Alkaline aqueous solution for semiconductor, method for use as low-toxicity alkaline aqueous solution for semiconductor, and method for producing alkaline aqueous solution for semiconductor

Abstract

An alkaline aqueous solution for a semiconductor, said solution comprising (A)-(D). (A) A quaternary ammonium ion represented by formula (1), (B) a halide ion, (C) a hydroxide ion, and (D) water (in the formula, R1, R2, R3, and R4 are each independently an alkyl group having 1-16 carbon atoms. However, the number of carbon atoms of one or more alkyl groups among R1, R2, R3 and R4 is 2-16.)

Description

Alkaline aqueous solution for semiconductors, method for using it as a low-toxicity alkaline aqueous solution for semiconductors, and method for producing alkaline aqueous solution for semiconductors

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

[0002] Quaternary ammonium compounds are used as phase transfer catalysts, surfactants, disinfectants, etc. Among quaternary ammonium compounds, tetramethylammonium hydroxide, in particular, is a type of organic alkali that exhibits strong basicity and is used 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 wt % tetramethylammonium hydroxide, which contains metal ions and halogen ions at predetermined values.

[0004] Japanese Patent Application Publication No. 4-226466

[0005] 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 for semiconductors. Another object of the present invention is to provide a method for using the low-toxicity alkaline aqueous solution for semiconductors. Another object of the present invention is to provide a method for producing the low-toxicity alkaline aqueous solution for semiconductors.

[0006] The present inventors have conducted extensive research to obtain a low-toxicity alkaline aqueous solution for semiconductors, and as a result have found that an alkaline aqueous solution for semiconductors containing a specific quaternary ammonium ion, a halide ion, a hydroxide ion, and water has low toxicity, leading to the completion of the present invention.

[0007] That is, the present invention is configured as follows: Item 1: An alkaline aqueous solution for semiconductors, comprising the following (A) to (D): (A) a quaternary ammonium ion represented by the following formula (1), (B) a halide ion, (C) a hydroxide 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, 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 for semiconductors according to Item 1, wherein not all of R in formula (1) are the same alkyl group. １ , R ２ , and R ３ is a methyl group, and R ４Item 4. The alkaline aqueous solution for semiconductor use 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 for semiconductor use according to any one of Items 1 to 4, wherein the parts by mass of the halide ion are 0.0000001 to 0.01 parts by mass when the mass of the hydroxide ion in the alkaline aqueous solution for semiconductor use is 1 part by mass. Item 6. The alkaline aqueous solution for semiconductor use according to any one of Items 1 to 5, wherein the LD50 value calculated assuming that the hydroxide of the quaternary ammonium ion is 100% by mass 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 for semiconductors according to any one of Items 1 to 6, wherein the EC50 value, calculated assuming that the hydroxide of the quaternary ammonium ion is 100 mass %, exceeds 3 mg / L in an OECD TG202 Daphnia acute immobilization test. Item 8: The alkaline aqueous solution for semiconductors 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 for semiconductors according to any one of Items 1 to 8, further comprising a surfactant, the concentration of the surfactant in the alkaline aqueous solution for semiconductors being less than 100 mass ppm. Item 10: A polishing composition comprising the alkaline aqueous solution for semiconductors according to any one of Items 1 to 9 and abrasive grains. Item 11: A method for using the alkaline aqueous solution for semiconductors according to any one of Items 1 to 9 as a low-toxicity alkaline aqueous solution for semiconductors. Item 12: A method for producing the alkaline aqueous solution for semiconductors according to any one of Items 1 to 7, comprising an electrolysis step of electrolyzing an aqueous solution of a quaternary ammonium halide containing the following (A), (B), and (D): (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 R４ wherein one or more alkyl groups have 2 to 16 carbon atoms.) Item 13. The method for producing an alkaline aqueous solution for semiconductors 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.

[0008] According to the present invention, a low-toxicity alkaline aqueous solution for semiconductors is provided. As a result, an alkaline aqueous solution for semiconductors 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 semiconductors is provided. Furthermore, a method for producing the low-toxicity alkaline aqueous solution for semiconductors is provided.

[0009] FIG. 2 is an explanatory diagram showing an electrolytic cell.

[0010] 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.

[0011] 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.

[0012] The alkaline aqueous solution for semiconductors of the present invention contains the following (A) to (D): (A) a quaternary ammonium ion represented by the following formula (1), (B) a halide ion, (C) a hydroxide 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 (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).

[0013] By including the quaternary ammonium ion represented by the formula (1) above, the alkaline aqueous solution for semiconductors tends to be less toxic than an alkaline aqueous solution for semiconductors that uses tetramethylammonium hydroxide. Furthermore, by including the quaternary ammonium ion represented by the formula (1) above, the etching rate can 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, and the etching rate may decrease. １ ~R ４ If the number of carbon atoms exceeds the above range, the quaternary ammonium halide described below becomes difficult to dissolve, which may make it difficult to produce an alkaline aqueous solution for semiconductors.

[0014] In terms of low toxicity, etching rate, and ease of preparation of an alkaline aqueous solution for semiconductors, 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, it is preferable that R is any of the quaternary ammonium ions shown in (1) to (3) below. 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 mentioned above. 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, as described below. 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, as described below. Among these, quaternary ammonium ions in which the remaining two alkyl groups have 2 to 8 carbon atoms are more preferred, those in which the remaining two alkyl groups have 2 to 4 carbon atoms are even more preferred, and those in which the remaining two alkyl groups have 3 or 4 are most preferred. 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 Among these, quaternary ammonium ions in which the remaining three alkyl groups have 2 to 8 carbon atoms are more preferred, those in which the remaining three alkyl groups have 2 to 4 carbon atoms are even more preferred, and those in which the remaining three alkyl groups have 3 or 4 carbon atoms are most preferred.

[0015] 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.

[0016] 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, butyltrimethylammonium ion, etc. These quaternary ammonium ions may be used alone or in combination.

[0017] 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.

[0018] The amount of halide ions in an alkaline aqueous solution for semiconductors in parts by mass, when the mass of hydroxide ions is taken as 1 part by mass, 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 parts by mass varies greatly depending on the method for producing an alkaline aqueous solution for semiconductors; in particular, a solution with reduced halide ions can be prepared by using a production method that involves 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.

[0019] Having the halide ion content in the above range is desirable because, when the alkaline aqueous solution for semiconductors is used as a semiconductor processing liquid, such as an etching liquid 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 for semiconductors 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 temperature for the etching method can be, for example, 25 to 90°C, preferably 30 to 80°C.

[0020] The parts by mass of halide ions in an alkaline aqueous solution for semiconductors 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 for semiconductors into an ion chromatography for anions, the cations in the alkaline aqueous solution are exchanged for 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.

[0021] The alkaline aqueous solution for semiconductors contains hydroxide ions. The fact that the alkaline aqueous solution for semiconductors contains quaternary ammonium ions represented by the above formula (1) and hydroxide ions can also be said to indicate that the alkaline aqueous solution for semiconductors contains quaternary ammonium hydroxide containing quaternary ammonium ions represented by the above formula (1) and hydroxide ions. The inclusion of quaternary ammonium hydroxide allows the alkaline aqueous solution for semiconductors to be used as a processing liquid during semiconductor manufacturing.

[0022] The concentrations of the quaternary ammonium ions represented by the above formula (1) and hydroxide ions in the alkaline aqueous solution for semiconductors are not particularly limited, and it is preferable to produce an alkaline aqueous solution for semiconductors containing 1.0 to 65.0 mass% 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 for semiconductors 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.

[0023] The concentration of the quaternary ammonium ion represented by formula (1) in the alkaline aqueous solution for semiconductors is preferably 0.8 to 61.7 mass%. It is more preferably 0.8 to 9.5 mass%, and even more preferably 1.2 to 6.7 mass%. The concentration of the quaternary ammonium ion in the high-concentration quaternary ammonium hydroxide before dilution is preferably 8.0 to 47.5 mass%, and even more preferably 16.0 to 38.0 mass%. The concentration of the hydroxide ion in the alkaline aqueous solution for semiconductors is preferably 0.05 to 10.6 mass%, and even more preferably 0.05 to 1.6 mass%, and even more preferably 0.1 to 1.2 mass%. The concentration of the hydroxide ion in the high-concentration quaternary ammonium hydroxide is preferably 0.5 to 8.0 mass%, and even more preferably 1.0 to 6.4 mass%.

[0024] The alkaline aqueous solution for semiconductors 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 99.0 mass%, more preferably 93.0 to 98.0 mass%, and even more preferably 97.0 to 98.0 mass%.

[0025] The alkaline aqueous solution for semiconductors 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 for semiconductors is not particularly limited, but is preferably 0.1 to 10,000 ppm by mass, and more preferably 0.1 to 100 ppm 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 increase the likelihood of adsorption inhibition during semiconductor processing.

[0026] 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. The valence of the amine is also 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 semiconductor processing.

[0027] The alkaline aqueous solution for semiconductors may contain a surfactant. The concentration of the surfactant in the alkaline aqueous solution for semiconductors is preferably less than 100 ppm by mass. The semiconductor processing solution may not contain a surfactant. The quaternary ammonium ion represented by formula (1) contained in the alkaline aqueous solution for semiconductors 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 for semiconductors 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 for semiconductors, 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 quaternary ammonium hydroxide is recovered from a used alkaline aqueous solution for semiconductors by separation, purification, etc., and then reused, if a surfactant is required for the alkaline aqueous solution for semiconductors, it must be added again. However, if a surfactant is not required, the recovered solution can be used as is as the alkaline aqueous solution for semiconductors. Furthermore, if a low surfactant concentration is acceptable, this is preferable because the amount of surfactant added again can be reduced. 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. Note that the surfactant is a compound different from the compound containing the quaternary ammonium ion that may be contained in the alkaline aqueous solution for semiconductors.

[0028] To evaluate the toxicity of alkaline aqueous solutions for semiconductors, in toxicity tests using rats based on OECD TG420 acute oral toxicity, the median lethal dose (LD50) value, calculated with the hydroxide of the quaternary ammonium ion as 100% by mass, preferably exceeds 50 mg / kg. This enhances 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 exceeding 50 mg / kg is preferable. 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).

[0029] As a toxicity evaluation of an alkaline aqueous solution for semiconductors, 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).

[0030] 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.

[0031] The alkaline aqueous solution for semiconductors can be used as a processing solution during semiconductor production, such as an etching solution, a cleaning solution, or a developing solution. That is, the alkaline aqueous solution of the present invention can be used to produce semiconductors. Furthermore, the alkaline aqueous solution for semiconductors can be used as a low-toxicity alkaline aqueous solution for semiconductors. That is, one aspect of the present invention is a method of using the alkaline aqueous solution for semiconductors of the present invention as a low-toxicity alkaline aqueous solution for semiconductors.

[0032] In addition, as another embodiment of the alkaline aqueous solution for semiconductors of the present invention, it can be used as a constituent component of a chemical mechanical polishing (CMP) composition (polishing composition). Conventionally commonly used inorganic bases such as sodium hydroxide and potassium hydroxide have concerns about metal ion contamination during use, while the organic base tetramethylammonium hydroxide (TMAH) is highly toxic, so it is subject to strict regulations regarding storage and transportation, and also places a heavy burden on the environment in terms of waste liquid treatment after use. In contrast, the alkaline aqueous solution for semiconductors of the present invention is low in toxicity, so the above problems are less likely to occur when preparing and using a polishing composition using it.

[0033] The polishing composition of this embodiment contains the alkaline aqueous solution for semiconductors and abrasive grains. The conditions for the alkaline aqueous solution for semiconductors used in the polishing composition of this embodiment can be the same as those described above. The quaternary ammonium ion represented by formula (1) is preferably one having two types of alkyl groups. In this embodiment, the R １ , R ２ , R ３ , and R ４ When three of the alkyl groups are methyl groups and the remaining alkyl group has 2 to 16 carbon atoms, not only can a low-toxicity polishing composition be prepared, but also a good polishing rate and improved appearance after polishing can be achieved. Among these, quaternary ammonium ions in which the remaining alkyl group has 2 to 8 carbon atoms are more preferred, with quaternary ammonium ions in which 2, 3, or 4 carbon atoms being even more preferred, and 3 or 4 being most preferred. Two or more types of quaternary ammonium ions represented by formula (1) may also be used in combination, and 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).

[0034] The amount of hydroxide having a quaternary ammonium ion contained in the alkaline aqueous solution for semiconductors used in the polishing composition of this embodiment is not particularly limited, but it is preferable to adjust the concentration and mixing amount of the alkaline aqueous solution for semiconductors so that the amount of hydroxide of the quaternary ammonium ion represented by formula (1) in the polishing composition is usually 0.0001 to 15 parts by mass, preferably 0.005 to 10 parts by mass, and more preferably 0.01 to 5 parts by mass.

[0035] The parts by mass of halide ions contained in the alkaline aqueous semiconductor solution used in the polishing composition of this embodiment are not particularly limited, but the mass of hydroxide ions 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, per part by mass of hydroxide ions, which can also reduce contamination of the workpiece during CMP processing. The pH (25°C) range of the polishing composition may be appropriately selected depending on the intended use, but is not limited, for example, when polishing silicon wafers, it may usually be used at 8 to 12, preferably 9 to 11, and for example, a polishing composition containing an oxidizing agent may usually be used at a pH of 1 to 8, preferably 2 to 7.

[0036] The polishing composition of this embodiment contains abrasive grains, and examples of abrasive grains that can be used in aqueous polishing compositions include inorganic particles, organic particles, and organic-inorganic composite particles. Examples of inorganic particles include silicon dioxide, aluminum oxide, cerium oxide, titanium oxide, silicon nitride, and zirconium oxide. Among these, examples of silicon dioxide that can be used include fumed silica and colloidal silica. Examples of organic particles include styrene copolymers, (meth)acrylic copolymers, and polyimides. Known materials can be used as appropriate for these abrasive grains. The average particle size of the abrasive grains can be appropriately selected depending on the application and is not particularly limited. For example, the average primary particle size can be, for example, 10 to 50 nm, preferably 20 to 40 nm. The average primary particle size of the abrasive grains can be determined, for example, by the specific surface area S (m ) measured by the BET method. ２ / g), the average primary particle size (nm) can be calculated using the formula: average primary particle size (nm) = 2727 / S. Measurement of the specific surface area of ​​the abrasive grains can be carried out using, for example, a surface area measuring device manufactured by Micromeritics, trade name "Flow Sorb II 2300." The average secondary particle size of the abrasive grains can be, for example, 10 to 200 nm, preferably 20 to 150 nm. The average secondary particle size of the abrasive grains can be measured as the volume-average particle size by dynamic light scattering using, for example, a model "UPA-UT151" manufactured by Nikkiso Co., Ltd.

[0037] The amount of abrasive grains in the polishing composition of this embodiment is not particularly limited, but is, for example, 0.01 to 20% by mass, preferably 0.03 to 15% by mass, and more preferably 0.05 to 10% by mass relative to the polishing composition. The polishing composition of this embodiment may optionally contain an oxidizing agent, a chelating agent, a surfactant, a water-soluble compound, etc. Examples of oxidizing agents include hydrogen peroxide, peracetic acid, perbenzoic acid, perchloric acid, organic peroxides, nitric acid compounds, persulfates, and salts of polyvalent metals such as cerium ammonium nitrate, as well as heteropolyacids such as silicotungstic acid and silicomolybdic acid. These may be used alone or in combination of two or more. When the polishing composition of this embodiment contains an oxidizing agent, the amount of the oxidizing agent in the polishing composition is not particularly limited, but is, for example, 0.001 to 50% by mass, preferably 0.01 to 30% by mass, and more preferably 0.05 to 25% by mass relative to the polishing composition. Examples of chelating agents include aminocarboxylic acid-based and phosphonic acid-based chelating agents. Examples of surfactants include the nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants described above. These surfactants may be used alone or in combination of two or more. When the polishing composition of this embodiment contains an oxidizing agent, the amount of chelating agent in the polishing composition is not particularly limited, but is, for example, 0.0001 to 1 mass %, preferably 0.001 to 0.5 mass %, and more preferably 0.005 to 0.1 mass %, relative to the polishing composition. Examples of water-soluble compounds include hydroxyethyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, glycerin, polyglycerin, polyvinyl alcohol, and polyethylene glycol. These surfactants may be used alone or in combination of two or more. When the polishing composition of this embodiment contains a water-soluble compound, the amount of the water-soluble compound in the polishing composition is not particularly limited, but is, for example, 0.001 to 10 mass %, preferably 0.003 to 3 mass %, and more preferably 0.005 to 0.5 mass % of the polishing composition. The polishing composition of this embodiment contains the alkaline aqueous solution for semiconductors and abrasive grains, and the remainder of the polishing composition other than the abrasive grains, the above-mentioned components, and other optional additives is the alkaline aqueous solution for semiconductors.The polishing composition of this embodiment may be used as it is, or may be prepared and then diluted with water before use. The polishing composition of this embodiment may be applied to any wafer, including, but not limited to, silicon wafers, SiC wafers, GaN wafers, GaAs wafers, GaP wafers, glass wafers, aluminum wafers, and sapphire wafers.

[0038] Although the method for producing an alkaline aqueous solution for semiconductors is not particularly limited, it is preferable to obtain the solution by electrolyzing an aqueous quaternary ammonium halide solution from the viewpoint of suppressing the halide ion concentration. That is, it is preferable to include an electrolysis step of electrolyzing an aqueous quaternary ammonium halide solution. Specifically, it is preferable to include an electrolysis step of electrolyzing an aqueous quaternary ammonium halide 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).

[0039] To produce an alkaline solution for semiconductors 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 solution as a raw material, and a base chamber (cathode chamber) for producing a quaternary ammonium hydroxide solution. In this production method using an electrolytic cell, quaternary ammonium ions contained in the quaternary ammonium halide solution pass through the cation exchange membrane disposed on the cathode side during electrolysis. This produces a quaternary ammonium hydroxide 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 solution.

[0040] 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.

[0041] The method for producing an alkaline aqueous solution for semiconductors 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.

[0042] 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 formula (1). Specifically, the alkyl groups contained in the trialkylamine and the alkyl halide can be those in which at least one alkyl group has 2 to 16 carbon atoms (preferably 2 to 8, more preferably 2 to 4), and the remaining alkyl groups have 1 to 16 carbon atoms (preferably 1 to 8, more preferably 1 to 4). The halide ion, which is the anion of the alkyl halide, can be the same as that described in (B) above. Because impurities contained in the quaternary ammonium halide diffuse into and become mixed into the aqueous quaternary ammonium hydroxide solution, it is preferable to use a high-purity quaternary ammonium halide. Specifically, the alcohol concentration in the aqueous quaternary ammonium halide solution is preferably 0.1 to 10,000 ppm by mass, and the amine concentration is preferably 0.1 to 10,000 ppm by mass.

[0043] 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.

[0044] (Examples 1 to 13, Comparative Example 1) [Alkaline aqueous solution for semiconductors] Aqueous solutions of quaternary ammonium hydroxides were prepared to the concentrations shown in Table 1, and various evaluations were carried out. 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) [Surfactants] Surfynol (registered trademark) 465 (manufactured by Nissin Chemical Industry Co., Ltd.)

[0045] [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.

[0046] 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 and used in Examples 1, 2, 12, and 13 at the concentrations shown in Table 1.

[0047] 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 Example 3 was obtained in the same manner as the ETMAH used in Examples 1, 2, 12, 13, and 14, 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, in Examples 14 to 16 and Comparative Example 2, surfactants listed in Table 1 were added. Furthermore, the amine concentrations in the alkaline aqueous solutions of Examples 1 to 16 and Comparative Examples 1 and 2 were all less than 100 ppm by mass. Furthermore, the alcohol concentrations in the alkaline aqueous solutions of Examples 1 to 16 and Comparative Examples 1 and 2 were all less than 100 ppm by mass.

[0048] [Evaluation Method] 1) Measurement of Halide Ion Concentration When the quaternary ammonium hydroxide concentration of the alkaline aqueous solution for semiconductors 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.

[0049] 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 aqueous alkaline solution for semiconductors was calculated from the amount of 0.1 mol / L hydrochloric acid required for neutralization.

[0050] 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 mg / kg or less Low-toxicity alkaline aqueous solutions for semiconductors are preferably rated A or B, with A being more preferred.

[0051] 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 to B indicates a low-toxicity alkaline aqueous solution for semiconductors, with an A rating being preferable. Furthermore, even if the ecotoxicity rating is C, if the acute oral toxicity rating is A to B, it can be evaluated as low-toxic.

[0052] 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 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 for semiconductors were dropped onto the wafer. The development time was 8 or 12 minutes, and the wafer was left to stand at 23°C. After rinsing with ultrapure water and drying, a 20 μm contact hole pattern was obtained. 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.

[0053] 6) Etching Test 100 mL of an alkaline aqueous solution for semiconductors was prepared and heated to 40°C, and a 2 x 2 cm silicon single crystal substrate (100-sided silicon) was immersed in the solution for 10 minutes. The amount of etching was calculated from the change in mass before and after etching, and the silicon etching rate was calculated by dividing this by the etching time. The obtained etching rates were evaluated based on the following criteria. The results are shown in Table 1. A: Etching rate of 50 nm / min or more B: Etching rate of 10 nm / min or more but less than 50 nm / min C: Etching rate of 1 nm / min or more but less than 10 nm / min D: Etching rate of less than 1 nm / min As an etching solution for semiconductors, a rating of A to C indicates that the solution can be used as an etching solution for semiconductors, with a rating of A to B being preferred, and a rating of A being more preferred. In addition, the surface of the silicon substrate after etching was observed using a field emission scanning electron microscope (JSM-7800F Prime, manufactured by JEOL Ltd.) to confirm the presence or absence of surface roughness, and the evaluation was based on the following criteria. The surface roughness is ranked from A to D in descending order, with ratings A to C being acceptable levels, with ratings A to B being preferred, and rating A being more preferred. A: No surface roughness is observed. B: Slight surface roughness is observed (surface roughness is less than 30% of the entire surface). C: Roughness is observed over the entire surface (surface roughness is 30 to 100% of the entire surface). D: Roughness is observed over the entire surface, and the roughness is severe (irregularities larger than 1 x 1 μm are present).

[0054] <Preparation of Polishing Composition> Colloidal silica (primary particle diameter 35 nm, secondary particle diameter 70 nm) as abrasive grains was mixed and dispersed in water using a stirrer to prepare a slurry with a colloidal silica concentration of 4 mass%. 50 parts by mass of this slurry, 40 parts by mass of ultrapure water, and 10 parts by mass of an alkaline aqueous solution of a quaternary ammonium hydroxide compound shown in Table 3, which had been previously adjusted to 1.5 mass% (7.5 parts by mass in Examples 20 and 21), were mixed to prepare a polishing composition with the composition shown in Table 3. (Polishing) A 4-inch p-type low-resistivity silicon substrate (100 surface) was polished under the following conditions. (Polishing Conditions) Polishing machine: EJ-380IN manufactured by Engis Polishing pressure: 100 gf / cm２ Polishing pad: SUBA-800, Nitta Haas Corporation Platen rotation speed: 100 rpm Supply amount of polishing composition: 200 ml / min Polishing time: 20 minutes In the evaluation of the characteristics of the polished surface, the polishing rate was calculated by measuring the mass before and after polishing and using the following formula: Polishing rate = (substrate mass before polishing - substrate mass after polishing) / polished area of ​​substrate / density / polishing time Appearance confirmation: Evaluation results by projection observation of the surface: ○: Good upon confirmation; △: Slight polishing marks can be confirmed upon confirmation; ×: Clear polishing scratches can be confirmed. When a polishing composition using the alkaline aqueous semiconductor solution of the present invention is used to perform CMP processing on a silicon substrate, a practical polishing rate is achieved, and the halide ion concentration is low, reducing the risk of contamination of the workpiece. TMAH shown in Experimental Example 23 is highly toxic and presents handling issues. Furthermore, among low-toxicity quaternary ammonium ions, those with a quaternary ammonium structure that differs only in part in its structure exhibited good polishing rates.

[0055] 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 for semiconductors, comprising the following (A) to (D): (A) a quaternary ammonium ion represented by the following formula (1); (B) a halide ion; (C) a hydroxide 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.

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

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

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

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

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

7. The alkaline aqueous solution for semiconductors 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 swimming inhibition test.

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

10. A polishing composition comprising the alkaline aqueous solution for semiconductors according to any one of claims 1 to 9 and abrasive grains.

11. A method for using the alkaline aqueous solution for semiconductors according to any one of claims 1 to 9 as a low-toxicity alkaline aqueous solution for semiconductors.

12. A method for producing an alkaline aqueous solution for semiconductors according to any one of claims 1 to 7, comprising an electrolysis step of electrolyzing an aqueous solution of a quaternary ammonium halide containing the following (A), (B), and (D): (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 for semiconductors according to claim 12, further comprising a preparation step of preparing the aqueous solution of a quaternary ammonium halide 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 solution of a quaternary ammonium halide.

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