An assembly method for low-loss sintered purification of aluminum nitride raw material

Abstract

The application relates to the technical field of aluminum nitride raw material processing, in particular to a low-loss sintering and purification aluminum nitride raw material assembling method. The method comprises the following steps: sequentially arranging a bottom tungsten sheet layer, a primary sintering and crushing material layer, a middle tungsten sheet layer, a mixed material layer and a top tungsten sheet layer from bottom to top at the bottom of a tungsten crucible; finally, a crucible cover is added to the top of the crucible to complete the assembling. After the assembling is completed, the crucible is placed in a single crystal growth furnace for sintering, a gradient sintering process is adopted for the sintering, and a yellowish brown high-quality AlN polycrystalline sintered body can be obtained after the sintering is completed. The sintered body has low impurity content, uniform condensation and low loss rate, so that the sintered material meets the needs of high-quality AlN single crystal growth in terms of granularity, impurity content and loss rate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aluminum nitride raw material processing, in particular to a low-loss sintering and purification assembly method of aluminum nitride raw material. BACKGROUND

[0002] Aluminum nitride is a wide band gap semiconductor material with a theoretical band gap of 6.2eV. In addition, it also has a series of excellent physical and chemical properties: high thermal conductivity, high breakdown field strength, strong anti-radiation ability, high chemical stability, corrosion resistance, high electron saturation rate, etc. Therefore, it is very suitable for preparing high-temperature, high-power and high-frequency semiconductor devices.

[0003] In order to obtain high-quality semiconductor devices, high-quality aluminum nitride crystals are essential, and in order to obtain high-quality aluminum nitride crystals, high-purity aluminum nitride raw materials that meet the requirements of the semiconductor industry are necessary. At present, due to the limitations of production process, 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 processing method. However, due to the selection of different sintering processes and different assembly processes, the purity, loss rate, and crystalline state of the raw material obtained after sintering are very different. In addition, many laboratories have carried out research on the sintering process of aluminum nitride raw materials, but the assembly process of the raw material before sintering is quite scarce.

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

[0005] The present application provides a low-loss sintering and purification assembly method of aluminum nitride raw material to solve the problems of high sintering loss rate and uneven sintering body in the current sintering process of aluminum nitride raw material. The assembly method of the present application adopts a layered assembly method, which achieves the purpose of the present application by layering different functional layers. After assembly using the assembly method of the present application and conventional sintering, a yellow-brown high-quality AlN polycrystalline sintered body can be obtained. The sintered body has low impurity content, uniform condensation, and the particles grow during the sintering process. At the same time, the loss rate is also kept 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, and loss rate.

[0006] To achieve the above purpose, the present application provides the following technical solutions:

[0007] A low-loss sintering and purification assembly method of aluminum nitride raw material, comprising the following steps:

[0008] S1: Take a tungsten crucible with a height of 132mm, an inner diameter of 87mm, and a wall thickness of 5mm as the filling crucible;

[0009] S2: Place a certain amount of tungsten sheets in a single layer at the bottom of the tungsten crucible to obtain the bottom tungsten sheet layer; the area of ​​each tungsten sheet is 50-100 mm². 2 The thickness is 0.1-0.3mm, and the total placement area of ​​the tungsten sheets is 75-85% of the bottom area of ​​the crucible;

[0010] S3: Sinter the aluminum nitride raw material powder at 700-750 torr and 1700-1800℃ for 12-14 hours to obtain a primary sintered body. Crush and screen the primary sintered body to obtain primary sintered pulverized material. Take 300g of primary sintered pulverized material and fill it above the tungsten sheet layer at the bottom of the tungsten crucible.

[0011] S4: Take a certain amount of tungsten sheets and place them in a single layer on top of the primary sintering pulverized material to obtain a middle tungsten sheet layer; the area of ​​each tungsten sheet is 50-100 mm². 2 The thickness is 0.1-0.3mm, and the total area of ​​the tungsten sheets is 45-55% of the bottom area of ​​the crucible;

[0012] S5: The primary sintered pulverized material described in step S3 is subjected to gradient sintering under a pressure of 740-780 torr. First, the temperature is raised to 2250-2330℃ and sintered at a constant temperature for 12-14 hours. Then, the temperature is lowered to 2150-2200℃ and sintered at a constant temperature for 12-14 hours. The material is then allowed to cool naturally to room temperature to obtain a secondary sintered body. The secondary sintered body is pulverized and screened to obtain secondary sintered pulverized material. 100g of the primary sintered pulverized material and 100g of the secondary sintered pulverized material are taken and thoroughly mixed to obtain a mixture. The mixture is then filled above the tungsten sheet layer.

[0013] S6: Take a certain amount of tungsten sheets and place them in a single layer on top of the mixture described in step S5 to obtain a top tungsten sheet layer; the area of ​​each tungsten sheet is 400-500 mm². 2 The thickness is 0.1-0.3mm, and the total area of ​​the tungsten sheets is 45-55% of the bottom area of ​​the crucible;

[0014] S7: Place the crucible lid on top of the crucible to complete the assembly.

[0015] Preferably, in step S3, the particle size of the primary sintering pulverized material is 15-20 μm, and should not be too large or too small.

[0016] Preferably, in step S5, when screening the secondary sintering pulverized material, a standard sieve with a mesh size of 50 or higher is used for screening.

[0017] Preferably, in step S5, a three-dimensional motion mixer is used to mix the primary sintering pulverized material and the secondary sintering pulverized material for 5 hours to achieve thorough mixing of the two.

[0018] Preferably, the mass ratio of the primary sintering pulverized material in step S3 to the mass ratio of the mixture in step S5 is 3:2; and the mass ratio of the primary sintering pulverized material to the secondary sintering pulverized material in the mixture in step S5 is 1:1.

[0019] Preferably, in step S7, the distance between the top of the crucible and the top tungsten sheet should be more than 1 cm to prevent uneven heating.

[0020] Preferably, in step S7, before covering the crucible with the lid, a bottomless crucible section with a height of 42mm is added to the top of the tungsten crucible described in step S1 to increase the thickness of the air layer and improve the purification effect of the raw materials.

[0021] After assembly using this method, sintering is performed. The specific sintering process is as follows: under a pressure of 740-780 torr, gradient sintering is carried out. First, the temperature is raised to 2250-2330℃ and sintered at a constant temperature for 12-14 hours. Then, the temperature is lowered to 2150-2200℃ and sintered at a constant temperature for 12-14 hours. Finally, the temperature is naturally cooled to room temperature. The resulting sintered body can be directly used for the next step of AlN single crystal growth.

[0022] In step S3, the particle size of the particles obtained from the crushing of the sintered body should be kept as consistent as possible.

[0023] The assembly method described herein is applicable to the assembly of a resistance-type single crystal growth furnace for raw material purification.

[0024] Using this assembly method for sintering, the resulting sintered body can meet the requirements of crystal growth, while the loss rate can be controlled within 5%.

[0025] Compared with existing technologies, the low-loss sintering purification aluminum nitride raw material assembly method disclosed in this invention further refines the raw material assembly process by employing a layered assembly method. The transition from a completely single-stage sintering pulverized material to a mixture of single-stage and secondary sintering pulverized material makes it easier for the final sintered body to agglomerate into a uniform sintered body. Simultaneously, due to the limitation of the thermal field, the top region of the sintered material is usually underheated during conventional sintering processes. This assembly method improves the sintering effect of the upper sintered body, promoting the transformation to a crystalline state. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the tungsten crucible and its internal filler layer distribution in the assembly method of the present invention.

[0027] The components are: 1. Bottom tungsten sheet layer; 2. First-sintered pulverized material layer; 3. Middle tungsten sheet layer; 4. Mixed material layer; 5. Top tungsten sheet layer; 6. Crucible lid; 7. Tungsten crucible.

[0028] Figure 2 This is a top view of the tungsten crucible after steps S2, S3, S4, S5, and S6 in Embodiment 1 of the present invention.

[0029] Figure 3 These are diagrams of the primary sintering pulverized material (a) and the secondary sintering pulverized material (b) in Embodiment 1 of the present invention.

[0030] Figure 4 This is a side view of the sintered body obtained after sintering according to Embodiment 1 of the present invention.

[0031] Figure 5 This is a grain morphology diagram of aluminum nitride obtained by sintering in Example 1 of the present invention.

[0032] Figure 6 This is a top view of the aluminum nitride sintered body obtained by sintering in Embodiment 1 of the present invention. Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments, and the advantages and features of the present invention will become clearer with the description. However, the embodiments are merely exemplary and do not constitute any limitation on the scope of the present invention. Those skilled in the art should understand that modifications or substitutions can be made to the details and form of the technical solutions of the present invention without departing from the spirit and scope of the present invention, but all such modifications and substitutions fall within the protection scope of the present invention.

[0034] An assembly method for low-loss sintering and purification of aluminum nitride raw materials includes the following steps:

[0035] S1: Take tungsten crucible 7, with a height of 132mm, an inner diameter of 87mm, and a wall thickness of 5mm. See [reference needed]. Figure 1 and Figure 2 During the assembly of aluminum nitride raw materials, a layered assembly method is adopted. The crucible contains the following layers from bottom to top: 1. Bottom tungsten sheet layer; 2. First sintering and crushing material layer; 3. Middle tungsten sheet layer; 4. Mixed material layer; 5. Top tungsten sheet layer; 6. Crucible lid.

[0036] S2: Place a certain amount of tungsten sheets in a single layer at the bottom of the tungsten crucible to obtain the bottom tungsten sheet layer; the area of ​​each tungsten sheet is 50-100 mm². 2 The thickness is 0.1-0.3mm, and the total placement area of ​​the tungsten sheets is 75-85% of the bottom area of ​​the crucible;

[0037] S3: Sinter the aluminum nitride raw material powder at 700-750 torr and 1700-1800℃ for 12-14 hours to obtain a primary sintered body. Crush and screen the primary sintered body to obtain primary sintered pulverized material. Take 300g of primary sintered pulverized material and fill it above the tungsten sheet layer at the bottom of the tungsten crucible.

[0038] S4: Take a certain amount of tungsten sheets and place them in a single layer on top of the primary sintering pulverized material to obtain a middle tungsten sheet layer; the area of ​​each tungsten sheet is 50-100 mm². 2 The thickness is 0.1-0.3mm, and the total area of ​​the tungsten sheets is 45-55% of the bottom area of ​​the crucible;

[0039] S5: The primary sintered pulverized material described in step S3 is subjected to gradient sintering under a pressure of 740-780 torr. First, the temperature is raised to 2250-2330℃ and sintered at a constant temperature for 12-14 hours. Then, the temperature is lowered to 2150-2200℃ and sintered at a constant temperature for 12-14 hours. The material is then allowed to cool naturally to room temperature to obtain a secondary sintered body. The secondary sintered body is pulverized and screened to obtain secondary sintered pulverized material. 100g of the primary sintered pulverized material and 100g of the secondary sintered pulverized material are taken and thoroughly mixed to obtain a mixture. The mixture is then filled above the tungsten sheet layer.

[0040] S6: Take a certain amount of tungsten sheets and place them in a single layer on top of the mixture described in step S5 to obtain a top tungsten sheet layer; the area of ​​each tungsten sheet is 400-500 mm². 2 The thickness is 0.1-0.3mm, and the total area of ​​the tungsten sheets is 45-55% of the bottom area of ​​the crucible;

[0041] S7: Place the crucible lid on top of the crucible to complete the assembly.

[0042] This invention discloses a low-loss sintering purification method for aluminum nitride raw materials. By employing a layered assembly approach, the assembly of raw materials is further refined. The transition from a completely primary sintering pulverized material to a mixture of primary sintering pulverized material and secondary sintering screening material allows the final sintered body to more easily agglomerate into a uniform sintered body. Simultaneously, due to thermal field limitations, the top region of the sintered material is typically underheated during conventional sintering processes. This assembly method improves the sintering effect of the upper sintered body, promoting its transformation to a crystalline state.

[0043] Example 1

[0044] An assembly method for low-loss sintering and purification of aluminum nitride raw materials includes the following steps:

[0045] S1: Take a tungsten crucible with a height of 132mm, an inner diameter of 87mm, and a wall thickness of 5mm as the filling crucible;

[0046] S2: Place a certain amount of tungsten sheets in a single layer at the bottom of a tungsten crucible to obtain a bottom tungsten sheet layer; the area of ​​each tungsten sheet is 50 mm². 2 -100mm 2 The thickness is between 0.1-0.3 mm, and in the bottom tungsten sheet layer, the total placement area of ​​the tungsten sheets is 75-85% of the bottom area of ​​the crucible;

[0047] S3: Sinter the aluminum nitride raw material powder at 730 torr and 1750℃ for 12 hours to obtain a primary sintered body. Then, crush and screen the primary sintered body to obtain primary sintered pulverized material. Take 300g of primary sintered pulverized material (particle size of 15-20μm) and continue to fill it above the tungsten sheet layer at the bottom of the tungsten crucible.

[0048] S4: Take a certain amount of tungsten sheets and place them in a single layer on top of the primary sintering pulverized material to obtain a middle tungsten sheet layer; the area of ​​each tungsten sheet is 50 mm². 2 -100mm 2 The thickness is between 0.1-0.3 mm, and in the middle tungsten sheet layer, the total placement area of ​​the tungsten sheets is 45-55% of the bottom area of ​​the crucible;

[0049] S5: The primary sintering pulverized material is sintered in a gradient under a pressure of 760 torr. First, the temperature is raised to 2300℃ and sintered at a constant temperature for 12 hours. Then, the temperature is lowered to 2150℃ and sintered at a constant temperature for 12 hours. Finally, it is naturally cooled to room temperature to obtain a secondary sintered body. The secondary sintered body is then pulverized and screened using a 60-mesh standard sieve. 100g of the secondary sintering pulverized material and 100g of the primary sintering pulverized material are taken and thoroughly mixed using a three-dimensional motion mixer. The mixture is then filled above the middle tungsten sheet layer in the tungsten crucible.

[0050] S6: Take a certain amount of tungsten sheets and place them in a single layer on top of the mixture described in step S5 to obtain a top tungsten sheet layer; the area of ​​each tungsten sheet is 400 mm². 2 -500mm 2 The thickness is between 0.1-0.3mm, the total placement area of ​​the tungsten sheets is 45-55% of the bottom area of ​​the crucible, and the distance between the top of the crucible and the top tungsten sheet layer should be maintained at 10-15mm;

[0051] S7: Finally, add a bottomless crucible section with a height of 42mm to the top of the tungsten crucible, and then put the crucible lid on top of the bottomless crucible to complete the assembly. After the assembly is completed, sintering is carried out. The specific sintering process is as follows: under a pressure of 760 torr, sinter in a gradient manner. First, heat up to 2300℃ and sinter at a constant temperature for 12 hours, then cool down to 2150℃ and sinter at a constant temperature for 12 hours, and then cool naturally to room temperature to obtain the sintered body required for single crystal growth.

[0052] Comparative Example 1

[0053] The difference from Example 1 is that removing the bottom tungsten sheet layer causes the sintered body to stick to the bottom of the crucible, making it easy for the sintered body to break when it is removed, and reducing the bottom impurity removal effect.

[0054] Comparative Example 2

[0055] The difference from Example 1 is that the middle tungsten sheet layer is removed, which reduces the impurity removal effect in the middle.

[0056] Comparative Example 3

[0057] The difference from Example 1 is that removing the top tungsten sheet layer increases the loss rate and reduces the top impurity removal effect.

[0058] Comparative Example 4

[0059] The difference from Example 1 is that the powder is filled entirely as a one-time sintered pulverized material, which increases the loss rate, makes the sintered body prone to breakage when removed, results in poor crystallization at the top of the sintered body, and reduces the overall impurity removal effect.

[0060] Comparative Example 5

[0061] The difference from Example 1 is that the sintering pressure is reduced to 500-600 torr, resulting in a significantly increased loss rate and a large amount of powder deposited on the crucible lid. It should be noted that due to variations in crucible size and the size of the single-crystal growth furnace used, as well as the thermal field and other conditions, the specific amount of aluminum nitride material to be added and the number of tungsten sheets must be adjusted accordingly.

[0062] Figure 3 The images show primary sintering pulverized material a) and secondary sintering pulverized material b), respectively. It can be seen that the particle size difference between the two is quite large. Therefore, they must be thoroughly mixed before being filled into the middle tungsten sheet layer of the crucible to ensure uniform mixing.

[0063] Figure 4 The image shown is a side view of a sintered body obtained by gradient sintering using the assembly method described in Embodiment 1 of the present invention. Observation shows that the sintered body exhibits uniform condensation, good crystallization, and maintains a cylindrical shape similar to that of the crucible. There are no obvious shape changes, indicating that the overall loss rate is low.

[0064] Based on the sintering results after assembly, under the premise of using this assembly method, in order to minimize the material loss caused by the sintering process, a higher sintering pressure should be provided, with a pressure range of 740 torr-780 torr.

[0065] The high quality of the aluminum nitride raw material obtained by the method described in this application is mainly reflected in the following aspects:

[0066] (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 aluminum nitride raw material powder and secondary material powder obtained by sintering were tested by nitrogen, oxygen and hydrogen analyzer and carbon and sulfur analyzer, respectively. The O content decreased from 6700ppm to 810ppm and the C content decreased from 520ppm to 150ppm, which has met the requirements of high purity raw materials.

[0067] (2) Particle size: During the growth of aluminum nitride single crystals, the raw materials need to reach a certain particle size. After sintering using this assembly method, the particle size of the raw materials can reach 60-80μm, and the standard aluminum nitride grain morphology can be observed by SEM, such as... Figure 5 As shown in the figure, it proves that it can yield high-quality aluminum nitride grains;

[0068] (3) Crystallization state: through the attachment Figure 4 It can be seen that the sintered body has uniform condensation and color, and the top of the sintered body has good crystallization. The top view of the sintered body is as follows. Figure 6 As shown in the image, its high quality can also be described.

Claims

1. An assembly method for low-loss sintering and purification of aluminum nitride raw materials, characterized in that, Includes the following steps: S1: Take a tungsten crucible with a height of 132mm, an inner diameter of 87mm, and a wall thickness of 5mm as the filling crucible; S2: Place a certain amount of tungsten sheets in a single layer at the bottom of the tungsten crucible to obtain the bottom tungsten sheet layer; the area of ​​each tungsten sheet is 50-100 mm². 2 The thickness is 0.1-0.3mm, and the total placement area of ​​the tungsten sheets is 75-85% of the bottom area of ​​the crucible; S3: Sinter the aluminum nitride raw material powder at 700-750 torr and 1700-1800℃ for 12-14 hours to obtain a primary sintered body. Crush and screen the primary sintered body to obtain primary sintered pulverized material. Take 300g of primary sintered pulverized material and 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 in a single layer on top of the primary sintering pulverized material to obtain a middle tungsten sheet layer; the area of ​​each tungsten sheet is 50-100 mm². 2 The thickness is 0.1-0.3mm, and the total placement area of ​​the tungsten sheets is 45-55% of the bottom area of ​​the crucible; S5: The primary sintered pulverized material described in step S3 is subjected to gradient sintering under a pressure of 740-780 torr. First, the temperature is raised to 2250-2330℃ and sintered at a constant temperature for 12-14 hours. Then, the temperature is lowered to 2150-2200℃ and sintered at a constant temperature for 12-14 hours. The material is then allowed to cool naturally to room temperature to obtain a secondary sintered body. The secondary sintered body is pulverized and screened to obtain secondary sintered pulverized material. 100g of the primary sintered pulverized material and 100g of the secondary sintered pulverized material are taken and thoroughly mixed to obtain a mixture. The mixture is then filled above the tungsten sheet layer. S6: Take a certain amount of tungsten sheets and place them in a single layer on top of the mixture described in step S5 to obtain a top tungsten sheet layer; the area of ​​each tungsten sheet is 400-500 mm². 2 The thickness is 0.1-0.3mm, and the total placement area of ​​the tungsten sheets is 45-55% of the bottom area of ​​the crucible; S7: Place the crucible lid on top of the crucible to complete the assembly.

2. The assembly method for low-loss sintering and purification of aluminum nitride raw materials according to claim 1, characterized in that, In step S3, the particle size of the primary sintering pulverized material is 15-20 μm.

3. The assembly method for low-loss sintering and purification of aluminum nitride raw materials according to claim 1, characterized in that, In step S5, when screening the secondary sintering pulverized material, a standard sieve with a mesh size of 50 or higher is used for screening.

4. The assembly method for low-loss sintering and purification of aluminum nitride raw materials according to claim 1, characterized in that, In step S5, a three-dimensional motion mixer is used to mix the primary sintering pulverized material and the secondary sintering pulverized material for 5 hours.

5. The assembly method for low-loss sintering and purification of aluminum nitride raw materials according to claim 1, characterized in that, In step S7, the distance between the top of the crucible and the top tungsten sheet is more than 1 cm.

6. The assembly method for low-loss sintering and purification of aluminum nitride raw materials according to claim 1, characterized in that, In step S7, before covering the crucible with the lid, a bottomless crucible section with a height of 42 mm is added to the top of the tungsten crucible described in step S1.

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