Preparation method of electronic grade ammonium fluoride aqueous solution

Abstract

The present application relates to a kind of electronic grade ammonium fluoride aqueous solution preparation method, belong to wet electronic chemical technology field.The present application with ammonolysis of fluosilicic acid obtained ammonium fluoride aqueous solution as raw material, is concentrated crystallization and obtains crude ammonium fluoride solid, is dissolved in organic solvent, recrystallization and obtains ppm grade ammonium fluoride solid, then heating sublimation, under inert gas flow cooling condensation, gas-solid separation obtains high-purity ammonium fluoride, finally dissolved in high-purity water, after three-stage microfiltration membrane filtration, electronic grade ammonium fluoride aqueous solution is prepared.The present application uses organic solvent to recrystallize ammonium fluoride and remove most impurities, then with the way of ammonium fluoride sublimation-condensation, high-purity ammonium fluoride is obtained by deeply removing impurities;Process used medium organic solvent, inert gas can be recycled, cost is lower, whole process does not generate waste residue waste liquid, green environmental protection;The impurity content of obtained product is very low, reaches UP-SS grade.

Description

Technical Field

[0001] This invention belongs to the field of wet electronic chemicals technology, specifically relating to a method for preparing an electronic-grade ammonium fluoride aqueous solution. Background Technology

[0002] With the rise of the domestic semiconductor manufacturing industry, the demand for buffered oxidation etchants in China has been increasing year by year. Buffered oxidation etchants are mainly used in the microelectronics industry as cleaning agents and etchants. In the semiconductor industry, they are often used to etch oxide layers without photoresist shields. Their main components are hydrofluoric acid and ammonium fluoride, and they are generally prepared by electronic grade hydrofluoric acid, electronic grade ammonium fluoride aqueous solution, and additives.

[0003] Currently, the most common method for preparing electronic-grade ammonium fluoride aqueous solution is to evaporate and filter industrial ammonia water to remove impurities, and then absorb it with high-purity hydrofluoric acid. Patent CN103112872B uses a type 5A molecular sieve to filter and remove impurities from ammonia gas, and patent CN102557076B uses activated carbon to filter and remove impurities from ammonia gas. However, once the filter material is saturated, it is difficult to regenerate and reuse it, resulting in high costs and the generation of a large amount of waste residue.

[0004] Patent CN101671037A provides a method for preparing high-purity ammonium hydrogen fluoride, which discloses that "ammonium hydrogen fluoride crystals are sublimated at a temperature between 222-230°C, and ammonium hydrogen fluoride vapor is collected to obtain high-purity ammonium hydrogen fluoride product", which does not provide any teaching or inspiration for this application. Summary of the Invention

[0005] To overcome the above shortcomings, the present invention adopts the following technical solution:

[0006] This invention provides a method for preparing electronic-grade ammonium fluoride aqueous solution, mainly comprising the following steps:

[0007] S1, using an aqueous solution of ammonium fluoride obtained by ammonolysis of fluorosilicic acid as raw material, is concentrated, cooled and crystallized to obtain crude ammonium fluoride solid;

[0008] S2, the crude ammonium fluoride solid obtained in S1 is dissolved in an organic solvent, filtered, concentrated, cooled, crystallized and dried to obtain ammonium fluoride solid with impurity content reduced to ppm level;

[0009] S3, the ppm-level ammonium fluoride obtained in S2 is heated and sublimated, cooled and condensed in an inert gas flow, and high-purity ammonium fluoride is obtained by gas-solid separation.

[0010] S4: Dissolve the high-purity ammonium fluoride obtained in S3 in high-purity water, and filter it through a three-stage microfiltration membrane to obtain an electronic-grade ammonium fluoride aqueous solution.

[0011] The ammonolysis of fluorosilicic acid is a conventional technique that has been widely used for the comprehensive utilization of fluorosilicic acid, a byproduct of wet-process phosphoric acid production. The main impurities in the ammonium fluoride aqueous solution obtained by this method include fluorosilicates, phosphates, sulfates, and chlorides.

[0012] In step S1, the concentration, cooling, and crystallization involve evaporating water at 80-100°C to saturate the ammonium fluoride, continuing to evaporate 50-80% of the solvent, and then cooling to 0-10°C, causing the ammonium fluoride to crystallize out.

[0013] In step S2, the organic solvent is selected from methanol or acetonitrile, with a purity > 99.9%; the concentration, cooling and crystallization are carried out by evaporating 50-80% of the solvent at 60-85℃, cooling to 0-10℃, crystallizing ammonium fluoride, and then drying at a vacuum of -60 to -90 kPa and a temperature of 40-70℃ for 4-8 hours to obtain ppm-level ammonium fluoride solid.

[0014] Furthermore, in step S2, after the organic solvent and ammonium fluoride are separated into solid and liquid phases, the organic solvent is distilled to remove impurities and then reused.

[0015] In step S3, the inert gas flow is nitrogen, with a flow rate of 50-500 L / min and a pressure of 0.02-0.1 MPa; the gas-solid separation uses a cyclone separator; the heating sublimation temperature is 100-120℃, at which temperature ammonium fluoride sublimates into gas, while trace impurities such as metal salts, ammonium nitrate, and ammonium chloride do not sublimate or react; trace impurities such as ammonium fluorosilicate decompose into ammonium fluoride and silicon tetrafluoride gases; and trace impurities such as ammonium sulfate undergo an auto-oxidation-reduction reaction to generate nitrogen oxide gas and sulfur dioxide gas. The trace impurity (NH4) is also present. n H 3-n PO4 (1≤n≤3) decomposes into ammonia and liquid phosphoric acid. Phosphoric acid is non-volatile and, carried by an inert gas flow, carries away ammonium fluoride, silicon tetrafluoride, nitrogen oxides, sulfur dioxide, ammonia, etc. The mixture is cooled to 70-90℃ in a gas-solid separator, where the ammonium fluoride gas recondenses into solid particles and settles at the bottom of the separator. Other impurities are discharged as gases with the inert gas. Through this sublimation and recondensation process, most impurities in the ammonium fluoride are removed, yielding high-purity ammonium fluoride.

[0016] Furthermore, in step S3, the inert gas discharged from the gas-solid separator is reused after being treated with alkali and dried.

[0017] In step S4, the high-purity ammonium fluoride is dissolved in high-purity water to obtain a high-purity ammonium fluoride solution with a concentration of 39-41%. This solution is then filtered sequentially through three stages of microfiltration membranes (0.2 μm, 0.05 μm, and 0.01 μm) at a pressure of 0.05-0.2 MPa to remove particulate impurities, yielding an electronic-grade ammonium fluoride aqueous solution. Testing shows that particles with a diameter ≥0.2 μm are ≤10 pcs / ml, and the concentration of any single metal ion is ≤0.1 ppb, meeting the UP-SS grade requirements (GB / T 30901-2014).

[0018] In steps S1-S4, the inner walls of the containers, heating kettles, gas-solid separators, and pipelines used are all lined with PFA or PTFE, and the entire production process is carried out in a Class 1000 cleanroom.

[0019] The beneficial effects of this invention are as follows: This invention uses an aqueous solution of ammonium fluoride obtained by ammonolysis of fluorosilicic acid as raw material, which is inexpensive; most impurities are removed by recrystallizing ammonium fluoride with an organic solvent, and then further impurities are removed by sublimation-condensation of ammonium fluoride to obtain high-purity ammonium fluoride; the organic solvent and inert gas used in the process can be recycled repeatedly, which is low in cost; no waste residue or waste liquid is generated in the whole process, which is green and environmentally friendly; the impurity content of the obtained product is very low, reaching UP-SS grade. Detailed Implementation

[0020] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. The raw material used is ammonium fluoride solution obtained by ammonolysis of fluorosilicic acid purchased from Duofuduo New Materials Co., Ltd. The concentration of ammonium fluoride is 10.6 wt%, the concentration of impurity fluorosilicate is 0.22 wt%, the concentration of impurity phosphate is 0.14 wt%, and the concentration of impurity sulfate is 0.06 wt%. The purity of methanol and acetonitrile used is greater than 99.9%. The inner walls of the containers, heating kettles, gas-solid separators and pipelines used are all lined with PFA or PTFE. The entire production process is carried out in a Class 1000 cleanroom.

[0021] Example 1

[0022] S1. The aqueous solution of ammonium fluoride is heated to 100°C to evaporate the solvent. After crystallization begins, the solution is heated to evaporate another 50% of the solvent. Then the temperature is lowered to 0°C, allowed to stand for crystallization, and filtered to obtain crude ammonium fluoride solid.

[0023] S2, the crude ammonium fluoride solid obtained in S1 is added to methanol and stirred until it no longer dissolves. The insoluble matter is removed by filtration, then 50% of the solvent is evaporated at 70°C, cooled to 0°C, allowed to stand for crystallization, the liquid is filtered off, and dried at -60 kPa and 60°C for 8 hours to obtain ppm-grade ammonium fluoride solid with impurities of 62 ppm fluorosilicate, 21 ppm phosphate, and 9 ppm sulfate.

[0024] S3, the pure ammonium fluoride obtained in S2 is heated to 110℃, and high-purity nitrogen gas is blown into the heating vessel at a flow rate of 300L / min and a pressure of 0.05MPa. The nitrogen gas carries the ammonium fluoride vapor into the cyclone separator, and the temperature of the cyclone separator is controlled at 80-85℃. The ammonium fluoride vapor cools down and condenses, and is deposited as solid particles at the bottom of the cyclone separator to obtain high-purity ammonium fluoride.

[0025] S4. The high-purity ammonium fluoride obtained in S3 was dissolved in high-purity water to prepare an aqueous solution with a concentration of 40.5 wt%. Then, it was filtered sequentially through three microfiltration membranes of 0.2 μm, 0.05 μm, and 0.01 μm at pressures of 0.05 MPa, 0.12 MPa, and 0.18 MPa, respectively, to obtain an electronic-grade ammonium fluoride aqueous solution. The test results showed that the number of particles with a diameter ≥ 0.2 μm was ≤ 10 pcs / ml, the concentration of a single metal ion was ≤ 0.1 ppb, and the concentration of a single anion was ≤ 0.2 ppm.

[0026] Example 2

[0027] S1. The aqueous solution of ammonium fluoride is heated to 90°C to evaporate the solvent. After crystallization begins, the solution is heated to evaporate another 70% of the solvent. Then the temperature is lowered to 5°C, and the solution is allowed to stand to crystallize. The solution is then filtered to obtain crude ammonium fluoride solid.

[0028] S2, the crude ammonium fluoride solid obtained in S1 is added to methanol and stirred until it no longer dissolves. The insoluble matter is removed by filtration. Then, 80% of the solvent is evaporated at 60°C, cooled to 10°C, allowed to stand for crystallization, the liquid is filtered off, and dried at -90 kPa and 40°C for 6 h to obtain ppm-grade ammonium fluoride solid with impurities of 81 ppm fluorosilicate, 29 ppm phosphate, and 14 ppm sulfate.

[0029] S3, the pure ammonium fluoride obtained in S2 is heated to 120℃, and high-purity nitrogen gas is blown into the heating vessel at a flow rate of 500L / min and a pressure of 0.1MPa. The nitrogen gas carries the ammonium fluoride vapor into the cyclone separator. The temperature of the cyclone separator is controlled at 75-80℃. The ammonium fluoride vapor cools down and condenses, and is deposited as solid particles at the bottom of the cyclone separator to obtain high-purity ammonium fluoride.

[0030] S4. The high-purity ammonium fluoride obtained in S3 was dissolved in high-purity water to prepare an aqueous solution with a concentration of 40.1 wt%. Then, it was filtered sequentially through three microfiltration membranes of 0.2 μm, 0.05 μm, and 0.01 μm at pressures of 0.05 MPa, 0.12 MPa, and 0.2 MPa, respectively, to obtain an electronic-grade ammonium fluoride aqueous solution. The test results showed that the number of particles with a diameter ≥ 0.2 μm was ≤ 10 pcs / ml, the concentration of a single metal ion was ≤ 0.1 ppb, and the concentration of a single anion was ≤ 0.2 ppm.

[0031] Example 3

[0032] S1. The aqueous solution of ammonium fluoride is heated to 80°C to evaporate the solvent. After crystallization begins, the solution is heated to evaporate another 80% of the solvent. Then the temperature is lowered to 10°C, allowed to stand for crystallization, and filtered to obtain crude ammonium fluoride solid.

[0033] S2, the crude ammonium fluoride solid obtained in S1 is added to acetonitrile and stirred until it no longer dissolves. The insoluble matter is removed by filtration. Then, 70% of the solvent is evaporated at 85°C, cooled to 8°C, allowed to stand for crystallization, the liquid is filtered off, and dried at -80 kPa and 70°C for 4 h to obtain ppm-grade ammonium fluoride solid. The impurity fluorosilicate content is 42 ppm, the impurity phosphate content is 16 ppm, and the impurity sulfate content is 7 ppm.

[0034] S3, the pure ammonium fluoride obtained in S2 is heated to 102℃, and high-purity nitrogen gas is blown into the heating vessel at a flow rate of 100L / min and a pressure of 0.02MPa. The nitrogen gas carries the ammonium fluoride vapor into the cyclone separator. The temperature of the cyclone separator is controlled at 70-75℃. The ammonium fluoride vapor cools down and condenses, and is deposited as solid particles at the bottom of the cyclone separator to obtain high-purity ammonium fluoride.

[0035] S4. The high-purity ammonium fluoride obtained in S3 was dissolved in high-purity water to prepare an aqueous solution with a concentration of 39.8 wt%. Then, it was filtered sequentially through three microfiltration membranes of 0.2 μm, 0.05 μm, and 0.01 μm at pressures of 0.06 MPa, 0.15 MPa, and 0.2 MPa, respectively, to obtain an electronic-grade ammonium fluoride aqueous solution. The test results showed that the particle size ≥ 0.2 μm was ≤ 10 pcs / ml, the concentration of a single metal ion was ≤ 0.1 ppb, and the concentration of a single anion was ≤ 0.5 ppm.

[0036] The product test results obtained from Examples 1-3 are listed in the table below:

[0037]

[0038]

[0039] Note: ND means Not Detected.

Claims

1. A method for preparing an electronic-grade ammonium fluoride aqueous solution, characterized in that, Includes the following steps: S1, using an aqueous solution of ammonium fluoride obtained by ammonolysis of fluorosilicic acid as raw material, is concentrated, cooled and crystallized to obtain crude ammonium fluoride solid; S2, the crude ammonium fluoride solid obtained in S1 is dissolved in an organic solvent, filtered, concentrated, cooled, crystallized and dried to obtain ammonium fluoride solid with impurity content reduced to ppm level; S3: The ppm-level ammonium fluoride obtained in S2 is heated to 100-120℃ to sublimate. An inert gas stream carries the ammonium fluoride vapor into a cyclone separator. The temperature of the cyclone separator is controlled at 70-90℃. The ammonium fluoride vapor cools down and condenses, and high-purity ammonium fluoride is obtained through gas-solid separation. S4: Dissolve the high-purity ammonium fluoride obtained in S3 in high-purity water, and filter it through a three-stage microfiltration membrane to obtain an electronic-grade ammonium fluoride aqueous solution.

2. The method for preparing electronic-grade ammonium fluoride aqueous solution according to claim 1, characterized in that, In step S3, the inert gas flow is nitrogen, the nitrogen flow rate is 50-500 L / min, and the pressure is 0.02-0.1 MPa.

3. The method for preparing electronic-grade ammonium fluoride aqueous solution according to claim 1, characterized in that, In step S3, the inert gas discharged from the gas-solid separation is reused after being treated with alkaline solution and dried.

4. The method for preparing electronic-grade ammonium fluoride aqueous solution according to claim 1, characterized in that, In step S2, the organic solvent is selected from methanol or acetonitrile, with a purity > 99.9%.

5. The method for preparing electronic-grade ammonium fluoride aqueous solution according to claim 1, characterized in that, In step S2, the concentration is achieved by evaporating 50-80% of the solvent at 60-85℃, the crystallization is achieved by cooling to 0-10℃ and allowing to stand, and the drying is achieved by drying under vacuum of -60 to -90 kPa and at a temperature of 40-70℃ for 4-8 hours.

6. The method for preparing electronic-grade ammonium fluoride aqueous solution according to claim 1, characterized in that, In step S2, after the organic solvent and ammonium fluoride are separated into solid and liquid phases, the organic solvent is distilled to remove impurities and then reused.

7. The method for preparing electronic-grade ammonium fluoride aqueous solution according to claim 1, characterized in that, In step S1, the concentration is achieved by evaporating water at 80-100°C, and the cooling is achieved by lowering the temperature to 0-10°C.

8. The method for preparing electronic-grade ammonium fluoride aqueous solution according to claim 1, characterized in that, The three-stage microfiltration The membrane filtration process involves sequentially passing the membrane through microporous membranes with pore sizes of 0.2μm, 0.05μm, and 0.01μm, made of PFA and / or PTFE, at a pressure of 0.05-0.2MPa.

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