Ultra-high purity graphite powder for SiC wafer production, preparation method, and additives used in preparation.

Abstract

This invention relates to the field of ultra-high purity graphite powder production technology, and particularly to ultra-high purity graphite powder for SiC wafer production, its preparation method, and additives. By utilizing a synergistic process of "additive-assisted + physical high-temperature purification," specific process parameters are introduced, and specific additives are matched to promote the conversion of metal (Al, V, Ti, Fe, etc.) oxide impurities and non-metal (B, Si, etc.) carbide impurities in the graphite powder into easily volatile chlorides and fluorides under high-temperature conditions. This separation and purification achieves a graphite powder purity of 5N or higher, even reaching 5N8 (99.9998%). This effectively avoids the use of acidic and alkaline solutions and halogen gases (fluorine, chlorine, etc.), ensuring a green and safe production process.

Description

Technical Field

[0001] This invention relates to the field of ultra-high purity graphite powder production technology, and particularly to ultra-high purity graphite powder for SiC wafer production, its preparation method, and additives for preparation. Background Technology

[0002] Third-generation semiconductors are based on silicon carbide (SiC) materials. Leveraging their advantages of high saturated electron velocity, strong radiation resistance, and high energy density, they are widely used in new energy, photovoltaics, 5G communications, aerospace, and other fields. Ultra-high purity graphite powder, as the core raw material for manufacturing silicon carbide wafers, is crucial in determining whether wafers meet standards due to its purity and quality.

[0003] Currently, the main methods for obtaining ultra-high purity graphite powder include chemical purification and physical purification.

[0004] Chemical purification involves removing impurities using liquid acids and alkalis. For example, the continuous production method for chemical purification of high-purity graphite disclosed in patent number 201410268162.3 involves adding water to a reaction vessel and then adding graphite material. A mixed acid solution is added at a ratio of 20%-75% of the weight of the graphite material. The heating device is turned on, and then the stirring is started to mix the material evenly for reaction. The reaction time is 6-16 hours, and the reaction temperature is 80℃-230℃. After the reaction, the material in the reaction vessel is added to a flotation machine filled with deionized water. The material is stirred and floated multiple times in the flotation machine until it is close to neutral. The nearly neutral material after flotation in step three is sent to a vacuum filter for vacuum filtration to obtain high-purity graphite with a purity of 99.9%-99.99%.

[0005] Physical purification removes impurities through high-temperature treatment. For example, patent application number 202210355819.4 discloses a process for purifying high-purity carbon powder. It adopts an intermittent processing method, which involves mixing additives into graphite powder, heating, sintering for purification, cooling, and finally collecting the material. The resulting carbon powder has a purity of up to 5N (99.999%) and a chromium content of less than 0.01ppm. For example, patent number 202110970557.8 discloses a method for preparing ultra-high purity carbon powder from Atchison furnace core graphite powder. Graphite powder raw material is added to a graphite boat, which is then placed in a high-temperature purification device. The device is evacuated and then purged with inert gas. After purging for a certain time, the temperature is increased to 1800-2000℃ at a programmed heating rate of 5-15℃ / min, held for 1-2 hours, and then evacuated again. Once a certain vacuum value is reached, inert gas is introduced for pressurization. Once a certain pressurization value is reached, the temperature is further increased to 2400-2600℃ at a heating rate of 5-15℃ / min, held for 1-2 hours, and then evacuated again. Once a certain vacuum value is reached, inert gas is introduced for pressurization again. Once a certain pressurization value is reached, the temperature is further increased to 3000-3100℃ at a heating rate of 5-15℃ / min. Heat to ℃, keep warm for 1-3 hours, then cool to room temperature to obtain high-purity carbon powder. The purity can reach 5N (99.999%).

[0006] In summary, the high-purity carbon powder obtained by physical purification can reach 5N (99.999%) or higher. Compared with the high-purity carbon powder obtained by chemical purification, it has higher purity and can better meet the production requirements of silicon carbide wafers.

[0007] However, the key impurities in high-purity toner that affect silicon carbide wafer production are B, V, and Zr. Therefore, in the production process of high-purity toner, the purity of the toner should be ensured while the content of key impurities should be reduced. Summary of the Invention

[0008] Based on the above-mentioned technical problems, the present invention provides ultra-high purity graphite powder for SiC wafer production, its preparation method, and additives for preparation.

[0009] The specific technical solution is as follows:

[0010] One of the objectives of this invention is to provide a method for preparing ultra-high purity graphite powder for SiC wafer production, comprising the following steps:

[0011] (1) Graphite powder with a purity of 99.9% is crushed to a particle size ≤20μm, and then fed into a spheroidizing machine to spheroidize to a tap density ≥0.6g / cm³. 3 Then it is sent to a demagnetizing device for demagnetization treatment to obtain graphite powder;

[0012] (2) Mix the graphite powder and additives evenly at a mass ratio of 1-1.5:1 to obtain a mixture;

[0013] (3) Load the mixture into a graphite boat, then place the boat into a crucible located in the high-temperature furnace, close the high-temperature furnace, evacuate to ≤1000Pa, then fill with argon until the furnace pressure is at least 1000Pa greater than the external atmospheric pressure, then heat to 2500-2800℃ and keep at a constant temperature for 24-28h, cool to room temperature using cooling water circulation, release the argon, take out the material and package it to obtain the final product.

[0014] By employing a synergistic process of "additive assistance + physical high-temperature purification," specific process parameters are introduced, and specific additives are matched to promote the conversion of metal (Al, V, Ti, Fe, etc.) oxide impurities and non-metal (B, Si, etc.) carbide impurities in graphite powder under high-temperature conditions. These impurities are then converted into easily volatile chlorides and fluorides, achieving separation from the graphite powder and subsequent purification. This results in a graphite powder purity of 5N or higher, even reaching 5N8 (99.9998%). This effectively avoids the use of acidic and alkaline solutions and halogen gases (fluorine, chlorine, etc.), ensuring a green and safe production process.

[0015] Preferably, the raw material components of the additive consist of fluorine-containing components and chlorine-containing components, wherein the fluorine-containing components are a mixture of sodium fluoride, magnesium fluoride, and sodium fluoroaluminate in equal mass ratios, and the chlorine-containing components are a mixture of sodium chloride and magnesium chloride in equal mass ratios; and the mass ratio of the fluorine-containing components to the chlorine-containing components is 0.625-5:1.

[0016] More preferably, the mass ratio of the fluorine-containing component to the chlorine-containing component is 2:1.

[0017] Preferably, in step (2), the graphite powder and the additives are mixed evenly in a mass ratio of 1:1, 1.2:1 or 1.5:1.

[0018] Preferably, the heating rate is 5-15℃ / min.

[0019] The second objective of this invention is to provide ultra-high purity graphite powder for SiC wafer production prepared by the above method.

[0020] The third objective of this invention is to provide an additive for the production of ultra-high purity graphite powder, wherein the raw material composition consists of fluorine-containing and chlorine-containing components. The fluorine-containing component is a mixture of sodium fluoride, magnesium fluoride, and sodium fluoroaluminate in equal mass ratios, and the chlorine-containing component is a mixture of sodium chloride and magnesium chloride in equal mass ratios. The mass ratio of the fluorine-containing component to the chlorine-containing component is 0.625-5:1.

[0021] Preferably, the mass ratio of the fluorine-containing component to the chlorine-containing component is 2:1.

[0022] Compared with the prior art, the technical effects of this invention are reflected in:

[0023] The process of this invention is simple, easy to operate and control. After pulverizing, spheroidizing and demagnetizing graphite powder with a purity of 99.9% under controlled process parameters, the graphite powder is then mixed with specific additives and purified at high temperature. Combined with temperature control during the high-temperature purification process, the content of key impurities such as B, V and Zr can be effectively reduced, so that the purity of graphite powder reaches 5N (99.999%) or higher, which meets the requirements of SiC wafer production.

[0024] Testing showed that the graphite powder obtained by this invention has a purity of 5N (99.999%) or higher, with B < 0.01 ppm, V < 0.01 ppm, and Zr < 0.05 ppm. Compared with existing technologies, this invention not only ensures extremely high purity but also significantly reduces the content of key impurities such as B, V, and Zr, thereby improving the quality of the graphite powder.

[0025] The invention has a simple process, readily available raw materials, low cost, and is easy to industrialize and promote. Attached Figure Description

[0026] In order to enable those skilled in the art to fully understand the technical solution of the present invention, the following description is made in conjunction with the technical solution content and the accompanying drawings.

[0027] Figure 1 A schematic diagram of the process flow for this invention.

[0028] Figure 2 The test report of the sample prepared in Example 28 of this invention was sent to a third-party testing agency.

[0029] Figure 3 A schematic diagram showing the completed installation of the high-temperature purification furnace for pilot production of this invention. Detailed Implementation

[0030] To facilitate a correct understanding of the present invention by those skilled in the art, and to enable them to fully understand the technical content of the present invention, the technical solution of the present invention will be further described below in conjunction with specific embodiments. However, this description does not limit the scope of protection claimed by the present invention. Those skilled in the art should not limit the scope of protection of the present invention to the following description. Any equivalent substitutions or changes made by those skilled in the art or those familiar with the art based on the present invention, and based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

[0031] like Figure 1 and Figure 3 As shown, in some embodiments, the method for preparing ultra-high purity graphite powder for SiC wafer production includes the following steps:

[0032] (1) Graphite powder with a purity of 99.9% is crushed to a particle size ≤20μm, and then fed into a spheroidizing machine to spheroidize to a tap density ≥0.6g / cm³. 3 For example: 0.6 g / cm 3 0.7 g / cm 3 0.8 g / cm 3 0.9 g / cm 3 Then, it is sent to a demagnetizing device for demagnetization treatment to obtain graphite powder.

[0033] (2) Mix graphite powder and additives in a mass ratio of 1-1.5:1, such as 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1 or 1.6:1 to obtain a mixture;

[0034] (3) Load the mixture into a graphite boat, then place the boat into a crucible located inside the high-temperature furnace. Close the high-temperature furnace and evacuate to ≤1000Pa, such as 1000Pa, 900Pa, 800Pa, 700Pa, 600Pa, 500Pa, 400Pa, 300Pa, etc. Then fill with argon gas until the furnace pressure is at least 1000Pa greater than the external atmospheric pressure, such as 1kPa, 1.3kPa, 1.4kPa, 1.5kPa, 1.8kPa, 2.0kPa, 2.2kPa, 2 Heat the material at a pressure of 0.5 kPa or 3 kPa, then raise the temperature at a rate of 5-15℃ / min, for example, 5℃ / min, 7℃ / min, 8℃ / min, 10℃ / min, 12℃ / min or 15℃ / min, to 2500-2800℃, for example, 2500℃, 2600℃, 2700℃, 2800℃, and maintain this temperature for 24-28 hours, for example, 24 hours, 25 hours, 26 hours, 27 hours, 28 hours, etc., using circulating cooling water to cool it to room temperature, release the argon gas, and then package the material to obtain the final product.

[0035] After graphite powder is pulverized, spheroidized, and demagnetized to prepare graphite powder, specific additives are added and mixed. Then, it is purified at high temperature. With temperature control in the high-temperature purification process, the content of key impurities such as B, V, and Zr can be effectively reduced, so that the purity of graphite powder reaches 5N (99.999%) or higher, which meets the requirements of SiC wafer production.

[0036] In some embodiments, the additive's raw material components consist of a fluorine-containing component and a chlorine-containing component. The fluorine-containing component is a mixture of sodium fluoride (99% purity), magnesium fluoride (>97% purity), and sodium fluoroaluminate (analytical grade) in an equal mass ratio. The chlorine-containing component is a mixture of sodium chloride (analytical grade) and magnesium chloride (analytical grade) in an equal mass ratio. The mass ratio of the fluorine-containing component to the chlorine-containing component is 0.625-5:1. For example: 0.625:1, 0.7:1, 0.8:1, 0.9:1, 1.0:1, 2:1, 3:1, 4:1, or 5:1, etc. Figure 2 As shown, under specific process conditions and parameters, when the mass ratio of the fluorine-containing component to the chlorine-containing component is 2:1, the purity of the obtained graphite powder can reach 99.9998%, and B < 0.01 ppm, V < 0.01 ppm and Zr < 0.05 ppm, which greatly improves the quality of the graphite powder.

[0037] In order to better verify the technical effects that the present invention can bring, the researchers of the present invention conducted the following experimental studies.

[0038] Example 1

[0039] Graphite powder with a purity of 99.9% was fed into a vacuum pulverizer and pulverized to a particle size ≤20μm. It was then fed into a spheroidizing machine for spheroidizing treatment, yielding a tap density of 0.6 g / cm³. 3 Spheroidized graphite powder is obtained by processing it in a demagnetizing device. The graphite powder is then mixed with additives at a mass ratio of 1:1 to obtain a mixture. The additives consist of fluorine and chlorine components. The fluorine component is a mixture of sodium fluoride, magnesium fluoride, and sodium fluoroaluminate in equal mass ratios, while the chlorine component is a mixture of sodium chloride and magnesium chloride in equal mass ratios. The mass ratio of the fluorine to chlorine components is 2.5:1. The mixture is placed in a graphite boat, which is then placed in a crucible inside a high-temperature furnace. The furnace is closed, and a vacuum of 1000 Pa is created. Argon gas is then introduced until the furnace pressure exceeds the external atmospheric pressure by 1000 Pa. The temperature is then increased to 2500°C at a rate of 5°C / min and maintained at this temperature for 24 hours. The mixture is then cooled to room temperature using circulating cooling water, the argon gas is released, and the material is collected and packaged.

[0040] Example 2

[0041] Based on Example 1, graphite powder with a purity of 99.9% was fed into a vacuum pulverizer and pulverized to a particle size of ≤20μm. After being directly fed into a demagnetizing device for processing, graphite powder was obtained. Everything else was the same as in Example 1.

[0042] Example 3

[0043] Based on Example 1, the mixture was loaded into a graphite boat, and then the boat was placed in a crucible located inside a high-temperature furnace. The high-temperature furnace was closed, and a vacuum was drawn to -100 Pa. Argon gas was then introduced until the furnace pressure was greater than the external atmospheric pressure by 100 Pa. Everything else was the same as in Example 1.

[0044] Example 4

[0045] Based on Example 1, the temperature was increased to 3000℃ at a rate of 20℃ / min and kept constant, with all other aspects the same as in Example 1.

[0046] Example 5

[0047] Based on Example 1, spheroidizing treatment yielded a tap density of 0.7 g / cm³. 3 Spheroidized graphite powder was obtained and processed in a demagnetizing device to obtain graphite powder. The graphite powder was mixed with additives to obtain a mixture. The mixture was loaded into a graphite boat, which was then placed in a crucible inside a high-temperature furnace. The high-temperature furnace was closed, and a vacuum of 800 Pa was drawn. Argon gas was then introduced until the furnace pressure was greater than the external atmospheric pressure by 2000 Pa. The temperature was then increased to 2800°C at 15°C / min and kept constant for 28 hours. The mixture was then cooled to room temperature using circulating cooling water, the argon gas was released, and the material was packaged to obtain the final product. All other aspects were the same as in Example 1.

[0048] Example 6

[0049] Based on Example 1, spheroidizing treatment yielded a tap density of 0.9 g / cm³. 3 Spheroidized graphite powder was obtained and processed in a demagnetizing device to obtain graphite powder. The graphite powder was mixed with additives to obtain a mixture. The mixture was loaded into a graphite boat, which was then placed in a crucible inside a high-temperature furnace. The high-temperature furnace was closed, and a vacuum of 500 Pa was drawn. Argon gas was then introduced until the furnace pressure was greater than the external atmospheric pressure by 1500 Pa. The temperature was then increased to 2700°C at 10°C / min and kept constant for 25 hours. The mixture was then cooled to room temperature using circulating cooling water, the argon gas was released, and the material was packaged to obtain the final product. All other aspects were the same as in Example 1.

[0050] Example 7

[0051] Based on Example 1, spheroidizing treatment yielded a tap density of ≥0.8 g / cm³. 3Spheroidized graphite powder was obtained and processed in a demagnetizing device to obtain graphite powder. The graphite powder was mixed evenly with additives to obtain a mixture. The mixture was loaded into a graphite boat, which was then placed in a crucible located inside a high-temperature furnace. The high-temperature furnace was closed, and a vacuum of 600 Pa was drawn. Argon gas was then introduced until the furnace pressure was greater than the external atmospheric pressure by 1300 Pa. The temperature was then increased to 2700°C at 14°C / min and kept constant for 27 hours. The mixture was then cooled to room temperature using a cooling water circulation system, the argon gas was released, and the material was collected and packaged to obtain the final product. All other aspects were the same as in Example 1.

[0052] Example 8

[0053] Based on Example 5, graphite powder and additives were mixed evenly at a mass ratio of 1.1:1 to obtain a mixture, and all other aspects were the same as in Example 5.

[0054] Example 9

[0055] Based on Example 5, graphite powder and additives were mixed evenly at a mass ratio of 1.2:1 to obtain a mixture, and all other aspects were the same as in Example 5.

[0056] Example 10

[0057] Based on Example 5, graphite powder and additives were mixed evenly at a mass ratio of 1.3:1 to obtain a mixture, and all other aspects were the same as in Example 5.

[0058] Example 11

[0059] Based on Example 5, graphite powder and additives were mixed evenly at a mass ratio of 1.4:1 to obtain a mixture, and all other aspects were the same as in Example 5.

[0060] Example 12

[0061] Based on Example 5, graphite powder and additives were mixed evenly at a mass ratio of 1.5:1 to obtain a mixture, and all other aspects were the same as in Example 5.

[0062] Example 13

[0063] Based on Example 5, graphite powder and additives were mixed evenly at a mass ratio of 1.6:1 to obtain a mixture, and all other aspects were the same as in Example 5.

[0064] Example 14

[0065] Based on Example 5, graphite powder and additives were mixed evenly at a mass ratio of 1.7:1 to obtain a mixture, and all other aspects were the same as in Example 5.

[0066] Example 15

[0067] Based on Example 5, graphite powder and additives were mixed evenly at a mass ratio of 0.9:1 to obtain a mixture, and all other aspects were the same as in Example 5.

[0068] Example 20

[0069] Based on Example 5, graphite powder and additives were mixed evenly at a mass ratio of 0.8:1 to obtain a mixture, and all other aspects were the same as in Example 5.

[0070] Example 21

[0071] Based on Example 5, graphite powder and additives were mixed evenly at a mass ratio of 0.7:1 to obtain a mixture, and all other aspects were the same as in Example 5.

[0072] Example 22

[0073] Based on Example 10, the mass ratio of the fluorine-containing component to the chlorine-containing component is 0.6:1, and all other aspects are the same as in Example 10.

[0074] Example 23

[0075] Based on Example 10, the mass ratio of the fluorine-containing component to the chlorine-containing component is 0.625:1, and all other aspects are the same as in Example 10.

[0076] Example 24

[0077] Based on Example 10, the mass ratio of the fluorine-containing component to the chlorine-containing component is 0.65:1, and all other aspects are the same as in Example 10.

[0078] Example 25

[0079] Based on Example 10, the mass ratio of the fluorine-containing component to the chlorine-containing component is 0.75:1, and all other aspects are the same as in Example 10.

[0080] Example 26

[0081] Based on Example 10, the mass ratio of the fluorine-containing component to the chlorine-containing component is 0.95:1, and all other aspects are the same as in Example 10.

[0082] Example 27

[0083] Based on Example 10, the mass ratio of the fluorine-containing component to the chlorine-containing component is 1.5:1, and all other aspects are the same as in Example 10.

[0084] Example 28

[0085] Based on Example 10, the mass ratio of the fluorine-containing component to the chlorine-containing component is 2:1, and all other aspects are the same as in Example 10.

[0086] Example 29

[0087] Based on Example 10, the mass ratio of the fluorine-containing component to the chlorine-containing component is 3:1, and all other aspects are the same as in Example 10.

[0088] Example 30

[0089] Based on Example 10, the mass ratio of the fluorine-containing component to the chlorine-containing component is 4:1, and all other aspects are the same as in Example 10.

[0090] Example 31

[0091] Based on Example 10, the mass ratio of the fluorine-containing component to the chlorine-containing component is 5:1, and all other aspects are the same as in Example 10.

[0092] Example 32

[0093] Based on Example 10, the mass ratio of the fluorine-containing component to the chlorine-containing component is 6:1, and all other aspects are the same as in Example 10.

[0094] Example 33

[0095] Based on Example 10, the mass ratio of the fluorine-containing component to the chlorine-containing component is 7:1, and all other aspects are the same as in Example 10.

[0096] The graphite powders obtained in Examples 1 to 33 were tested, and the results are shown in Table 1 below:

[0097] Table 1

[0098]

[0099] As shown in Table 1, the graphite powder prepared by this invention through a specific process and the combination of specific additives achieves a purity of over 5N and reduces the content of key impurities such as B, V, and Zr, significantly improving the quality of the graphite powder. The amount of additives used must be within an appropriate range; otherwise, the removal of key impurities such as B, V, and Zr will be poor, resulting in unsatisfactory overall quality of the graphite powder.

[0100] For any other matters not covered in this invention, they can be addressed by referring to existing technologies or common knowledge known to those skilled in the art, and by using conventional technical means.

Claims

1. A method for preparing ultra-high purity graphite powder for SiC wafer production, characterized in that, Includes the following steps: (1) Graphite powder with a purity of 99.9% is crushed to a particle size ≤20μm, and then fed into a spheroidizing machine to spheroidize to a tap density ≥0.6g / cm³. 3 Then it is sent to a demagnetizing device for demagnetization treatment to obtain graphite powder; (2) Mix the graphite powder and additives evenly at a mass ratio of 1-1.5:1 to obtain a mixture; (3) Load the mixture into a graphite boat, then place the boat into a crucible located in the high-temperature furnace, close the high-temperature furnace, evacuate to ≤1000Pa, then fill with argon until the furnace pressure is at least 1000Pa greater than the external atmospheric pressure, then heat to 2500-2800℃ and keep at a constant temperature for 24-28h, cool to room temperature using cooling water circulation, release the argon, take out the material and package it to obtain the final product.

2. The method as described in claim 1, characterized in that, The additive's raw material components consist of fluorine-containing and chlorine-containing components. The fluorine-containing components are a mixture of sodium fluoride, magnesium fluoride, and sodium fluoroaluminate in equal mass ratios, and the chlorine-containing components are a mixture of sodium chloride and magnesium chloride in equal mass ratios. The mass ratio of the fluorine-containing components to the chlorine-containing components is 0.625-5:

1.

3. The method as described in claim 2, characterized in that, The mass ratio of the fluorine-containing component to the chlorine-containing component is 2:

1.

4. The method as described in claim 1, characterized in that, In step (2), graphite powder and additives are mixed evenly at a mass ratio of 1:

1.

5. The method as described in claim 1, characterized in that, In step (2), graphite powder and additives are mixed evenly at a mass ratio of 1.2:

1.

6. The method as described in claim 1, characterized in that, In step (2), graphite powder and additives are mixed evenly at a mass ratio of 1.5:

1.

7. The method as described in claim 1, characterized in that, The heating rate is 5-15℃ / min.

8. The ultra-high purity graphite powder for SiC wafer production prepared by the method according to any one of claims 1-7, wherein the purity is ≥5N, and B < 0.01ppm, V < 0.01ppm.

9. An additive for the production of ultra-high purity graphite powder, characterized in that, The raw material consists of fluorine-containing and chlorine-containing components. The fluorine-containing components are a mixture of sodium fluoride, magnesium fluoride, and sodium fluoroaluminate in equal mass ratios. The chlorine-containing components are a mixture of sodium chloride and magnesium chloride in equal mass ratios. The mass ratio of the fluorine-containing components to the chlorine-containing components is 0.625-5:

1.

10. The additive for producing ultra-high purity graphite powder as described in claim 9, characterized in that, The mass ratio of the fluorine-containing component to the chlorine-containing component is 2:1.

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