Aqueous alkali solution containing corrosion inhibitor, and method for using same as low-toxicity aqueous alkali solution

Abstract

Provided is an aqueous alkali solution containing (A) through (E). (A) is a quaternary ammonium ion represented by formula (1), (B) is a halide ion, (C) is a hydroxide ion, (D) is water, and (E) is a corrosion inhibitor. (In the formula, R1, R2, R3, and R4 are each independently a C1-16 alkyl group, and at least one of R1, R2, R3 and R4 is a C2-16 alkyl group.)

Description

Alkaline aqueous solution containing a corrosion inhibitor and a method for using the same as a low-toxicity alkaline aqueous solution

[0001] The present invention relates to an alkaline aqueous solution containing a corrosion inhibitor and a method for using the same as a low-toxicity alkaline aqueous solution. More specifically, the present invention relates to an alkaline aqueous solution containing a specific quaternary ammonium ion, a halide ion, a hydroxide ion, water, and a corrosion inhibitor.

[0002] Quaternary ammonium compounds are used as phase transfer catalysts, surfactants, disinfectants, cleaning agents, etc. Among quaternary ammonium compounds, tetramethylammonium hydroxide, in particular, is a type of organic alkali that exhibits strong basicity and is used primarily in alkaline aqueous solutions for semiconductors, which are used for cleaning, etching, developing solutions, etc. during semiconductor manufacturing.

[0003] For example, Patent Document 1 discloses an aqueous solution of 2.35% by weight of tetramethylammonium hydroxide, which contains metal ions and halogen ions at predetermined values.

[0004] Furthermore, since quaternary ammonium compounds are alkaline in aqueous solution, it is known that when a treatment solution containing quaternary ammonium hydroxide comes into contact with a metal, corrosion occurs. From the viewpoint of suppressing metal corrosion, for example, Patent Document 2 proposes adding a sugar or a sugar alcohol to tetramethylammonium hydroxide or choline to suppress aluminum corrosion.

[0005] JP-A-4-226466 JP-A-4-48633

[0006] However, the present inventors have noticed that aqueous tetramethylammonium hydroxide (hereinafter also referred to as TMAH) solutions are highly toxic and require careful handling. Therefore, an object of the present invention is to provide a low-toxicity alkaline aqueous solution. Another object of the present invention is to provide a method for using a low-toxicity alkaline aqueous solution for a specific purpose. Another object of the present invention is to provide a method for producing a low-toxicity alkaline aqueous solution.

[0007] The present inventors have conducted extensive research to obtain a low-toxicity alkaline aqueous solution, and as a result have found that an alkaline aqueous solution containing a specific quaternary ammonium ion, a halide ion, a hydroxide ion, and water is low-toxic, and that when a corrosion inhibitor is added to the low-toxicity organic alkaline aqueous solution and the solution is used for a specific purpose, it is possible to inhibit metal corrosion, leading to the completion of the present invention.

[0008] That is, the present invention is configured as follows: Item 1: An alkaline aqueous solution containing the following (A) to (E): (A) a quaternary ammonium ion represented by the following formula (1), (B) a halide ion, (C) a hydroxide ion, (D) water, and (E) a corrosion inhibitor. (In the formula, R １ , R ２ , R ３ , and R ４ are each independently an alkyl group having 1 to 16 carbon atoms, provided that R １ , R ２ , R ３ , and R ４ Among these, one or more alkyl groups have 2 to 16 carbon atoms.) Item 2 R in the formula (1) １ , R ２ , R ３ , and R ４ Item 3. The alkaline aqueous solution according to Item 1, wherein all of R in formula (1) are not the same alkyl group. １ , R ２ , and R ３ is a methyl group, and R ４Item 4. The alkaline aqueous solution according to any one of Items 1 to 3, wherein the (B) halide ion is a chloride ion or a bromide ion. Item 5. The alkaline aqueous solution according to any one of Items 1 to 4, wherein the amount of the halide ion is 0.0000001 to 0.01 parts by mass when the amount of the hydroxide ion in the alkaline aqueous solution for semiconductors is 1 part by mass. Item 6. The alkaline aqueous solution according to any one of Items 1 to 5, wherein the LD50 value calculated based on 100% by mass of the hydroxide of the quaternary ammonium ion exceeds 50 mg / kg in a toxicity test using rats based on the OECD TG420 acute oral toxicity test. Item 7. The alkaline aqueous solution according to any one of Items 1 to 6, wherein the EC50 value calculated based on 100% by mass of the hydroxide of the quaternary ammonium ion exceeds 3 mg / L in an OECD TG202 Daphnia acute immobilization test. Item 8: The alkaline aqueous solution according to any one of Items 1 to 7, further comprising one or more compounds selected from the group consisting of alcohols and amines. Item 9: The alkaline aqueous solution according to any one of Items 1 to 8, further comprising a surfactant, the concentration of the surfactant in the alkaline aqueous solution being less than 100 ppm by mass. Item 10: The alkaline aqueous solution according to any one of Items 1 to 9, wherein the (E) corrosion inhibitor is one or more selected from the group consisting of azoles, alkyne compounds, and aromatic hydroxy compounds. Item 11: A method for using the alkaline aqueous solution according to any one of Items 1 to 10 as a low-toxicity alkaline aqueous solution for semiconductors. Item 12: A method for producing the alkaline aqueous solution according to any one of Items 1 to 10, comprising an electrolysis step of electrolyzing an aqueous quaternary ammonium halide solution containing the following (A), (B), and (D), and a step of adding the (E) corrosion inhibitor to the aqueous solution obtained in the electrolysis step: (A) a quaternary ammonium ion represented by the following formula (1): (B) a halide ion; and (D) water. (In the formula, R １ , R ２ , R ３ , and R ４ are each independently an alkyl group having 1 to 16 carbon atoms, provided that R １ , R２ , R ３ , and R ４ wherein one or more alkyl groups have 2 to 16 carbon atoms.) Item 13. The method for producing an alkaline aqueous solution according to Item 12, further comprising a preparation step of preparing the aqueous quaternary ammonium halide solution before the electrolysis step, wherein the preparation step is a step of reacting a trialkylamine with an alkyl halide in ultrapure water to obtain the aqueous quaternary ammonium halide solution.

[0009] According to the present invention, a low-toxicity alkaline aqueous solution containing a corrosion inhibitor is provided. As a result, an alkaline aqueous solution that is highly safe during use and also leads to a low environmental impact is provided. Also, a method for using the low-toxicity alkaline aqueous solution for a specific purpose is provided. Furthermore, a method for producing the low-toxicity alkaline aqueous solution is provided.

[0010] FIG. 2 is an explanatory diagram showing an electrolytic cell.

[0011] Although the present invention will be described in detail below with reference to the preferred embodiments, the present invention is not limited to these embodiments as long as they do not depart from the spirit of the present invention. Furthermore, the present invention can be implemented by modifying it as desired within the scope of the present invention.

[0012] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits, and "A to B" means that the range is from A to B. Furthermore, when a numerical range is expressed in stages, the upper and lower limits of each numerical range can be combined in any way.

[0013] The alkaline aqueous solution of the present invention contains the following (A) to (E): (A) a quaternary ammonium ion represented by the following formula (1), (B) a halide ion, (C) a hydroxide ion, (D) water, and (E) a corrosion inhibitor. (In the formula, R １ , R ２ , R ３ , and R ４ are each independently an alkyl group having 1 to 16 carbon atoms (preferably 1 to 8, more preferably 1 to 4), provided that R １ , R ２ , R ３ , and R ４Among these, one or more alkyl groups have 2 to 16 carbon atoms (preferably 2 to 8, more preferably 2 to 4).

[0014] By including the quaternary ammonium ion represented by the formula (1) above, the alkaline aqueous solution is likely to be less toxic than an alkaline aqueous solution using tetramethylammonium hydroxide. Furthermore, by including the quaternary ammonium ion represented by the formula (1) above, when the alkaline aqueous solution is used as, for example, a cleaning solution, an etching solution, or a developing solution, the cleaning rate, the etching rate, and the developing rate can all be improved. １ ~R ４ If the number of carbon atoms in R exceeds the above range, the steric hindrance of the quaternary ammonium ion becomes large, which may decrease the etching rate and development rate. １ ~R ４ If the number of carbon atoms exceeds the above range, the quaternary ammonium halide described below may become difficult to dissolve, making it difficult to prepare an alkaline aqueous solution.

[0015] In the formula (1), R １ , R ２ , R ３ , and R ４ It is also preferable that not all of R are the same alkyl group. In other words, the quaternary ammonium ions shown in (1) to (3) below are preferred. (1) R １ , R ２ , R ３ , and R ４ (2) A quaternary ammonium ion in which any three of R are the same alkyl group and the remaining one is a different alkyl group. １ , R ２ , R ３ , and R ４ (3) A quaternary ammonium ion in which any two of R are the same alkyl group and the remaining two are different alkyl groups (the remaining two may be the same or different). １ , R ２ , R ３ , and R ４ In the case of (1) above, R １, R ２ , R ３ , and R ４ and the remaining one is an alkyl group having 1 to 16 carbon atoms, the first three and the remaining one are different alkyl groups, and either the first three or the remaining one has 2 to 16 carbon atoms. １ , R ２ , R ３ , and R ４ Preferably, three of the groups are the same and the remaining one is an alkyl group having 2 to 16 carbon atoms different from the groups. In this case, the quaternary ammonium ion represented by formula (1) has two types of alkyl groups. In this embodiment, R １ , R ２ , R ３ , and R ４ When any three of the alkyl groups are methyl groups and the remaining alkyl group has 2 to 16 carbon atoms, the quaternary ammonium ion is more likely to function as a surfactant. Among these, a quaternary ammonium ion in which the remaining alkyl group has 2 to 8 carbon atoms is more preferred, a quaternary ammonium ion in which the remaining alkyl group has 2 to 4 carbon atoms is even more preferred, and 3 or 4 is most preferred. In the case of (2) above, R １ , R ２ , R ３ , and R ４ and R are the same alkyl groups having 1 to 16 carbon atoms, the remaining two are alkyl groups having 1 to 16 carbon atoms different from the first two, and the remaining two are the same or different alkyl groups, and either the first two or the remaining two are alkyl groups having 2 to 16 carbon atoms. In this case, the quaternary ammonium ion represented by formula (1) has two or three types of alkyl groups. In this embodiment, R １ , R ２ , R ３ , and R ４ A quaternary ammonium ion in which any two of R are methyl groups and the remaining two alkyl groups have 2 to 16 carbon atoms is preferred. １ , R ２ , R ３ , and R ４When any two of these are methyl groups, the quaternary ammonium ion is more likely to function as a surfactant. Among these, the remaining two alkyl groups are more preferably quaternary ammonium ions having 2 to 8 carbon atoms, even more preferably quaternary ammonium ions having 2 to 4 carbon atoms, and most preferably 3 or 4. In the case of (3) above, R １ , R ２ , R ３ , and R ４ are all different alkyl groups, at least one of which has 2 to 16 carbon atoms. In this case, the quaternary ammonium ion represented by formula (1) has four types of alkyl groups. In this embodiment, R １ , R ２ , R ３ , and R ４ A quaternary ammonium ion in which any one of R is a methyl group and the remaining three alkyl groups have 2 to 16 carbon atoms is preferred. １ , R ２ , R ３ , and R ４ When any one of the alkyl groups is a methyl group, the quaternary ammonium ion is more likely to function as a surfactant. Among these, quaternary ammonium ions in which the remaining three alkyl groups have 2 to 8 carbon atoms are more preferred, quaternary ammonium ions in which the remaining three alkyl groups have 2 to 4 carbon atoms are even more preferred, and 3 or 4 are most preferred. When the quaternary ammonium ion represented by formula (1) also functions as a surfactant, the amount of surfactant added, which will be described later, can be reduced.

[0016] In addition, in the formula (1), R １ , R ２ , R ３ , and R ４ may all be the same alkyl group. For example, R １ , R ２ , R ３ , and R ４ may all be ethyl, propyl, or butyl.

[0017] Specific examples of the quaternary ammonium ion represented by the above formula (1) include tetraethylammonium ion, tetrapropylammonium ion, tetrabutylammonium ion, ethyltrimethylammonium ion, diethyldimethylammonium ion, triethylmethylammonium ion, propyltrimethylammonium ion, and butyltrimethylammonium ion. These quaternary ammonium ions may be used singly or in combination. Preferred combinations include a combination of ethyltrimethylammonium ion and propyltrimethylammonium ion, and a combination of ethyltrimethylammonium ion and butyltrimethylammonium ion. These combinations may also be combined with another quaternary ammonium ion represented by formula (1).

[0018] The halide ion is not particularly limited, but specific examples include one or more selected from the group consisting of chloride ion, bromide ion, and iodide ion, and chloride ion or bromide ion is preferred.

[0019] The amount of halide ions in an alkaline aqueous solution, expressed as 1 part by mass of hydroxide ions, is not particularly limited, but is preferably 0.0000001 to 0.01 parts by mass, more preferably 0.0000001 to 0.001 parts by mass, and even more preferably 0.0000001 to 0.0005 parts by mass. The amount of halide ions in an alkaline aqueous solution varies significantly depending on the method for producing the aqueous solution. In particular, a solution containing reduced amounts of halide ions can be prepared by using a production method involving electrolysis. The amount can also be adjusted by changing conditions such as the structure of the electrolytic vessel used for electrolysis, the selection of a cation exchange membrane, and the current density.

[0020] Having the halide ion content in the above range is desirable because, when the alkaline aqueous solution is used as a semiconductor processing solution such as an etching solution for silicon, a sufficient etching rate is maintained and surface roughening due to etching is suppressed. The substrate used for silicon etching may be single-crystalline, polycrystalline, or amorphous, and the etching method is not particularly limited. As an example of an etching method, an alkaline aqueous solution contains a quaternary ammonium ion represented by the above formula (1), and etching can be performed by immersing a silicon substrate in the alkaline aqueous solution for a predetermined time, for example, 3 to 30 minutes, preferably 5 to 15 minutes. The etching temperature can be, for example, 25 to 90°C, preferably 30 to 80°C.

[0021] The parts by mass of halide ions in an alkaline aqueous solution can be analyzed by ion chromatography. When the alkaline aqueous solution is highly concentrated, neutralization analysis is particularly effective. Specifically, before introducing the alkaline aqueous solution into anion ion chromatography, the cations in the alkaline aqueous solution are exchanged with hydrogen ions, and the hydroxide ions are converted into water. This allows the hydroxide ions to be removed. Furthermore, concentration enhances sensitivity. This method allows the measurement of low concentrations of halide ions. Details will be described later.

[0022] The alkaline aqueous solution contains hydroxide ions. The fact that the alkaline aqueous solution contains the quaternary ammonium ion represented by the above formula (1) and hydroxide ions can also be said to indicate that the alkaline aqueous solution contains quaternary ammonium hydroxide containing the quaternary ammonium ion represented by the above formula (1) and hydroxide ions. The inclusion of quaternary ammonium hydroxide allows the alkaline aqueous solution to be used as a cleaning solution for various components or as a processing solution (semiconductor processing solution) during semiconductor manufacturing.

[0023] The concentrations of the quaternary ammonium ions represented by the above formula (1) and hydroxide ions in the alkaline aqueous solution are not particularly limited, and are preferably prepared at 1.0 to 65.0 mass% as quaternary ammonium hydroxide. When used in semiconductor applications, for example, the quaternary ammonium hydroxide is more preferably 1.0 to 10.0 mass%, and even more preferably 2.0 to 7.0 mass%. Furthermore, 1.0 to 3.0 mass% is also more preferable, and 2.38 mass% is particularly preferable. Furthermore, the molar concentration of the quaternary ammonium hydroxide is preferably 0.10 to 0.50 mol / L, and more preferably 0.15 to 0.35 mol / L. Furthermore, high-concentration quaternary ammonium hydroxide can also be diluted for use. By using a high concentration, the volume during transportation can be reduced, thereby reducing transportation costs. Furthermore, even if contamination occurs in the alkaline aqueous solution during filling into a container or transportation, the impact of contamination can be reduced by the amount of dilution compared to when dilution is not performed. The high-concentration quaternary ammonium hydroxide is preferably 10.0 to 50.0% by mass, more preferably 20.0 to 40.0% by mass. The concentration of quaternary ammonium hydroxide can be confirmed by neutralization titration with an acid or the like.

[0024] The concentration of the quaternary ammonium ion represented by formula (1) in the alkaline aqueous solution is preferably 0.8 to 61.7% by mass. It is more preferably 0.8 to 9.5% by mass, and even more preferably 1.2 to 6.7% by mass. The concentration of the quaternary ammonium ion in the high-concentration quaternary ammonium hydroxide before dilution is preferably 8.0 to 47.5% by mass, and even more preferably 16.0 to 38.0% by mass. The concentration of the hydroxide ion in the alkaline aqueous solution is preferably 0.05 to 10.6% by mass. It is more preferably 0.05 to 1.6% by mass, and even more preferably 0.1 to 1.2% by mass. The concentration of the hydroxide ion in the high-concentration quaternary ammonium hydroxide is preferably 0.5 to 8.0% by mass, and even more preferably 1.0 to 6.4% by mass.

[0025] The alkaline aqueous solution contains water. The type of water is not particularly limited, and any known water can be used, with ultrapure water having reduced metal impurities being particularly preferred. The water content in the alkaline aqueous solution for semiconductors is not particularly limited, but is preferably 90.0 to 99.9 mass%, more preferably 93.0 to 99.0 mass%, and even more preferably 97.0 to 98.0 mass%.

[0026] The alkaline aqueous solution contains a corrosion inhibitor. Metals such as aluminum and copper corrode when they come into contact with alkali, but the inclusion of a corrosion inhibitor reduces the corrosion rate, allowing treatment to be carried out without affecting the corrosion rate. In particular, corrosion prevention effects can be achieved even when the alkaline aqueous solution contains a compound represented by formula (1). The corrosion inhibitor can be one or more selected from the group consisting of one or more azoles selected from the group consisting of triazoles, thiazoles, benzotriazoles, and imidazoles, alkyne compounds such as acetylene alcohols, aromatic hydroxy compounds, and mercapto group-containing compounds. Preferably, one or more selected from the group consisting of azoles, alkyne compounds, and aromatic hydroxy compounds are used, with azoles being more preferred, and benzotriazoles being even more preferred. These corrosion inhibitors can be used singly or in combination. The concentration in the alkaline aqueous solution is preferably 0.01 to 10% by mass, more preferably 0.1 to 3% by mass. By setting the concentration within this range, the corrosion prevention effect on metals such as aluminum can be enhanced while maintaining processing performance such as cleaning, stripping, and development.

[0027] The alkaline aqueous solution may also contain one or more compounds selected from the group consisting of alcohols and amines. The concentration of the one or more compounds selected from the group consisting of alcohols and amines in the alkaline aqueous solution is not particularly limited, but is preferably 0.1 to 50% by mass, and more preferably 0.5 to 40% by mass. The alcohol is not particularly limited, and known alcohols can be used. Examples include primary alcohols such as methanol, ethanol, and 1-propanol, secondary alcohols such as 2-propanol and 2-butanol, and tertiary alcohols such as 2-methyl-2-propanol. The valence of the alcohol is not particularly limited, and either monohydric alcohols or dihydric or higher alcohols may be used. Among these, alcohols having 16 or fewer carbon atoms (more preferably 2 to 8, even more preferably 2 to 4) are preferred, as longer chains are more likely to cause adsorption inhibition during semiconductor processing, for example.

[0028] The amine is not particularly limited, and known amines can be used. Examples include primary amines such as methylamine, secondary amines such as dimethylamine, and tertiary amines such as trimethylamine. Furthermore, the valence of the amine is not particularly limited, and either monovalent amines or divalent or higher amines can be used. Among these, amines having 16 or fewer carbon atoms (more preferably 2 to 8, and even more preferably 2 to 4) are preferred, as longer chains are more likely to cause adsorption inhibition during processing. As described below, when an alkaline aqueous solution is used as a developer, stripper, or cleaning solution, specific examples of the amine include one or more selected from the group consisting of N,N-diethylethanolamine, N,N-dimethylethanolamine, N-(2-aminoethyl)ethanolamine, N-methyldiethanolamine, N,N-dibutylethanolamine, N-methylethanolamine, ethanolamine, diethanolamine, triethanolamine, and propanolamine. When an alkaline aqueous solution is used as a developer and contains these amines, the concentration can be, for example, 0.1 to 25% by mass. More preferably, it can be 1 to 5% by mass. By setting the concentration in this range, the solubility of the resist can be increased and the dissolution rate of the resist can be appropriately controlled. Furthermore, when an alkaline aqueous solution is used as a stripping solution or a cleaning solution and contains these amines, the concentration can be, for example, 1 to 50 mass %. More preferably, it can be 10 to 40 mass %. By setting the concentration in this range, the removability of the resin layer and the like can be increased and the stripping rate can be appropriately controlled.

[0029] The alkaline aqueous solution may contain a surfactant. The concentration of the surfactant in the alkaline aqueous solution is preferably less than 100 ppm by mass. The alkaline aqueous solution may not contain a surfactant. The quaternary ammonium ion represented by formula (1) contained in the alkaline aqueous solution has an asymmetric shape with respect to the nitrogen atom and has a structure represented by R １ , R ２ , R ３ , and R ４Among these, it is believed that the alkyl group itself functions as a surfactant because one or more alkyl groups have 2 to 16 carbon atoms. Specifically, the alkyl group with a longer carbon number is lipophilic, while the alkyl group with a shorter carbon number is hydrophilic. Therefore, the quaternary ammonium ion represented by the above formula (1) has both a lipophilic and a hydrophilic portion in its ionic structure, and functions as a surfactant. Therefore, the alkaline aqueous solution may be completely free of surfactants, or, if it contains surfactants, its concentration may be as low as less than 100 ppm by mass. The concentration of the surfactant is more preferably less than 50 ppm by mass, even more preferably less than 30 ppm by mass, and particularly preferably less than 10 ppm by mass. By not including surfactants in the alkaline aqueous solution, or if it contains surfactants, its concentration may be less than 100 ppm by mass, for example, foaming of the alkaline aqueous solution for semiconductors can be suppressed, and impurities derived from surfactants can be suppressed. Furthermore, when a quaternary ammonium hydroxide is recovered from a used alkaline aqueous solution by separation, purification, etc., and then reused, if a surfactant is required in the alkaline aqueous solution, it must be added again. However, if a surfactant is not required, the recovered solution can be used as is as an alkaline aqueous solution. Furthermore, if a low surfactant concentration is acceptable, the amount of surfactant added again can be reduced, which is preferable. The lower limit of the surfactant is not particularly specified, but to achieve its effect, it is desirable to contain 0.01 ppm by mass or more, preferably 0.1 ppm by mass or more. The surfactant is a compound having a hydrophilic group and a hydrophobic group (lipophilic group) in one molecule, such as a nonionic surfactant, anionic surfactant, cationic surfactant, or amphoteric surfactant. Examples of nonionic surfactants include acetylene glycol-based surfactants. Examples of acetylene glycol-based surfactants include one or more selected from the group consisting of acetylene glycol, ethylene oxide adducts of acetylene glycol, and acetylene alcohol. These compounds may be used alone or in combination.Furthermore, when the alkaline aqueous solution is used as a developer, stripper, or cleaning solution, it is preferable to add a nonionic surfactant to the alkaline aqueous solution, and the concentration thereof can be 0.1 ppm by mass to 10% by mass, or can be 1 ppm by mass to 1% by mass. The upper limit of the surfactant concentration can be less than 100 ppm by mass, less than 30 ppm by mass, or less than 10 ppm by mass, as mentioned above. Note that the surfactant is a compound different from the above-mentioned compounds that can be contained in the alkaline aqueous solution.

[0030] To evaluate the toxicity of an alkaline aqueous solution, a median lethal dose (LD50) value calculated based on 100% by mass of the hydroxide of the quaternary ammonium ion in a toxicity test using rats based on OECD TG420 acute oral toxicity is preferably greater than 50 mg / kg. This increases safety during use. Furthermore, in the GHS classification, an LD50 value of 50 mg / kg or less corresponds to Category 2, which imposes stricter regulations on storage and transportation, and a value of 5 mg / kg or less corresponds to Category 1, which is even stricter. Therefore, a value greater than 50 mg / kg is preferred. The upper limit of the LD50 value is not particularly limited, but is more preferably greater than 50 mg / kg and less than 10,000 mg / kg, and even more preferably greater than 300 mg / kg and less than 10,000 mg / kg. The LD50 value can be adjusted by changing the type of quaternary ammonium ion represented by the above formula (1).

[0031] As a toxicity evaluation of an alkaline aqueous solution, in the OECD TG202 Daphnia acute immobilization test, the median effective concentration (EC50) value, calculated assuming that the hydroxide of the quaternary ammonium ion is 100% by mass, preferably exceeds 3 mg / L. This makes it easier to reduce environmental impact. Furthermore, the EC50 value of TMAH, which is highly toxic and likely to lead to environmental impact, is 3 mg / L, and from the perspective of reducing environmental impact, it is preferable for it to exceed 3 mg / L. The upper limit of the EC50 value is not particularly limited, but is more preferably greater than 3 mg / L and 1000 mg / L or less, and even more preferably greater than 10 mg / L and 1000 mg / L or less. The EC50 value can be adjusted by changing the type of quaternary ammonium ion represented by the above formula (1).

[0032] In view of the toxicity obtained in the OECD TG420 acute oral toxicity test and the TG202 Daphnia acute immobilization test, for example, R １ , R ２ , and R ３ is an alkyl group having one carbon atom, and R ４ is a quaternary ammonium ion, R is an alkyl group having 2 to 4 carbon atoms, １ , R ２ , R ３ , and R ４ is a quaternary ammonium ion, R is an alkyl group having 2 carbon atoms, １ , R ２ , R ３ , and R ４ is a quaternary ammonium ion, R is an alkyl group having 3 carbon atoms, １ , R ２ , R ３ , and R ４ is an alkyl group having 4 carbon atoms. More specifically, an ethyltrimethylammonium ion, a propyltrimethylammonium ion, a butyltrimethylammonium ion, a tetraethylammonium ion, a tetrapropylammonium ion, or a tetrabutylammonium ion is preferred.

[0033] The alkaline aqueous solution of the present invention can be used as a low-toxicity alkaline aqueous solution. That is, one aspect of the present invention is a method of using the alkaline aqueous solution of the present invention as a low-toxicity alkaline aqueous solution. "Use as a low-toxicity alkaline aqueous solution" means that, as described below, the alkaline aqueous solution of the present invention can be used in specific applications, specifically various industrial applications, by taking advantage of its low toxicity. The low-toxicity alkaline aqueous solution can be used, for example, for cleaning metal members, and can also be used as a processing solution (semiconductor processing solution) during semiconductor production, such as an etching solution, cleaning solution, or developer. That is, the low-toxicity alkaline aqueous solution of the present invention can be used as a low-toxicity alkaline aqueous solution for producing semiconductors.

[0034] Tetramethylammonium hydroxide (TMAH), an organic base that has been commonly used in developing solutions, which are specific examples of semiconductor processing solutions, is highly toxic, and therefore is subject to strict regulations regarding storage and transportation, and also places a heavy burden on the environment in terms of waste liquid disposal after use. In contrast, the alkaline aqueous solution of the present invention is low in toxicity, and therefore the above-mentioned problems are less likely to occur when preparing and using a developing solution using it. When the alkaline aqueous solution of the present invention is used as a developing solution, in addition to the components (A) to (E) listed above, it may contain the surfactant and amine listed above. The concentrations of these components in the alkaline aqueous solution can be within the ranges listed above. Furthermore, when the alkaline aqueous solution is used as a developing solution, the concentration of the quaternary ammonium ion represented by the formula (1) can be within the ranges listed above.

[0035] When the alkaline aqueous solution of the present invention is used as a developer, various resist materials known to be developed by alkaline compounds can be used. The resist may be either positive or negative. Positive resists are not particularly limited, but examples include (meth)acrylic resins such as polymethyl (meth)acrylate, urethane resins such as polyurethane, phenolic resins such as novolac resins, styrene resins such as polyhydroxystyrene (PHS) resin, and resins having an aliphatic polycyclic skeleton. These resins may be used alone or in combination of two or more. Negative resists are not particularly limited, but examples include polyvinyl cinnamate and mixtures of resins having unsaturated carbon bonds and azide compounds. When the alkaline aqueous solution of the present invention is used as a stripper, it is suitable for stripping resin layers during the production of semiconductor substrates, etc., and can simultaneously achieve high stripping effectiveness and sufficient corrosion protection for metal wiring (especially Al-based and Cu-based). Furthermore, when the alkaline aqueous solution of the present invention is used as a cleaning solution, it enhances wettability to foreign matter on a semiconductor substrate, providing excellent cleaning effects, and simultaneously realizing sufficient corrosion prevention effects for metal wiring (particularly Al-based and Cu-based).

[0036] The method for producing the alkaline aqueous solution is not particularly limited, but from the viewpoint of suppressing the halide ion concentration, it is preferable to produce it by adding the above-mentioned (E) corrosion inhibitor to an aqueous solution obtained by electrolyzing a quaternary ammonium halide aqueous solution. It is preferable to include an electrolysis step of electrolyzing the quaternary ammonium halide aqueous solution. Specifically, it is preferable to include an electrolysis step of electrolyzing a quaternary ammonium halide aqueous solution containing the following (A), (B), and (D). (A), (B), and (D) can be those described above. (A) A quaternary ammonium ion represented by the following formula (1): (B) A halide ion (D) Water (In the formula, R １ , R ２ , R ３ , and R ４ are each independently an alkyl group having 1 to 16 carbon atoms (preferably 1 to 8, more preferably 1 to 4), provided that R １ , R ２ , R ３ , and R ４ Among these, one or more alkyl groups have 2 to 16 carbon atoms (preferably 2 to 8, more preferably 2 to 4, and most preferably 3 or 4).

[0037] To produce an alkaline aqueous solution by electrolysis, an electrolytic cell can be used, which has one or more cation exchange membranes disposed between an anode and a cathode, a raw material chamber for supplying a quaternary ammonium halide aqueous solution as a raw material, and a base chamber (cathode chamber) for producing a quaternary ammonium hydroxide aqueous solution. In this production method using an electrolytic cell, quaternary ammonium ions contained in the quaternary ammonium halide aqueous solution pass through the cation exchange membrane disposed on the cathode side during electrolysis. This produces a quaternary ammonium hydroxide aqueous solution in the base chamber. While the above example illustrates the use of one or more cation exchange membranes, an electrolytic cell containing multiple membranes selected from the group consisting of cation exchange membranes, anion exchange membranes, and bipolar membranes (composite membranes consisting of a cation exchange membrane and an anion exchange membrane) may also be used, as long as it can produce a quaternary ammonium hydroxide aqueous solution.

[0038] At this time, halide ions, which are anions of the quaternary ammonium halide, move to the anode side, but some of the halide ions also move to the cathode side due to diffusion. For this reason, depending on the concentration of the liquid used as the raw material, halide ions of about 1 to several tens of ppm may be mixed into the aqueous quaternary ammonium hydroxide solution.

[0039] The method for producing an alkaline aqueous solution may include, prior to the electrolysis step, a preparation step of preparing a quaternary ammonium halide aqueous solution to be used as a raw material in the electrolysis step. The preparation step is not particularly limited, and for example, the quaternary ammonium halide aqueous solution can be prepared by producing a quaternary ammonium halide aqueous solution. Furthermore, the method for producing the quaternary ammonium halide aqueous solution is not particularly limited. For example, from the viewpoints of productivity and quality, a step of reacting a trialkylamine with an alkyl halide in ultrapure water to obtain a quaternary ammonium halide is preferred.

[0040] The trialkylamine and alkyl halide used as raw materials are not particularly limited as long as they can produce the quaternary ammonium ion represented by the above formula (1), but specifically, among the alkyl groups contained in the trialkylamine and the alkyl halide, one or more alkyl groups have 2 to 16 carbon atoms (preferably 2 to 8, more preferably 2 to 4, and most preferably 3 or 4), and the other alkyl groups have 1 to 16 carbon atoms (preferably 1 to 8, more preferably 1 to 4, and most preferably 1). In addition, the halide ion, which is the anion of the alkyl halide, can be the same as that described above in (B).

[0041] Examples will be given below to specifically explain the present invention, but the present invention is not limited to these. The evaluations carried out in the examples and comparative examples were determined by the following methods.

[0042] (Reference Examples 1 to 13, Comparative Example 1) [Aqueous Alkaline Solution] Aqueous solutions of quaternary ammonium hydroxide were prepared to the concentrations shown in Table 1, and various evaluations were carried out as the aqueous alkaline solutions. Ethyltrimethylammonium hydroxide (ETMAH, prepared from raw materials) Diethyldimethylammonium hydroxide (DEDMAH, manufactured by Sigma-Aldrich) Propyltrimethylammonium hydroxide (PTMAH, prepared from raw materials) Butyltrimethylammonium hydroxide (BTMAH, prepared from raw materials) Tetraethylammonium hydroxide (TEAH, manufactured by Tokyo Chemical Industry Co., Ltd.) Tetrapropylammonium hydroxide (TPAH, manufactured by Tokyo Chemical Industry Co., Ltd.) Tetrabutylammonium hydroxide (TBAH, manufactured by Tokyo Chemical Industry Co., Ltd.) Hexadecyltrimethylammonium hydroxide (HTMAH, manufactured by Tokyo Chemical Industry Co., Ltd.) Tetramethylammonium hydroxide (TMAH, manufactured by Tokuyama Chemical Industry Co., Ltd.) [Surfactants] Surfynol (registered trademark) 465 (manufactured by Nissin Chemical Industry Co., Ltd.) [Corrosion inhibitors] Benzotriazole (manufactured by Tokyo Chemical Industry Co., Ltd.) 2-Butyne-1,4-diol (manufactured by Tokyo Chemical Industry Co., Ltd.) Catechol (manufactured by Tokyo Chemical Industry Co., Ltd.) [Amine] N,N-diethylethanolamine (Tokyo Chemical Industry Co., Ltd.)

[0043] [Preparation of Quaternary Ammonium Hydroxide Aqueous Solutions] ETMAH, PTMAH, and BTMAH were prepared according to the following procedure. A quaternary ammonium halide aqueous solution was prepared from the raw materials trialkylamine and alkyl halide, and then electrolysis was performed using this raw material to prepare a quaternary ammonium hydroxide aqueous solution. Specifically, in the case of ETMAH, trimethylamine and ethyl chloride were charged in a 1:1 molar ratio into a reaction vessel containing ultrapure water, and the reaction temperature was maintained at 60°C to prepare a 50% by mass ethyltrimethylammonium chloride aqueous solution. Unreacted trimethylamine and ethyl chloride, as well as by-product ethanol, were removed under reduced pressure until their concentrations were each less than 100 ppm. ETMAH was then prepared using the electrolytic cell shown in Figure 1. In Figure 1, 1 represents an anode, 2 represents a cathode, 3 represents a power source, 4 represents an anode chamber, 5 represents a raw material chamber, 6 represents an intermediate chamber, 7 represents a cathode chamber, 8 represents an anion exchange membrane, and 9 represents a cation exchange membrane.

[0044] A platinum-plated nickel plate was used as the cathode, a platinum-plated titanium plate as the anode, two Nafion N324 (manufactured by Chemours) cation exchange membranes, and ASE (manufactured by Astom) anion exchange membrane. 0.5N hydrochloric acid was circulated in the anode chamber, a 50% by mass aqueous solution of ethyltrimethylammonium chloride was circulated in the raw material chamber between the anion exchange membrane and the cathode-side cation exchange membrane, and ultrapure water was circulated in the intermediate chamber between the cathode chamber and the two cation exchange membranes. The current density was gradually increased until a final current density of 30 A / dm was achieved. ２ Electrolysis was carried out continuously while maintaining the temperature at 40°C. During the electrolysis, an aqueous solution of ethyltrimethylammonium chloride was replenished so that the ethyltrimethylammonium chloride concentration in the source chamber was maintained at 40 mass% or more. When the ETMAH concentration in the cathode chamber increased to 30 mass%, the electrolysis was terminated to obtain an aqueous ETMAH solution. This aqueous ETMAH solution was diluted with ultrapure water to the concentrations shown in Table 1 and used in Reference Examples 1, 2, 12, 13, and 14 and Examples 1 and 10.

[0045] PTMAH and BTMAH were prepared in the same manner as ETMAH, except that propyl chloride and butyl chloride were used as the alkyl halides, respectively. Furthermore, the ETMAH used in Reference Example 3 was obtained in Reference Examples 1, 2, 12, 13, and 14 in the same manner as the ETMAH used in Examples 1 and 10, except that the number of cation exchange membranes in FIG. 1 was reduced from two to one, and an electrolytic cell without an intermediate chamber was used. Furthermore, a surfactant listed in Table 1 was added in Reference Examples 14 to 16 and Comparative Example 2, a corrosion inhibitor listed in Table 1 was added in Examples 1 to 13 and Comparative Example 3, and an amine listed in Table 1 was added in Example 13.

[0046] [Evaluation Method] 1) Measurement of Halide Ion Concentration When the quaternary ammonium hydroxide concentration of the alkaline aqueous solution was 5% by mass or less, the solution was passed directly, or when it exceeded 5% by mass, the solution was diluted with ultrapure water to 5% by mass and passed through a 2.5 cc Onguard Cartridge IIH+ (manufactured by Thermo Fisher Scientific). Thereafter, the solution was recovered, and anion analysis of the recovered solution was performed using an ion chromatograph (Integrion, manufactured by Thermo Fisher Scientific) to determine the halide ion concentration.

[0047] 2) Hydroxide ion concentration Neutralization titration of 1 mL of the aqueous solution prepared in each of the examples and comparative examples with 0.1 mol / L hydrochloric acid was performed using a Hiranuma automatic titrator (COM-1700, manufactured by HIRANUMA). The hydroxide ion concentration of the alkaline aqueous solution was calculated from the amount of 0.1 mol / L hydrochloric acid required for neutralization.

[0048] 3) Acute Oral Toxicity Data on the median lethal dose (LD50) was collected from toxicity tests using rats. For materials for which data was not disclosed, toxicity tests based on OECD TG420 Acute Oral Toxicity were conducted to obtain data. The obtained LD50 was converted to 100% by mass of quaternary ammonium hydroxide aqueous solution, and evaluation was performed based on the following criteria. When two or more types of quaternary ammonium hydroxide aqueous solutions were mixed, the LD50 of each quaternary ammonium hydroxide aqueous solution was multiplied by the mixing ratio and the sum was calculated. The results are shown in Table 1. A: LD50 greater than 300 mg / kg B: LD50 greater than 50 mg / kg to 300 mg / kg or less C: LD50 or less A rating of A or B indicates a low-toxicity alkaline aqueous solution for semiconductors, with A being preferable.

[0049] 4) Ecotoxicity (Acute) Data on the 50% effective concentration (EC50) in the Daphnia acute immobilization test was collected. For samples without disclosed data, toxicity tests were conducted based on the OECD TG202 Daphnia acute immobilization test to obtain data. The obtained LC50 was converted to 100% by mass of quaternary ammonium hydroxide aqueous solution, and evaluation was performed based on the following criteria. When two or more quaternary ammonium hydroxide aqueous solutions were mixed, the LC50 of each quaternary ammonium hydroxide aqueous solution was multiplied by the mixing ratio and the sum was calculated. The results are shown in Table 1. A: 50% effective concentration greater than 10 mg / L B: 50% effective concentration greater than 3 mg / L to 10 mg / L or less C: 50% effective concentration less than 3 mg / L A rating of A or B indicates a low-toxicity alkaline aqueous solution, with an A rating being preferable. Furthermore, even if the ecotoxicity rating is C, if the acute oral toxicity rating is A or B, it can be evaluated as low-toxic.

[0050] 5) Development Test: A 4-inch silicon wafer was prepared and its surface was cleaned with sulfuric acid-hydrogen peroxide (volume ratio 4:1). It was then baked on a hot plate at 200°C for 60 seconds. A positive photoresist (novolac resin) was then applied to the silicon wafer using a spinner, yielding a positive photoresist film with a film thickness of 3.5 μm. The photoresist film was then irradiated with g-, h-, and i-rays with wavelengths of 300 to 500 μm through a mask pattern, after which various alkaline aqueous solutions were dropped onto it. The development time was 8 or 12 minutes, and the wafer was left to stand at 23°C. Afterwards, the wafer was washed with ultrapure water and dried, yielding a 20 μm contact hole pattern. The presence or absence of scum and the shape of the resulting resist pattern were confirmed using an SEM, and evaluated based on the following criteria. The results are shown in Table 2. A: No scum was generated at both 8-minute and 12-minute development times, and the side walls of the recesses in the pattern were upright. B: After 8 minutes of development, scum was observed in some of the recesses, but after 12 minutes of development, no scum was generated and the side walls of the recesses in the pattern were upright. C: After 8 minutes of development, scum was generated and / or the side walls of the recesses in the pattern were not upright. A rating of A is preferable for a developer for semiconductors, but even a rating of B can be used under appropriate conditions.

[0051] 6) Corrosion Test 100 mL of an alkaline aqueous solution was prepared, and a 2 x 2 cm aluminum piece was immersed in it at 25°C for 10 minutes, after which the aluminum piece was rinsed with pure water. The amount of corrosion (amount dissolved) was determined from the change in mass before and after treatment, and the corrosion rate was determined by dividing this by the immersion time in the alkaline aqueous solution. The obtained corrosion rates were evaluated based on the following criteria: A: Corrosion rate less than 1 nm / min B: Corrosion rate 1 nm / min or more but less than 10 nm / min C: Corrosion rate 10 nm / min or more From the viewpoint of corrosion inhibition, an A rating is preferable.

[0052] 1: Anode 2: Cathode 3: Power supply 4: Anode chamber 5: Raw material chamber 6: Intermediate chamber 7: Cathode chamber 8: Anion exchange membrane 9: Cation exchange membrane

Claims

1. An alkaline aqueous solution containing the following (A) to (E): (A) a quaternary ammonium ion represented by the following formula (1); (B) a halide ion; (C) a hydroxide ion; (D) water; and (E) a corrosion inhibitor. (In the formula, R １ , R ２ , R ３ , and R ４ are each independently an alkyl group having 1 to 16 carbon atoms, provided that R １ , R ２ , R ３ , and R ４ Among these, at least one alkyl group has 2 to 16 carbon atoms.

2. R in the above formula (1) １ , R ２ , R ３ , and R ４ The alkaline aqueous solution according to claim 1 , wherein not all of are the same alkyl group.

3. R ​​in the above formula (1) １ , R ２ , and R ３ is a methyl group, and R ４ The alkaline aqueous solution according to claim 1, wherein is an alkyl group having 2 to 16 carbon atoms.

4. The alkaline aqueous solution according to any one of claims 1 to 3, wherein the (B) halide ion is a chloride ion or a bromide ion.

5. The alkaline aqueous solution according to any one of claims 1 to 4, wherein the mass parts of the halide ions are 0.0000001 to 0.01 parts by mass when the mass of the hydroxide ions in the alkaline aqueous solution is taken as 1 part by mass.

6. The alkaline aqueous solution according to any one of claims 1 to 5, in which an LD50 value calculated based on 100 mass% of the hydroxide of the quaternary ammonium ion in a toxicity test using rats based on the OECD TG420 acute oral toxicity test exceeds 50 mg / kg.

7. The alkaline aqueous solution according to any one of claims 1 to 6, which has an EC50 value calculated assuming that the hydroxide of the quaternary ammonium ion is 100 mass% and exceeds 3 mg / L in an OECD TG202 Daphnia acute immobilization test.

8. The alkaline aqueous solution according to any one of claims 1 to 7, further comprising one or more compounds selected from the group consisting of alcohols and amines.

9. The alkaline aqueous solution according to any one of claims 1 to 8, further comprising a surfactant, the concentration of the surfactant in the alkaline aqueous solution being less than 100 ppm by mass.

10. The alkaline aqueous solution according to any one of claims 1 to 9, wherein the corrosion inhibitor (E) is at least one member selected from the group consisting of azoles, alkyne compounds, and aromatic hydroxy compounds.

11. A method for using the alkaline aqueous solution according to any one of claims 1 to 10 as a low-toxicity alkaline aqueous solution for semiconductors.

12. A method for producing an alkaline aqueous solution according to any one of claims 1 to 10, comprising an electrolysis step of electrolyzing an aqueous solution of a quaternary ammonium halide containing the following (A), (B), and (D), and a step of adding (E) a corrosion inhibitor to the aqueous solution obtained in the electrolysis step: (A) a quaternary ammonium ion represented by the following formula (1): (B) a halide ion; and (D) water. (In the formula, R １ , R ２ , R ３ , and R ４ are each independently an alkyl group having 1 to 16 carbon atoms, provided that R １ , R ２ , R ３ , and R ４ Among these, at least one alkyl group has 2 to 16 carbon atoms.

13. The method for producing an alkaline aqueous solution according to claim 12, further comprising a preparation step of preparing the aqueous quaternary ammonium halide solution prior to the electrolysis step, the preparation step being a step of reacting a trialkylamine with an alkyl halide in ultrapure water to obtain the aqueous quaternary ammonium halide solution.

Images