Recycling method of aluminum nitride polycrystalline powder

Abstract

The invention belongs to the technical field of semiconductor material preparation, and discloses a cyclic utilization method of aluminum nitride polycrystalline powder. The method comprises the following steps: alternately filling a crucible with small-particle aluminum nitride polycrystal powder obtained by crushing and screening an aluminum nitride raw material and a sintered body after growing aluminum nitride crystals in layers, then putting the crucible into a resistance furnace, vacuumizing, heating to a high temperature T1, and keeping the temperature for a period of time t1; after heat preservation is finished, the temperature is reduced to T2, and heat preservation continues to be conducted for a period of time t2; after the temperature is reduced to the room temperature, the aluminum nitride polycrystalline powder and the aluminum nitride raw material are converted into an aluminum nitride polycrystalline sintered body, and compared with the aluminum nitride raw material, the polycrystalline sintered body is higher in purity, fewer in impurity and easier to sublimate and can meet the growth requirement of aluminum nitride single crystals. The method is simple in process, low in equipment requirement and low in cost; according to the method, waste of the polycrystal powder screened out after the long crystals are broken is prevented, and meanwhile the polycrystal powder can be purified again.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor material preparation, and in particular relates to a recycling method for aluminum nitride polycrystalline powder. Background Art

[0002] Aluminum nitride (AlN) has a wide direct bandgap (6.2 eV) and high thermal conductivity (319 W m−1 K−1), making it a promising substrate material for deep ultraviolet (DUV) optoelectronic devices such as light-emitting diodes (LEDs), photodetectors (PDs), and laser diodes (LDs). AlN single crystals can be grown using physical vapor transport (PVT). Commercially available AlN raw materials, due to their production methods, often contain significant impurities, which significantly impact the growth of AlN single crystals. Therefore, researchers sinter commercially available AlN raw materials at high temperatures to obtain purified AlN polycrystalline material. The polycrystalline material is then crushed and placed in a crucible for growth to produce AlN single crystals. Extensive experiments have demonstrated that using powder with a particle size of 10-100 μm directly for AlN crystal growth is ineffective. This results in excessively fast growth rates, resulting in poor quality crystals. Therefore, larger AlN polycrystalline particles are often used for growing AlN single crystals. However, before crystal growth, aluminum nitride polycrystalline blocks need to be crushed and screened. Polycrystalline particles with a size of 0.5 mm are screened out according to the crystal growth requirements, while the remaining aluminum nitride polycrystalline powder with a size of less than 0.5 mm cannot be effectively utilized, resulting in a waste of raw materials and an increase in the cost of aluminum nitride single crystals. Therefore, there is an urgent need in the art to provide a method for recycling the aluminum nitride polycrystalline powder remaining after crushing and screening the polycrystalline blocks, so as to improve raw material utilization, reduce production costs, and promote the widespread application of aluminum nitride single crystals in the field of optoelectronic devices. Summary of the Invention

[0003] In order to solve the problem of waste of powder left after crushing the existing aluminum nitride raw material sintered body, the present invention provides a recycling method for aluminum nitride polycrystalline powder.

[0004] A method for recycling aluminum nitride polycrystalline powder, the method comprising: Step 1: Alternately layering the small-particle aluminum nitride polycrystalline powder obtained by crushing and screening the sintered body after growing aluminum nitride crystals and the aluminum nitride raw material into a crucible, placing the crucible in a resistance furnace after the filling is completed, and first filling the bottom of the crucible with the aluminum nitride raw material; Step 2: Evacuate the resistance furnace, then heat the aluminum nitride polycrystalline powder and aluminum nitride raw material to a high temperature T1 and maintain the temperature for a period of time t1. After the temperature is maintained, cool the material to T2 and continue to maintain the temperature for a period of time t2. After cooling to room temperature, open the furnace body, remove the crucible, and convert the aluminum nitride polycrystalline powder and aluminum nitride raw material into an aluminum nitride polycrystalline sintered body. The aluminum nitride polycrystalline sintered body can be used to grow aluminum nitride single crystals. The aluminum nitride polycrystalline powder obtained after the polycrystalline sintered body is crushed can still be continuously recycled using the above method.

[0005] Furthermore, the mesh number of the aluminum nitride polycrystalline powder obtained by sieving in step 1 is 14 mesh or 24 mesh.

[0006] Furthermore, in step one, the aluminum nitride polycrystalline powder and the aluminum nitride raw material are layered in the crucible as follows: from bottom to top, the first layer is the aluminum nitride raw material with a mass of m1, the second layer is the aluminum nitride polycrystalline powder with a mass of m2, the third layer is the aluminum nitride raw material with a mass of m3, and the fourth layer is the aluminum nitride polycrystalline powder with a mass of m4; (m1+m3)<(m2+m4).

[0007] The purpose of adding the first layer of aluminum nitride raw material and the third layer of aluminum nitride raw material is to make the sintered material more brittle and have lower hardness than the polycrystalline powder after sintering, so as to facilitate the subsequent removal of the sintered body from the crucible. If the mass of m1+m3 is much smaller than the mass of m2+m4 or even 0, it will make the polycrystalline block difficult to remove. The purpose of the present invention is to fully reuse the polycrystalline powder sieved after the crushing of the sintered body after growing aluminum nitride crystals, so the mass of m1+m3 cannot be greater than the mass of m2+m4.

[0008] Furthermore, when the crucible height is 160 mm and the bottom size is 3 inches, the m1 is 90-110 g, m2 is 270-300 g, m3 is 110-130 g, and m4 is 200-220 g.

[0009] Furthermore, in step 2, T1 is 2310-2330° C., t1 is 10-12 h, T2 is 2240-2260° C., and t2 is 12-16 h.

[0010] Beneficial effects of the present invention: (1) The aluminum nitride polycrystalline recycling method provided by the present invention has a simple process. The prepared aluminum nitride polycrystalline sintered material is easier to sublime during the crystal growth process after being crushed, thereby improving the utilization rate of the aluminum nitride raw material and reducing the cost of aluminum nitride crystal growth.

[0011] (2) The method of the present invention has low equipment requirements and low cost, which is conducive to the industrial production of aluminum nitride single crystals. (3) The present invention combines high temperature and low temperature sintering to prepare an aluminum nitride polycrystalline sintered body with a higher purity than the aluminum nitride raw material, and the impurities therein are also removed, thereby ensuring the purity of the aluminum nitride polycrystalline raw material used for crystal growth in the later stage. In addition, the polycrystalline block obtained by sintering is easier for the aluminum nitride polycrystalline raw material to sublime in the subsequent crystal growth process, which can increase the sublimation amount. It can prevent the waste of polycrystalline powder screened out after the crystal is broken, and can also purify the polycrystalline powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a picture of aluminum nitride polycrystalline powder; Figure 2 This is a diagram of aluminum nitride raw materials; Figure 3 This is the SEM image of aluminum nitride raw material; Figure 4 Schematic diagram of the layered loading of aluminum nitride polycrystalline powder and aluminum nitride raw material in a crucible in the present invention; Figure 5 This is a diagram of the aluminum nitride polycrystalline sintered body in Example 1; Figure 6 This is a diagram of the aluminum nitride polycrystalline sintered body in Example 2; Figure 7 This is a diagram of aluminum nitride polycrystalline material that cannot be removed in the comparative example of the present invention. DETAILED DESCRIPTION

[0013] To more clearly illustrate the overall concept of this application, the following is a detailed description using examples. However, it should be noted that the following specific embodiments are merely illustrative examples of the specific operation of the present invention. Basic operating variables not specifically provided in this invention are well known to those skilled in the art and do not affect the present invention. The scope of protection of this invention is limited solely by the claims.

[0014] It is obvious to those skilled in the art that various other improvements and replacements can be made to the embodiments of the present invention within the scope of protection defined by the claims of the present invention, and still achieve the same technical effects and the ultimate technical purpose of the present invention.

[0015] In the present application, all ratios are weight ratios, the unit of power is W, the unit of frequency is MHz, the unit of temperature is ° C, and the unit of wavelength is m. In addition, all numerical ranges described in the present invention are inclusive and may include new numerical ranges obtained by arbitrarily combining the upper and lower limits of the disclosed ranges. For example, if the weight percentage of a certain component is disclosed as 10-30%, preferably 15-25%, and more preferably 20-23%, it is equivalent to simultaneously disclosing the following numerical ranges: 10-15%, 10-25%, 10-20%, 10-23%, 15-30%, 15-20%, 15-23%, 20-25%, and 23-25%.

[0016] In order to clearly illustrate the technical features of this solution, the present invention is described in detail below through specific implementation methods in conjunction with the accompanying drawings.

[0017] Example 1 A method for recycling aluminum nitride polycrystalline powder, comprising the following steps: Step 1: Screen the aluminum nitride polycrystalline powder obtained from the sintered body after the aluminum nitride crystal is grown (such as Figure 1 As shown) (the mesh size is 14 mesh) and aluminum nitride raw material (such as Figure 2 The first layer is aluminum nitride raw material, the purity of the initial aluminum nitride raw material is 99%, the particle size is 1-3μm, and its SEM is as follows Figure 3 As shown. m1 is 90g, the second layer is aluminum nitride polycrystalline powder, m2 is 270g, the third layer is aluminum nitride raw material, m3 is 110g, the fourth layer is aluminum nitride polycrystalline powder, m4 is 200g, after filling, the crucible is placed in a resistance furnace, Figure 4 Schematic diagram of filling AlN material; Step 2: Evacuate the resistance furnace, then heat the aluminum nitride polycrystalline powder and aluminum nitride raw material to a high temperature of 2310°C, and keep it warm for 10 hours; after the end of the heat preservation, cool it to T2 2240°C, and continue to keep it warm for 12 hours; then cool it to room temperature, open the furnace body, take out the crucible, and obtain the aluminum nitride polycrystalline sintered body (such as Figure 5 The powder obtained after the polycrystalline sintered body is crushed can be recycled using the above method.

[0018] Example 2 A method for recycling aluminum nitride polycrystalline powder, comprising the following steps: Step 1: After the aluminum nitride crystals are grown, the aluminum nitride polycrystalline powder (24 mesh) obtained by crushing and screening the sintered body is layered with the aluminum nitride raw material and placed in a crucible. The first layer is the aluminum nitride raw material. The purity of the initial aluminum nitride raw material is 99%, and the particle size is 1-3μm. Its SEM is as follows: Figure 3 As shown. m1 is 100g, the second layer is aluminum nitride polycrystalline powder, m2 is 280g, the third layer is aluminum nitride raw material, m3 is 120g, the fourth layer is aluminum nitride polycrystalline powder, m4 is 210g, after filling, the crucible is placed in a resistance furnace, Figure 4 Schematic diagram of filling AlN material; Step 2: Evacuate the resistance furnace, then heat the powder and raw materials to a high temperature of 2330°C and keep them warm for 10 hours; after the end of the heat preservation, cool them to 2260°C and continue to keep them warm for 12 hours; then cool them to room temperature, open the furnace, take out the crucible, and obtain the aluminum nitride polycrystalline sintered body (such as Figure 6 The powder obtained after the polycrystalline sintered body is crushed can be recycled using the above method.

[0019] Comparative Example 1 A method for recycling aluminum nitride polycrystalline powder, comprising the following steps: Step 1: 710 g of aluminum nitride polycrystalline powder (24 mesh) obtained by crushing and screening the sintered body after growing aluminum nitride crystals was directly loaded into a crucible. After completion, the crucible was placed in a resistance furnace for comparison with Example 2. Step 2: Evacuate the resistance furnace and then heat the aluminum nitride polycrystalline powder to a high temperature of 2330°C. The purity of the initial aluminum nitride raw material is 99%, and the particle size is 1-3 μm. The SEM is as follows: Figure 3 The furnace was kept warm for 10 hours. After the heat preservation, the temperature was lowered to 2260°C and kept warm for 12 hours. The temperature was then lowered to room temperature. The furnace was opened and the crucible was taken out to obtain a sintered body. The sintered body was found to be in agglomerates and deposited on the crucible wall. It was very hard and could not be taken out of the crucible. Figure 7 shown.

[0020] The AlN raw material and the polycrystalline material after sintering according to Example 1 were tested for C and O impurities using a glow discharge mass spectrometer. The test results are shown in Table 1. After sintering, it was found that the carbon and oxygen impurities in the raw material were effectively reduced, indicating that this method has a certain purification effect.

[0021] Table 1. C and O impurity contents in AlN raw material and polycrystalline material after sintering in Example 1

[0022] The present invention will be further described below in conjunction with specific embodiments. The advantages and features of the present invention will be more clearly reflected in the description. However, the embodiments are merely exemplary and do not limit the scope of the present invention in any way. It should be understood by those skilled in the art that the details and forms of the technical solutions may be modified or replaced without departing from the spirit and scope of the present invention, and such modifications and replacements all fall within the scope of protection of the present invention.

Claims

1. A method for recycling aluminum nitride polycrystalline powder, characterized in that: The method comprises: Step 1: Alternately layering the small-particle aluminum nitride polycrystalline powder obtained by crushing and screening the sintered body after growing aluminum nitride crystals and the aluminum nitride raw material into a crucible, placing the crucible in a resistance furnace after the filling is completed, and first filling the bottom of the crucible with the aluminum nitride raw material; Step 2: Evacuate the resistance furnace, then heat the aluminum nitride polycrystalline powder and aluminum nitride raw material to a high temperature T1, and keep it warm for a period of time t1; after the insulation is completed, cool it to T2, and continue to keep it warm for a period of time t2; after cooling to room temperature, open the furnace body, take out the crucible, and convert the aluminum nitride polycrystalline powder and aluminum nitride raw material into an aluminum nitride polycrystalline sintered body, which can be used for the growth needs of aluminum nitride single crystals.

2. The method for recycling aluminum nitride polycrystalline powder according to claim 1, characterized in that: The mesh number of the aluminum nitride polycrystalline powder obtained by sieving in step 1 is 14 mesh or 24 mesh.

3. The method for recycling aluminum nitride polycrystalline powder according to claim 1, characterized in that: In step 1, the aluminum nitride polycrystalline powder and the aluminum nitride raw material are layered in the crucible as follows: from bottom to top, the first layer is the aluminum nitride raw material with a mass of m1, the second layer is the aluminum nitride polycrystalline powder with a mass of m2, the third layer is the aluminum nitride raw material with a mass of m3, and the fourth layer is the aluminum nitride polycrystalline powder with a mass of m4; (m1 + m3) < (m2 + m4).

4. The method for recycling aluminum nitride polycrystalline powder according to claim 3, characterized in that: When the crucible height is 160 mm and the bottom size is 3 inches, the m1 in step 2 is 90-110 g, m2 is 270-300 g, m3 is 110-130 g, and m4 is 200-220 g.

5. The method for recycling aluminum nitride polycrystalline powder according to claim 1, characterized in that: In step 2, T1 is 2310-2330° C., t1 is 10-12 h, T2 is 2240-2260° C., and t2 is 12-16 h.

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