Acid pickling purification method and application of powder for high-quality aluminum nitride crystal growth

Abstract

The invention relates to an acid pickling purification method and application of powder for high-quality aluminum nitride crystal growth. The method comprises the following steps: adding aluminum nitride raw material powder into a mixed acid solution which is hydrofluoric acid and nitric acid, carrying out pickling stirring at a certain temperature, a certain stirring speed and a certain pickling time, and filtering and washing the pickled mixed solution to obtain pickled aluminum nitride powder; and drying the pickled aluminum nitride powder at a specific temperature for a specific time to finally obtain the purified aluminum nitride powder. The purification method provided by the invention is simple to operate, the content of metal impurities in the aluminum nitride powder can be reduced to 100 ppm or below, the oxygen content can be reduced to 1.2 wt% or below, the purity of the aluminum nitride powder is remarkably improved, and a new method and data support are provided for the purification technology of the powder for aluminum nitride crystal growth.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor material preparation, and mainly relates to a pickling purification method and application of powder materials for growing high-quality aluminum nitride crystals. Background Art

[0002] With higher requirements for material properties in various industries, the development of the semiconductor industry has been greatly promoted. Among them, the third-generation semiconductor materials represented by aluminum nitride (AlN), silicon carbide (SiC), and gallium nitride (GaN) make up for the deficiencies in the intrinsic properties of the first and second-generation materials. Semiconductor materials and synthesis technologies are the cornerstones of the development process of modern information technology.

[0003] Aluminum nitride (AlN) has unique performance characteristics. It has a high breakdown field strength, up to 11.7 MV / cm, a low dielectric constant, and relatively excellent thermal conductivity, which enables it to be widely used in the field of electronic materials for high-temperature, high-pressure, high-frequency high-power electrical appliances. At the same time, AlN has a theoretical melting point as high as 2800 °C, good chemical stability, a direct bandgap of 6.2 eV, and a large spectral bandwidth. Its emission band can reach as deep as 200 nm, making it an extremely important blue and violet light-emitting material.

[0004] Currently, there are mainly two types of synthesis methods for aluminum nitride. One is hydride vapor phase epitaxy (HVPE), and the other is physical vapor transport (PVT). Due to the difference in synthesis principles, the synthesis temperature of the HVPE method is relatively low, but its growth rate is slow, which is more suitable for the growth of thin films; although the PVT method has a faster synthesis speed, its synthesis temperature is high, so this method is suitable for crystal growth. When growing crystals by the PVT method, the process is to sublime and decompose AlN powder in the high-temperature zone and grow crystals in the low-temperature zone. During the growth process, the carbon and oxygen impurity elements carried by the powder will affect the crystal properties, such as ultraviolet transmittance, thermal conductivity, and high-voltage resistance. Even when a large amount of impurity elements accumulate, it will cause the crystal to crack and other situations. To solve this problem, it is necessary to carry out impurity removal work on the raw material powder. Currently, the technologies for purifying aluminum nitride powder mainly include multiple raw material purifications by the PVT method, cleaning and purification with organic solvents, and cleaning and purification with organic solvents (ethanol + acetone). These methods can improve the purity of aluminum nitride powder to a certain extent, but there are problems such as low removal rate of alumina impurities and low purification efficiency. There is an urgent need for a method to accurately remove impurities such as alumina on the surface of aluminum nitride powder and at the same time improve the powder particle size. Summary of the Invention

[0005] To solve the above technical problems, the purpose of the present invention is to provide a pickling purification method and application of powder materials for growing high-quality aluminum nitride crystals.

[0006] A pickling and purification method for powders used in the growth of high-quality aluminum nitride crystals, comprising the following steps: (1) Add the aluminum nitride raw material powder to the mixed acid solution to obtain solution A. The mixed acid solution is hydrofluoric acid and nitric acid, both with a concentration of 25%. The volume ratio of hydrofluoric acid to nitric acid is 5:3, and the solid-liquid ratio of the aluminum nitride raw material powder to the mixed acid solution is 1:20 - 50, g / mL; (2) Stir and pickle solution A, set the stirring speed to 300 r / min, and the pickling duration is 5 h; (3) Filter the pickled mixed acid solution to separate the solid and the liquid; (4) Use deionized water to wash the solid obtained by filtration in step (3) multiple times until the pH of the filtrate reaches 6.5 - 7.5; (5) Dry the washed solid at a temperature of 100 °C for 5 h to finally obtain the purified aluminum nitride powder.

[0007] Preferably, in step (2), the pickling temperature of the powder is 50 - 60 °C.

[0008] Preferably, in step (3), vacuum filtration or centrifugal filtration can be used for filtration.

[0009] Preferably, the filter medium used in the filtration step of step (3) should have acid and corrosion resistance, and the cut-off molecular weight is 4500 - 6000 Da.

[0010] Preferably, in step (5), the washed solid is dried under a high-purity inert protective gas to avoid secondary contamination caused by the mixing of oxygen or water vapor.

[0011] Preferably, in step (5), the drying method is air-blowing drying or vacuum drying; the drying temperature is 100 °C, and the drying time is 5 h.

[0012] More preferably, when the drying method in step (5) is air-blowing drying, the air-blowing speed is 0.8 - 1.2 m / s; when the drying method is vacuum drying, the vacuum degree is 0.06 Mpa - 0.1 Mpa.

[0013] Preferably, the above operations are all carried out in a glove box to avoid secondary contamination.

[0014] The present invention also provides the application of the purified aluminum nitride powder obtained above in the growth of aluminum nitride single crystals by the PVT method.

[0015] The beneficial effects of the present invention are as follows: The pickling and purification method of aluminum nitride powder obtained by the present invention is simple to operate. Through the reasonable ratio of different volatile acids, the removal of impurities and the purification of raw materials are reasonably designed. After multiple experiments and adjustments of the ratio of hydrofluoric acid to nitric acid, when the ratio of hydrofluoric acid to nitric acid is close to 5:3, the metal impurity content in the aluminum nitride powder can be reduced to less than 100 ppm, and the oxygen content can be reduced to 1.2 wt%, significantly improving the purity of the aluminum nitride powder. The present invention provides a new method and data support for the purification technology of powders for aluminum nitride crystal growth, and has a positive promoting effect on the development of aluminum nitride crystal growth technology in the field of semiconductor materials. At the same time, it also provides a useful reference for the powder purification research of other similar materials. Description of the Drawings

[0016] Figure 1 SEM image of the purified aluminum nitride powder prepared in Example 3; Figure 2 SEM image of the purified aluminum nitride powder prepared in Comparative Example 1; Figure 3 SEM image of the purified aluminum nitride powder prepared in Comparative Example 2; Figure 4 SEM image of the purified aluminum nitride powder prepared in Comparative Example 3; Figure 5 SEM image of the purified aluminum nitride powder prepared in Comparative Example 4; Figure 6 Line graph of oxygen content and nitrogen content in the purified aluminum nitride powder obtained in Example 3 and Comparative Examples 1-4. Detailed Description of the Invention

[0017] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0018] Example 1 A pickling and purification method for powders for high-quality aluminum nitride crystal growth (1) Add 5 g of aluminum nitride raw material powder to 100 mL of mixed acid solution to obtain solution A. The mixed acid solution is hydrofluoric acid and nitric acid, both with a concentration of 25%. The volume ratio of hydrofluoric acid to nitric acid is 5:3. The aluminum nitride raw material powder contains various metal impurities (such as Na, W, Fe, Zn, Ti, Mn, etc.) and oxygen impurities. The initial content of metal impurities is: Na content 2603 ppm, W content 1141 ppm, Fe content 197 ppm, etc., and the oxygen content is 15.6 wt%.

[0019] (2) Place solution A in a constant temperature water bath at 60 °C and stir it with a magnetic stirrer at a speed of 300 r / min for 5 h. The reaction process is as follows: Al 2 O 3 (s) + 6HF(aq) → 2AlF 3 (s) + 3H 2 O(l) Al 2 O 3 (s) + 8HF(aq) → 2AlF 4 - (aq) + 2H + (aq) + 3H 2 O(l) Al 2 O 3 (s) + 10HF(aq) → 2AlF 5 2- (aq) + 4H + (aq) + 3H 2 O(l) Al 2 O 3 (s) + 12HF(aq) → 2AlF 6 3- (aq) + 6H + (aq) + 3H 2 O(l) (3) Filter the pickled mixed acid solution using a vacuum filtration device. Use a polytetrafluoroethylene (PTFE) filter membrane with a pore size of 0.45 μm (which has good acid corrosion resistance and a molecular weight cut-off of 5500 Da) to separate the solid and liquid.

[0020] (4) Wash the solid obtained by filtration in step (3) with deionized water. The amount of water used each time is 50 mL, and it is washed 5 times until the pH of the filtrate reaches 6.5 - 7.5.

[0021] (5) Transfer the washed solid to a drying oven and dry it at 100 °C under a vacuum of 0.08 Mp for 5 h. Introduce high-purity nitrogen gas into the drying oven as a protective gas to prevent the mixing of oxygen or water vapor.

[0022] (6) After cleaning, detect the purified aluminum nitride powder. The metal impurity content is reduced to: Na content 95 ppm, W content 38 ppm, Fe content 33 ppm, etc., all below 100 ppm, and the oxygen content is reduced to 1.2 wt%.

[0023] Example 2 A pickling and purification method for high-quality aluminum nitride crystal growth powder (1) Add 10 g of aluminum nitride raw material powder to 500 mL of mixed acid solution to obtain solution A. The mixed acid solution is hydrofluoric acid and nitric acid, both with a concentration of 25%. The volume ratio of hydrofluoric acid to nitric acid is 5:3. The impurity content of the aluminum nitride raw material powder is basically the same as that in Example 1.

[0024] (2) Under a constant temperature environment of 50 °C, use ultrasonic stirring assistance (frequency 40 kHz) for solution A, and at the same time carry out pickling for 5 h at a mechanical stirring speed of 300 r / min. This reaction process is: Al 2 O 3 (s)+6HF(aq)→2AlF 3 (s)+3H 2 O(l) Al 2 O 3 (s)+8HF(aq)→2AlF 4 - (aq)+2H + (aq)+3H 2 O(l) Al 2 O 3 (s)+10HF(aq)→2AlF 5 2- (aq)+4H + (aq)+3H 2 O(l) Al 2 O 3 (s)+12HF(aq)→2AlF 6 3- (aq)+6H + (aq)+3H 2 O(l) (3) Filter the pickled mixed acid solution, and carry out atmospheric pressure filtration using a glass fiber filter paper with a pore size of 1 μm (acid-resistant and a molecular weight cut-off of 6000 Da).

[0025] (4) Wash the solid obtained by filtration in step (3) with deionized water, with 60 mL of water used for each wash, and wash 7 times until the pH of the filtrate reaches 6.5 - 7.5.

[0026] (5) Place the washed solid in a forced-air drying oven and dry it at 100 °C for 5 h. During the drying process, introduce high-purity helium for protection, with a blowing speed of 1 m / s to ensure uniform heating of the powder.

[0027] (6) After cleaning, test the purified aluminum nitride powder. The metal impurity content is reduced to: Na content 95 ppm, W content 35 ppm, Fe content 30 ppm, etc., all below 100 ppm, and the oxygen content is reduced to 1.16 wt%. The purity is further improved.

[0028] Example 3 A pickling and purification method for powders used in the growth of high-quality aluminum nitride crystals (1) Add 10 g of aluminum nitride raw material powder to 500 mL of a mixed acid solution to obtain solution A. The mixed acid solution is hydrofluoric acid and nitric acid, both with a concentration of 25%, and the volume ratio of hydrofluoric acid to nitric acid is 5:3. The impurity content of the aluminum nitride raw material powder is basically the same as that in Example 1.

[0029] (2) Place solution A in a constant-temperature water bath at 60 °C and stir it at a speed of 300 r / min for 5 h using a magnetic stirrer.

[0030] (3) Filter the pickled mixed acid solution. The filter membrane is an acid-resistant organic ultrafiltration membrane (with a molecular weight cut-off of 5000 Da) to separate the solid and the liquid.

[0031] (4) Wash the solid obtained by filtration in step (3) with deionized water, with 100 mL of water used for each wash, and wash a total of 8 times until the pH of the filtrate reaches 6.5 - 7.5.

[0032] (5) Transfer the washed solid to a drying oven and dry it at 100 °C / vacuum degree 0.08 Mp for 5 h. Introduce high-purity nitrogen into the drying oven as a protective gas to prevent the mixing of oxygen or water vapor.

[0033] (6) After cleaning, test the purified aluminum nitride powder. The metal impurity content is reduced to: Na content 99 ppm, W content 42 ppm, Fe content 30 ppm, etc., all below 100 ppm, and the oxygen content is reduced to 1.15 wt%.

[0034] Comparative Example 1 Change the volume ratio of hydrofluoric acid to nitric acid to 2:1, and the other steps are the same as in Example 3.

[0035] The purified aluminum nitride powder was tested. The metal impurity content was reduced to: Na content 115 ppm, W content 45 ppm, Fe content 32 ppm, etc. The metal impurity elements were relatively abundant, and the oxygen content was reduced to 1.5 wt%.

[0036] Comparative Example 2 The volume ratio of hydrofluoric acid to nitric acid was changed to 1:1, and the remaining steps were the same as in Example 3.

[0037] The purified aluminum nitride powder was tested. The metal impurity content was reduced to: Na content 108 ppm, W content 43 ppm, Fe content 31 ppm, etc. The metal impurity elements were relatively abundant, and the oxygen content was reduced to 1.35%, which was higher than that in Experimental Example 3.

[0038] Comparative Example 3 The volume ratio of hydrofluoric acid to nitric acid was changed to 4:3, and the remaining steps were the same as in Example 3.

[0039] The purified aluminum nitride powder was tested. The metal impurity content was reduced to: Na content 102 ppm, W content 40 ppm, Fe content 33 ppm, etc. The metal impurity elements were relatively abundant, and the oxygen content was reduced to 1.25%, which was higher than that in Experimental Example 3.

[0040] Comparative Example 4 The volume ratio of hydrofluoric acid to nitric acid was changed to 3:2, and the remaining steps were the same as in Example 3.

[0041] The purified aluminum nitride powder was tested. The metal impurity content was reduced to: Na content 105 ppm, W content 41 ppm, Fe content 31 ppm, etc. The metal impurity elements were relatively abundant, and the oxygen content was reduced to 1.22%, which was higher than that in Experimental Example 3.

[0042] Test Example 1 The purified aluminum nitride powders obtained in Example 3 and Comparative Examples 1-4 were respectively tested by SEM (scanning electron microscope), as Figures 1-5 shown. When the volume ratio of hydrofluoric acid to nitric acid was 5:3, the particle size of the powder was the smallest, which was most conducive to the growth of aluminum nitride single crystals. The particle size of the powder required for sintering aluminum nitride ceramics is usually about 0.5-5 microns, but the particle size of the powder required for the growth of aluminum nitride single crystals usually needs to reach the general requirement of submicron level or even smaller, usually dozens of nanometers to hundreds of nanometers. The particle size of the aluminum nitride powder obtained in Example 3 was significantly smaller than that of the aluminum nitride powder obtained in the comparative examples, meeting the requirements for single crystal growth.

[0043] Comparing the purified aluminum nitride powders obtained using different ratios of mixed acid solutions, as Figure 6As shown, after treatment with the 5:3 mixed acid solution, the impurity content is lower, further proving the superiority of the 5:3 ratio mixed acid solution adopted in the present invention in terms of impurity removal. The treated powder has the lowest oxygen content and the highest nitrogen content. This indicates that the pickling purification method has a significant effect on removing impurities in aluminum nitride powder, can effectively improve the powder purity, and provides a high-purity raw material basis for the subsequent growth of high-quality aluminum nitride crystals.

Claims

1. A method for acid washing and purification of powder for high-quality aluminum nitride crystal growth, characterized in that: The following steps are involved: (1) adding aluminum nitride raw material powder to a mixed acid solution to obtain solution A, wherein the mixed acid solution is hydrofluoric acid and nitric acid, each having a concentration of 25%, a volume ratio of hydrofluoric acid to nitric acid of 5:3, and a solid-liquid ratio of aluminum nitride raw material powder to the mixed acid solution of 1:20-50, g / mL; (2) Solution A was stirred and pickled at a temperature of 50-60°C, a stirring speed of 300 r / min, and a pickling duration of 5 h; (3) filtering the mixed acid solution after pickling to separate the solid and the liquid; (4) washing the solid filtered in step (3) multiple times with deionized water until the pH of the filtrate reaches 6.5-7.5; (5) The washed solid is dried at 100° C. for 5 h to obtain purified aluminum nitride powder.

2. The purification method according to claim 1, characterized in that The filtration in step (3) can be performed by vacuum filtration or centrifugal filtration.

3. The purification method according to claim 2, characterized in that The filter medium used in the vacuum filtration in step (3) is a polytetrafluoroethylene (PTFE) filter membrane, an organic ultrafiltration membrane or a glass fiber filter paper, and the molecular weight cutoff of the filter medium is 4500-6000Da.

4. The purification method according to claim 1, characterized in that The washed solid in step (5) is dried under high-purity inert protective gas.

5. The purification method according to claim 1, characterized in that: The drying method in step (5) is air drying or vacuum drying.

6. The purification method according to claim 5, characterized in that When the drying method in step (5) is air drying, the air speed is 0.8-1.2 m / s; When the drying method is vacuum drying, the vacuum degree is 0.06Mpa-0.1Mpa.

7. The purification method according to claim 1, characterized in that: In the step (5), the drying temperature is 100° C. and the drying time is 5 h.

8. Aluminum nitride powder obtained by the purification method according to any one of claims 1 to 7.

9. Use of the purified aluminum nitride powder as claimed in claim 8 in growing aluminum nitride single crystals by a PVT method.

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