A method for preparing an aluminum nitride single crystal material

Abstract

The application relates to the field of semiconductor materials, and provides a preparation method of an aluminum nitride single crystal material, which solves the defects of small size, poor quality, slow speed and difficult production of the aluminum nitride single crystal material prepared by the prior art; the method comprises the following steps: 1) raw material preparation: including AlN powder and SiC seed crystal; 2) AlN powder purification treatment; 3) TaC crucible preparation; 4) SiC seed crystal fixing and bonding; and 5) aluminum nitride single crystal material growth.

Description

Technical Field

[0001] This invention relates to the field of semiconductor materials, and more particularly to a method for preparing aluminum nitride single crystal material. Background Technology

[0002] With the rapid development of new energy, communications, rail transportation, aerospace and other fields, the semiconductor industry is playing an increasingly important role. Aluminum nitride (AlN) has become a leader among third-generation semiconductor materials due to its direct bandgap, wide bandgap, high thermal conductivity, high thermal stability, high breakdown field strength and strong radiation resistance. It is suitable for manufacturing high-frequency, high-temperature resistant, high-radiation resistant, high-power electronic and optoelectronic devices.

[0003] Chinese patent application CN202210793673.1 discloses a method for preparing AlN crystal materials based on size and shape control. The method uses AlN powder to prepare AlN crystals in an AlN crystal material preparation system. The preparation system includes an outer crucible and an inner crucible disposed within the outer crucible. The inner crucible includes: a shell with an internal space extending vertically; an upper cover located at the upper end of the shell, the upper cover including a first surface extending horizontally; a lower cover located at the lower end of the shell for holding aluminum nitride powder, the lower cover including a second surface extending horizontally; and pillars disposed within the internal space of the inner crucible. Multiple pillars are arranged at predetermined intervals; each pillar has a third surface extending horizontally. Through loading, heating, growth, and cooling steps, multiple growth processes are performed to obtain aluminum nitride seed crystals with a particle size greater than 20 mm on the third surface of the pillars. This invention results in slow homoepitaxial expansion of aluminum nitride single crystals, leading to small sizes and difficulty in mass production.

[0004] Chinese patent application CN202311691504.8 discloses a method for preparing an aluminum nitride single-crystal composite substrate, comprising: depositing an aluminum nitride polycrystalline film on the surface of a substrate; annealing to recrystallize the aluminum nitride polycrystalline film to form an aluminum nitride single-crystal film; maintaining the annealing atmosphere and annealing temperature; thinning the substrate from the side away from the aluminum nitride single-crystal film; and cooling to obtain an aluminum nitride single-crystal composite substrate. This preparation method reduces stress introduced by thermal mismatch between the substrate and the aluminum nitride single-crystal film during cooling by thinning the substrate after high-temperature annealing and recrystallization, thereby reducing dislocation generation and improving the crystal quality of the aluminum nitride single-crystal film, ultimately obtaining an aluminum nitride single-crystal composite substrate with high crystal quality. However, the aluminum nitride polycrystalline film deposited on the substrate surface is prone to detachment, resulting in poor quality of the grown AlN crystals. Summary of the Invention

[0005] Therefore, in view of the above problems, the present invention provides a method for preparing aluminum nitride single crystal materials, which solves the defects of small size, poor quality, slow speed and difficulty in mass production of aluminum nitride single crystal materials produced by the prior art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing aluminum nitride single crystal material, characterized by comprising the following steps:

[0008] S1. Preparation of raw materials: including AlN powder and SiC seed crystals;

[0009] S2. AlN Powder Purification Process: AlN powder is packed into a TaC crucible and heated to 1800℃ at a heating rate of 150℃ / h under a N2 protective atmosphere, held for 20-24h, and then naturally cooled to room temperature to obtain a primary preform. The primary preform is then pulverized and ground, and then packed into a TaC crucible. Under a N2 protective atmosphere, the temperature is raised to 1900℃ at a heating rate of 250℃ / h, held for 20-24h, and then naturally cooled to room temperature to obtain a secondary preform. The secondary preform is then pulverized and ground, and then packed into a TaC crucible again. Under a N2 protective atmosphere, the temperature is raised to 2000℃ at a heating rate of 250℃ / h, held for 24-28h, and then naturally cooled to room temperature to obtain a high-purity AlN raw material.

[0010] S3. Preparation of TaC crucible: The tantalum cap and tantalum crucible are cleaned with deionized water, dried and placed in a graphite crucible. Graphite powder is filled to completely cover the tantalum crucible. The graphite powder is compacted evenly. Under N2 atmosphere protection, the temperature is raised to 2000℃ at 100℃ / h and held for 6-8h. The temperature is then slowly lowered to room temperature. The crucible is removed and the graphite powder is wiped clean. It is ultrasonically cleaned with anhydrous ethanol for 15-30 minutes, then rinsed with deionized water 3-5 times. After drying, the TaC crucible is obtained. The TaC crucible includes a hemispherical bottom crucible body and a crucible cap.

[0011] S4. Pre-treat the TaC crucible and surface-treat the SiC seed crystal, and dry them respectively. Then, fix and bond the dried SiC seed crystal to the crucible cover. Place the crucible body in the matching graphite crucible. Load the high-purity AlN raw material obtained in step S2 into the crucible body, compacting it as you load. Stop loading when the high-purity AlN raw material is 5mm away from the crucible opening at the top of the crucible body. Cover the crucible with the graphite crucible cover.

[0012] S5. Growth of aluminum nitride single crystal material: The graphite crucible treated in step S4 is heated to 1850-2020℃ at a heating rate of 10℃ / min under a high-purity N2 protective atmosphere with a pressure of 60-70kPa, and held at that temperature for 40h. Then, it is cooled to 1800℃ at a cooling rate of 1℃ / min, and then cooled to room temperature at a cooling rate of 2℃ / min to obtain the aluminum nitride single crystal material.

[0013] Furthermore, the diameter of the aluminum nitride single crystal material is 40-45 mm.

[0014] Furthermore, the thickness of the aluminum nitride single crystal material is ≥10mm.

[0015] Furthermore, the SiC seed crystal is 4H-SiC or 6H-SiC.

[0016] Furthermore, the SiC seed crystal is 2 inches in size.

[0017] Furthermore, the purity of the AlN powder is ≥99.8%.

[0018] Furthermore, the fixing and bonding process is as follows:

[0019] a. Cut flexible graphite paper into a circle with the same size as the crucible lid, and cut tantalum foil into a metal tantalum ring with an outer diameter that is the same size as the crucible lid and an inner diameter that is the same size as the SiC seed crystal;

[0020] b. Apply an adhesive to the back of the flexible graphite paper, the tantalum ring, and the SiC seed crystal obtained in step a;

[0021] c. Under N2 atmosphere and gas pressure of 1-1.2 atm, raise the temperature of the bottom of the crucible to 1700-1800℃ at a heating rate of 5℃ / min and hold for 5-8 minutes. Then, bond the SiC seed crystal, tantalum ring, flexible graphite paper and crucible lid in the order of stacking from top to bottom.

[0022] Further, in step S4, the pretreatment is: ultrasonic cleaning with acetone, anhydrous ethanol and deionized water in sequence; the surface treatment is: mechanical and chemical polishing of the SiC seed crystal, the surface is free of scratches and the root mean square roughness is <0.2nm, and then acid washing is performed in dilute sulfuric acid with a concentration of 10-15%.

[0023] Furthermore, the binder is the high-purity AlN raw material obtained in step S2.

[0024] By adopting the aforementioned technical solution, the beneficial effects of the present invention are as follows:

[0025] 1. Purify AlN powder with a purity of ≥99.8% to reduce oxygen and carbon impurities in the raw material and improve the crystallinity of AlN powder;

[0026] 2. Using a TaC crucible with a hemispherical bottom ensures more uniform stress distribution during carbonization, preventing cracking and extending the crucible's lifespan. Raw material utilization is typically measured by the weight loss-to-evaporation ratio, which is the ratio of the weight lost to the weight evaporated. A lower weight loss-to-evaporation ratio indicates more evaporated raw material crystallizes at the crystal sites. Preventing cracking prevents raw material leakage, thus reducing the weight loss-to-evaporation ratio and promoting the growth of AlN single crystal materials.

[0027] 3. Following the order of stacking from top to bottom, the SiC seed crystal, tantalum ring, flexible graphite paper, and crucible lid are bonded together. The tantalum ring can alleviate the edge decomposition of the SiC seed crystal, which helps maintain the size of the SiC seed crystal, prevents the flexible graphite paper from reacting with Al vapor, and avoids the SiC seed crystal from falling off. High-purity AlN raw material is used as a binder. When the temperature is raised to 1700-1800℃, the binder sublimates and deposits to form a polycrystalline bonding layer, thereby fixing the SiC seed crystal onto the crucible lid.

[0028] 4. The SiC seed crystal is subjected to surface treatment, and the SiC seed crystal is mechanically and chemically polished to make the surface of the SiC seed crystal free of scratches and the root mean square roughness <0.2nm, so as to obtain a high-quality substrate.

[0029] 5. During the growth process of aluminum nitride single crystal material, the cooling rate is 1℃ / min. Before cooling to 1800℃, the temperature of the crystallization zone is kept higher than that of the sublimation zone to suppress nucleation on the surface of SiC seed substrate and secondary crystallization on the surface of AlN crystal during the cooling stage. Detailed Implementation

[0030] Example 1

[0031] A method for preparing aluminum nitride single crystal material, characterized by comprising the following steps:

[0032] (1) Preparation of raw materials: including AlN powder with a purity of ≥99.8% and 6H-SiC seed crystals with a size of 2 inches;

[0033] (2) AlN powder purification treatment: AlN powder is loaded into a TaC crucible and heated to 1800℃ at a heating rate of 150℃ / h under a N2 protective atmosphere, held for 24h, and naturally cooled to room temperature to obtain a primary preform; the primary preform is crushed and ground, then loaded into a TaC crucible and heated to 1900℃ at a heating rate of 250℃ / h under a N2 protective atmosphere, held for 24h, and naturally cooled to room temperature to obtain a secondary preform; the secondary preform is crushed and ground, then loaded into a TaC crucible again and heated to 2000℃ at a heating rate of 250℃ / h under a N2 protective atmosphere, held for 28h, and naturally cooled to room temperature to obtain a high-purity AlN raw material;

[0034] (3) Preparation of TaC crucible: The tantalum cap and tantalum crucible are cleaned with deionized water, dried and placed in the graphite crucible. Graphite powder is filled to completely cover the tantalum crucible. The graphite powder is compacted evenly. Under N2 atmosphere protection, the temperature is raised to 2000℃ at 100℃ / h and kept at 2000℃ for 8h. The temperature is slowly lowered to room temperature. The graphite powder is removed and wiped clean. The crucible is ultrasonically cleaned with anhydrous ethanol for 30min. It is then rinsed with deionized water 3 times and dried to obtain the TaC crucible. The TaC crucible includes a hemispherical bottom crucible body and a crucible cap.

[0035] (4) Fixation and bonding of SiC seed crystals

[0036] (4-1) The TaC crucible is pretreated by ultrasonic cleaning with acetone, anhydrous ethanol and deionized water in sequence, and then dried; the SiC seed crystal is surface treated by mechanical and chemical polishing to obtain a SiC seed crystal with no scratches and root mean square roughness <0.2nm, and then acid washed in 10% dilute sulfuric acid and dried.

[0037] (4-2) Cut flexible graphite paper into a circle with the same size as the crucible lid, and cut tantalum foil into a metal tantalum ring with an outer diameter with the same size as the crucible lid and an inner diameter with the same size as the SiC seed crystal;

[0038] (4-3) Coat the back of the flexible graphite paper, the tantalum ring and the SiC seed crystal obtained in step (4-2) with the high-purity AlN raw material;

[0039] (4-4) Under N2 atmosphere and gas pressure of 1 atm, the temperature of the bottom of the crucible body is raised to 1700℃ at a heating rate of 5℃ / min and held for 5min. The SiC seed crystal, tantalum ring, flexible graphite paper and crucible cover are bonded in the order of stacking from top to bottom.

[0040] (4-5) Place the crucible body in the matching graphite crucible, and load the high-purity AlN raw material obtained in step (2) into the crucible body while loading and compacting it. Stop loading when the high-purity AlN raw material is 5mm away from the crucible opening at the top of the crucible body, cover it with the crucible lid that has been bonded and fixed in step (4-4), and cover it with the graphite crucible lid.

[0041] (5) Growth of aluminum nitride single crystal material: The graphite crucible treated in step S4 is heated to 1850°C at a heating rate of 10°C / min under a high-purity N2 protective atmosphere with a gas pressure of 60 kPa, and held at that temperature for 40 h. Then, it is cooled to 1800°C at a cooling rate of 1°C / min, and then cooled to room temperature at a cooling rate of 2°C / min to obtain the aluminum nitride single crystal material with a diameter of 45 mm and a thickness of 10 mm.

[0042] Example 2

[0043] A method for preparing aluminum nitride single crystal material, characterized by comprising the following steps:

[0044] (1) Preparation of raw materials: including AlN powder with a purity of ≥99.8% and 6H-SiC seed crystals with a size of 2 inches;

[0045] (2) AlN powder purification treatment: AlN powder is loaded into a TaC crucible and heated to 1800℃ at a heating rate of 150℃ / h under a N2 protective atmosphere, held for 20h, and then naturally cooled to room temperature to obtain a primary preform; the primary preform is crushed and ground, then loaded into a TaC crucible and heated to 1900℃ at a heating rate of 250℃ / h under a N2 protective atmosphere, held for 20h, and then naturally cooled to room temperature to obtain a secondary preform; the secondary preform is crushed and ground, then loaded into a TaC crucible again and heated to 2000℃ at a heating rate of 250℃ / h under a N2 protective atmosphere, held for 24h, and then naturally cooled to room temperature to obtain a high-purity AlN raw material;

[0046] (3) Preparation of TaC crucible: The tantalum cap and tantalum crucible are cleaned with deionized water, dried and placed in the graphite crucible. Graphite powder is filled to completely cover the tantalum crucible. The graphite powder is compacted evenly. Under the protection of N2 atmosphere, the temperature is raised to 2000℃ at 100℃ / h and kept at 6h. The temperature is slowly lowered to room temperature. The graphite powder is removed and wiped clean. The crucible is ultrasonically cleaned with anhydrous ethanol for 20min. It is then rinsed with deionized water 3 times and dried to obtain the TaC crucible. The TaC crucible includes a hemispherical bottom crucible body and a crucible cap.

[0047] (4) Fixation and bonding of SiC seed crystals

[0048] (4-1) The TaC crucible is pretreated by ultrasonic cleaning with acetone, anhydrous ethanol and deionized water in sequence, and then dried; the SiC seed crystal is surface treated by mechanical and chemical polishing to obtain a SiC seed crystal with no scratches and root mean square roughness <0.2nm, and then acid washed in 10% dilute sulfuric acid and dried.

[0049] (4-2) Cut flexible graphite paper into a circle with the same size as the crucible lid, and cut tantalum foil into a metal tantalum ring with an outer diameter with the same size as the crucible lid and an inner diameter with the same size as the SiC seed crystal;

[0050] (4-3) Coat the back of the flexible graphite paper, the tantalum ring and the SiC seed crystal obtained in step (4-2) with the high-purity AlN raw material;

[0051] (4-4) Under N2 atmosphere and gas pressure of 1.1 atm, the temperature of the bottom of the crucible body is raised to 1750°C at a heating rate of 5°C / min and held for 6 min. The SiC seed crystal, tantalum ring, flexible graphite paper and crucible cover are bonded in the order of stacking from top to bottom.

[0052] (4-5) Place the crucible body in the matching graphite crucible, load the high-purity AlN raw material obtained in step (2) into the crucible body, compact it while loading, and stop loading when the high-purity AlN raw material is 5mm away from the crucible opening at the top of the crucible body. Cover the crucible with the lid and then cover it with the graphite crucible lid.

[0053] (5) Growth of aluminum nitride single crystal material: The graphite crucible treated in step S4 is heated to 1900°C at a heating rate of 10°C / min under a high-purity N2 protective atmosphere with a gas pressure of 65 kPa, and held at that temperature for 40 h. Then, it is cooled to 1800°C at a cooling rate of 1°C / min, and then cooled to room temperature at a cooling rate of 2°C / min to obtain the aluminum nitride single crystal material with a diameter of 40 mm and a thickness of 10 mm.

[0054] Example 3

[0055] A method for preparing aluminum nitride single crystal material, characterized by comprising the following steps:

[0056] (1) Preparation of raw materials: including AlN powder with a purity of ≥99.8% and 6H-SiC seed crystals with a size of 2 inches;

[0057] (2) AlN powder purification treatment: AlN powder is loaded into a TaC crucible and heated to 1800℃ at a heating rate of 150℃ / h under a N2 protective atmosphere, held for 22h, and then naturally cooled to room temperature to obtain a primary preform; the primary preform is crushed and ground, then loaded into a TaC crucible and heated to 1900℃ at a heating rate of 250℃ / h under a N2 protective atmosphere, held for 22h, and then naturally cooled to room temperature to obtain a secondary preform; the secondary preform is crushed and ground, then loaded into a TaC crucible again and heated to 2000℃ at a heating rate of 250℃ / h under a N2 protective atmosphere, held for 26h, and then naturally cooled to room temperature to obtain a high-purity AlN raw material;

[0058] (3) Preparation of TaC crucible: The tantalum cap and tantalum crucible are cleaned with deionized water, dried and placed in the graphite crucible. Graphite powder is filled to completely cover the tantalum crucible. The graphite powder is compacted evenly. Under N2 atmosphere protection, the temperature is raised to 2000℃ at 100℃ / h and kept at 7h. The temperature is slowly lowered to room temperature. The graphite powder is removed and wiped clean. The crucible is ultrasonically cleaned with anhydrous ethanol for 15min. It is then rinsed with deionized water 3 times and dried to obtain the TaC crucible. The TaC crucible includes a hemispherical bottom crucible body and a crucible cap.

[0059] (4) Fixation and bonding of SiC seed crystals

[0060] (4-1) The TaC crucible is pretreated by ultrasonic cleaning with acetone, anhydrous ethanol and deionized water in sequence, and then dried; the SiC seed crystal is surface treated by mechanical and chemical polishing to obtain a SiC seed crystal with no scratches and root mean square roughness <0.2nm, and then acid washed in 15% dilute sulfuric acid and dried.

[0061] (4-2) Cut flexible graphite paper into a circle with the same size as the crucible lid, and cut tantalum foil into a metal tantalum ring with an outer diameter with the same size as the crucible lid and an inner diameter with the same size as the SiC seed crystal;

[0062] (4-3) Coat the back of the flexible graphite paper, the tantalum metal ring and the SiC seed crystal obtained in step (4-2) with the high-purity AlN raw material;

[0063] (4-4) Under N2 atmosphere and gas pressure of 1.2 atm, the temperature of the bottom of the crucible body is raised to 1800°C at a heating rate of 5°C / min and held for 8 min. The SiC seed crystal, tantalum ring, flexible graphite paper and crucible cover are bonded in the order of stacking from top to bottom.

[0064] (4-5) Place the crucible body in the matching graphite crucible, load the high-purity AlN raw material obtained in step (2) into the crucible body, compact it while loading, and stop loading when the high-purity AlN raw material is 5mm away from the crucible opening at the top of the crucible body. Cover the crucible with the lid and then cover it with the graphite crucible lid.

[0065] (5) Growth of aluminum nitride single crystal material: The graphite crucible treated in step S4 is heated to 2000℃ at a heating rate of 10℃ / min under a high-purity N2 protective atmosphere with a gas pressure of 70kPa, and held at that temperature for 40h. Then, it is cooled to 1800℃ at a cooling rate of 1℃ / min, and then cooled to room temperature at a cooling rate of 2℃ / min to obtain the aluminum nitride single crystal material with a diameter of 45mm and a thickness of 10mm.

[0066] Although the invention has been specifically shown and described in conjunction with preferred embodiments, those skilled in the art should understand that various changes in form and detail may be made to the invention without departing from the spirit and scope of the invention as defined in the appended claims, all of which shall be within the scope of protection of the invention.

Claims

1. A method for preparing aluminum nitride single crystal material, characterized in that, Includes the following steps: S1. Preparation of raw materials: including AlN powder and SiC seed crystals; S2. AlN Powder Purification Process: AlN powder is packed into a TaC crucible and heated to 1800℃ at a heating rate of 150℃ / h under a N2 protective atmosphere, held for 20-24h, and then naturally cooled to room temperature to obtain a primary preform. The primary preform is then pulverized and ground, and then packed into a TaC crucible. Under a N2 protective atmosphere, the temperature is raised to 1900℃ at a heating rate of 250℃ / h, held for 20-24h, and then naturally cooled to room temperature to obtain a secondary preform. The secondary preform is then pulverized and ground, and then packed into a TaC crucible again. Under a N2 protective atmosphere, the temperature is raised to 2000℃ at a heating rate of 250℃ / h, held for 24-28h, and then naturally cooled to room temperature to obtain a high-purity AlN raw material. S3. Preparation of TaC crucible: The tantalum cap and tantalum crucible are cleaned with deionized water, dried and placed in a graphite crucible. Graphite powder is filled to completely cover the tantalum crucible. The graphite powder is compacted evenly. Under N2 atmosphere protection, the temperature is raised to 2000℃ at 100℃ / h and held for 6-8h. The temperature is then slowly lowered to room temperature. The crucible is removed and the graphite powder is wiped clean. It is ultrasonically cleaned with anhydrous ethanol for 15-30min, then rinsed with deionized water 3-5 times. After drying, the TaC crucible is obtained. The TaC crucible includes a hemispherical bottom crucible body and a crucible cap. S4. Pre-treat the TaC crucible and surface-treat the SiC seed crystal, and dry them respectively. Then, fix and bond the dried SiC seed crystal to the crucible cover. Place the crucible body in the matching graphite crucible. Load the high-purity AlN raw material obtained in step S2 into the crucible body, compacting it as you load. Stop loading when the high-purity AlN raw material is 5mm away from the crucible opening at the top of the crucible body. Cover the crucible with the graphite crucible cover. S5. Growth of aluminum nitride single crystal material: The graphite crucible treated in step S4 is heated to 1850-2020℃ at a heating rate of 10℃ / min under a high-purity N2 protective atmosphere with a pressure of 60-70kPa, and held at that temperature for 40h. Then, it is cooled to 1800℃ at a cooling rate of 1℃ / min, and then cooled to room temperature at a cooling rate of 2℃ / min to obtain the aluminum nitride single crystal material. The SiC seed crystal is 6H-SiC; the size of the SiC seed crystal is 2 inches; and the purity of the AlN powder is ≥99.8%. The bonding process is as follows: a) Cut flexible graphite paper into a circle with the same size as the TaC crucible lid, and cut tantalum foil into a tantalum ring with an outer diameter matching the TaC crucible lid and an inner diameter matching the SiC seed crystal; b) Apply adhesive to the back of the flexible graphite paper, the tantalum ring, and the SiC seed crystal obtained in step a; c) Under a N2 atmosphere and a pressure of 1-1.2 atm, raise the temperature of the bottom of the TaC crucible body to 1700-1800℃ at a heating rate of 5℃ / min, hold for 5-8 minutes, and bond the SiC seed crystal, the tantalum ring, the flexible graphite paper, and the TaC crucible lid in a top-to-bottom stacking order. In step S4, the pretreatment is performed by ultrasonic cleaning with acetone, anhydrous ethanol and deionized water in sequence; the surface treatment is performed by mechanical and chemical polishing of the SiC seed crystal to obtain a SiC seed crystal with no scratches and a root mean square roughness of <0.2nm, and then acid washing in dilute sulfuric acid with a concentration of 10-15%. The binder is the high-purity AlN raw material obtained in step S2.

2. The method for preparing aluminum nitride single crystal material according to claim 1, characterized in that: The diameter of the aluminum nitride single crystal material is 40-45 mm.

3. The method for preparing aluminum nitride single crystal material according to claim 1, characterized in that: The thickness of the aluminum nitride single crystal material is ≥10mm.