Method for producing quaternary alkylammonium hypobromite solution and method for treating semiconductor wafer

Abstract

A method for producing a quaternary alkylammonium hypobromite solution comprising: a preparation step in which a quaternary alkylammonium hydroxide solution is prepared in a reaction vessel; and a reaction step in which the quaternary alkylammonium hydroxide solution is brought into contact with liquid bromine and / or bromine gas in the reaction vessel.

Description

Method for producing quaternary alkylammonium hypobromite solution and method for treating semiconductor wafers

[0001] The present disclosure relates to a method for producing a quaternary alkylammonium hypobromite solution and a method for treating semiconductor wafers.

[0002] In recent years, the miniaturization of semiconductor device design rules has led to increasingly stringent requirements for impurity control in semiconductor device manufacturing processes. Because the impurities generated during semiconductor device manufacturing vary from process to process, it is important to identify the source of contamination for each process and to control the concentration of those contaminants. Furthermore, to improve semiconductor device manufacturing efficiency, large-diameter semiconductor wafers exceeding 300 mm are being used. Large-diameter semiconductor wafers have larger edge and backside areas where electronic devices are not fabricated compared to small-diameter semiconductor wafers. Therefore, during processes for forming metal wiring and barrier metal, metal wiring materials and barrier metal materials (hereinafter sometimes collectively referred to as "metal materials, etc.") are more likely to adhere not only to the surface of the semiconductor wafer where semiconductor devices are formed, but also to the edge and backside of the wafer. As a result, the amount of excess metal materials adhering to the edge and backside of large-diameter semiconductor wafers is greater than that of small-diameter wafers.

[0003] Excess metal materials adhering to the edge or backside of a semiconductor wafer contaminate the manufacturing equipment as metal or metal oxide particles during oxygen ashing processes and plasma dry etching processes, which are processes that occur after the formation of metal wiring and barrier metals. This can lead to cross-contamination. Therefore, it is necessary to remove metal materials adhering to the edge or backside before carrying them to the next process. Among these metal materials, precious metals such as platinum and ruthenium are difficult to oxidize, dissolve, or remove during subsequent etching and cleaning processes. Therefore, it is preferable to remove these precious metals from semiconductor wafers prior to other metal materials. Ruthenium, in particular, is widely used as a wiring material for semiconductor device design rules of 10 nm or less because it can reduce resistance compared to copper. Therefore, rapid removal from unnecessary areas is desirable.

[0004] Patent Document 1 discloses that a quaternary alkylammonium hypochlorite solution can be suitably used as an etching solution or a cleaning solution for use in manufacturing semiconductor elements, and also discloses a method for producing a quaternary alkylammonium hypochlorite solution that exhibits little change in hypochlorite ion concentration over time and has excellent storage stability.

[0005] Furthermore, Patent Document 2 discloses a semiconductor processing solution containing hypobromite ions that can etch ruthenium. As a method for continuously producing a solution containing a halogen oxyacid such as hypochlorous acid or hypobromous acid, Patent Document 3 discloses a method for stably and efficiently producing a halogen oxyacid by continuously supplying an organic alkaline solution and a halogen.

[0006] International Publication No. 2019 / 225541 International Publication No. 2021 / 059666 International Publication No. 2021 / 210682

[0007] Patent Document 1 discloses batch-type reaction conditions for a method for producing a quaternary alkylammonium hypochlorite solution. However, no detailed discussion is provided regarding the use of bromine instead of chlorine as a raw material, i.e., the production of a quaternary alkylammonium hypobromite solution. Meanwhile, Patent Documents 2 and 3 disclose methods for producing solutions containing hypobromite ions and halogen oxygen acids, but do not provide detailed information regarding batch-type reaction conditions, particularly regarding the method for producing a quaternary alkylammonium hypobromite solution by directly reacting a quaternary alkylammonium hydroxide solution with liquid bromine and / or bromine gas, and there is a need for the development of a more efficient production method.

[0008] Furthermore, the present inventors have newly discovered a problem that when a quaternary alkylammonium hypobromite solution is produced by directly reacting a quaternary alkylammonium hydroxide solution with liquid bromine and / or bromine gas in a batchwise reaction, more precise control of the reaction conditions is required for efficient production, unlike when a quaternary alkylammonium hydroxide solution is reacted with chlorine.

[0009] That is, an object of the present disclosure is to provide an industrially advantageous method for producing a quaternary alkylammonium hypobromite solution.

[0010] As a result of extensive research to solve the above-mentioned problems, the inventors have inferred that the above-mentioned problems are caused by the lower reactivity of bromine compared to chlorine, and have found that production efficiency can be improved by controlling conditions such as the supply rate to specific conditions.The inventors have also found that the problems can be solved by reacting a quaternary alkylammonium hydroxide solution with liquid bromine and / or bromine gas in a specific manner.

[0011] That is, the gist of the present disclosure is specifically as follows. <1> A method for producing a quaternary alkylammonium hypobromite solution, comprising: a preparation step of preparing a quaternary alkylammonium hydroxide solution in a reaction vessel; and a reaction step of contacting the quaternary alkylammonium hydroxide solution with liquid bromine and / or bromine gas in the reaction vessel. <2> A method for producing a quaternary alkylammonium hypobromite solution according to <1>, wherein the supply rate of liquid bromine and / or bromine gas in the reaction step is 0.01 mmol / min to 500 mol / min per 1 L of the quaternary alkylammonium hydroxide solution. <3> A method for producing a quaternary alkylammonium hypobromite solution according to <1> or <2>, wherein the number of carbon atoms in the alkyl groups of the quaternary alkylammonium hydroxide independently is 1 to 10. <4> The method for producing a quaternary alkylammonium hypobromite solution according to any one of <1> to <3>, wherein the reaction temperature in the reaction step is 0°C or higher and 70°C or lower. <5> The method for producing a quaternary alkylammonium hypobromite solution according to any one of <1> to <4>, wherein the carbon dioxide concentration in the gas phase in the reaction step is 100 ppm by volume or lower. <6> The method for producing a quaternary alkylammonium hypobromite solution according to any one of <1> to <5>, wherein the pH at 23°C of the liquid phase in the reaction step is 10.5 or higher. <7> The method for producing a quaternary alkylammonium hypobromite solution according to any one of <1> to <6>, wherein the carbon dioxide concentration in the quaternary alkylammonium hydroxide solution in the reaction step is 500 ppm or lower. <8> The method for producing a quaternary alkylammonium hypobromite solution according to any one of <1> to <7>, wherein the reaction step includes a step of stirring the quaternary alkylammonium hydroxide solution with a stirring blade, and a step of contacting the quaternary alkylammonium hydroxide solution with liquid bromine under conditions where the tip speed of the stirring blade is 0.1 m / s to 20.0 m / s.<9> The method for producing a quaternary alkylammonium hypobromite solution according to any one of <1> to <7>, wherein the preparation step further comprises a gas preparation step of preparing liquid bromine and generating bromine gas from the liquid bromine, and wherein the reaction step involves contacting a quaternary alkylammonium hydroxide solution with the bromine gas generated in the gas preparation step. <10> The method for producing a quaternary alkylammonium hypobromite solution according to <9>, comprising a step of supplying an inert gas to the bromine gas generated in the gas preparation step and contacting the mixed gas of the bromine gas and the inert gas with a quaternary alkylammonium hydroxide solution. <11> The method for producing a quaternary alkylammonium hypobromite solution according to <10>, wherein the supply rate of the inert gas is 10 mL / min to 200 L / min. <12> A method for treating a semiconductor wafer, comprising treating a surface of a semiconductor wafer with a quaternary alkylammonium hypobromite solution obtained by the method according to any one of <1> to <11>. <13> The processing method according to <12>, wherein the semiconductor wafer is a semiconductor wafer containing at least one selected from the group consisting of copper, tungsten, tantalum, titanium, cobalt, ruthenium, molybdenum, chromium, manganese, aluminum, silicon, silicon oxide, and compounds thereof.

[0012] According to one embodiment of the present disclosure, production efficiency can be improved when a quaternary alkylammonium hydroxide solution is produced by directly reacting a quaternary alkylammonium hydroxide solution with liquid bromine and / or bromine gas through a batch reaction.

[0013] 1 is a schematic diagram showing one embodiment of a reaction apparatus used in a method for producing a quaternary alkylammonium hypobromite solution according to an embodiment of the present disclosure. 2 is a schematic diagram showing one embodiment of a reaction apparatus used in a method for producing a quaternary alkylammonium hypobromite solution according to an embodiment of the present disclosure. 3 is a schematic diagram showing one embodiment of a reaction apparatus used in a method for producing a quaternary alkylammonium hypobromite solution according to an embodiment of the present disclosure.

[0014] Although the embodiments of the present disclosure will be described in detail below, the present disclosure is not limited to these details as long as they do not deviate from the gist of the present disclosure. Furthermore, the present disclosure can be implemented with any modifications within the scope of the gist of the present disclosure.

[0015] 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 equal to or greater than A and equal to or less than B. In this specification, the units of concentration, "ppm" and "ppb," are based on mass unless otherwise specified.

[0016] One embodiment of the present disclosure is a method for producing a quaternary alkylammonium hypobromite solution, comprising: a preparation step of preparing a quaternary alkylammonium hydroxide solution in a reaction vessel; and a reaction step of contacting the quaternary alkylammonium hydroxide solution with liquid bromine and / or bromine gas in the reaction vessel. Herein, liquid bromine and / or bromine gas means "liquid bromine and bromine gas, as well as liquid bromine or bromine gas." Details are provided below.

[0017] <Preparation step of preparing a quaternary alkyl ammonium hydroxide solution> The method for preparing the quaternary alkyl ammonium hydroxide solution is not particularly limited, and may be prepared by a known method. For example, a desired amount of the quaternary alkyl ammonium hydroxide solution may be placed in an alkali-resistant resin flask.

[0018] <Quaternary alkyl ammonium hydroxide solution> The quaternary alkyl ammonium hydroxide solution is not particularly limited, and known solutions can be used. For example, the quaternary alkyl ammonium hydroxide solution may be an aqueous solution in which quaternary alkyl ammonium hydroxide is dissolved in water, or a solution in which quaternary alkyl ammonium hydroxide is dissolved in a non-aqueous solvent. The quaternary alkyl ammonium hydroxide solution can be obtained by dissolving a quaternary alkyl ammonium hydroxide solution in water or a non-aqueous solvent, or by diluting a commercially available quaternary alkyl ammonium hydroxide solution to the desired concentration. Examples of non-aqueous solvents include known organic solvents capable of dissolving quaternary alkyl ammonium hydroxide solutions. Specific examples include alcohols and glycols, with at least one non-aqueous solvent selected from the group consisting of methanol and propylene glycol being preferred. As the aqueous solvent, at least one aqueous solvent selected from the group consisting of water, distilled water, and ion-exchanged water is preferred because it is industrially easily available and can produce a high-purity quaternary alkyl ammonium hydroxide solution.

[0019] The solvent for the quaternary alkylammonium hydroxide solution may be prepared as an aqueous solution using only water as the solvent, or may be mixed with an organic solvent to form a non-aqueous solution. The solvent may be changed appropriately depending on the application of the quaternary alkylammonium hypobromite solution and the object to be cleaned. For example, when the object to be cleaned is ruthenium, sufficient cleaning can be achieved using only water as the solvent, so the solution may be prepared as an aqueous quaternary alkylammonium hydroxide solution.

[0020] The concentration of the quaternary alkylammonium hydroxide solution is not particularly limited, but if the concentration of the quaternary alkylammonium hydroxide solution becomes high, the salt will precipitate and become a solid. Therefore, the concentration of the quaternary alkylammonium hydroxide solution is preferably 0.01 to 30.0 mass%, more preferably 0.05 to 27.5 mass%, and even more preferably 0.1 to 25.0 mass%.

[0021] The quaternary alkylammonium hydroxide solution used in the reaction typically contains carbon dioxide derived from the atmosphere. Carbon dioxide exists in the solution as carbonate ions or bicarbonate ions. The carbon dioxide concentration in the quaternary alkylammonium hydroxide solution is not particularly limited, but is preferably 0.001 ppm to 500 ppm, more preferably 0.005 ppm to 300 ppm, and even more preferably 0.01 ppm to 100 ppm, calculated as carbonate ions. By ensuring that the carbon dioxide concentration in the quaternary alkylammonium hydroxide solution is 0.001 ppm to 500 ppm, pH changes in the resulting quaternary alkylammonium hypobromite solution can be suppressed. As a result, the storage stability of the quaternary alkylammonium hypobromite solution can be improved. Commercially available quaternary alkylammonium hydroxide solutions with such carbon dioxide concentrations can be used.

[0022] In this embodiment, the quaternary alkylammonium hydroxide solution is preferably a solution of a quaternary alkylammonium hydroxide having an alkyl group with 1 to 10 carbon atoms, and more preferably a solution of a quaternary alkylammonium hydroxide having 1 to 5 carbon atoms. Specific examples of quaternary alkylammonium hydroxide include at least one selected from the group consisting of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, ethyltrimethylammonium hydroxide, propyltrimethylammonium hydroxide, butyltrimethylammonium hydroxide, diethyldimethylammonium hydroxide, and triethylmethylammonium hydroxide. These quaternary alkylammonium hydroxides may be used alone or in combination of two or more. Furthermore, the four alkyl groups contained in the quaternary alkylammonium hydroxide may have the same number of carbon atoms or may be different from each other.

[0023] In the process of producing a quaternary alkylammonium hypobromite solution by reacting a quaternary alkylammonium hydroxide solution with liquid bromine and / or bromine gas, the pH of the solution containing the quaternary alkylammonium hypochlorite solution produced in the reaction vessel decreases. Considering the conditions of the filtration operation described below and the solubility of the quaternary alkylammonium hydroxide, in this embodiment, the lower limit of the pH of the raw material quaternary alkylammonium hydroxide solution is preferably 10.5 or higher, more preferably 11.0 or higher, even more preferably 11.5 or higher, and particularly preferably greater than 12.0. The upper limit of the pH of the quaternary alkylammonium hydroxide solution is not particularly limited and varies depending on the concentration of the quaternary alkylammonium hydroxide, but is, for example, 14.0 or lower. In this specification, pH is measured at 23°C unless otherwise specified.

[0024] Furthermore, the quaternary alkylammonium hydroxide solution used in this embodiment may contain metals as impurities. Specifically, the contents of sodium, potassium, aluminum, calcium, nickel, and zinc are preferably 0.01 ppb or more and 20 ppb or less, respectively. Note that the amount of metals contained in the quaternary alkylammonium hydroxide solution used may be less than 0.01 ppb, but such a quaternary alkylammonium hydroxide solution is not easy to obtain.

[0025] Therefore, by using a quaternary alkylammonium hydroxide solution in which the metal content satisfies the above range, the solution itself becomes easy to obtain, and the metal impurities can be easily removed or reduced by filtration during and after the production of the quaternary alkylammonium hypobromite solution. The reason why metal impurities can be removed or reduced by filtration is unclear, but it is thought to be as follows: When the amount of metal impurities is below the above lower limit, the metal impurities are thought to exist in a colloidal state that is difficult to remove by filtration. On the other hand, the presence of a certain amount of metal impurities is thought to generate impurity particles of a certain size rather than a colloidal state, making them removable by filtration. As a result, the quaternary alkylammonium hydroxide solution used in this embodiment can be suitably used even if it is not an ultra-high purity quaternary alkylammonium hydroxide solution, because the solid metal impurities can be removed or reduced by filtration due to the lowered pH. In order to further enhance this effect and further remove and reduce impurities that are alkaline and in the form of ions, the metal amounts of sodium, potassium, aluminum, magnesium, iron, nickel, copper, silver, cadmium, and lead contained in the quaternary alkylammonium hydroxide solution are preferably 0.01 ppb or more and 5 ppb or less, and even more preferably 0.01 ppb or more and 2 ppb or less.

[0026] Commercially available quaternary alkylammonium hydroxide solutions can be used as the above-mentioned quaternary alkylammonium hydroxide solutions. Among these, quaternary alkylammonium hydroxide solutions that have been highly purified by electrolysis and / or contact with ion exchange resins, etc. and are used as photoresist developers for semiconductor devices, are particularly suitable. These commercially available solutions can also be diluted with a solvent that does not contain metal impurities, such as ultrapure water, before use.

[0027] In addition to the quaternary alkylammonium hydroxide and the metal impurities, the quaternary alkylammonium hydroxide solution may contain other components to the extent that they do not impair the effects of the present disclosure. For example, the solution may 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 is not particularly limited, but is preferably 0.1 ppb by mass to 1.0% by mass, and more preferably 1 ppb by mass to 0.1% 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 monohydric alcohols or dihydric or higher alcohols may be used. Among these, primary alcohols are preferred from the viewpoint of low cost and easy availability. Furthermore, alcohols having a carbon number of 16 or less (more preferably 2 to 8, even more preferably 2 to 4) are preferred from the viewpoint that short chains can reduce the possibility of adsorption inhibition during semiconductor processing.

[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. The valence of the amine is not particularly limited, and either monovalent amines or divalent or higher amines can be used. Among these, tertiary amines are preferred from the viewpoint of low cost and easy availability. Furthermore, amines having a carbon number of 16 or less (more preferably 2 to 8, and even more preferably 2 to 4) are preferred from the viewpoint that a short chain can suppress the possibility of adsorption inhibition during semiconductor processing.

[0029] The quaternary alkylammonium hydroxide solution may also contain halide ions. While the halide ions are not particularly limited, specific examples include one or more selected from the group consisting of chloride ions, bromide ions, and iodide ions. While the concentration of the halide ions is not particularly limited, it is preferably 0.01 ppm by mass to 20.0% by mass, more preferably 0.1 ppm by mass to 10.0% by mass, and even more preferably 0.1 ppm by mass to 5.0% by mass.

[0030] <Reaction step of contacting a quaternary alkylammonium hydroxide solution with liquid bromine and / or bromine gas> By contacting and reacting a quaternary alkylammonium hydroxide solution with liquid bromine and / or bromine gas, the hydroxide ions of the quaternary alkylammonium hydroxide are substituted with hypobromite ions generated by bromine, and a quaternary alkylammonium hypobromite solution is produced.

[0031] In the present embodiment, the liquid bromine and / or bromine gas used are not particularly limited, and commercially available products can be used. For example, in the case of liquid bromine, high-purity liquid bromine such as that used for etching semiconductor materials or as a raw material for semiconductor materials can be used, and in the case of bromine gas, bromine gas generated from the above-mentioned high-purity liquid bromine can be used.

[0032] Among liquid bromine and / or bromine gases, those with a particularly low water content are preferred, and specifically, those with a water content of 10 ppm by volume or less are preferred. The reasons for this are unclear, but the following is thought to be the case. For example, when producing a quaternary alkylammonium hypobromite solution, liquid bromine and / or bromine gas are usually transported via piping. Therefore, if a large amount of water is present, hydrogen bromide is generated, corroding metal components such as piping and flow meters, and corroded metal impurities are likely to be introduced into the system along with the liquid bromine and / or bromine gas. Therefore, it is preferable to use liquid bromine and / or bromine gas with a water content of 10 ppm by volume or less. Commercially available liquid bromine and / or bromine gas can be used as is, or the water content of the liquid bromine and / or bromine gas can be reduced by contacting it with a desiccant or the like immediately before introduction into the reaction system. The lower limit of the water content of liquid bromine and / or bromine gas is not particularly limited, but considering industrially available liquid bromine and / or bromine gases, it is 0.1 ppm by volume.

[0033] In this embodiment, the concentration of carbon dioxide contained in the liquid bromine and / or bromine gas is not particularly limited, but is preferably 0.001 to 80 ppm by volume, more preferably 0.005 to 50 ppm by volume, and even more preferably 0.01 to 2 ppm by volume. When the carbon dioxide concentration contained in the liquid bromine and / or bromine gas is in the range of 0.001 to 80 ppm by volume, pH change in the resulting quaternary alkylammonium hypobromite solution can be suppressed. As a result, the storage stability of the quaternary alkylammonium hypobromite solution can be improved. Commercially available liquid bromine and / or bromine gas having such a carbon dioxide concentration can be used.

[0034] In this embodiment, the method for contacting the quaternary alkylammonium hydroxide solution with liquid bromine and / or bromine gas is not particularly limited. However, to avoid contamination of the reaction system with carbon dioxide, it is preferable to carry out the reaction in a closed system. Simply, as shown in FIG. 1 , sufficient reaction can be achieved by blowing bromine gas into a quaternary alkylammonium hydroxide solution prepared in a three-neck flask while appropriately controlling the supply rate, thereby efficiently producing a quaternary alkylammonium hypobromite solution. Similarly, when liquid bromine is used, the liquid bromine may be directly supplied to the three-neck flask, or bromine gas generated from the liquid bromine may be blown in as shown in FIG. 3 . Furthermore, a reaction apparatus having the configuration shown in FIG. 2 may also be used, as will be described in detail later. In this embodiment, the method for contacting the quaternary alkylammonium hydroxide solution with bromine gas is not particularly limited. However, blowing bromine gas into the quaternary alkylammonium hydroxide solution using a bubbler or the like can sufficiently react the quaternary alkylammonium hydroxide solution, improving the reaction efficiency. It is preferable to blow bromine gas at a rate of 10 mL / min to 20 mL / min, and in this case, the average value of the hole size (diameter) of the bubbler is preferably 0.1 μm to 10,000 μm, more preferably 0.1 μm to 1,000 μm, and even more preferably 0.1 μm to 100 μm. This hole size is preferable even if the scale of production changes.

[0035] When liquid bromine is directly supplied to the system, it is preferable to first fill a container made of an organic polymer highly resistant to corrosion by bromine with the liquid bromine to be used, and then supply the prepared liquid bromine to the quaternary alkylammonium hydroxide solution by pressure transfer using an inert gas or by dropwise addition. This prevents the incorporation of metal impurities. Furthermore, from the viewpoint of removing metal impurities contained in the liquid bromine as a raw material, it is preferable to prepare the liquid bromine in a sealed container or the like, generate bromine gas from the liquid bromine (gas preparation step), collect the generated bromine gas, and then condense it to obtain a high-purity liquid bromine raw material with few metal impurities. It is also preferable to contact the quaternary alkylammonium hydroxide solution with the bromine gas generated in the gas preparation step. Furthermore, a method in which an inert gas is supplied to the sealed container or the like, and a mixed gas of the generated bromine gas and the inert gas is blown into the quaternary alkylammonium hydroxide solution is also preferable. A mixed gas of bromine gas and an inert gas may be prepared by bubbling an inert gas into liquid bromine, or by contacting only the generated gas without injecting an inert gas into the liquid bromine. In this embodiment, when the mixed gas of the generated bromine gas and an inert gas is contacted with a quaternary alkylammonium hydroxide solution to react, a lower bromine concentration in the mixed gas improves the reaction efficiency. When the temperature of the mixed gas is 25°C, the bromine concentration in the mixed gas is preferably 0.1% to 30%, more preferably 5% to 25%, and even more preferably 10% to 20%, by volume. A bromine concentration of 0.1% by volume or more in the mixed gas is sufficient to supply bromine per unit time, shortening the time required for the hypobromite ion concentration in the solution to reach a predetermined concentration, which is preferable from the viewpoint of production efficiency. Here, the production efficiency is the amount of quaternary alkylammonium hypobromite solution produced per unit time when the flow rate of the mixed gas of bromine gas and inert gas blown into the quaternary alkylammonium hydroxide solution is constant. Furthermore, if the bromine concentration in the mixed gas is 0.1% by volume or more, the consumption of the inert gas in the mixed gas of bromine gas and inert gas can be reduced, thereby reducing raw material costs.Furthermore, since the production equipment can be made small-scale, this is preferable in that costs associated with the production equipment can be reduced. Furthermore, when the bromine concentration in the mixed gas is 30% by volume or less, bromine is less likely to condense in the gas piping, thereby preventing corrosion of piping components. Furthermore, bromine droplets are less likely to be generated in the reaction liquid, preventing corrosion inside the reaction vessel and the liquid piping. Furthermore, although the cause is not clear, this prevents decomposition of hypobromite ions due to contact between the generated hypobromite ions and bromine droplets.

[0036] From the viewpoint of efficiently generating bromine gas, it is preferable to heat the container filled with liquid bromine, preferably to 30 to 80°C, more preferably to 40 to 70°C.

[0037] Examples of the inert gas include nitrogen gas and argon gas. The supply rate of the inert gas is not particularly limited and may be appropriately adjusted so that the supply rate of the bromine gas becomes a suitable rate, but is preferably 10 mL / min to 20 L / min, more preferably 50 mL / min to 5 L / min per 1 L of the volume of the reaction solution.

[0038] (Organic Polymer Material Used for the Inner Surface of a Container Filled with Liquid Bromine) In this embodiment, examples of the organic polymer material that can be used include vinyl chloride resins (soft and hard vinyl chloride resins), nylon resins, silicone resins, polyolefin resins (polyethylene, polypropylene), and fluorine-based resins. Among these, fluorine-based resins are preferred in consideration of ease of moldability, solvent resistance, and low impurity elution. The fluorine-based resin is not particularly limited as long as it is a resin (polymer) containing fluorine atoms, and known fluorine-based resins can be used. Examples include polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-ethylene copolymer, chlorotrifluoroethylene-ethylene copolymer, and cyclized polymer of perfluoro(butenyl vinyl ether). Among these, polyvinylidene fluoride or tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer is preferred in consideration of ease of availability of the reaction vessel itself, productivity, and the like. Methods for forming the inner surface of a reaction vessel from an organic polymer material include forming the entire reaction vessel from the organic polymer material, or covering only the inner surface of a glass or stainless steel reaction vessel with the organic polymer material. Methods for forming the inner surface of a reaction vessel from an organic polymer material include forming the entire reaction vessel from the organic polymer material, or covering only the inner surface of a glass or stainless steel reaction vessel with the organic polymer material. Furthermore, to prevent elution of metal components from the organic polymer material, the reaction vessel can be washed before use. Specifically, it is preferable to thoroughly wash the reaction vessel with an acid such as high-purity nitric acid or hydrochloric acid (e.g., by immersing the reaction vessel in a solution with an acid concentration of 1 mol / L for 12 hours), followed by further washing with ultrapure water or the like. Furthermore, to ensure a stable reaction, it is preferable to wash the inner surface of a reaction vessel formed from an organic polymer material using the above-mentioned method before reacting the quaternary alkylammonium hydroxide solution with liquid bromine and / or bromine gas.

[0039] In this embodiment, the amount of liquid bromine and / or bromine gas used (total amount of bromine used) is not particularly limited, but is preferably 0.001 to 1.0 mol per 1 L of quaternary alkylammonium hydroxide solution at 0°C and 1 atm. Using liquid bromine and / or bromine gas within this range suppresses sudden pH changes in the reaction system and facilitates the removal and reduction of metal impurities by filtration. However, the amount of liquid bromine and / or bromine gas used can also be determined based on the pH of the resulting solution, i.e., the pH of the resulting quaternary alkylammonium hypobromite solution, and may be outside the above range.

[0040] The present inventors have discovered that when producing a quaternary alkylammonium hypobromite solution by directly reacting a quaternary alkylammonium hydroxide solution with liquid bromine and / or bromine gas in a batchwise reaction, the supply rate of liquid bromine and / or bromine gas is important. If the supply rate of liquid bromine and / or bromine gas is too slow, the yield and production efficiency of the quaternary alkylammonium hypobromite solution decrease, while if it is too fast, the yield of the quaternary alkylammonium hypobromite solution may decrease. This is presumably due to the fact that the reactivity of bromine is lower than that of chlorine, which is also a halogen. Therefore, in this embodiment, the supply rate of liquid bromine and / or bromine gas into the reaction system is preferably 0.01 mmol / min to 500 mol / min per 1 L of quaternary alkylammonium hydroxide volume. By satisfying this range, sufficient reactivity is achieved, and a quaternary alkylammonium hypobromite solution can be efficiently produced without residual unreacted liquid bromine or a sudden decrease or fluctuation in pH. From the viewpoint of the yield and production efficiency of the quaternary alkylammonium hypobromite solution, the supply rate is more preferably 0.1 mmol / min to 100 mmol / min, further preferably 0.1 mmol / min to 50 mmol / min, and particularly preferably 0.5 mmol / min to 10 mmol / min, per 1 L of the volume of the quaternary alkylammonium hydroxide.

[0041] In the reaction step between liquid bromine and / or bromine gas and a quaternary alkylammonium hydroxide solution, it is preferable to stir the quaternary alkylammonium hydroxide solution to enhance reactivity, and it is preferable to contact the liquid bromine and / or bromine gas with the quaternary alkylammonium hydroxide solution while stirring. In this embodiment, the tip speed of the stirring blade used to stir the quaternary alkylammonium hydroxide solution is preferably 0.1 m / s to 20.0 m / s. The tip speed of the stirring blade is the speed of the tip (the position of the stirring blade farthest from the rotation axis) when a rotary stirring blade is rotated. By satisfying the above range, sufficient reactivity is achieved, and a quaternary alkylammonium hypobromite solution can be efficiently produced without residual unreacted liquid bromine or localized pH decreases or fluctuations. A tip speed of the stirring blade of 0.1 m / s or more can suppress a decrease in reaction efficiency due to residual unreacted liquid bromine in the solution and decomposition of hypobromite ions due to localized pH decreases or fluctuations. Furthermore, if the tip speed of the stirring blade is 20.0 m / s or less, the load on the stirring blade is reduced, and breakdowns can be suppressed.

[0042] From the same viewpoint, the tip speed of the stirring blade is more preferably 0.5 m / s to 10.0 m / s, and even more preferably 1.0 m / s to 5.0 m / s. The stirring method for the quaternary alkylammonium hypobromite solution is not particularly limited as long as it is industrially usable. Examples include an electric motor stirrer, an air motor stirrer, and a magnetic stirrer. The stirring blade in this embodiment is not particularly limited as long as it is one used in a general stirring device, and specific examples include an inclined paddle blade, a flat paddle blade, a propeller blade, an anchor blade, a turbine blade, and a three-blade swept blade.

[0043] The size of the stirring blade is not particularly limited, and a size can be selected according to the production equipment. A suitable stirring blade size is one in which the relationship d / D between the inner diameter D of the reactor and the rotation diameter (d) of the stirring blade is preferably 0.2 to 0.8, more preferably 0.3 to 0.7. The stirring blades may be used in a single stage or in multiple stages, and different blades may be used in combination. In the case of a magnetic stirrer that uses a magnet to rotate a stirrer at high speed to stir a liquid, the tip speed of the tip of the stirrer is preferably 0.5 m / s to 10.0 m / s, and even more preferably 1.0 m / s to 5.0 m / s, similar to the tip speed of the stirring blade. Such a stirrer is also considered to be an "stirring blade" in this embodiment.

[0044] (Gas Phase in Reaction Step) The carbon dioxide concentration in the gas phase in the reaction step is preferably 100 ppm by volume or less. In this embodiment, the gas phase refers to the portion occupied by the gas that comes into contact with the quaternary alkylammonium hydroxide solution in the reaction step. For example, in the case of the reaction apparatus shown in FIG. 1, this refers to the portion (head space) occupied by the gas in the three-neck flask 11.

[0045] When the carbon dioxide concentration in the gas phase in the reaction step is 100 ppm by volume or less, the generation of carbonate ions and bicarbonate ions due to the reactions of formulas (1) and (2) during the reaction step can be suppressed, and a decrease in the pH of the quaternary alkylammonium hypobromite solution can be suppressed. ２ + OH － → HCO ３ － ... (1) HCO ３ － + OH － → CO ３ ２－ + H ２ O ... (2) By suppressing the decrease in pH due to the above chemical reaction, it is possible to suppress the decomposition of hypobromite ions during storage of the resulting quaternary alkylammonium hypobromite solution, which would deteriorate the storage stability. The carbon dioxide concentration in the gas phase is preferably 0.001 to 100 ppm by volume, more preferably 0.01 to 80 ppm by volume.

[0046] In the reaction step of this embodiment, the pH of the liquid phase at 23°C is preferably 10.5 or higher. While there is no particular upper limit, if the pH during the reaction is excessively high, prolonged storage at the same pH after the reaction may result in decomposition of hypobromite ions and a decrease in the effective bromine concentration. Therefore, the pH of the liquid phase at 23°C during the reaction step is preferably 14 or lower, more preferably 13.9 or lower, and even more preferably 11 or higher and 13.8 or lower. If the pH is within the above range, decomposition of hypobromite ions is suppressed during storage of the resulting quaternary alkylammonium hypochlorite solution, improving storage stability. Even if the pH during the reaction is high, appropriate control of the pH during storage can improve storage stability. On the other hand, if the pH during the reaction step is too low, storage stability may be reduced due to the chemical reaction shown in formula (3): 2HBrO + BrO － + 2OH － → BrO ３ － + 2Br － +2H ２ O... (3)

[0047] (Temperature of Reaction Step) The reaction temperature range of the quaternary alkylammonium hydroxide solution in the reaction step of this embodiment is preferably from 0° C. to 70° C., more preferably from 10° C. to 60° C., and even more preferably from 30° C. to 50° C. If the reaction temperature is within the above range, the quaternary alkylammonium hydroxide solution and bromine react sufficiently, and the quaternary alkylammonium hypobromite solution can be obtained with high production efficiency.

[0048] Note that a reaction temperature of 0°C or higher can suppress solidification of the quaternary alkylammonium hydroxide solution, making the reaction with bromine more likely to proceed satisfactorily. On the other hand, a reaction temperature of 70°C or lower can suppress thermal decomposition of hypobromite ions generated in the quaternary alkylammonium hydroxide solution. In particular, when the pH during the reaction exceeds 13.8, the decomposition of hypobromite ions becomes more pronounced as the reaction temperature increases, so it is more preferable to set the reaction temperature to 70°C or lower. The production efficiency of quaternary alkylammonium hypobromite can be evaluated by the ratio of the number of moles of hypobromite ions generated to the number of moles of bromine molecules supplied as a raw material.

[0049] (Organic Polymer Material Used for the Inner Surface of the Reaction Vessel) In this embodiment, the surface of the reaction vessel that comes into contact with the quaternary alkylammonium hydroxide solution (hereinafter sometimes simply referred to as the "inner surface of the reaction vessel") is preferably formed from an organic polymer material. When a reaction vessel made of general-purpose borosilicate glass (hereinafter referred to as glass) is used as the reaction vessel, the quaternary alkylammonium hydroxide solution used as a raw material dissolves metal components contained in the glass reaction vessel, such as sodium, potassium, and aluminum. This is thought to be due to the alkaline nature of the quaternary alkylammonium hydroxide solution used as a raw material. Therefore, by forming the inner surface of the reaction vessel from an organic polymer material, the incorporation of impurities containing the above metals (metal impurities) can be reduced. Other parts of the reaction vessel that do not come into contact with the quaternary alkylammonium hydroxide solution may be made of glass, stainless steel, or passivated stainless steel, but it is preferable to form them, including the stirring rod, from the same organic polymer material.

[0050] In this embodiment, when an organic solvent is used as the solvent, it is preferable that the reaction apparatus has an explosion-proof structure. Therefore, in order to simplify the apparatus configuration, it is preferable that the quaternary alkylammonium hydroxide solution uses water as the solvent.

[0051] In this embodiment, examples of the organic polymer material that can be used include vinyl chloride resins (soft and hard vinyl chloride resins), nylon resins, silicone resins, polyolefin resins (polyethylene, polypropylene), fluorine resins, etc. Among these, fluorine resins are preferred in view of ease of molding, solvent resistance, and low elution of impurities.

[0052] The fluorine-based resin is not particularly limited as long as it is a resin (polymer) containing fluorine atoms, and known fluorine-based resins can be used. For example, at least one selected from the group consisting of polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-ethylene copolymer, chlorotrifluoroethylene-ethylene copolymer, and cyclized polymer of perfluoro(butenyl vinyl ether) can be mentioned. Among these, in consideration of the ease of availability of the reaction vessel itself, productivity, etc., it is preferable to use a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer.

[0053] Methods for forming the inner surface of a reaction vessel from an organic polymer material include a method for forming the entire reaction vessel from an organic polymer material, and a method for covering only the inner surface of a glass or stainless steel reaction vessel with an organic polymer material.

[0054] Furthermore, the organic polymer material can be washed before use to prevent elution of metal components from the material. Specifically, it is preferable to thoroughly wash the material with an acid such as high-purity nitric acid or hydrochloric acid (for example, by immersing the material in a solution with an acid concentration of 1 mol / L for 12 hours), followed by further washing with ultrapure water or the like. Furthermore, to ensure a stable reaction, it is preferable to wash the inner surface of a reaction vessel made of an organic polymer material by the above-mentioned method before reacting the quaternary alkylammonium hydroxide solution with liquid bromine and / or bromine gas.

[0055] (Reaction Apparatus) An example of a reaction apparatus that can be suitably used in this embodiment will be described with reference to the drawings. Figure 2 shows a schematic diagram of a reaction apparatus 31.

[0056] In the reaction apparatus 31, the surface 34 of the reaction vessel 32 that comes into contact with the quaternary alkylammonium hydroxide solution 33 (the inner surface of the reaction vessel) may be made of the organic polymer material. The reaction apparatus 31 may also be provided with a thermometer (thermocouple) 35 that can monitor the temperature. It is also preferable to provide a stirring motor 36, a stirring rod 37, and a stirring blade 38 so that the reaction system can be mixed. The portions of the thermometer 35, the stirring rod 37, and the stirring blade 38 that come into contact with the quaternary alkylammonium hydroxide solution 33 are also preferably made of an organic polymer material.

[0057] The reaction apparatus 31 may also be provided with a bromine supply pipe 39 for supplying liquid bromine and / or bromine gas, and the quaternary alkylammonium hydroxide solution 33 may be contacted with the liquid bromine and / or bromine gas via a bromine inlet pipe 40 for introducing the liquid bromine and / or bromine gas into the reaction system through the supply pipe 39. As described above, since it is preferable that carbon dioxide is not present in the reaction system, an inert gas supply pipe 41 may also be provided. In FIG. 2 , the inert gas supply pipe 41 merges with the bromine supply pipe 39 midway, and the inert gas is introduced through the bromine inlet pipe 40. However, the bromine inlet pipe 40 may be separated into a bromine inlet pipe and an inert gas inlet pipe. Alternatively, as shown in FIG. 3 , the inert gas may be introduced into a vessel containing liquid bromine and then blown into the reaction vessel 32 together with the generated bromine gas. The bromine inlet pipe 40 is also preferably formed from the organic polymer material described above, since it comes into contact with the quaternary alkylammonium hydroxide solution 33.

[0058] As will be described in detail below, in this embodiment, when a quaternary alkylammonium hydroxide solution is contacted with liquid bromine and / or bromine gas to produce a quaternary alkylammonium hypobromite solution, the pH in the reaction system may decrease, resulting in the precipitation of solid matter containing metal components. In this embodiment, a filtration device may be provided to remove or reduce the amount of these solid matter by filtration. This filtration device includes a reaction solution transfer pipe 42, a pump 43, a filtration filter 44, and a reaction solution return pipe 45. Since each of these components of the filtration device comes into contact with the reaction solution containing the quaternary alkylammonium hypobromite, it is preferable that they be formed from the organic polymer material.

[0059] A chemical diaphragm pump, a tube pump, a magnetic pump, etc. can be used as the pump 43. Among these, it is preferable to use a pump whose liquid-contacting part is made of the above-mentioned fluororesin in order to prevent contamination by metal components, and among these, it is preferable to use a magnetic pump in consideration of ease of availability.

[0060] It is preferable to use a material and a form described in detail below for the filtration filter 44. Although Fig. 2 shows an example in which one filtration filter 44 is provided, multiple filtration filters 44 may be arranged in series and / or parallel depending on the intended use (impurities to be removed).

[0061] By providing such a filter, a filtration operation can be performed during the reaction. Alternatively, the supply of liquid bromine and / or bromine gas can be stopped, and after the reaction, a solution containing quaternary alkylammonium hypobromite can be circulated by pump 43, and solids containing metal components can be removed or reduced by filter 44. While FIG. 2 shows a configuration in which the reaction apparatus and the filter are integrated, the reaction apparatus and the filter may be installed separately if filtration is performed after the reaction.

[0062] It is also possible to provide a bromine gas exhaust pipe 46 for releasing unreacted bromine gas that has been supplied, and a bromine gas trap 47. The bromine gas trap 47 may contain, for example, an aqueous solution of sodium hydroxide at about 5% by mass.

[0063] Furthermore, a reaction bath 48 for controlling the reaction temperature can be provided around the reaction vessel 32 .

[0064] The thermometer 35, stirring rod 37, bromine inlet pipe 40, reaction liquid transfer pipe 42, reaction liquid return pipe 45 and bromine gas outlet pipe 46 can be connected to the reaction vessel 32 by half joints 49 or the like.

[0065] <Filtration Step> When the quaternary alkylammonium hydroxide solution comes into contact with liquid bromine and / or bromine gas to produce a quaternary alkylammonium hypobromite solution, the pH of the solution in the reaction system decreases. In this case, solid matter containing metal impurities may precipitate, and a filtration step is preferably included to remove or reduce this. That is, it is preferable to filter the quaternary alkylammonium hypobromite solution obtained by supplying liquid bromine and / or bromine gas during the reaction of this embodiment or until the solution reaches a predetermined concentration. The filtration step may be performed after the storage step or dilution step described below.

[0066] In the filtration step, the metal components filtered out may vary depending on the pH of the quaternary alkylammonium hypobromite solution. Specifically, when the pH of the quaternary alkylammonium hypobromite solution is 13.5 or less, preferably when the pH of the solution is greater than 12.5 and less than 13.5, hydroxides of magnesium, iron, cadmium, etc., and oxides of nickel and silver are solidified, and these impurities can also be removed or reduced by performing a filtration operation.

[0067] Furthermore, when the pH of the quaternary alkylammonium hypobromite solution is 12.5 or less, preferably when the pH of the solution is 9.0 or more and 12.5 or less, copper and lead oxides solidify in addition to the above impurities, and these impurities can also be removed or reduced by performing a filtration operation. Note that the pH of the solution may vary depending on the temperature. The above pH is based on the value at 23°C. The liquid temperature during the actual filtration step is not limited to 23°C, but is preferably 20 to 28°C, more preferably 23 to 25°C.

[0068] Such solid metal impurities can be generated even when the purity of the raw material quaternary alkylammonium hydroxide solution and bromine is increased. In particular, such solids can be generated when the inner surface of the reaction vessel is made of an organic polymer material. The reason for this is unclear, but it is believed that the use of bromine, a highly corrosive raw material, causes metal impurities to enter the reaction system from somewhere within the reactor.

[0069] The filtration operation may be performed at a pH at which the metals to be removed or reduced are solidified. Therefore, the filtration operation may be performed only once, or multiple times at each pH. In this case, multiple filtration filters with different pore sizes are prepared for each pH, ​​and filtration is performed in order from the largest pore size to the largest pore size, thereby improving filtration efficiency. Specifically, this can be performed by removing coarse particles in the first stage and fine particles in the second stage. Note that, among solid substances containing metal components, such as simple metal impurities, metal oxides, metal hydroxides, and / or colloidal substances, particles of 1 μm to 100 μm in size may be referred to simply as "coarse particles" hereinafter. Meanwhile, particles of 0.01 μm to less than 1 μm in size may be referred to simply as "fine particles" hereinafter. Note that the particle size of a solid substance refers to the circle-equivalent diameter measured by laser diffraction.

[0070] The filtration operation is not particularly limited and can be carried out using a known filtration device or filter. However, in order to prevent the increase of unnecessary metal components, it is preferable that the surface of the filtration device that may come into contact with the quaternary alkylammonium hypobromite solution is made of the organic polymer material.

[0071] Specific examples of suitable filters include filters made of organic polymeric materials or inorganic materials. Examples include at least one filter selected from the group consisting of polyolefins (polypropylene, polyethylene, and ultra-high molecular weight polyethylene), polysulfone, cellulose acetate, polyimide, polystyrene, the fluorine-based resins, and quartz fibers. Furthermore, it is preferable to use a combination of a positively charged membrane and a negatively charged membrane for the filter. This is because many metal oxides and metal hydroxides are negatively charged in an alkaline atmosphere, and a positively charged filter can effectively remove metal components through electrostatic adsorption. Furthermore, some metal components exist in a cationic state and are positively charged. Therefore, a negatively charged filter can effectively remove ionized metal components through electrostatic adsorption.

[0072] The pore size of the filter is not particularly limited, but a filter having a pore size of 1 μm or more or a microfiltration filter can be used to remove coarse particles, while a microfiltration filter, an ultrafiltration filter, or a nanofiltration membrane having a pore size of 0.001 μm or more but less than 1 μm can be used to remove fine particles.

[0073] The above-mentioned filters can be commercially available. Specifically, polytetrafluoroethylene filters manufactured by Nippon Entegris Co., Ltd., such as "Fluoroguard ATX filter (pore size 0.05 μm)," "Quick Change ATE filter (pore size 0.03 μm)," "Torrent ATE filter (pore size 0.02 μm)," "Quick Change ATE filter (pore size 0.03 μm)," and "Fluoroline P-1500 (pore sizes 0.05 μm, 0.1 μm)," can be used.

[0074] The above filtration operation can be performed before adjusting the pH of the quaternary alkylammonium hypobromite solution to a range suitable for its intended use. In this case, after the filtration operation, the solution can be mixed again with liquid bromine and / or bromine gas to obtain a quaternary alkylammonium hypobromite solution with the desired pH. Alternatively, a quaternary alkylammonium hypobromite solution with the desired pH can be obtained by mixing with water, an acid such as hydrogen bromide, and / or an alkali such as an aqueous quaternary ammonium hydroxide solution. On the other hand, if the pH of the produced quaternary alkylammonium hypobromite solution is suitable for use as a cleaning solution, the solution can be filtered and used directly as a cleaning solution for semiconductor device fabrication.

[0075] By carrying out such a filtration operation, it is possible to reduce metal components such as magnesium, iron, nickel, copper, silver, cadmium, and lead.

[0076] <Storage Step> After the reaction step in this embodiment or the filtration step, the quaternary alkylammonium hypobromite solution can be used as is for a specific purpose, such as a cleaning solution, but is generally used after a storage step (including storage and transportation). Quaternary alkylammonium hypobromite solutions have poor storage stability when used alone, and the addition of a stabilizer has been required. Stabilizers can cause organic residues, and improvements have been sought. However, by undergoing the storage step described below, it is possible to provide a quaternary alkylammonium hypobromite solution with improved storage stability.

[0077] The method for producing a quaternary alkylammonium hypobromite solution according to one embodiment of the present disclosure may include a storage step of storing the reaction solution after the reaction step, and in the storage step, the pH of the quaternary alkylammonium hypobromite solution at 23° C. may be adjusted to 12.0 or more and less than 14.0. Note that a filtration step may be performed after the reaction step, and then the storage step may be performed.

[0078] The concentration of the quaternary alkylammonium hypobromite solution to be preserved is not particularly limited, but considering industrial production, a quaternary alkylammonium hypobromite solution containing 0.001 to 20% by mass of hypobromite ions and 0.001 to 50% by mass of quaternary alkylammonium ions at a predetermined pH is preferred. Note that the "predetermined pH" refers to a pH of 12.0 or more and less than 14.0 selected as the pH for the preservation step.

[0079] Here, "storage" refers to the period from the start of storage of the quaternary alkylammonium hypobromite solution at a pH of 12 or more and less than 14 at 23°C until the concentration and / or pH of the quaternary alkylammonium hypobromite solution is adjusted. Note that if the pH of the solution after pH adjustment is 12 or more and less than 14, further storage of the solution also falls under the storage of the present disclosure. If the pH of the quaternary alkylammonium hypobromite solution is 12 or more and less than 14 from the beginning, it can be stored as is; if the pH is less than 12 or 14 or more, it can be stored after adjusting the pH to a range of 12 or more and less than 14.

[0080] The pH of the solution may vary depending on the temperature. The pH value at 23°C is used as a guideline. The actual solution storage temperature is not limited to 23°C. Therefore, although the storage conditions are not particularly limited, it is preferable to store the solution under general storage conditions, i.e., at −25°C to 50°C in a known container, a canister, or a plastic storage container. It is even more preferable to store the solution in a light-shielding storage container, a transport container such as a canister, or a plastic storage container filled with an inert gas at −20°C to 40°C in a dark place. If the storage temperature exceeds the above range, hypobromite ions may thermally decompose to form oxygen molecules during long-term storage, causing the container to expand and possibly break.

[0081] In a preferred embodiment, the solution is stored as a quaternary alkylammonium hypobromite solution having a pH of 12 or more and less than 14 at 23°C. Within this pH range, the hypobromite ion concentration does not decrease, allowing for long-term storage. If the pH is less than 12, the disproportionation reaction of hypobromite proceeds, resulting in decomposition of hypobromite ions and a decrease in the oxidizing power of the quaternary alkylammonium hypobromite solution. On the other hand, if the pH is 14 or more, it is believed that the organic ions (cations) may decompose. As a result, it is believed that the disproportionation reaction of hypobromite ions inhibited by the bulkiness of the organic ions proceeds again, resulting in decomposition of the hypobromite ions. It is preferable to store the solution as a quaternary alkylammonium hypobromite solution having a pH of 12 or more and less than 13.9 at 23°C, and more preferably at a pH of 12 or more and less than 13.8 at 23°C.

[0082] The reason why the above-mentioned storage method improves storage stability is unclear, but the inventors speculate as follows. In the quaternary alkylammonium hypobromite solution, some of the quaternary alkylammonium hypobromite dissociates into hypobromite ions and organic ions, but most of the hypobromite ions and organic ions are ionic bonds, and it is speculated that the steric bulkiness of the organic ions inhibits the disproportionation reaction of the hypobromite ions. Therefore, it is believed that the greater the steric bulkiness of the organic ions, the more the disproportionation reaction is inhibited, and the improved storage stability is achieved. If the organic ion is a bulky quaternary alkylammonium ion, such as a tetramethylammonium ion, the disproportionation reaction can be sufficiently inhibited.

[0083] According to the above-described storage method, the oxidizing power of the quaternary alkylammonium hypobromite solution remains almost unchanged during storage, even if the storage period is 30 days, preferably 60 days, or even more preferably 90 days. Therefore, after storage, the quaternary alkylammonium hypobromite solution can be used for various purposes simply by diluting it depending on the conditions of use. The longer the storage period, the greater the expected effect of improving productivity.

[0084] As described above, this storage method can provide a quaternary alkylammonium hypobromite solution that can maintain sufficient cleaning and removing power even 30 days after production. By providing a quaternary alkylammonium hypobromite solution with excellent storage stability, costs associated with transporting and storing the quaternary alkylammonium hypobromite solution can be reduced, which is of great industrial importance.

[0085] (Dilution step) The quaternary alkylammonium hypobromite solution may be diluted appropriately depending on its intended use. In the dilution step, after the preservation step described above and preserving the quaternary alkylammonium hypobromite solution at a pH of 12 or higher, the quaternary alkylammonium hypobromite solution is diluted with a solution having a pH of less than 13 to adjust the pH to 8.0 or higher and less than 13.0.

[0086] The method for diluting the quaternary alkylammonium hypobromite solution may be any method capable of relatively increasing the hydrogen ion concentration contained in the quaternary alkylammonium hypobromite solution, and the quaternary alkylammonium hypobromite solution may be diluted with water, with a solution containing an acid, or with a solution having a lower pH than the pH of the quaternary alkylammonium hypobromite solution during storage. For example, an example of a solution having a lower pH than the quaternary alkylammonium hypobromite solution stored using the above-mentioned storage method is an alkaline solution, such as a quaternary alkylammonium hydroxide solution with a pH of less than 13.

[0087] Furthermore, the solution added to dilute the quaternary alkylammonium hypobromite solution may or may not contain quaternary alkylammonium hypobromite. For example, when diluting with a solution containing quaternary alkylammonium hypobromite, not only the pH but also the concentration of the quaternary alkylammonium hypobromite solution can be adjusted as desired.

[0088] In this embodiment, the solution added to dilute the quaternary alkylammonium hypobromite solution is preferably a solution having a pH greater than 0 and equal to or less than 7. Use of an acidic solution can minimize the decrease in concentration of the quaternary alkylammonium hypobromite that occurs during pH adjustment. Specific examples of solutions having a pH greater than 0 and equal to or less than 7 include inorganic acids such as solutions containing at least one acid selected from the group consisting of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, boric acid, hydrofluoric acid, bromic acid, chloric acid, perchloric acid, iodic acid, periodic acid, and carbonic acid, and organic acids such as solutions containing at least one acid selected from the group consisting of formic acid, acetic acid, glacial acetic acid, propionic acid, citric acid, oxalic acid, malic acid, lactic acid, and benzoic acid.

[0089] In addition, if the impurity concentration of the solution used for dilution is high, the use of the obtained diluted solution will be limited, so it is preferable that the solution used for dilution has fewer impurities. For example, when a quaternary alkylammonium hypobromite solution is used as a processing solution for semiconductor wafers, high purity is required, so it is preferable to dilute a high-purity quaternary alkylammonium hypobromite solution with hydrochloric acid, sulfuric acid, etc., which can be easily purified industrially.

[0090] The method for diluting the quaternary alkylammonium hypobromite solution is not particularly limited, and dilution may be performed by a known method. For example, a method may be used in which the quaternary alkylammonium hypobromite solution and the solution used for dilution are supplied from two supply ports of a container, respectively, and mixed by stirring using a propeller or rotor, or a method may be used in which the liquid is circulated using a pump. Alternatively, the solution used for dilution may be supplied to a container in which the quaternary alkylammonium hypobromite solution is stored, and then diluted.

[0091] As another dilution method, the quaternary alkyl ammonium hypobromite solution can be diluted by mixing the quaternary alkyl ammonium hypobromite solution with a solution used for dilution at the location where the composition containing the quaternary alkyl ammonium hypobromite solution is used. For example, by supplying the quaternary alkyl ammonium hypobromite solution and the solution used for dilution to the point of use from two nozzles, respectively, dilution can be performed at the point of use. This method is particularly effective when processing semiconductor wafers.

[0092] Alternatively, when using a diluted solution for semiconductor cleaning, a method can be employed in which an inorganic or organic acid is added to a quaternary alkylammonium hypobromite solution to dilute it. Dilution can be achieved by merging and mixing the pipe supplying the quaternary alkylammonium hypobromite solution with the pipe supplying the inorganic or organic acid, and then supplying the resulting diluted solution to the semiconductor wafer, which is the surface to be cleaned. This mixing can be achieved by known methods, such as a method in which the liquids are impinged and mixed through a narrow passage under pressure; a method in which the liquid flow is repeatedly divided, separated, and merged by filling the pipe with a filler such as a glass tube; or a method in which a power-driven rotating blade is provided in the pipe.

[0093] As described above, by employing the dilution process, it is possible to utilize a diluted solution that stably maintains its oxidizing power compared to when a quaternary alkylammonium hypobromite solution is stored at the pH at which it will be used. Generally, when a quaternary alkylammonium hypobromite solution is used as a cleaning solution, it is diluted to a pH of approximately 8 to 13. However, storing a quaternary alkylammonium hypobromite solution at this pH can result in a decrease in the hypobromite ion concentration and a decrease in cleaning properties. However, by undergoing the dilution process after storage via the above-described storage process, a diluted solution (cleaning solution) with a high hypobromite ion concentration can be obtained.

[0094] (Semiconductor Wafer Treatment Method) The surface of a semiconductor wafer can be treated using the quaternary alkylammonium hypobromite solution according to this embodiment. The semiconductor wafer treatment method according to this embodiment is a treatment method that can etch, clean, and remove various metals and their compounds present on a semiconductor wafer without damaging the semiconductor wafer. However, the treatment target is not limited to this, and the method can also be used to clean semiconductor wafers that do not have metals on their surfaces, and can also be used for wet etching of metals.

[0095] The treatment method according to this embodiment is preferably applied to semiconductor wafers containing at least one compound selected from the group consisting of copper, tungsten, tantalum, titanium, cobalt, ruthenium, molybdenum, chromium, manganese, aluminum, silicon, silicon oxide, and compounds thereof. The treatment method according to this embodiment can effectively utilize the strong oxidizing action of hypobromite ions, and therefore can be suitably used to treat precious metals, which are not easily oxidized among the above metals. Therefore, this treatment method can be suitably used when cleaning and removing precious metals, particularly ruthenium. For example, when cleaning and removing ruthenium, a known cleaning method can be used.

[0096] <Quaternary alkylammonium hypobromite solution> By using the manufacturing method of this embodiment and further a filtration process, a quaternary alkylammonium hypobromite solution with a reduced content of metal components can be produced. The solvent for the quaternary alkylammonium hypobromite solution is the same as the solvent for the raw material quaternary alkylammonium hydroxide solution, but other solvents can also be added as long as they do not impair the effects of the present disclosure. In consideration of operability, ease of handling, versatility, etc., the solvent for the quaternary alkylammonium hypobromite solution is preferably water.

[0097] Examples of quaternary alkylammonium hypobromite solutions obtainable by the present disclosure include tetramethylammonium hypobromite, tetraethylammonium hypobromite, tetrapropylammonium hypobromite, tetrabutylammonium hypobromite, ethyltrimethylammonium hypobromite, propyltrimethylammonium hypobromite, butyltrimethylammonium hypobromite, diethyldimethylammonium hypobromite, and triethylmethylammonium hypobromite.

[0098] The resulting quaternary alkylammonium hypobromite solution can have metal components, specifically sodium, potassium, and aluminum, each of which is less than 1 ppb (by mass). The contents of these metal components are measured by inductively coupled plasma mass spectrometry as shown in the examples.

[0099] Furthermore, by carrying out the filtration procedure described above, the resulting quaternary alkylammonium hypobromite solution can have a magnesium, iron, nickel, copper, silver, cadmium, and lead content of less than 1 ppb (by mass). The contents of these metal components are also values ​​measured by inductively coupled plasma mass spectrometry as shown in the examples.

[0100] Therefore, it is most preferable that the quaternary alkylammonium hypobromite solution contains less than 1 ppb of each of sodium, potassium, aluminum, magnesium, calcium, iron, nickel, copper, and zinc. The form of the metal components in the quaternary alkylammonium hypobromite solution is not particularly limited, and they may be contained as metal atoms or ions, or in the form of fine particles such as oxides or hydroxides, complexes, etc.

[0101] The pH of the resulting quaternary alkylammonium hypobromite solution is not particularly limited and may be appropriately determined depending on the intended use. For example, when the pH is greater than 12.5, the solution can be used as a photoresist remover (developer) or for planarizing a noble metal layer when forming a semiconductor device.

[0102] In particular, by adjusting the pH to 9.0 or more and 13.0 or less, the resulting quaternary alkylammonium hypobromite solution can also be used for etching precious metals. In this case, the pH can be adjusted to 9.0 or more and 13.0 or less while supplying liquid bromine and / or bromine gas to a high-pH quaternary alkylammonium hydroxide solution, making production easy. In addition, by performing a filtration operation during or after production, the content of metal components can be further reduced.

[0103] In addition, various additives may be added to the quaternary alkylammonium hypobromite solution as desired depending on its intended use. For example, additives such as metal chelating agents, complexing agents, metal dissolution promoters, metal corrosion inhibitors, surfactants, acids, and alkalis can be added. Addition of these additives is expected to promote or inhibit metal dissolution, improve surface roughness, increase processing speed, and reduce particle adhesion during semiconductor wafer processing, making cleaning solutions containing these additives suitable for use in semiconductor wafer processing. Furthermore, known additives such as common stabilizers, such as benzotriazoles, benzophenones, oxanilides, and salicylates, can also be added. Addition of these stabilizers improves storage stability.

[0104] As described above, according to the manufacturing method of this embodiment, a quaternary alkylammonium hypobromite solution can be efficiently manufactured. The quaternary alkylammonium hypobromite solution obtained by the manufacturing method of this embodiment can be suitably used in the manufacturing process of semiconductor devices.

[0105] Examples of the present disclosure will be described below, but the present disclosure is not limited to the following examples.

[0106] <pH Measurement Method> The pH of 30 mL of the quaternary alkylammonium hydroxide solution and the quaternary alkylammonium hypobromite solution was measured using a tabletop pH meter (LAQUA F-73, manufactured by HORIBA, Ltd.) The pH measurement was performed after the solution had stabilized at 23°C.

[0107] <Method for calculating hypobromite ion concentration> The hypobromite ion concentration was measured using an ultraviolet-visible spectrophotometer (V-700, manufactured by JASCO Corporation). A calibration curve was created from absorbance and concentration using hypobromite ions with known concentrations, and the hypobromite ion concentration in the produced quaternary alkylammonium hypobromite solution was determined.

[0108] <Method for calculating the carbon dioxide concentration in the gas phase> The carbon dioxide concentration in the gas phase of the reaction solution is calculated by CO ２ Monitor (CUSTOM, CO ２ -M1).

[0109] <Reaction efficiency> The reaction efficiency was calculated from the ratio (%) of the number of moles of hypobromite ions generated to the number of moles of bromine molecules supplied. If all of the added bromine reacts (no decomposition occurs), the reaction efficiency is 100%. If hypobromite ions decompose during the reaction or if unreacted bromine remains in the reactor, the reaction efficiency decreases.

[0110] <Evaluation method for storage stability> The quaternary alkylammonium hypobromite solution was transferred into a glove bag, and after the carbon dioxide concentration in the glove bag became 1 ppm or less, the solution was transferred into a polyfluoroalkyl ether (PFA) container and sealed. After storing in a light-shielded environment at 23°C for 10 days, the hypobromite ion concentration of the quaternary alkylammonium hypobromite solution in the PFA container was measured.

[0111] <Evaluation of Metal Etching Performance> The ruthenium, tungsten, and molybdenum films used in the examples were formed as follows. An oxide film was formed on a silicon wafer using a batch-type thermal oxidation furnace, and a ruthenium film (500 Å), a tungsten film (500 Å), or a molybdenum film (500 Å) was formed thereon using a sputtering method. Sheet resistance was measured using a four-point probe resistance meter (Loresta GP, manufactured by Mitsubishi Chemical Analytech Co., Ltd.) and converted to film thickness. The resulting quaternary alkylammonium hypobromite solution was diluted with ultrapure water and HCl to a predetermined pH and hypobromite ion concentration. Each sample piece of each metal film-coated wafer, cut to 10 × 20 mm, was immersed in the resulting quaternary alkylammonium hypobromite solution for 1 minute. The change in film thickness before and after treatment was divided by the immersion time to calculate the etching rate, which was then evaluated as the etching rate of each metal film.

[0112] <Method for measuring metal concentration in quaternary alkylammonium hypobromite solution> High-resolution inductively coupled plasma mass spectrometry was used to measure the metal concentration in the quaternary alkylammonium hypobromite solution. Ultrapure water and 1.25 mL of high-purity nitric acid (Ultrapure-100 nitric acid, manufactured by Kanto Chemical Co., Ltd.) were added to a 25 mL polyfluoroalkyl ether (PFA) measuring flask (manufactured by AsOne, PFA measuring flask). Next, 0.25 mL of the quaternary alkylammonium hypobromite solution was collected using a pipette (manufactured by AsOne, Pipetman P1000) and a fluororesin pipette tip (manufactured by AsOne, fluororesin pipette tip), added to the PFA measuring flask, and stirred. Next, the solution was diluted with ultrapure water to prepare a measurement sample diluted 100 times. Furthermore, a high-resolution inductively coupled plasma mass spectrometer (ThermoFisher Scientific, Elements 2) was used to quantify the amount of metal using a calibration curve method. In order to confirm the increase or decrease in sensitivity due to the matrix, impurities were added to the measurement solution to a concentration of 2 ppb, and measurements were also taken. The measurement conditions were RF output of 1500 W, argon gas flow rates of plasma gas 15 L / min, auxiliary gas 1.0 L / min, and nebulizer gas 0.7 L / min.

[0113] Example 1: 364.6 g of a 25% by weight aqueous solution of tetramethylammonium hydroxide (TMAH) and 9635.4 g of ion-exchanged water were mixed in a 10 L three-neck flask (Asahi Seisakusho Co., Ltd.) to obtain a 0.10 mol TMAH aqueous solution. The pH was 13.0. Next, a PTFE stirring rod (AsOne, with blades) was attached to a general-purpose stirrer (BLh3000, Shinto Scientific Co., Ltd.) and placed in the center of the three-neck flask. A thermometer tube 12 and a thermocouple 13 were inserted into one of the left and right openings, and a dropping funnel (Kiriyama Seisakusho Co., Ltd., 50 mL capacity) was attached to the other opening. 25.8 mL of bromine (Fujifilm Wako Pure Chemical Industries, Ltd.) was weighed into the dropping funnel. The stirring speed of the general-purpose stirrer was set so that the tip speed of the stirring blade was 0.1 m / s. Bromine was added dropwise to the TMAH aqueous solution at a bromine supply rate of 0.1 mmol / min (0.01 mmol / min per 1 L of the quaternary alkylammonium hydroxide solution). A portion of the resulting treated solution was poured into a dropping funnel, and the remaining bromine was dissolved and poured from the dropping funnel into the treated solution.

[0114] <Evaluation> 30 mL of the obtained aqueous solution of quaternary alkylammonium hypobromite was dispensed into a fluororesin container, and the pH and hypobromite ion concentration were evaluated. The results are shown in Table 2.

[0115] Examples 2 to 19 In Examples 2 to 19, quaternary alkylammonium hypobromite solutions were prepared and evaluated in the same manner as in Example 1, except that (A) the concentration of quaternary alkylammonium hydroxide, (B) the amount of bromine supplied, (C) the bromine supply rate, (D) the reaction temperature, (E) the carbon dioxide concentration in the gas phase, and (F) the stirring impeller tip speed were adjusted to satisfy the conditions shown in Table 1. The results are shown in Table 2. In each of the following tables, (C) represents the bromine supply rate per 1 L of quaternary alkylammonium hydroxide volume.

[0116]

[0117] Example 20 A 2 L polytetrafluoroethylene reaction vessel (AsOne Corporation, C-type cylindrical reaction vessel, 2000 cc) was prepared with multiple polytetrafluoroethylene half joints (AsOne Corporation, I-type half female joint, 6φ) attached. 72.92 g of a 25% by weight aqueous TMAH solution and 1927.08 g of ion-exchanged water were mixed into the reaction vessel to obtain a 0.10 mol aqueous TMAH solution. The pH at this time was 13.0. A stirring rod (AsOne Corporation, tetrafluoroethylene (PTFE) stirring rod with stirring blades, total length 450 mm x diameter 8 mm) was placed in the center of the reaction solution, and the top was fixed with a stirring motor (Shinto Scientific Co., Ltd., Three-One Motor BLh600). A thermometer was installed in the reaction vessel to monitor the temperature during the reaction.

[0118] The tip of a gas inlet tube made of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (Flon Industries, PFA tube) capable of switching between bromine gas and nitrogen gas was immersed in the bottom of the solution. One half joint was connected via a bromine gas outlet tube to a bromine gas trap (AsOne, gas washing bottle) filled with a 5% by mass aqueous solution of sodium hydroxide. One half joint was connected to the inlet side of a magnetic pump (AsOne, Teflon-coated magnetic pump) via a PFA tube, which serves as a reaction solution transfer tube.

[0119] Next, 15.98 g of liquid bromine was weighed into a 100 mL PFA container (Flon Industries, PFA trap bottle). The gas inlet of the PFA container was connected to nitrogen gas, and the gas outlet was connected to the reaction solution. Nitrogen gas with a carbon dioxide concentration of less than 1 ppm was flowed through a nitrogen gas supply pipe and a gas supply pipe (PFA tube) at 100 mL / min for 20 minutes to expel carbon dioxide from the gas phase in the reaction vessel. Nitrogen was supplied to 100 mL of PFA solution at 700 mL / min to supply a mixed gas of nitrogen gas and bromine gas to the reaction vessel. Nitrogen gas was supplied until liquid bromine could no longer be visually confirmed, and after liquid bromine could no longer be visually confirmed, nitrogen gas was continued to be supplied for an additional 10 minutes.

[0120] <Evaluation> 30 mL of the obtained aqueous solution of quaternary alkylammonium hypobromite was dispensed into a fluororesin container, and the pH and hypobromite ion concentration were evaluated. The results are shown in Table 4.

[0121] Examples 21 to 25 In Examples 21 to 23, quaternary alkylammonium hypobromite solutions were prepared and evaluated in the same manner as in Example 20, except that (A) the concentration of quaternary alkylammonium hydroxide, (B) the amount of bromine supplied, (C) the supply rate, (D) the reaction temperature, (E) the carbon dioxide concentration in the gas phase, (F) the stirring impeller tip speed, and (G) the nitrogen supply rate were adjusted to the conditions shown in Table 3. The results are shown in Table 4. Furthermore, in Examples 24 and 25, quaternary alkylammonium hypobromite solutions were prepared and evaluated in the same manner as in Example 20, except that a bubbler (e.g., AS ONE, PTFE bubbler (round) φ50 × 15) corresponding to the average bubbler hole diameter (H) shown in Table 3 was attached to the gas outlet. The results are shown in Table 4. Examples 26-29 In Examples 26-29, quaternary alkylammonium hypobromite solutions were prepared and evaluated in the same manner as in Example 20, except that the following conditions were adjusted to satisfy the conditions shown in Table 5: (A) quaternary alkylammonium hydroxide concentration, (B) bromine supply amount and (C) supply rate, (D) reaction temperature, (E) carbon dioxide concentration in the gas phase, (F) stirring impeller tip speed, (G) nitrogen supply rate, (H) average bubbler hole diameter, and (I) airborne bromine concentration. The results are shown in Table 6. (I) Airborne bromine concentration refers to the concentration (volume %) of bromine contained in the gas contacting the reaction solution. Evaluation 30 mL of the resulting aqueous quaternary alkylammonium hypobromite solution was dispensed into a fluororesin container, and the pH and hypobromite ion concentration were evaluated. The results are shown in Table 6. Furthermore, the production efficiency under each condition was evaluated based on the time required for hypobromite to reach a predetermined concentration. Production efficiency was evaluated according to the following criteria. A: 100 g or more of aqueous solution of quaternary alkyl ammonium hypobromite can be produced per minute. B: 50 g or more but less than 100 g of aqueous solution of quaternary alkyl ammonium hypobromite can be produced per minute. C: 1 g or more but less than 50 g of aqueous solution of quaternary alkyl ammonium hypobromite can be produced per minute.

[0122]

[0123] <Measurement of Metal Concentration in Quaternary Alkylammonium Hypobromite Solutions> The metal concentrations in the quaternary alkylammonium hypobromite solutions obtained in Examples 1 and 20 were measured according to the above-mentioned "Method for Measuring Metal Concentration in Quaternary Alkylammonium Hypobromite Solutions." The results are shown in Table 7. <Metal Etching Performance> Using the quaternary alkylammonium hypobromite solutions obtained in Examples 1 and 20, the etching performance of each metal was evaluated according to the above-mentioned "Evaluation of Metal Etching Performance." The results are shown in Table 8.

[0124]

[0125] REFERENCE SIGNS LIST 10 Ice water 11 Three-neck flask 12 Thermometer protection tube 13 Thermocouple 14 Rotor 15 PFA tube 16 Gas washing bottle 17 5 mass% sodium hydroxide aqueous solution 18 Flow meter 19 Water bath 21 Glass beaker 22 Thermometer protection tube 23 Thermocouple 24 Rotor 25 PFA tube 26 Flow meter 27 Water bath 28 Ice water 31 Reaction apparatus 32 Reaction vessel 33 Quaternary alkylammonium hydroxide solution (before reaction) 34 Inner surface of reaction vessel 35 Thermometer 36 Stirring motor 37 Stirring rod 38 Stirring blade 39 Bromine supply pipe 40 Bromine introduction pipe 41 Nitrogen gas supply pipe 42 Reaction liquid transfer pipe 43 Pump 44 Filtration filter 45 Reaction liquid return pipe 46 Bromine gas exhaust pipe 47 Bromine gas trap 48 Reaction bath 49 Half joint

Claims

1. A method for producing a quaternary alkylammonium hypobromite solution, comprising: a preparation step of preparing a quaternary alkylammonium hydroxide solution in a reaction vessel; and a reaction step of bringing the quaternary alkylammonium hydroxide solution into contact with liquid bromine and / or bromine gas in the reaction vessel.

2. The method for producing a quaternary alkylammonium hypobromite solution according to claim 1, wherein the supply rate of the liquid bromine and / or bromine gas in the reaction step is 0.01 mmol / min to 500 mol / min per 1 L of the volume of the quaternary alkylammonium hydroxide solution.

3. The method for producing a quaternary alkylammonium hypobromite solution according to claim 1 or 2, wherein the carbon number of the alkyl group of the quaternary alkylammonium hydroxide is independently 1 to 10 for each.

4. The method for producing a quaternary alkylammonium hypobromite solution according to any one of claims 1 to 3, wherein the reaction temperature in the reaction step is 0°C or higher and 70°C or lower.

5. The method for producing a quaternary alkylammonium hypobromite solution according to any one of claims 1 to 4, wherein the carbon dioxide concentration in the gas phase part in the reaction step is 100 ppm by volume or less.

6. The method for producing a quaternary alkylammonium hypobromite solution according to any one of claims 1 to 5, wherein the pH at 23°C in the liquid phase part in the reaction step is 10.5 or higher.

7. The method for producing a quaternary alkylammonium hypobromite solution according to any one of claims 1 to 6, wherein the carbon dioxide concentration in the quaternary alkylammonium hydroxide solution in the reaction step is 500 ppm or less.

8. The method for producing a quaternary alkylammonium hypobromite solution according to any one of claims 1 to 7, wherein the reaction step includes a step of stirring the quaternary alkylammonium hydroxide solution with a stirring blade, and a step of bringing the quaternary alkylammonium hydroxide solution into contact with liquid bromine under the condition that the tip speed of the stirring blade is 0.1 m / s to 20.0 m / s.

9. The preparation step further includes a gas preparation step of preparing liquid bromine and generating bromine gas from the liquid bromine, and in the reaction step, the quaternary alkylammonium hydroxide solution is brought into contact with the bromine gas generated in the gas preparation step. The method for producing a quaternary alkylammonium hypobromite solution according to any one of claims 1 to 8.

10. The method for producing a quaternary alkylammonium hypobromite solution according to claim 9, including a step of supplying an inert gas to the bromine gas generated in the gas preparation step and bringing a mixed gas of the bromine gas and the inert gas into contact with the quaternary alkylammonium hydroxide solution.

11. The method for producing a quaternary alkylammonium hypobromite solution according to claim 10, wherein the supply rate of the inert gas is 10 mL / min to 200 L / min.

12. A method for treating a semiconductor wafer, wherein the surface of the semiconductor wafer is treated with the quaternary alkylammonium hypobromite solution obtained by the method according to any one of claims 1 to 11.

13. The treatment method according to claim 12, wherein the semiconductor wafer is a semiconductor wafer containing at least one selected from the group consisting of copper, tungsten, tantalum, titanium, cobalt, ruthenium, molybdenum, chromium, manganese, aluminum, silicon, silicon oxide, and compounds thereof.

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