Method for preparing aluminum nitride crystal by controlling nucleation of aluminum nitride crystal in reverse temperature field
By first applying a temperature gradient in the reverse axis and then converting it to the positive axis in the aluminum nitride crystal growth device, the nucleation process of aluminum nitride crystals is solved, and the multi-nucleation sites and polycrystals in conventional physical gas phase transport methods are solved. The problem of academic orientation has achieved high-quality aluminum nitride crystal growth.
Patent Information
- Application Number
- CN202411401298.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-09
- Publication Date
- 2025-01-03
AI Technical Summary
At this stage, the growth and preparation technology of aluminum nitride crystals is difficult to achieve high-quality industrial production, especially in conventional physical gas phase transmission methods. Excessive axial temperature gradient leads to high supersaturation of aluminum vapor, which is prone to multiple nucleation sites. and polycrystalline orientation, resulting in a decrease in crystal quality.
Nucleation is performed by controlling the reverse axial temperature gradient in the aluminum nitride crystal growth device, and then converting it to a positive axial temperature gradient, and the temperature gradient in the crystal growth region is regulated to achieve small-site nucleation under seedless conditions and High-quality growth.
Effectively inhibit the uncontrolled nucleation process, provide high-quality single-oriented crystal nucleation, and improve the nucleation quality and growth integrity of aluminum nitride crystals.
Smart Images
Figure CN119243326A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of semiconductor crystal materials, and in particular relates to a method for preparing aluminum nitride crystals by controlling aluminum nitride crystal nucleation with a reverse temperature field. Background Art
[0002] As one of the representatives of the third-generation semiconductor materials, aluminum nitride has an ultra-wide bandgap, high breakdown voltage, high saturated electron mobility, high thermal conductivity and excellent chemical stability. It can be used in high-power microelectronic devices, deep ultraviolet optoelectronic devices, ultra-high integrated circuits, lasers and many other fields under high temperature and strong radiation environments.
[0003] Based on the above analysis, aluminum nitride crystals have broad application prospects, but their growth and preparation technology is still incomplete at this stage, making it difficult to achieve high-quality industrial production. At present, researchers generally recognize physical vapor transport (PVT) as a reliable method for growing high-quality, large-size aluminum nitride crystals. This method has the advantages of fast growth rate and high crystal integrity, and has long been the research focus of growing aluminum nitride crystals.
[0004] In the physical vapor transport method, the positive axial temperature gradient from the raw material area to the growth area is the main driving force for crystal growth, so the regulation of the overall temperature field distribution in the crucible and the temperature gradient in the crystal growth area is the key to obtaining high-quality bulk aluminum nitride crystals. In the nucleation process of aluminum nitride crystals grown by conventional physical vapor transport, excessive axial temperature gradients lead to high supersaturation of aluminum vapor in the growth zone, which easily produces multiple nucleation sites and multiple crystallographic orientations in the nucleation stage, ultimately leading to a decrease in crystal quality. Therefore, it is urgent to develop a temperature field control strategy based on physical vapor transport to achieve the growth and preparation of high-quality aluminum nitride crystals while ensuring the growth rate and crystal integrity. Summary of the invention
[0005] In view of the problem of low quality of aluminum nitride crystals in the prior art, the present invention provides a method for preparing aluminum nitride crystals by controlling the nucleation of aluminum nitride crystals by a reverse temperature field, which achieves the few-site nucleation and high-quality growth of aluminum nitride crystals under seedless conditions by regulating the temperature gradient in the crystal growth area.
[0006] The present invention is achieved through the following technical solutions: A method for preparing aluminum nitride crystal by controlling aluminum nitride crystal nucleation by reverse temperature field comprises the following steps: (1) placing raw materials for growing aluminum nitride crystals in a crucible, placing the crucible device in an aluminum nitride crystal growth device, and sealing the aluminum nitride crystal growth device; (2) Controlling the high-purity nitrogen atmosphere in the aluminum nitride crystal growth equipment and maintaining the pressure, starting the temperature increase program to increase the temperature in the crucible to a preset temperature, maintaining the reverse axial temperature gradient from the raw material area to the crystal growth area during the temperature increase process, and maintaining the temperature to perform aluminum nitride nucleation; (3) After nucleation is completed, the temperature is raised to the crystal growth temperature, and the positive axial temperature gradient from the raw material area to the crystal growth area is controlled, and the temperature is maintained to grow the aluminum nitride crystal; (4) After the insulation procedure in step (3) is completed, the temperature is lowered to room temperature, the crystal growth crucible is taken out, and the aluminum nitride crystal is obtained.
[0007] Furthermore, the raw material for producing aluminum nitride crystals in step (1) is aluminum nitride powder; and the distance between the upper surface of the aluminum nitride raw material and the seed crystal rack is 20 to 40 mm.
[0008] Furthermore, the pressure in the aluminum nitride crystal growth equipment in step (2) is 400-800 mbar.
[0009] Furthermore, in step (2), the heating rate is 3-10 °C / min, and the preset temperature is 1800-2200 °C.
[0010] Furthermore, it is characterized in that in step (2), the reverse axial temperature gradient is -1 to -10 °C / mm, and the insulation time is 8 to 18 h.
[0011] Furthermore, in step (3), the heating rate is 3-10°C / min, and the crystal growth temperature is 2250-2400°C.
[0012] Furthermore, in step (3), the positive axial temperature gradient is 0.1-10 °C / mm, and the insulation time is 24-72 h.
[0013] Furthermore, the cooling rate in step (4) is 0.5-1 °C / min.
[0014] The beneficial effects achieved by the present invention are: The method for preparing aluminum nitride crystals by controlling the nucleation of aluminum nitride crystals by reverse temperature field of the present invention belongs to the category of physical vapor transport method. By applying a reverse temperature field to the growth zone in the nucleation stage, the uncontrolled nucleation process is effectively suppressed, providing high-quality single-oriented crystal nuclei for the growth of aluminum nitride crystals. BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Figure 1 Figure 1 is a diagram of aluminum nitride crystal growth equipment. The thick arrow indicates the direction of the reverse temperature field, and the dotted arrow indicates the direction of the suppressed gas phase transmission. Among them, 1. upper heater, 2. crystal growth crucible, 3. lower heater, 4. motion system, 5. seed crystal rack, 6. aluminum nitride raw material, 7. insulation system, 8. infrared temperature measurement system. Figure 2 This is a picture of the finished product after the nucleation stage of Example 1; Figure 3 This is a picture of the finished product after the nucleation stage of Example 5; Figure 4 This is the finished product picture of comparative example 1 after the nucleation stage is completed. DETAILED DESCRIPTION
[0016] The above contents of the present invention are further described in detail below through examples, but this should not be understood as the scope of the above subject matter of the present invention being limited to the following examples, and all technologies implemented based on the above contents of the present invention belong to the scope of the present invention.
[0017] In the diagram of the aluminum nitride crystal growth equipment of the present invention, the thick arrow indicates the direction of the reverse temperature field, and the dotted arrow indicates the direction of the suppressed gas phase transmission; wherein 1 is an upper heater, 2 is a crystal growth crucible (made of tungsten), 3 is a lower heater, 4 is a motion system, 5 is a seed crystal rack, 6 is an aluminum nitride raw material, 7 is a heat preservation system, and 8 is an infrared temperature measurement system.
[0018] The method for preparing aluminum nitride crystal by controlling the nucleation and growth of aluminum nitride crystal by reverse temperature field of the present invention is now described in detail in conjunction with the accompanying drawings and specific embodiments.
[0019] Example 1 (1) The inner wall and outer surface of the crystal growth crucible 2 are cleaned with anhydrous ethanol, and the aluminum nitride raw material (aluminum nitride powder, such as Figure 1 As shown in the figure, the aluminum nitride raw material 6 is placed in an aluminum nitride crystal growth device without placing a seed crystal. The distance between the upper surface of the aluminum nitride raw material 6 and the seed crystal rack is 25 mm, and the aluminum nitride crystal growth device is sealed; (2) Turn on the vacuum system and evacuate the furnace chamber of the aluminum nitride crystal growth equipment to a pressure no higher than 10 -3 Pa. High-purity nitrogen (technical index is ≥99.999%) is introduced to control the high-purity nitrogen atmosphere in the furnace chamber of the aluminum nitride crystal growth equipment and maintain the pressure at 500 mbar; the upper heater 1 and the lower heater 3 are turned on to control the reverse axial temperature gradient from the growth zone to the raw material zone to be -1 ℃ / mm (the temperature from the raw material zone to the growth zone gradually increases), and the temperature is increased to 2000 ℃ at a heating rate of 3 ℃ / min, and the temperature is kept for 5 hours for aluminum nitride nucleation; (3) After the nucleation (heat preservation) in step (2) is completed, the positive axial temperature gradient from the raw material area to the growth area is controlled to be 5 °C / mm (the temperature from the raw material area to the growth area gradually decreases) by the upper heater 1 and the lower heater 3, and the temperature is increased to 2300 °C at a heating rate of 5 °C / min, and the temperature is kept for 48 h to grow aluminum nitride crystals; (4) After the heat preservation procedure in step (3) is completed, the temperature is lowered to room temperature at a rate of 1 °C / min, and the crystal growth crucible 2 is taken out to obtain aluminum nitride crystals. The finished product is shown in the figure below. Figure 2 As shown, it can be seen that there are relatively few nucleation sites, the individual grains are larger, and the nucleation of grains with different crystallographic orientations is suppressed.
[0020] Example 2 (1) The inner wall and outer surface of the crystal growth crucible 2 are cleaned with anhydrous ethanol, and the aluminum nitride raw material (aluminum nitride powder, such as Figure 1 As shown in the figure, the aluminum nitride raw material 6 is placed in an aluminum nitride crystal growth device without placing a seed crystal. The distance between the upper surface of the aluminum nitride raw material 6 and the seed crystal rack is 25 mm, and the aluminum nitride crystal growth device is sealed; (2) Turn on the vacuum system and evacuate the furnace chamber of the aluminum nitride crystal growth equipment to a pressure no higher than 10 -3 Pa. High-purity nitrogen (technical index is ≥99.999%) is introduced to control the high-purity nitrogen atmosphere in the furnace chamber of the aluminum nitride crystal growth equipment and maintain the pressure at 500 mbar; the upper heater 1 and the lower heater 3 are turned on to control the reverse axial temperature gradient from the growth zone to the raw material zone to be -5 ℃ / mm (the temperature from the raw material zone to the growth zone gradually increases), and the temperature is increased to 2100 ℃ at a heating rate of 5 ℃ / min, and the temperature is kept for 5 hours for aluminum nitride nucleation; (3) After the nucleation (heat preservation) in step (2) is completed, the positive axial temperature gradient from the raw material area to the growth area is controlled to be 8 °C / mm (the temperature from the raw material area to the growth area gradually decreases) by the upper heater 1 and the lower heater 3, and the temperature is increased to 2300 °C at a heating rate of 5 °C / min, and the temperature is kept for 72 h to grow aluminum nitride crystals; (4) After the insulation program in step (3) is completed, the temperature is lowered to room temperature at a rate of 1 °C / min, and the crystal growth crucible is taken out to obtain aluminum nitride crystals.
[0021] Example 3 (1) The inner wall and outer surface of the crystal growth crucible 2 are cleaned with anhydrous ethanol, and the aluminum nitride raw material (aluminum nitride powder, such as Figure 1 As shown in the figure, the aluminum nitride raw material 6 is placed in an aluminum nitride crystal growth device without placing a seed crystal. The distance between the upper surface of the aluminum nitride raw material 6 and the seed crystal rack is 25 mm, and the aluminum nitride crystal growth device is sealed; (2) Turn on the vacuum system and evacuate the furnace chamber of the aluminum nitride crystal growth equipment to a pressure no higher than 10 -3Pa. High-purity nitrogen (technical index is ≥99.999%) is introduced to control the high-purity nitrogen atmosphere in the furnace chamber of the aluminum nitride crystal growth equipment and maintain the pressure at 500 mbar; the upper heater 1 and the lower heater 3 are turned on to control the reverse axial temperature gradient from the growth zone to the raw material zone to be -10 ℃ / mm (the temperature from the raw material zone to the growth zone gradually increases), and the temperature is raised to 1800 ℃ at a heating rate of 7 ℃ / min, and the temperature is kept for 5 hours for aluminum nitride nucleation; (3) After the nucleation (heat preservation) in step (2) is completed, the positive axial temperature gradient from the raw material area to the growth area is controlled to be 10 °C / mm (the temperature from the raw material area to the growth area gradually decreases) by the upper heater 1 and the lower heater 3, and the temperature is increased to 2300 °C at a heating rate of 10 °C / min, and the temperature is kept for 48 h to grow aluminum nitride crystals; (4) After the insulation program in step (3) is completed, the temperature is lowered to room temperature at a rate of 1 °C / min, and the crystal growth crucible is taken out to obtain aluminum nitride crystals.
[0022] Example 4 (1) The inner wall and outer surface of the crystal growth crucible 2 are cleaned with anhydrous ethanol, and the aluminum nitride raw material (aluminum nitride powder, such as Figure 1 As shown in the figure, the aluminum nitride raw material 6 is placed in an aluminum nitride crystal growth device without placing a seed crystal. The distance between the upper surface of the aluminum nitride raw material 6 and the seed crystal rack is 25 mm, and the aluminum nitride crystal growth device is sealed; (2) Turn on the vacuum system and evacuate the furnace chamber of the aluminum nitride crystal growth equipment to a pressure no higher than 10 -3 Pa. High-purity nitrogen (technical index is ≥99.999%) is introduced to control the high-purity nitrogen atmosphere in the furnace chamber of the aluminum nitride crystal growth equipment and maintain the pressure at 500 mbar; the upper heater 1 and the lower heater 3 are turned on to control the reverse axial temperature gradient from the growth zone to the raw material zone to be -8 ℃ / mm (the temperature from the raw material zone to the growth zone gradually increases), and the temperature is increased to 2200 ℃ at a heating rate of 3 ℃ / min, and the temperature is kept for 10 hours for aluminum nitride nucleation; (3) After the nucleation (heat preservation) in step (2) is completed, the positive axial temperature gradient from the raw material area to the growth area is controlled to be 8 °C / mm (the temperature from the raw material area to the growth area gradually decreases) by the upper heater 1 and the lower heater 3, and the temperature is increased to 2300 °C at a heating rate of 3 °C / min, and the temperature is kept for 48 h to grow aluminum nitride crystals; (4) After the insulation program in step (3) is completed, the temperature is lowered to room temperature at a rate of 1 °C / min, and the crystal growth crucible is taken out to obtain aluminum nitride crystals.
[0023] Example 5 The difference between this embodiment and embodiment 1 is that the assembly of the crucible in step (1) is adjusted, the aluminum nitride seed crystal is fixed on the seed crystal rack, and the distance between the upper surface of the aluminum nitride raw material 6 and the seed crystal is 25 mm. The finished product after the overall process is completed and cut is shown in the figure Figure 3 As shown, the obtained aluminum nitride crystals are slightly yellow, have good light transmittance, and have a consistent crystallographic orientation, which confirms that the conditions are suitable for the nucleation and growth of aluminum nitride crystals.
[0024] Comparative Example 1 (1) The inner wall and outer surface of the crystal growth crucible 2 are cleaned with anhydrous ethanol, and the aluminum nitride raw material (aluminum nitride powder, such as Figure 1 As shown in the figure, the aluminum nitride raw material 6 is placed in an aluminum nitride crystal growth device without placing a seed crystal. The distance between the upper surface of the aluminum nitride raw material 6 and the seed crystal rack is 25 mm, and the aluminum nitride crystal growth device is sealed; (2) Turn on the vacuum system and evacuate the furnace chamber of the aluminum nitride crystal growth equipment to a pressure no higher than 10 -3 Pa. High-purity nitrogen (technical index is ≥99.999%) is introduced to control the high-purity nitrogen atmosphere in the furnace chamber of the aluminum nitride crystal growth equipment and maintain the pressure at 500 mba; the lower heater is turned on to control the positive axial temperature gradient to 5 ℃ / mm (the temperature from the raw material area to the growth area gradually decreases), and the temperature is increased to 2000 ℃ at a heating rate of 3 ℃ / min, and the temperature is kept for 5 hours for aluminum nitride nucleation; (3) After the nucleation (heat preservation) in step (2) is completed, the positive axial temperature gradient from the raw material area to the growth area is controlled to be 5 °C / mm (the temperature from the raw material area to the growth area gradually decreases) by the lower heater, and the temperature is increased to 2300 °C at a heating rate of 5 °C / min, and the temperature is kept for 48 h to grow aluminum nitride crystals; (4) After the insulation program in step (3) is completed, the temperature is lowered to room temperature at a rate of 1 °C / min, and the crystal growth crucible is taken out to obtain aluminum nitride crystals. The finished product is shown in the figure below. Figure 4 As shown, it can be seen that there are relatively more nucleation sites, the individual grains are small, and the nucleation of different crystallographic orientations is not controlled.
Claims
1. A method for preparing aluminum nitride crystals by controlling the nucleation of aluminum nitride crystals by reverse temperature field, characterized in that: The following steps are involved: (1) placing raw materials for growing aluminum nitride crystals in a crucible, placing the crucible device in an aluminum nitride crystal growth device, and sealing the aluminum nitride crystal growth device; (2) Controlling the high-purity nitrogen atmosphere in the aluminum nitride crystal growth equipment and maintaining the pressure, starting the temperature increase program to increase the temperature in the crucible to a preset temperature, maintaining the reverse axial temperature gradient from the raw material area to the crystal growth area during the temperature increase process, and maintaining the temperature to perform aluminum nitride nucleation; (3) After nucleation is completed, the temperature is raised to the crystal growth temperature, and the positive axial temperature gradient from the raw material area to the crystal growth area is controlled, and the temperature is maintained to grow the aluminum nitride crystal; (4) After the insulation program in step (3) is completed, the temperature is lowered to room temperature, the crystal growth crucible is taken out, and the aluminum nitride crystal is obtained.
2. The method for preparing aluminum nitride crystal by controlling aluminum nitride crystal nucleation by reverse temperature field according to claim 1, characterized in that: The raw material for producing aluminum nitride crystals described in step (1) is aluminum nitride powder; the distance between the upper surface of the aluminum nitride raw material and the seed crystal rack is 20 to 40 mm.
3. The method for preparing aluminum nitride crystal by controlling aluminum nitride crystal nucleation by reverse temperature field according to claim 1, characterized in that: The pressure in the aluminum nitride crystal growth equipment in step (2) is 400-800 mbar.
4. The method for preparing aluminum nitride crystal by controlling aluminum nitride crystal nucleation by reverse temperature field according to claim 1, characterized in that: In step (2), the heating rate is 3-10 °C / min, and the preset temperature is 1800-2200 °C.
5. The method for preparing aluminum nitride crystal by controlling the nucleation growth of aluminum nitride crystal by reverse temperature field according to claim 1, characterized in that: In step (2), the reverse axial temperature gradient is -1 to -10 °C / mm, and the insulation time is 8 to 18 h.
6. The method for preparing aluminum nitride crystal by controlling aluminum nitride crystal nucleation by reverse temperature field according to claim 1, characterized in that: In step (3), the heating rate is 3-10 °C / min, and the crystal growth temperature is 2250-2400 °C.
7. The method for preparing aluminum nitride crystal by controlling aluminum nitride crystal nucleation by reverse temperature field according to claim 1, characterized in that: In step (3), the positive axial temperature gradient is 0.1-10 °C / mm, and the insulation time is 24-72 h.
8. The method for preparing aluminum nitride crystal by controlling aluminum nitride crystal nucleation by reverse temperature field according to claim 1, characterized in that: The cooling rate in step (4) is 0.5~1 ℃ / min.