Assembly method for sintering and purifying aluminum nitride raw material at low loss

Abstract

The invention relates to the technical field of aluminum nitride raw material treatment, in particular to an assembly method for low-loss sintering and purification of an aluminum nitride raw material. The method comprises the following steps: sequentially arranging a bottom tungsten sheet layer, a primary sintering crushed material layer, a middle tungsten sheet layer, a mixed material layer and a top tungsten sheet layer from bottom to top from the bottom of a tungsten crucible; and finally, the crucible cover covers the top of the crucible, and assembling is completed. After the assembly is completed, the crucible is placed in a single crystal growth furnace to be sintered, a gradient sintering process is adopted for sintering, a yellowish-brown high-quality AlN polycrystalline sintered body can be obtained after the sintering is completed, the impurity content of the sintered body is low, polycondensation is uniform, particles grow up in the sintering process, meanwhile, the loss rate is kept at a low level, and the yield of the AlN polycrystalline sintered body is greatly improved. Therefore, the sintered material meets the requirements of high-quality AlN single crystal growth in the aspects of granularity, impurity content, loss rate and the like.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum nitride raw material processing, in particular to an assembly method for low-loss sintering and purifying aluminum nitride raw materials. Background Art

[0002] As a wide bandgap semiconductor material, aluminum nitride has a theoretical bandgap width of 6.2eV. In addition, it also has a series of excellent physical and chemical properties: high thermal conductivity, high breakdown field strength, strong radiation resistance, high chemical stability, corrosion resistance, high electron saturation rate, etc. Therefore, it is very suitable for the preparation of high-temperature, high-power, and high-frequency semiconductor devices.

[0003] In order to obtain high-quality semiconductor devices, high-quality aluminum nitride crystals are indispensable, and in order to obtain high-quality aluminum nitride crystals, high-purity aluminum nitride raw materials that meet the requirements of the semiconductor industry must be available. At present, due to the limitations of production processes, etc., the synthesis of high-purity aluminum nitride raw materials is a very challenging problem. Therefore, sintering the existing aluminum nitride raw material powder to further obtain high-purity aluminum nitride raw materials is the current mainstream treatment method. During the sintering process, due to the selection of different sintering processes and different assembly processes, the purity, loss rate, and crystallization state of the raw materials obtained after sintering vary greatly. In addition, many laboratories have carried out research on the sintering process of aluminum nitride raw materials, but research on the assembly process of raw materials before sintering is quite scarce.

[0004] Therefore, how to ensure good particle size and low impurity content while maintaining a low loss rate has become a technical problem that needs to be solved urgently in the field of aluminum nitride raw material processing. Summary of the invention

[0005] The present invention aims to solve the problems of high sintering loss rate and uneven sintered body in the current sintering process of aluminum nitride raw materials, and provides an assembly method for sintering and purifying aluminum nitride raw materials with low loss. The assembly method of the present invention adopts a layered assembly method, and the purpose of the present invention is achieved by configuring functional layers with different functions in layers. Conventional sintering after assembly using the assembly method of the present invention can obtain a yellow-brown high-quality AlN polycrystalline sintered body, which has a low impurity content, uniform polycondensation, and particles grow during the sintering process. At the same time, the loss rate is also maintained at a low level, so that the sintered material meets the requirements of high-quality AlN single crystal growth in terms of particle size, impurity content, loss rate, etc.

[0006] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: A method for assembling a low-loss sintered purified aluminum nitride raw material comprises the following steps: S1: Take a tungsten crucible with a height of 132 mm, an inner diameter of 87 mm, and a wall thickness of 5 mm as a filling crucible; S2: Take a certain amount of tungsten sheets and place them on the bottom of the tungsten crucible to obtain the bottom tungsten sheet layer; the area of ​​each tungsten sheet is 50-100mm 2 , thickness is 0.1-0.3mm, and the total placement area of ​​tungsten sheet is 75-85% of the bottom area of ​​crucible; S3: Sintering the aluminum nitride raw material powder at 700-750 torr and 1700-1800°C for 12-14 hours to obtain a primary sintered body, crushing and screening the primary sintered body to obtain a primary sintered crushed material, and taking 300g of the primary sintered crushed material to fill it above the tungsten sheet layer at the bottom of the tungsten crucible; S4: Take a certain amount of tungsten sheets and place them on the first sintered crushed material in a single layer to obtain medium tungsten sheets; the area of ​​each tungsten sheet is 50-100mm 2 , thickness is 0.1-0.3mm, and the total placement area of ​​tungsten sheet is 45-55% of the bottom area of ​​crucible; S5: Sintering the primary sintered crushed material in step S3 at a pressure of 740-780 torr in a gradient manner, first heating to 2250-2330°C, sintering at a constant temperature for 12-14h, then cooling to 2150-2200°C, sintering at a constant temperature for 12-14h, and naturally cooling to room temperature to obtain a secondary sintered body; crushing and screening the secondary sintered body to obtain a secondary sintered crushed material; taking 100g of each of the primary sintered crushed material and the secondary sintered crushed material, and fully mixing them to obtain a mixed material; filling the mixed material above the tungsten flake layer; S6: Take another certain amount of tungsten sheets and place them in a single layer on top of the mixed material in step S5 to obtain a top tungsten sheet layer; the area of ​​each tungsten sheet is 400-500mm 2 , thickness is 0.1-0.3mm, and the total placement area of ​​tungsten sheet is 45-55% of the bottom area of ​​crucible; S7: Add the crucible cover to the top of the crucible to complete the assembly.

[0007] Preferably, in step S3, the particle size of the primary sintering crushed material is 15-20 μm, which should not be too large or too small.

[0008] Preferably, in step S5, when screening the secondary sintered crushed material, a standard sample sieve with a mesh size of 50 or above is used for screening.

[0009] Preferably, in step S5, a three-dimensional motion mixer is used to mix the primary sintered crushed material and the secondary sintered crushed material for 5 hours to achieve sufficient mixing of the two.

[0010] Preferably, the mass ratio of the primary sintered crushed material in step S3 to the mixed material in step S5 is 3:2; the mass ratio of the primary sintered crushed material to the secondary sintered crushed material in the mixed material in step S5 is 1:1.

[0011] Preferably, in step S7, the distance between the top of the crucible and the top tungsten sheet layer should be greater than 1 cm to prevent uneven heating.

[0012] Preferably, in step S7, before covering the crucible cover, a bottomless crucible with a height of 42 mm is added to the top of the tungsten crucible described in step S1 to increase the thickness of the air layer and improve the raw material purification effect.

[0013] After assembly by the assembly method, sintering is performed. The specific sintering process is: at a pressure of 740-780 torr, gradient sintering is performed, first heating to 2250-2330°C, sintering at a constant temperature for 12-14 hours, then cooling to 2150-2200°C, sintering at a constant temperature for 12-14 hours, and then naturally cooling to room temperature. The obtained sintered body can be directly used for the next step of AlN single crystal growth.

[0014] In step S3, the particle sizes of particles obtained by crushing the primary sintered body should be kept as consistent as possible.

[0015] The assembly method is suitable for assembling a resistive single crystal growth furnace for raw material purification.

[0016] The sintered body obtained by sintering using this assembly method can meet the needs of crystal growth, and the loss rate can also be controlled within 5%.

[0017] Compared with the prior art, the assembly method of the low-loss sintered purified aluminum nitride raw material disclosed in the present invention further refines the assembly problem of the raw material by adopting a layered assembly method, and the transition from the complete primary sintering crushed material to the mixture of the primary sintering crushed material and the secondary sintering crushed material can make the sintered body obtained by the final sintering easier to condense into a uniform sintered body. At the same time, due to the limitation of the thermal field, the top area of ​​the sintering material is usually insufficiently heated during the usual sintering process. Through this assembly method, the sintering effect of the upper sintered body can be improved, and the transformation to the crystalline state can be promoted. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the distribution of the tungsten crucible and the filling layer inside it in the assembly method of the present invention.

[0019] Among them, 1. bottom tungsten sheet layer; 2. primary sintered crushed material layer; 3. middle tungsten sheet layer; 4. mixed material layer; 5. top tungsten sheet layer; 6. crucible cover; 7. tungsten crucible.

[0020] Figure 2 It is a top view of the inside of the tungsten crucible after steps S2, S3, S4, S5, and S6 in Example 1 of the present invention.

[0021] Figure 31 is a diagram of the primary sintered crushed material (a) and the secondary sintered crushed material (b) in Example 1 of the present invention.

[0022] Figure 4 This is a side view of the sintered body obtained after sintering according to Example 1 of the present invention.

[0023] Figure 5 This is a grain morphology diagram of aluminum nitride obtained by sintering in Example 1 of the present invention.

[0024] Figure 6 It is a top view of the aluminum nitride sintered body obtained by sintering in Example 1 of the present invention. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with specific embodiments, and the advantages and features of the present invention will become clearer as the description proceeds. However, the embodiments are exemplary only and do not constitute any limitation to the scope of the present invention. It should be understood by those skilled in the art that the details and forms of the technical solution of the present invention may be modified or replaced without departing from the spirit and scope of the present invention, but these modifications and replacements all fall within the scope of protection of the present invention.

[0026] A method for assembling low-loss sintered purified aluminum nitride raw material comprises the following steps: S1: Take a tungsten crucible 7 with a height of 132 mm, an inner diameter of 87 mm, and a wall thickness of 5 mm, see Figure 1 and Figure 2 In the process of assembling the aluminum nitride raw materials, due to the layered assembly method, there are the following from bottom to top in the crucible: 1. bottom tungsten sheet layer; 2. primary sintered crushed material layer; 3. middle tungsten sheet layer; 4. mixed material layer; 5. top tungsten sheet layer; 6. crucible cover.

[0027] S2: Take a certain amount of tungsten sheets and place them on the bottom of the tungsten crucible to obtain the bottom tungsten sheet layer; the area of ​​each tungsten sheet is 50-100mm 2 , thickness is 0.1-0.3mm, and the total placement area of ​​tungsten sheet is 75-85% of the bottom area of ​​crucible; S3: Sintering the aluminum nitride raw material powder at 700-750 torr and 1700-1800°C for 12-14 hours to obtain a primary sintered body, crushing and screening the primary sintered body to obtain a primary sintered crushed material, and taking 300g of the primary sintered crushed material to fill it above the tungsten sheet layer at the bottom of the tungsten crucible; S4: Take a certain amount of tungsten sheets and place them on the first sintered crushed material in a single layer to obtain medium tungsten sheets; the area of ​​each tungsten sheet is 50-100mm 2 , thickness is 0.1-0.3mm, and the total placement area of ​​tungsten sheet is 45-55% of the bottom area of ​​crucible; S5: Sintering the primary sintered crushed material in step S3 at a pressure of 740-780 torr in a gradient manner, first heating to 2250-2330°C, sintering at a constant temperature for 12-14h, then cooling to 2150-2200°C, sintering at a constant temperature for 12-14h, and naturally cooling to room temperature to obtain a secondary sintered body; crushing and screening the secondary sintered body to obtain a secondary sintered crushed material; taking 100g of each of the primary sintered crushed material and the secondary sintered crushed material, and fully mixing them to obtain a mixed material; filling the mixed material above the tungsten flake layer; S6: Take another certain amount of tungsten sheets and place them in a single layer on top of the mixed material in step S5 to obtain a top tungsten sheet layer; the area of ​​each tungsten sheet is 400-500mm 2 , thickness is 0.1-0.3mm, and the total placement area of ​​tungsten sheet is 45-55% of the bottom area of ​​crucible; S7: Add the crucible cover to the top of the crucible to complete the assembly.

[0028] The assembly method of low-loss sintered purified aluminum nitride raw materials disclosed in the present invention further refines the assembly problem of raw materials by adopting a layered assembly method, and the transition from a complete primary sintering crushed material to a mixture of a primary sintering crushed material and a secondary sintering screening material can make the sintered body obtained by the final sintering easier to condense into a uniform sintered body. At the same time, due to the limitation of the thermal field, the top area of ​​the sintering material is usually insufficiently heated during the usual sintering process. Through this assembly method, the sintering effect of the upper sintered body can be improved, and the transformation to a crystalline state can be promoted.

[0029] Example 1 A method for assembling a low-loss sintered purified aluminum nitride raw material comprises the following steps: S1: Take a tungsten crucible with a height of 132 mm, an inner diameter of 87 mm, and a wall thickness of 5 mm as a filling crucible; S2: Take a certain amount of tungsten sheets and place them in a single layer at the bottom of the tungsten crucible to obtain a bottom tungsten sheet layer; the area of ​​each tungsten sheet is 50mm 2 -100mm 2 , the thickness is between 0.1-0.3mm, in the bottom tungsten sheet layer, the total placement area of ​​the tungsten sheet is 75-85% of the bottom area of ​​the crucible; S3: Sinter the aluminum nitride raw material powder at 730 torr and 1750°C for 12 hours to obtain a primary sintered body, then crush and screen the primary sintered body to obtain a primary sintered crushed material, and take 300g of the primary sintered crushed material (with a particle size of 15-20μm) to continue filling it above the tungsten sheet layer at the bottom of the tungsten crucible; S4: Continue to take a certain amount of tungsten sheets and place them in a single layer on top of the primary sintered crushed material to obtain a medium tungsten sheet layer; the area of ​​each tungsten sheet is 50mm 2 -100mm 2, the thickness is between 0.1-0.3mm, in the tungsten sheet layer, the total placement area of ​​the tungsten sheet is 45-55% of the bottom area of ​​the crucible; S5: The primary sintered crushed material is sintered in a gradient manner under a pressure of 760 torr. The temperature is first raised to 2300°C and sintered at a constant temperature for 12 hours. The temperature is then lowered to 2150°C and sintered at a constant temperature for 12 hours. The secondary sintered body is then naturally cooled to room temperature to obtain a secondary sintered body. The secondary sintered body is then crushed and screened with a 60-mesh standard sample sieve. 100g of the secondary sintered crushed material and the primary sintered crushed material are taken respectively. The two are fully mixed using a three-dimensional motion mixer. The mixture is filled above the middle tungsten sheet layer of the tungsten crucible.

[0030] S6: Continue to take a certain amount of tungsten sheets and place them in a single layer on top of the mixed material in step S5 to obtain a top tungsten sheet layer; the area of ​​each tungsten sheet is 400mm 2 -500mm 2 , the thickness is between 0.1-0.3mm, the total placement area of ​​the tungsten sheet is 45-55% of the bottom area of ​​the crucible, and the distance between the top of the crucible and the top tungsten sheet should be kept at 10-15mm; S7: Finally, add a 42mm high bottomless crucible on the top of the tungsten crucible, and then add the crucible cover on the bottomless crucible to complete the assembly. After the assembly is completed, sintering is carried out. The specific sintering process is: under a pressure of 760torr, gradient sintering, first heating to 2300℃, sintering at a constant temperature for 12h, then cooling to 2150℃, sintering at a constant temperature for 12h, and then naturally cooling to room temperature to obtain the sintered body required for single crystal growth.

[0031] Comparative Example 1 The difference from Example 1 is that removing the bottom tungsten sheet layer will cause the sintered body to adhere to the bottom of the crucible, which will easily cause the sintered body to break when taking it out, and the bottom impurity removal effect will be reduced.

[0032] Comparative Example 2 The difference from Example 1 is that the middle tungsten layer is removed, and the impurity removal effect in the middle portion is reduced.

[0033] Comparative Example 3 The difference from Example 1 is that by removing the top tungsten sheet layer, the loss rate will increase and the top impurity removal effect will decrease.

[0034] Comparative Example 4 The difference from Example 1 is that all the powder is filled as a primary sintering crushed material, the loss rate will increase, the sintered body is easy to break when taken out, the crystal state of the top of the sintered body is poor, and the overall impurity removal effect is reduced.

[0035] Comparative Example 5 The difference from Example 1 is that the sintering pressure is reduced to 500-600 torr, the loss rate is significantly increased, and a large amount of powder is deposited on the crucible cover. It should be noted that due to changes in the crucible size and the size and thermal field of the single crystal growth furnace used, the specific mass of the aluminum nitride raw material to be added and the number of tungsten sheets should change accordingly.

[0036] Figure 3 The figures show the primary sintered crushed material a) and the secondary sintered crushed material b). It can be seen that the particle sizes of the two are quite different. Therefore, they must be fully mixed before filling the tungsten flake layer in the crucible to ensure uniform mixing.

[0037] Figure 4 The figure shows a side view of a sintered body obtained by gradient sintering using the assembly method described in Example 1 of the present invention. Through observation, it can be found that the sintered body has uniform condensation, good crystallization state, and the shape basically remains cylindrical similar to the crucible, without obvious shape changes, indicating that the overall loss rate is low.

[0038] According to the sintering conditions after assembly, under the premise of using this assembly method, in order to minimize the loss of raw materials caused by the sintering process, a higher sintering pressure should be provided, with a pressure range of 740torr-780torr.

[0039] The high quality of the aluminum nitride raw material obtained by the method described in this application is mainly reflected in the following aspects: (1) Impurity content (purity): In the technical field of aluminum nitride raw material processing, the main problem to be solved is the removal of oxygen and carbon impurities. In this application, the O and C contents of the aluminum nitride raw material powder and the secondary material powder obtained by sintering were tested using a nitrogen, oxygen and hydrogen analyzer and a carbon and sulfur analyzer, respectively. The O content decreased from 6700 ppm to 810 ppm, and the C content decreased from 520 ppm to 150 ppm, which has met the requirements of high-purity raw materials; (2) Particle size: In the process of growing aluminum nitride single crystals, the raw materials need to reach a certain particle size. The particle size of the raw materials obtained after sintering using this assembly method can reach 60-80μm, and the standard aluminum nitride grain morphology can be observed by SEM, such as Figure 5 As shown in , it is proved that high-quality aluminum nitride grains can be obtained; (3) Crystallization state: through the attachment Figure 4 It can be seen that the sintered body is evenly condensed and has a uniform color. The top of the sintered body is in good crystal state. The top view of the sintered body is as follows: Figure 6 As shown in , it can also illustrate its high quality.

Claims

1. A method for assembling low-loss sintered purified aluminum nitride raw materials, characterized in that: The following steps are involved: S1: Take a tungsten crucible with a height of 132 mm, an inner diameter of 87 mm, and a wall thickness of 5 mm as a filling crucible; S2: Take a certain amount of tungsten sheets and place them on the bottom of the tungsten crucible to obtain the bottom tungsten sheet layer; the area of ​​each tungsten sheet is 50-100mm 2 , thickness is 0.1-0.3mm, and the total placement area of ​​tungsten sheet is 75-85% of the bottom area of ​​crucible; S3: Sintering the aluminum nitride raw material powder at 700-750 torr and 1700-1800°C for 12-14 hours to obtain a primary sintered body, crushing and screening the primary sintered body to obtain a primary sintered crushed material, and taking 300g of the primary sintered crushed material to fill it above the tungsten sheet layer at the bottom of the tungsten crucible; S4: Take a certain amount of tungsten sheets and place them on the first sintered crushed material in a single layer to obtain medium tungsten sheets; the area of ​​each tungsten sheet is 50-100mm 2 , thickness is 0.1-0.3mm, and the total placement area of ​​tungsten sheet is 45-55% of the bottom area of ​​crucible; S5: Sintering the primary sintered crushed material in step S3 at a pressure of 740-780 torr in a gradient manner, first heating to 2250-2330°C, sintering at a constant temperature for 12-14h, then cooling to 2150-2200°C, sintering at a constant temperature for 12-14h, and naturally cooling to room temperature to obtain a secondary sintered body; crushing and screening the secondary sintered body to obtain a secondary sintered crushed material; taking 100g of each of the primary sintered crushed material and the secondary sintered crushed material, and fully mixing them to obtain a mixed material; filling the mixed material above the tungsten flake layer; S6: Take another certain amount of tungsten sheets and place them in a single layer on top of the mixed material in step S5 to obtain a top tungsten sheet layer; the area of ​​each tungsten sheet is 400-500mm 2 , thickness is 0.1-0.3mm, and the total placement area of ​​tungsten sheet is 45-55% of the bottom area of ​​crucible; S7: Add the crucible cover to the top of the crucible to complete the assembly.

2. The method for assembling a low-loss sintered purified aluminum nitride raw material according to claim 1, characterized in that: In step S3, the particle size of the primary sintering crushed material is 15-20 μm.

3. The method for assembling a low-loss sintered purified aluminum nitride raw material according to claim 1, characterized in that: In step S5, when screening the secondary sintered crushed material, a standard sample sieve with a mesh size of 50 or above is used for screening.

4. The method for assembling a low-loss sintered purified aluminum nitride raw material according to claim 1, characterized in that: In step S5, the primary sintered pulverized material and the secondary sintered pulverized material are mixed for 5 hours using a three-dimensional motion mixer.

5. The method for assembling a low-loss sintered purified aluminum nitride raw material according to claim 1, characterized in that: The mass ratio of the primary sintered crushed material in step S3 to the mixed material in step S5 is 3:2; the mass ratio of the primary sintered crushed material to the secondary sintered crushed material in the mixed material in step S5 is 1:

1.

6. The method for assembling a low-loss sintered purified aluminum nitride raw material according to claim 1, characterized in that: In step S7, the distance between the top of the crucible and the top tungsten sheet layer is greater than 1 cm.

7. The method for assembling a low-loss sintered purified aluminum nitride raw material according to claim 1, characterized in that: In step S7, before covering the crucible cover, a bottomless crucible with a height of 42 mm is added on the top of the tungsten crucible described in step S1.

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