Silicon tetrafluoride purification method and preparation method of modified activated carbon for deep purification of silicon tetrafluoride

Abstract

The invention provides a silicon tetrafluoride purification method and a preparation method of modified activated carbon for deep purification of silicon tetrafluoride, and belongs to the technical field of silicon tetrafluoride purification. The silicon tetrafluoride purification method comprises the following steps that silicon tetrafluoride raw material gas is sequentially adsorbed with activated carbon and a molecular sieve, and primary purified silicon tetrafluoride is obtained; introducing ammonia gas into the primarily purified silicon tetrafluoride for reaction, carrying out gas-solid separation, and removing impurities from the obtained gas component by using modified activated carbon to obtain secondarily purified silicon tetrafluoride; a modification method of the modified activated carbon comprises the following steps: reacting activated carbon with fluorine-containing gas at 80-100 DEG C; and rectifying the secondarily purified silicon tetrafluoride to obtain the high-purity silicon tetrafluoride. The purity of the purified silicon tetrafluoride gas reaches 6N grade or above, the time for the modified activated carbon to reach adsorption saturation is long, the service cycle is long, and the production cost can be effectively reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of silicon tetrafluoride purification, and specifically relates to a method for purifying silicon tetrafluoride and a method for preparing modified activated carbon for deep purification of silicon tetrafluoride. Background Art

[0002] With the rapid development of the large-scale integrated circuit industry, the market demand for electronic special gases has increased significantly. Silicon tetrafluoride is one of the raw material gases with the highest silicon content and is mainly used for the etching of silicon nitride, tantalum silicide, etc. in the semiconductor industry. Since semiconductor circuits are becoming more and more miniaturized, more circuits need to be arranged in a small space. Even a slight impurity or foreign object will affect the conductivity and stability, and even lead to a complete paralysis. Therefore, the market has higher and higher requirements for the purity of silicon tetrafluoride gas. Currently, most manufacturers require a purity of 5N level (99.999%), and some manufacturers require 6N level (99.9999%).

[0003] Currently, the methods for producing high-purity silicon tetrafluoride above 5N level usually adopt adsorption and rectification to remove light components, heavy components, and metal impurities in the gas, such as H2, N2, O2, CH4, fluorosilane ether, etc. However, it is difficult to completely remove hydrogen chloride because the boiling point of hydrogen chloride is -85.1°C, while the boiling point of silicon tetrafluoride is -86°C, and the two boiling points are very close, so they cannot be completely separated during rectification. If an alkaline substance is used to remove hydrogen chloride, the alkaline substance will become ineffective because silicon tetrafluoride is also acidic.

[0004] Currently, there are already various gas purification technologies. For example, a Chinese invention patent with an application date of June 20, 2019, and a publication number of CN110606490B discloses a method for synthesizing and purifying high-purity silicon tetrafluoride. By separating light components and heavy components in the rectification section and adding a complex rectification process to remove azeotropes, the purity of the obtained silicon tetrafluoride only reaches 99.99% (4N level). Summary of the Invention

[0005] The first object of the present invention is to provide a method for purifying silicon tetrafluoride to solve the problem that the purity of purified silicon tetrafluoride in the prior art is difficult to reach 6N level.

[0006] The second object of the present invention is to provide a method for preparing modified activated carbon for deep purification of silicon tetrafluoride to solve the problem that it is difficult for existing activated carbon to achieve deep impurity removal.

[0007] To achieve the above first object, the technical solution adopted by the present invention is:

[0008] A method for purifying silicon tetrafluoride, comprising the following steps:

[0009] S1. Adsorb the silicon tetrafluoride raw material gas successively with activated carbon and molecular sieve to obtain primary purified silicon tetrafluoride;

[0010] S2. Introduce ammonia into the primary purified silicon tetrafluoride for reaction, perform gas-solid separation, and then remove impurities from the obtained gas components with modified activated carbon to obtain secondary purified silicon tetrafluoride; the modification method of the modified activated carbon is: react the activated carbon with a fluorine-containing gas at 80-100 °C;

[0011] S3. Distill the secondary purified silicon tetrafluoride to obtain high-purity silicon tetrafluoride.

[0012] The present invention belongs to a pioneering invention. The method of the present invention first uses activated carbon and molecular sieve to adsorb and remove most of the impurities, and then converts the difficult-to-remove hydrogen chloride impurities into ammonium chloride that is easy to remove. The chemical reaction equation is as shown in (1). After removing ammonium chloride through gas-solid separation and performing secondary adsorption and impurity removal, high-purity silicon tetrafluoride gas is obtained through two distillations. Among them, secondary adsorption and impurity removal use modified activated carbon. The surface of the modified activated carbon contains a lot of C-F bonds, which reduces the coverage of the adsorption surface by silicon tetrafluoride and reduces the adsorption of silicon tetrafluoride, thereby maintaining a strong adsorption capacity for other impurity gases. The purity of the prepared silicon tetrafluoride reaches above 6N level. At the same time, due to the lower content of gas impurities in contact with the modified activated carbon, the time for the modified activated carbon to reach adsorption saturation is longer and the service life is longer, thus reducing the production cost.

[0013] NH3 + HCl = NH4Cl (1)

[0014] Preferably, the concentration of fluorine gas in the fluorine-containing gas is 2-15 wt%, and the rest is inert gas. The dosage of the fluorine-containing gas is 0.5-5% of the weight of the activated carbon.

[0015] Further preferably, the diameter of the activated carbon in step S2 is 0.5-5 mm, and the specific surface area is 500-1200 m 2 / g; the reaction time of the activated carbon and the fluorine-containing gas is 5-30 min.

[0016] Preferably, the molecular sieve in step S1 includes one or two of 5A molecular sieve and 4A molecular sieve. The molecular sieve is used after drying and water removal. The conditions for drying and water removal are: temperature 300-400 °C, pressure -0.06 to -0.1 MPa, and reaction for 6-10 h, to avoid introducing water impurities by the highly adsorptive molecular sieve. Trace amounts of water will react with silicon tetrafluoride to generate new fluorosiloxane impurities.

[0017] Preferably, the addition amount of ammonia in step S2 is 1.1 to 3 times the theoretical demand, and the reaction time of ammonia is 5 to 60 minutes. First, detect the hydrogen chloride content in silicon tetrafluoride, calculate the theoretical demand of ammonia according to chemical equation (1), and the purity of the ammonia used is above 5N grade. In a dry environment, ammonia only reacts with hydrogen chloride and does not react with silicon tetrafluoride. The reaction is sensitive and can fully remove hydrogen chloride. The amount of ammonia used should be slightly more than the theoretical demand to ensure the full reaction of hydrogen chloride. Ammonia reacts with hydrogen chloride to form ammonium chloride, and ammonium chloride is easily removed by filtration as a solid. The excess ammonia is completely removed in the subsequent adsorption and rectification processes.

[0018] Preferably, the gas-solid separation in step S2 includes separation using a filter element. The filter element includes a sintered filter element or a PP filter element, which is used to filter out ammonium chloride particles to avoid clogging the micropores and reducing the adsorption effect of the modified activated carbon. After being used for a period of time, the filter element can be washed with water to remove ammonium chloride and continue to be used after drying.

[0019] More preferably, the rectification in step S3 includes two rectifications of light component removal and heavy component removal. The temperature for light component removal is -120 to -80 °C, and the pressure is 0.5 to 2 MPa. The temperature for heavy component removal is -15 to -10 °C, and the pressure is 1 to 2 MPa. Rectification can further remove volatile components and non-volatile components.

[0020] To achieve the above object, the technical solution adopted by the preparation method of the modified activated carbon for deep purification of silicon tetrafluoride provided by the present invention is as follows:

[0021] A preparation method of a modified activated carbon for deep purification of silicon tetrafluoride, wherein the activated carbon reacts with a fluorine-containing gas at 80 to 100 °C.

[0022] Preferably, the concentration of fluorine gas in the fluorine-containing gas is 2 to 15 wt%, and the rest is an inert gas. The amount of the fluorine-containing gas used is 0.5 to 5% of the weight of the activated carbon.

[0023] More preferably, the diameter of the activated carbon is 0.5 to 5 mm, and the specific surface area is 500 to 1200 m 2 / g; the reaction time of the activated carbon and the fluorine-containing gas is 5 to 30 minutes.

[0024] The beneficial effects of the above technical solution are as follows: After the activated carbon particles are modified, the surface contains many C-F bonds, which reduces the adsorption of silicon tetrafluoride, but still has a strong adsorption of other gases including ammonia. When used for secondary gas filtration, the gas in contact has been purified once in the previous step and the impurity content is low. After further filtration and impurity removal by the highly adsorbent modified activated carbon, a deep purification effect can be achieved, and the modified activated carbon particles can be reused after regeneration. The regeneration method is similar to the regeneration method of molecular sieves. Specific embodiments

[0025] The present invention mainly aims at the problem that the purity of silicon tetrafluoride in the prior art is difficult to reach 6N level. By using modified activated carbon, the adsorption efficiency of impurity gases is improved, hydrogen chloride impurities are removed by the reaction of ammonia and hydrogen chloride, and various impurities are removed by molecular sieves, filter elements and rectification. After purification, the purity of silicon tetrafluoride reaches above 6N level.

[0026] The raw material silicon tetrafluoride of this application comes from the decomposition of fluosilicic acid. Fluosilicic acid reacts with concentrated sulfuric acid to generate hydrogen fluoride and silicon tetrafluoride. After the concentrated sulfuric acid adsorbs and removes hydrogen fluoride, crude silicon tetrafluoride is obtained, which often contains various impurities such as H2, N2, O2, CO2, CH4, SO2, HCl, HF, metal ions, etc.

[0027] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0028] I. Specific embodiments of the silicon tetrafluoride purification method of the present invention and the preparation method of modified activated carbon for deep purification of silicon tetrafluoride

[0029] Example 1

[0030] The silicon tetrafluoride purification method of this example has the following specific purification steps:

[0031] Prepare modified activated carbon: Select 50 kg of activated carbon particles with a diameter of 1 - 4 mm and a specific surface area of 600 m 2 / g, contact with 2 kg of fluorine-nitrogen mixture in a closed container at 100 °C for 20 min. The proportion of fluorine in the fluorine-nitrogen mixture is 2 wt%, and modified activated carbon particles are prepared and loaded into a filtration container.

[0032] Treat the molecular sieve at a temperature of 350 °C and a vacuum of -0.09 MPa for 6 h, and install the treated molecular sieve in another filtration container.

[0033] Flow the silicon tetrafluoride gas through filters loaded with activated carbon, 5A molecular sieve, and 4A molecular sieve in sequence to obtain primary purified silicon tetrafluoride. Then, introduce 0.022 wt% (1.2 times the theoretical demand) of ammonia into the primary purified silicon tetrafluoride gas and react for 30 min. After the reaction, flow through a sintered filter element and modified activated carbon in sequence to obtain secondary purified silicon tetrafluoride. Then, perform two rectifications. The first rectification conditions are -120 to -110 °C and the pressure is 0.5 to 0.6 MPa. The second rectification conditions are -15 to -12 °C and the pressure is 1.0 to 1.2 MPa. Finally, high-purity silicon tetrafluoride is prepared.

[0034] Example 2

[0035] The silicon tetrafluoride purification method of this example has the following specific purification steps:

[0036] Preparation of modified activated carbon: Select 50 kg of activated carbon particles with a diameter of 0.5 - 3 mm and a specific surface area of 800 m 2 / g. Contact with 1 kg of fluorine-nitrogen mixture in a closed container at 90°C for 10 min. The proportion of fluorine in the fluorine-nitrogen mixture is 6 wt%. Prepare modified activated carbon particles and install them in a filter.

[0037] Treat the molecular sieve at a temperature of 300°C and a vacuum of -0.08 MPa for 10 h. Install the treated molecular sieve in another filtration container.

[0038] Flow silicon tetrafluoride gas through filters loaded with activated carbon, 5A molecular sieve, and 4A molecular sieve in sequence to obtain primary purified silicon tetrafluoride. Then introduce 0.054 wt% (3 times the theoretical demand) of ammonia into the primary purified silicon tetrafluoride gas and react for 10 min. After the reaction, flow through a sintered filter element and modified activated carbon in sequence to obtain secondary purified silicon tetrafluoride. Then perform two distillations. The first distillation conditions are -100 to -80°C and a pressure of 1.5 to 1.8 MPa. The second distillation conditions are -13 to -10°C and a pressure of 1.5 to 1.7 MPa. Finally, prepare high-purity silicon tetrafluoride.

[0039] Example 3

[0040] The silicon tetrafluoride purification method of this example has the following specific purification steps:

[0041] Preparation of modified activated carbon: Select 50 kg of activated carbon particles with a diameter of 2 - 5 mm and a specific surface area of 1000 m 2 / g. Contact with 0.5 kg of fluorine-nitrogen mixture in a closed container at 80°C for 6 min. The proportion of fluorine in the fluorine-nitrogen mixture is 14 wt%. Prepare modified activated carbon particles and install them in a filtration container.

[0042] Treat the molecular sieve at a temperature of 400°C and a vacuum of -0.06 MPa for 8 h. Install the treated molecular sieve in another filtration container.

[0043] Flow silicon tetrafluoride gas through filters loaded with activated carbon, 5A molecular sieve, and 4A molecular sieve in sequence to obtain primary purified silicon tetrafluoride. Then introduce 0.037 wt% (2 times the theoretical demand) of ammonia into the primary purified silicon tetrafluoride gas and react for 50 min. Then flow through a PP filter element and modified activated carbon in sequence to obtain secondary purified silicon tetrafluoride. Then perform two distillations. The first distillation conditions are -110 to -90°C and a pressure of 1.2 to 1.5 MPa. The second distillation conditions are -14 to -11°C and a pressure of 1.2 to 1.6 MPa. Finally, prepare high-purity silicon tetrafluoride.

[0044] The preparation methods of the modified activated carbon for deep purification of silicon tetrafluoride in Examples 1 to 3 are the same as those of the corresponding modified activated carbon in the corresponding examples, and will not be elaborated here.

[0045] Comparative Example 1

[0046] The purification method of silicon tetrafluoride in this comparative example is as follows:

[0047] For the first purification of silicon tetrafluoride, activated carbon and molecular sieve are not used, and the remaining steps are the same as those in Example 1 above.

[0048] Comparative Example 2

[0049] The purification method of silicon tetrafluoride in this comparative example is as follows:

[0050] After the first purification, ammonia gas is not introduced, and the remaining steps are the same as those in Example 1 above.

[0051] Comparative Example 3

[0052] The purification method of silicon tetrafluoride in this comparative example is as follows:

[0053] During the second purification of silicon tetrafluoride gas, ordinary activated carbon is used instead of modified activated carbon, and the remaining steps are the same as those in Example 1.

[0054] The silicon tetrafluoride gas prepared in the above examples and comparative examples was sampled and the impurity content was detected by infrared spectroscopy. The results are shown in Table 1:

[0055] Table 1 Detection results of silicon tetrafluoride impurities in each example and comparative example

[0056]

[0057] It can be seen from the results in the table that the purity of the products obtained in the examples is better than that in the comparative examples. No hydrogen chloride and fluorosiloxane impurities were detected in the examples, indicating that this method can remove hydrogen chloride and fluorosiloxane impurities completely, and the purity of the silicon tetrafluoride obtained in the examples has reached 6N level, which is much higher than that in the comparative examples. In addition, in Comparative Example 3, modified activated carbon was not used. Compared with the results of Example 1, the contents of CO2, CH4, SO2, HF and HCl impurities increased, and the product purity only reached 5N level, indicating that the modified activated carbon has an obvious deep impurity removal effect.

Claims

1. A method for purifying silicon tetrafluoride, characterized in that: The following steps are involved: S1, using activated carbon and molecular sieve to adsorb silicon tetrafluoride raw material gas in sequence to obtain primary purified silicon tetrafluoride; S2, introducing ammonia into the primary purified silicon tetrafluoride to react, separate the gas and solid, and remove impurities from the obtained gas components with modified activated carbon to obtain secondary purified silicon tetrafluoride; the modification method of the modified activated carbon is: reacting the activated carbon with the fluorine-containing gas at 80-100°C; S3, distilling the secondary purified silicon tetrafluoride to obtain high-purity silicon tetrafluoride.

2. The method for purifying silicon tetrafluoride according to claim 1, characterized in that: The concentration of fluorine gas in the fluorine-containing gas is 2-15wt%, and the rest is inert gas. The amount of the fluorine-containing gas used is 0.5-5% of the weight of the activated carbon.

3. The method for purifying silicon tetrafluoride according to claim 2, characterized in that: The activated carbon described in step S2 has a diameter of 0.5-5 mm and a specific surface area of ​​500-1200 m 2 / g; the reaction time of the activated carbon and the fluorine-containing gas is 5 to 30 minutes.

4. The method for purifying silicon tetrafluoride according to claim 1, characterized in that: The molecular sieve described in step S1 includes one or both of 5A molecular sieve and 4A molecular sieve.

5. The method for purifying silicon tetrafluoride according to claim 1, characterized in that: The amount of ammonia added in step S2 is 1.1 to 3 times the theoretical required amount, and the reaction time of ammonia is 5 to 60 minutes.

6. The method for purifying silicon tetrafluoride according to claim 1, characterized in that: The gas-solid separation described in step S2 includes separation using a filter element, and the filter element includes a sintered filter element or a PP filter element.

7. The method for purifying silicon tetrafluoride according to claim 1, characterized in that: The distillation described in step S3 includes two distillations, namely, light removal and heavy removal. The temperature of light removal is -120~-80°C and the pressure is 0.5~2MPa. The temperature of heavy removal is -15~-10°C and the pressure is 1~2MPa.

8. A method for preparing modified activated carbon for deep purification of silicon tetrafluoride, characterized in that: The activated carbon is reacted with fluorine-containing gas at 80-100°C.

9. The method for preparing modified activated carbon for deep purification of silicon tetrafluoride according to claim 8, characterized in that: The concentration of fluorine gas in the fluorine-containing gas is 2-15wt%, and the rest is inert gas. The amount of the fluorine-containing gas used is 0.5-5% of the weight of the activated carbon.

10. The method for preparing modified activated carbon for deep purification of silicon tetrafluoride according to claim 9, characterized in that: The activated carbon has a diameter of 0.5-5 mm and a specific surface area of ​​500-1200 m 2 / g; the reaction time of the activated carbon and the fluorine-containing gas is 5 to 30 minutes.

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