Method for producing purified isopropyl alcohol

Abstract

Provided is a method for producing purified isopropyl alcohol from crude isopropyl alcohol containing boron as an impurity, the method comprising a step for adding a boron scavenger to the crude isopropyl alcohol and obtaining a liquid, and a step for vaporizing the liquid. The liquid is substantially free of water, and the ratio of the boron scavenger to the isopropyl alcohol is 1-5000 mass ppm.

Description

Method for producing purified isopropyl alcohol

[0001] The present invention relates to a method for producing purified isopropyl alcohol.

[0002] Isopropyl alcohol (also known as 2-propanol) is an organic solvent used in a variety of applications, particularly as a cleaning or drying liquid in semiconductor manufacturing equipment.

[0003] In semiconductor manufacturing equipment, isopropyl alcohol is used in the cleaning or drying section (see Non-Patent Document 1). Chemical solutions applied to wafers that serve as semiconductor device substrates are rinsed with ultrapure water. However, by introducing isopropyl alcohol onto the surface of the cleaned wafer, replacing the ultrapure water with isopropyl alcohol, and then drying, a clean wafer surface without residual water droplets is obtained. It is known that if the isopropyl alcohol contains impurities, residues derived from the impurities may remain on the surface of the semiconductor device wafer, causing semiconductor device defects. Therefore, as semiconductor elements and wiring become increasingly miniaturized and highly integrated, the impact of residues becomes significant, creating a strong demand for improved isopropyl alcohol purity. Specifically, isopropyl alcohol used in semiconductor manufacturing equipment must have a purity of 99.99% or higher and a low content of impurities such as metals.

[0004] A known method for producing isopropyl alcohol is the direct hydration process using a solution catalyst (see Non-Patent Document 2). The resulting isopropyl alcohol is then purified by distillation and passed through a filter to remove impurities such as particles and metals. As a result, purified isopropyl alcohol with a low impurity content is obtained, which is suitable for use in semiconductor manufacturing equipment.

[0005] On the other hand, as semiconductor devices become more powerful, semiconductor manufacturing equipment is becoming more diverse and complex, and the number of cleaning and drying sections is increasing. This is also resulting in an increase in isopropyl alcohol waste. Currently, isopropyl alcohol waste is disposed of after being treated. However, in order to reduce waste treatment costs and environmental impact due to the increase in isopropyl alcohol waste, there is a need to recover and reuse the isopropyl alcohol waste discharged from semiconductor manufacturing equipment.

[0006] However, isopropyl alcohol waste liquid contains impurities derived from semiconductor manufacturing equipment, particularly boron, which is used in doping in semiconductor manufacturing equipment. Therefore, in order to reuse isopropyl alcohol waste liquid, it is necessary to remove the impurities, including boron.

[0007] Patent Document 1 proposes a method for purifying crude isopropyl alcohol containing at least one impurity element selected from As, B, Se, and Ge, by adding water in an amount exceeding the azeotropic composition with isopropyl alcohol and then distilling the mixture.

[0008] Japanese Patent Application Publication No. 10-109948

[0009] Koji Ban, "Silicon Wafer Drying Technology in Semiconductor Manufacturing," Surface Technology, Vol. 49 (1998) No. 3, pp. 253-259 Yukio Mizutani, "Transition of Isopropyl Alcohol Manufacturing Technology," Journal of the Society of Synthetic Organic Chemistry, Vol. 35 (1977) No. 9, pp. 761-766

[0010] Although the method for purifying crude isopropyl alcohol described in Patent Document 1 can remove boron from crude isopropyl alcohol to a high degree, it has been found that when a large amount of boron is contained in the crude isopropyl alcohol, adding a small amount of water and distilling the mixture cannot remove boron to a high degree. Therefore, distillation must be performed by adding a large amount of water, or by adding a small amount of water and repeatedly distilling the mixture. However, dehydration is required in a subsequent process, which requires a large amount of energy for dehydration.

[0011] Therefore, an object of the present invention is to provide a method for producing highly purified isopropyl alcohol by removing boron to a high degree from crude isopropyl alcohol containing boron as an impurity even when the amount of water added is reduced.

[0012] The present inventors have conducted extensive research to solve the above-mentioned problems. Isopropyl alcohol wastewater discharged from semiconductor manufacturing equipment contains a large amount of various metals. First, in an initial study, the possibility of separating metals was investigated by passing the isopropyl alcohol wastewater through a filter with a pore size of 10 nm. As a result, it was found that this method was effective for metals such as iron, sodium, and copper, but not for boron.

[0013] In addition, when the purification of isopropyl alcohol waste liquid containing boron as an impurity using a distillation column was investigated, it was also found that boron was entrained in the distillate containing isopropyl alcohol extracted from the top of the distillation column. Therefore, when a compound capable of forming a complex with boron or a boron compound, or a compound capable of reacting with boron or a boron compound to form a salt, i.e., a boron scavenger, was added and distilled, it was found that it was possible to suppress the entrainment of boron in the distillate containing isopropyl alcohol. Therefore, as a result of further investigation, it was found that by distilling isopropyl alcohol waste liquid to which a predetermined amount of boron scavenger was added, boron was highly removed and highly pure purified isopropyl alcohol was obtained, leading to the completion of the present invention.

[0014] That is, one aspect of the present invention is a method for producing purified isopropyl alcohol from crude isopropyl alcohol containing boron as an impurity, the method comprising the steps of adding a boron scavenger to the crude isopropyl alcohol to obtain a liquid, and vaporizing the liquid, wherein the liquid is substantially free of water, and the ratio of the boron scavenger to the isopropyl alcohol is 1 ppm by mass or more and 5000 ppm by mass or less.

[0015] In one aspect of the present invention, the following aspects are preferable: 1) The boron scavenger is a sugar alcohol and / or an inorganic alkali compound, 2) The liquid has a ratio of the boron scavenger to isopropyl alcohol of 500 ppm by mass or more and 1000 ppm by mass or less, and 3) The crude isopropyl alcohol has a boron content of 50 ppt by mass or more and 300 ppb by mass or less.

[0016] Another aspect of the present invention is a method for producing purified isopropyl alcohol from crude isopropyl alcohol containing boron as an impurity, comprising the steps of: adding a boron scavenger to the crude isopropyl alcohol to obtain a liquid; and vaporizing the liquid, wherein the liquid contains water, and the ratio of the boron scavenger to the total amount of isopropyl alcohol and water is 500 ppm by mass or more and 5000 ppm by mass or less, and the ratio of water to the total amount of isopropyl alcohol and water is 1% by mass or more and 50% by mass or less. This is a method for producing purified isopropyl alcohol.

[0017] In another aspect of the present invention, the following aspects are preferably taken: 1) the boron scavenger is a sugar alcohol and / or an inorganic alkali compound, and 2) the liquid has a boron content of 50 mass ppt or more and 300 mass ppb or less relative to the total amount of isopropyl alcohol and water.

[0018] The present invention preferably takes the following forms: 1) The crude isopropyl alcohol is a waste liquid discharged from a semiconductor manufacturing device.

[0019] According to the present invention, even if the amount of water added is reduced, boron can be highly removed from crude isopropyl alcohol containing boron as an impurity by a simple operation, and highly pure purified isopropyl alcohol can be industrially and stably produced.

[0020] Crude isopropyl alcohol, which is a waste liquid discharged from semiconductor manufacturing equipment, may contain high concentrations of boron. However, the present invention is particularly effective in removing boron from such crude isopropyl alcohol. Furthermore, the distillation process does not require the addition of a large amount of water, and dehydration time can be shortened. Furthermore, the resulting purified isopropyl alcohol has high purity and can be suitably used as a cleaning liquid or drying liquid for semiconductor devices, making it highly industrially applicable.

[0021] The method for producing purified isopropyl alcohol of this embodiment is characterized by including a step of adding a boron scavenger to crude isopropyl alcohol (hereinafter, isopropyl alcohol may be abbreviated as "IPA") containing boron as an impurity to obtain a liquid, and a step of vaporizing the liquid. The details of why the method for producing purified IPA of this embodiment can remove boron to a high degree are unknown, but the inventors speculate as follows. It is speculated that boron exists in the crude IPA in the form of boric acid. The sugar alcohol used as a boron scavenger can form a complex with boric acid, thereby capturing boron. Furthermore, the inorganic alkali compound used as a boron scavenger can form a salt through a neutralization reaction with boric acid, thereby capturing boron. It is speculated that capturing boron in this way prevents boron from volatilizing and moving to the top of the column when the liquid is vaporized, thereby suppressing the entrainment of boron into the vaporized IPA.

[0022] In this specification, unless otherwise specified, the notation "A to B" for numerical values ​​A and B means "A or more and B or less." In such notation, when a unit is assigned only to numerical value B, the unit also applies to numerical value A. In the following description, unless otherwise specified, "%", "ppm", "ppb", and "ppt" are all mass standards, including in the examples. The method for producing purified isopropyl alcohol of this embodiment will be described in detail below.

[0023] <Crude Isopropyl Alcohol Containing Boron as an Impurity> The crude IPA containing boron as an impurity used in the method for producing purified isopropyl alcohol of this embodiment is not particularly limited, and examples include IPA produced by direct hydration and waste liquid discharged from semiconductor manufacturing equipment. The boron content in IPA produced by direct hydration is approximately 0.1 to 1 ppt. The boron content in waste liquid discharged from semiconductor manufacturing equipment varies depending on the cleaning or drying section in which the IPA is used, but is typically in the range of 50 ppt to 300 ppb. Since boron can be removed to a high degree when the liquid is substantially free of water, the boron content in the crude isopropyl alcohol is preferably 50 ppt to 300 ppb, more preferably 50 ppt to 30 ppb, and particularly preferably 50 ppt to 3 ppb. In this case, the ratio of water to the total amount of isopropyl alcohol and water in the liquid is, for example, less than 1%.

[0024] Furthermore, crude IPA may further contain water. For example, the water content in IPA produced by the direct hydration method is in the range of 20 to 200 ppm. Furthermore, the water content in waste liquid discharged from semiconductor manufacturing equipment varies depending on the cleaning section or drying section in which the IPA is used, but is in the range of 1 to 90%. In this embodiment, the liquid may contain water, but if it contains a large amount of water, subsequent dehydration tends to require a great deal of energy. For this reason, the ratio of water to the total amount of IPA and water in the water-containing liquid is in the range of 1 to 50%, preferably in the range of 1 to 35%, and more preferably in the range of 1 to 12%. In this case, since boron can be removed to a high degree, the ratio of boron to the total amount of isopropyl alcohol and water in the liquid is preferably 50 ppt to 300 ppb, more preferably 50 ppt to 30 ppb, and particularly preferably 50 ppt to 3 ppb.

[0025] When the ratio of water to the total amount of IPA and water in the crude IPA is 1 to 50%, it can be directly subjected to the method for producing purified isopropyl alcohol of this embodiment. On the other hand, when the ratio of water to the total amount of IPA and water in the crude IPA is less than 1%, water is added so that the ratio of water to the total amount of IPA and water is 1 to 50%, and then it can be subjected to the method for producing purified isopropyl alcohol of this embodiment. Furthermore, when the ratio of water to the total amount of IPA and water in the crude IPA exceeds 50%, the crude IPA can be concentrated so that the ratio of water to the total amount of IPA and water is 1 to 50%, and then it can be subjected to the method for producing purified isopropyl alcohol of this embodiment.

[0026] <Boron Scavenger> In the method for producing purified isopropyl alcohol of this embodiment, a boron scavenger is used. The boron scavenger is a compound capable of forming a complex with boron or a boron compound, or a compound capable of reacting with boron or a boron compound to form a salt. By adding a boron scavenger to crude IPA and vaporizing it, the volatilization of boron is suppressed. Specific examples of boron scavenger include sugar alcohols and inorganic alkali compounds.

[0027] Sugar alcohols are those obtained by reducing the carbonyl groups of carbohydrates such as aldoses and ketoses. Because sugar alcohols have many hydroxyl groups, they can form complexes with boron or boron compounds (e.g., boric acid). The sugar alcohol is not particularly limited as long as it can form a complex with boron or a boron compound, and examples thereof include glycerin, erythritol, arabinitol, xylitol, galactitol, and mannitol. Among these, mannitol is preferred for use in terms of its boron-trapping ability.

[0028] The inorganic alkali compound is not particularly limited as long as it can react with boron or a boron compound (e.g., boric acid) to form a salt, and examples thereof include sodium hydroxide, calcium hydroxide, calcium carbonate, and sodium carbonate.

[0029] In this embodiment, a single boron scavenger may be used, or a combination of multiple boron scavenger agents may be used. When a combination of multiple boron scavenger agents is used, it is preferable to combine boron scavenger agents that exhibit the same type of action.

[0030] <Amount of Boron Scavenger Used> In this embodiment, when the liquid is substantially free of water, the ratio of boron scavenger to IPA in the liquid is in the range of 1 to 5000 ppm. If the ratio of boron scavenger to IPA in the liquid is 1 ppm or more, boron is removed to a high degree. Even if the ratio exceeds 5000 ppm, the boron removal effect will plateau, and there is a concern that the solubility of the boron scavenger will decrease. The ratio of boron scavenger to IPA in the liquid can be determined appropriately taking into account the boron content in the crude IPA, but is preferably in the range of 500 to 4000 ppm, and more preferably in the range of 1000 to 4000 ppm. Note that when multiple boron scavengers are combined, the total amount of the multiple boron scavenger should be within the above range.

[0031] On the other hand, when the liquid contains water, the ratio of the boron scavenger to the total amount of IPA and water in the liquid is 500 to 5000 ppm. If the ratio of the boron scavenger to the total amount of IPA and water in the liquid is 500 ppm or more, boron is removed to a high degree, and even if the ratio exceeds 5000 ppm, the boron removal effect will plateau and there is a concern that the solubility of the boron scavenger will decrease. The ratio of the boron scavenger to the total amount of IPA and water in the liquid can be determined appropriately taking into account the ratio of boron to isopropyl alcohol and the ratio of water to isopropyl alcohol in the liquid, but is preferably in the range of 500 to 1000 ppm, and more preferably in the range of 800 to 1000 ppm.

[0032] <Vaporization> In this embodiment, vaporization refers to the process in which a liquid boils or evaporates to form a gas. Any known method can be used to vaporize a liquid as long as it is capable of vaporizing IPA, and examples of such methods include distillation, flash distillation, and pervaporation. Among these, distillation is preferred from the viewpoint of boron removal when the liquid contains a large amount of boron. Any known distillation method can be used without particular limitations, and simple distillation and multi-stage distillation are commonly used. Furthermore, the liquid may be distilled using structured packing or irregular packing. Below, methods for distilling a liquid are described in detail.

[0033] <Distillation> The method for distilling a liquid is not particularly limited, and examples thereof include a method of distilling a liquid at about the boiling point of IPA under normal pressure, reduced pressure, or increased pressure. Furthermore, if the liquid contains water, the liquid can be distilled at the azeotropic temperature of IPA and water under normal pressure, reduced pressure, or increased pressure. Furthermore, when a multi-stage distillation method is used, the number of theoretical plates in the distillation column is not particularly limited, and may be set appropriately within the range of 20 to 60 plates.

[0034] <Subsequent Processing> In this embodiment, when the liquid contains water, an azeotropic mixture of IPA and water is obtained by vaporizing the liquid, and the water can be separated and purified by a known method. Examples of methods for purifying the azeotropic mixture include azeotropic distillation using an azeotropic agent such as benzene.

[0035] Furthermore, the crude IPA may contain metal impurities other than boron. Examples of metal impurities include sodium, magnesium, aluminum, potassium, phosphorus, calcium, chromium, manganese, silicon, iron, nickel, cobalt, copper, zinc, arsenic, molybdenum, silver, barium, and lead. When the content of metal impurities exceeds the range required for semiconductor applications, the metal impurities must be removed. Examples of methods for removing metal impurities include distillation, ion exchange resin, and filtration. Metal impurities can be removed by combining methods for removing metal impurities depending on the type of metal impurity in the crude IPA.

[0036] Examples of the present invention will be described in detail below, but the present invention is not limited to these examples.

[0037] <Method for measuring boron content> Instrument: ICP-MS Agilent 8800 (Agilent Technologies) First, standard solutions were prepared by adding boron to IPA at 0 ppt, 500 ppt, 1000 ppt, 2000 ppt, and 5000 ppt, and a calibration curve was created by measuring each solution in turn using ICP-MS. After that, the inside of the ICP-MS was thoroughly washed with 5% nitric acid (solvent: IPA), and then two samples were measured using ICP-MS, and the average value was taken as the boron content.

[0038] <Dissolution State> The dissolution state when the boron scavenger was added to crude IPA was visually evaluated.

[0039] <Experimental Apparatus> The experimental apparatus used in the Examples and Comparative Examples is an apparatus designed for simple distillation, consisting of a flask, a condenser, a PFA tube, a receiving flask, and a heater. The prepared sample is placed in the flask and heated by the heater. The vapor generated by evaporation passes through the PFA tube connecting the flask and the condenser and is condensed in the condenser. The condensed distillate is collected in the receiving flask. In addition, a quartz flask, condenser, and receiving flask were used to reduce contamination due to elution from the apparatus body.

[0040] Examples 1 to 5, Comparative Example 1 First, only IPA was charged, and the distillate obtained by simple distillation was sampled as a blank and analyzed to confirm that there was no contamination due to elution from the apparatus body.

[0041] D(-)-mannitol (manufactured by MERCK) (hereinafter referred to as mannitol) was added as a boron scavenger to 500 mL of crude IPA, which had a boron content of 3.0 ppb, impurities other than boron ranging from 0.1 to 100 ppt, and a purity of 99.99%, to obtain a liquid. The ratio of mannitol to IPA was set to the values ​​shown in Table 1. The crude IPA also contained boric acid as a boron compound. The resulting liquid was placed in a flask and heated using a heater. The heater temperature was set within a range of 150 to 170°C depending on the sample composition. The distillate obtained approximately 25 minutes after the start of heating was discarded to flush the apparatus. The distillate (purified IPA) obtained after approximately 50 minutes was then sampled. 10 mL of purified IPA was sampled in each of two PFA bottles. Next, a sample was prepared by adding nitric acid to the purified IPA to a concentration of 5%, and the boron content in the purified IPA was measured. The measurement results of the boron content in the purified IPA are shown in Table 1.

[0042]

[0043] From Table 1, it was confirmed that boron was removed to a high degree even without adding water in Examples 1 to 5. In contrast, in Comparative Example 1, boron was not removed to a high degree because no boron scavenger was added.

[0044] Examples 6 and 7, Comparative Examples 2 and 3 Mannitol was added to 500 ml of crude IPA, in which the ratios of boron and water to the total amount of IPA and water were the values ​​shown in Table 2, and the contents of each impurity other than boron were 0.1 to 100 ppt, to obtain a liquid. The ratio of mannitol to the total amount of IPA and water was the value shown in Table 2. The obtained liquid was placed in a flask, and the heater temperature was set to 170°C. The distillate (purified IPA) was then sampled using the same procedures as in Examples 1 to 5 and Comparative Example 1, and the boron content in the purified IPA was measured. The measurement results for the boron content in the purified IPA are shown in Table 2.

[0045]

[0046] From Table 2, it was confirmed that boron was removed to a high degree in Examples 6 and 7, even when the amount of water added was reduced. In contrast, in Comparative Example 2, no boron scavenger was added, so boron was not removed as much as in Example 6. Furthermore, in Comparative Example 3, no boron scavenger was added, so boron was not removed as much as in Example 7.

[0047] Comparative Example 4: To compare the boron separation method using the distillation process, boron was separated by a filter method. Specifically, crude IPA with a boron content of 12.3 ppt, impurity contents other than boron of 0.1 to 100 ppt, and purity of 99.99% was passed through a filter with a pore size of 10 nm, and then purified IPA was sampled and the boron content in the purified IPA was measured. The measurement results for the boron content in the purified IPA are shown in Table 3.

[0048]

[0049] From Table 3, it was confirmed that in Comparative Example 4, the boron cut rate was 4%, and boron was not removed to a high degree.

[0050] Examples 8 and 9 Distillate (purified IPA) was sampled and the boron content in the purified IPA was measured in the same manner as in Examples 1 to 5 and Comparative Example 1, except that sodium hydroxide was added as a boron scavenger and the ratio of sodium hydroxide to IPA was set to the value shown in Table 4. The measurement results of the boron content in the purified IPA are shown in Table 4.

[0051]

[0052] From Table 4, it was confirmed that in Examples 8 to 10, boron was removed to a high degree even without adding water.

Claims

1. A method for producing purified isopropyl alcohol from crude isopropyl alcohol containing boron as an impurity, comprising the steps of: adding a boron scavenger to the crude isopropyl alcohol to obtain a liquid; and vaporizing the liquid, wherein the liquid is substantially free of water, and the ratio of the boron scavenger to the isopropyl alcohol is 1 ppm by mass or more and 5,000 ppm by mass or less.

2. The method for producing purified isopropyl alcohol according to claim 1, wherein the boron scavenger is a sugar alcohol and / or an inorganic alkaline compound.

3. A method for producing purified isopropyl alcohol as described in claim 1 or 2, wherein the liquid has a ratio of the boron scavenger to isopropyl alcohol of 500 mass ppm or more and 1000 mass ppm or less.

4. The method for producing purified isopropyl alcohol according to claim 1 or 2, wherein the crude isopropyl alcohol has a boron content of 50 ppt by mass or more and 300 ppb by mass or less.

5. A method for producing purified isopropyl alcohol from crude isopropyl alcohol containing boron as an impurity, comprising the steps of: adding a boron scavenger to the crude isopropyl alcohol to obtain a liquid; and vaporizing the liquid, wherein the liquid contains water, and the ratio of the boron scavenger to the total amount of isopropyl alcohol and water is 500 ppm by mass or more and 5,000 ppm by mass or less, and the ratio of water to the total amount of isopropyl alcohol and water is 1% by mass or more and 50% by mass or less.

6. The method for producing purified isopropyl alcohol according to claim 5, wherein the boron scavenger is a sugar alcohol and / or an inorganic alkaline compound.

7. A method for producing purified isopropyl alcohol as described in claim 5 or 6, wherein the liquid has a ratio of boron to the total amount of isopropyl alcohol and water of 50 mass ppt or more and 300 mass ppb or less.

8. The method for producing purified isopropyl alcohol according to claim 1 or 5, wherein the crude isopropyl alcohol is a waste liquid discharged from a semiconductor manufacturing device.

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