is arranged on the inner side of the shell 351, the inner side of the pressure plate 352 is connected to a connecting block 353, the connecting block 353 is placed inside the shell 351, the other end of the connecting block 353 is against a cam 354, a connecting shaft 355 is arranged in the middle of the cam 354, the bottom of the connecting shaft 355 is rotatably connected to the shell 351, and the top of the connecting shaft 355 is connected to a bolt 356 installed on the upper end of the shell 351.

[0043] See also Figure 5-Figure 7 The auxiliary cleaning mechanism 4 includes a top seat 41 installed on the top of the protective bin 1, a second motor 42 is installed at the left end of the bottom of the top seat 41, the front end output shaft of the second motor 42 is connected to the rotating rod 43, the other end of the rotating rod 43 is hinged to the pull rod 44, the other end of the pull rod 44 is hinged to the sliding block 45, the front end of the sliding block 45 is connected to the guide member 46, the middle of the guide member 46 is provided with a slide groove, the upper end of the slide groove is connected to the connecting member 47, the lower end of the connecting member 47 is provided with a convex column, the convex column is movably embedded in the inside of the slide groove, the upper end of the front end surface of the connecting member 47 is connected to the support plate 4 8 is fixed, and embedding rods 49 are fixed at the left and right positions of the front and rear ends of the support plate 48. The top of the embedding rod 49 contacts the support seat 410, and the four ends of the bottom of the support seat 410 are provided with grooves for the embedding rod 49 to be embedded. The top of the support seat 410 is connected to the bottom of the top seat 41, and the front end of the support plate 48 is provided with an injection port 411 that can be connected to an external water supply device. A spray plate 412 is provided at the bottom of the support plate 48, and a spray hole is provided at the bottom of the spray plate 412. The interior of the spray plate 412 is communicated with the injection port 411, and the lower end of the top seat 41 is provided with a strip groove for the sliding block 45 to be movably embedded.

[0044] The specific implementation process is as follows:

[0045] When the processed substrate needs to be polished, first place the two sets of pressing plates 352 directly, then rotate the bolts 356 on the housing 351 to rotate the cam 354, and when the cam 354 rotates, it can act on the connecting block 353 to push the pressing plate 352 out to clamp and fix the substrate;

[0046] Then, the grinding belt 2 is started to grind the upper substrate. If the angle adjustment or flipping is required, the first motor 37 is started to work. The output shaft of the first motor 37 drives the swing rod 38 to swing. During the swinging process, the connecting rod 39 can be driven to move the housing 351. The housing 351 moves in the guide groove inside the main rail 34 through the slider 310. The left end can slide in the guide groove inside the auxiliary rail 33 through the slider 310 to achieve angle adjustment and flipping of the substrate.

[0047] When it is necessary to clean the substrate during the polishing process, first connect the injection port 411 to the external water supply equipment to supply water, and the bottom of the spray plate 412 can spray water to clean the substrate. When the matched and adjusted substrate needs to be cleaned, start the second motor 42, and the second motor 42 drives the rotating rod 43 to move. The rotating rod 43 can drive the pull rod 44 to move the sliding block 45 left and right, and the guide member 46 connected to the front end of the sliding block 45 follows the movement, and the guide member 46 drives the support plate 48 to flip up, so that the support plate 48 sprays and cleans at the corresponding angle of the substrate.

[0048] The above description is only a preferred example of the present invention and is not intended to limit the present invention. Although the present invention is described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing an aluminum nitride single crystal substrate, characterized in that: The specific steps are as follows: S1 equipment preparation: high temperature furnace: induction heating furnace or resistance heating furnace, working temperature range is 1800℃ to 2000℃, crucible design: high purity graphite or boron nitride crucible with upper and lower symmetrical structure, temperature gradient control: set two upper and lower temperature gradients in the crystal growth area, gas control system: ensure the supply of high purity nitrogen, nitrogen purity is 99.999%, flow rate is 10-30sccm; S2 material preparation: high-purity aluminum source: AlN powder, purity ≥ 99.999%, nitrogen source: high-purity nitrogen, used to provide reaction atmosphere; S3 reactor design and bidirectional growth environment: adopting a double crucible structure with symmetry up and down, placing seed AlN powder on the upper and lower sides of the crucible respectively, so that aluminum nitride crystals grow in the upper and lower directions, temperature gradient: upper growth zone temperature: 1800℃ to 2000℃, lower growth zone temperature: 1700℃ to 1900℃, temperature gradient: maintain 30-50℃ / cm; S4 crystal growth steps: a. Initial preparation: loading raw materials - vacuum treatment - introducing nitrogen; b. Crystal growth process: heating and temperature rise - bidirectional growth; c. Cooling and finishing: slow cooling - crystal cutting; S5 post-processing: completed with a grinding auxiliary device, rough grinding and fine polishing are used in the grinding process, combined with cerium oxide polishing liquid for mechanical polishing; S6 quality inspection: perform X-ray diffraction to check the crystal structure, ensure the single crystal quality of the crystal, and confirm that there are no significant lattice defects; The grinding auxiliary device includes a protection chamber for protection, a grinding belt arranged at the lower end of the protection chamber for grinding the substrate, an auxiliary adjustment mechanism arranged at the top of the grinding belt for clamping and adjusting the substrate, and an auxiliary cleaning mechanism arranged at the upper end of the protection chamber for cleaning the substrate; The auxiliary adjustment mechanism includes two sets of bottom plates arranged opposite to each other, a fixing rod arranged between the two sets of bottom plates, an auxiliary rail arranged on the top of the left bottom plate, a main rail installed on the top of the right bottom plate, a pressing mechanism arranged on the inner sides of the main rail and the auxiliary rail, a fixing seat arranged on the right end of the top of the right bottom plate, a first motor arranged on the right side of the fixing seat, a swing rod connected to the output shaft of the first motor and placed on the left side of the fixing seat, a connecting rod connected to the other end of the swing rod, and a slider arranged on the outer side of the pressing mechanism, the inner side of the connecting rod passes through the main rail and is connected to the pressing mechanism, and the bottom plate is installed on the top of the grinding belt; A placement groove is provided at the front and rear positions of the lower end of the main guide rail, and the connecting rod is placed inside the placement groove; The pressing mechanism includes an outer shell for protection and connected to a slider on the outside, a pressure plate arranged on the inner side of the outer shell, a connecting block connected to the inner side of the pressure plate and placed inside the outer shell, a cam arranged inside the outer shell and abutting against the connecting block, a connecting shaft arranged in the middle of the cam, the bottom of the connecting shaft is rotatably connected to the bottom of the outer shell, and a bolt arranged at the upper end of the outer shell and connected to the cam.

2. The method for preparing an aluminum nitride single crystal substrate according to claim 1, characterized in that: The crystal growth steps described in S4 are as follows: a. Initial preparation: Loading raw materials: Place high-purity AlN powder in the middle reaction zone of the graphite crucible, place seed crystals above and below, and ensure that they are kept 10-15mm away from the gas phase reaction zone; Vacuum treatment: Evacuate the reactor to 10 -5 Up to 10 -4 Torr to remove oxygen and moisture in the reactor; Introduce nitrogen: Through the nitrogen introduction system, maintain the nitrogen flow rate at 10-30sccm to ensure uniform nitrogen supply; b. Crystal growth process: Heating: Heating to 1800°C at a rate of 5°C / min to ensure that aluminum reacts with nitrogen to generate AlN gas phase substances. The temperatures of the upper and lower growth zones should be controlled at 1800-2000°C and 1700-1900°C, respectively. The temperature gradient diffuses upward and downward from the crystal growth center; Bidirectional growth: The gas phase AlN is transported in the upward and downward directions respectively through the temperature gradient, deposited and grown along the surface of the seed crystal, AlN grows simultaneously in two directions, and maintains the stability of the crystal structure. The growth rate is controlled to be 0.2-0.5mm / h, which is achieved by adjusting the nitrogen flow rate and temperature gradient; Growth time: The crystal growth time is 50 to 100 hours; c. Cooling and finishing: Slow cooling: After the growth is completed, slowly cool down to room temperature at a rate of 3-5℃ / min; Crystal cutting: Use laser cutting to cut the crystal into single crystal substrates with a thickness of 200-500 microns.

3. The method for preparing an aluminum nitride single crystal substrate according to claim 1, characterized in that: The auxiliary cleaning mechanism includes a top seat installed on the top of the protective bin, a second motor arranged at the left end of the bottom of the top seat, a rotating rod connected to the output shaft of the second motor, a pull rod hinged to the other end of the rotating rod, a sliding block hinged to the other end of the pull rod, a guide member arranged at the front end of the sliding block, a connecting member connected to the upper end of the guide member, a support plate connected to the upper end of the front end surface of the connecting member, an embedded rod arranged at the four ends of the outer side of the support plate, a support seat contacting the embedded rod and installed at the top of the protective bin, an injection port opened at the front end of the support plate, and a spray plate arranged at the bottom of the support plate.

4. The method for preparing an aluminum nitride single crystal substrate according to claim 3, characterized in that: A slide groove is provided in the middle of the guide member, the upper end of the slide groove is connected to the connecting member, and a convex column is provided at the lower end of the connecting member, and the convex column is movably embedded in the slide groove.

5. The method for preparing an aluminum nitride single crystal substrate according to claim 4, characterized in that: The lower end of the top seat is provided with a strip groove for the sliding block to be movably embedded.

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