JPH0788593B2 - Method for producing aqueous solution of quaternary ammonium hydroxide - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a quaternary ammonium hydroxide aqueous solution, and is particularly useful as a treatment agent for cleaning wafers and developing resist films in the manufacturing process of semiconductor devices. And a method for producing a quaternary ammonium hydroxide aqueous solution.

[Prior Art] Conventionally, in the manufacturing process of ICs and LSIs in the electronic industry, a strongly alkaline processing agent is used for cleaning the surface of a semiconductor substrate (wafer), etching, developing a resist, etc. In this way, a quaternary ammonium hydroxide aqueous solution containing no metal ion such as Na is used as a treating agent.

However, regarding the quaternary ammonium hydroxide aqueous solution used as this treating agent, impurities such as Li, N
Metal ions such as a, K, Fe, Ni, Al, Cr, Zn, Cl, Br,
If halogen ions such as I are contained, these impurities remain on the wafer or in the resist film after cleaning or development, which deteriorates the accuracy of the manufactured IC or LSI and causes malfunction of the electronic circuit. Further, even during storage of the quaternary ammonium hydroxide aqueous solution, the storage container is corroded due to highly corrosive impurities such as halogen ions remaining in the aqueous solution in a trace amount, which causes a decrease in purity and is manufactured in the same manner as above. Was done
There is a problem that it deteriorates the accuracy of ICs and LSIs and causes malfunction of electronic circuits.

This tendency becomes more and more remarkable with the recent high integration of semiconductor devices, and there is a demand for a quaternary ammonium hydroxide aqueous solution having higher purity and storage stability with respect to impurities such as metal ions and halogen ions. There is.

In order to meet the demands, the applicant of the present invention, in producing a quaternary ammonium hydroxide aqueous solution by electrolyzing a quaternary ammonium salt in an electrolytic cell using a cation exchange membrane as a diaphragm, By using a quaternary ammonium inorganic acid salt obtained by reacting a trialkylamine and a dialkyl carbonate as a salt, not only the production is easy, but also a metal ion or a halogen ion which is particularly harmful in the semiconductor production process. About ultra-high purity and excellent in storage stability in a stainless steel container, and thus, a method capable of inexpensively producing a quaternary ammonium hydroxide aqueous solution suitable as a wafer cleaning agent or a resist treating agent in a semiconductor device manufacturing process ( The invention of Japanese Patent Application No. 60-12,109) was able to achieve certain results.

[Problems to be Solved by the Invention] However, also in this method, when quaternary ammonium inorganic hydrochloric acid obtained by reacting a trialkylamine and a dialkyl carbonate in an electrolytic cell is electrolyzed, it is used as an anode. Expensive graphite electrodes, which are heavily consumed, must be replaced frequently, and the electrode thickness must be increased due to the heavy consumption, which increases the size of the electrolytic cell. If the space between the cathode and the cathode expands, the current efficiency will decrease, and the cation exchange membrane located between the electrodes may shift due to changes in liquid pressure, so it is necessary to use a protective plate to prevent this. There was a problem.

In addition, the graphite fine particles generated by exhaustion of the graphite electrode on the anode side during electrolysis are partitioned by a cation exchange membrane, but a part of them pass through the fine pores of this cation exchange membrane. Then, the product formed on the cathode side is transferred to an aqueous solution of quaternary ammonium hydroxide, and especially when it is used as a processing solution in the manufacturing process of VLSI, ultrafine particles of 0.2 μm or more poses a problem, so this is expensive It must be filtered with a 0.2 μm filter, and if the migration of graphite fine particles to the cathode side increases, frequent replacement of this expensive filter becomes necessary, and the labor and time required for this graphite fine particle filtration process also increase. There was a problem that it would be significantly increased.

Further, when the anode waste liquid is treated after the electrolysis is completed, if graphite fine particles are present in the anode waste liquid, it cannot be disposed as it is because of problems of pollution, and a coagulant is added to aggregate the graphite waste liquid. It is necessary to separate and remove, but these graphite fine particles have a slow sedimentation rate and are hard to aggregate,
There was also a problem that the efficiency of this graphite waste liquid was poor, because it had to be left for a long time after the coagulant was added.

Therefore, it is conceivable to use, for example, a platinum-plated titanium electrode, a platinum electrode made of platinum, or a stainless steel electrode made of stainless steel instead of the graphite electrode, but the platinum electrode itself is extremely expensive. Not only is it economically disadvantageous, but platinum that elutes from this platinum electrode has a great adverse effect on the semiconductor manufacturing process when it is transferred to the quaternary ammonium hydroxide aqueous solution of the product, even if it is an extremely small amount, In particular, there is a problem that strict control is required when manufacturing the processing liquid used in the VLSI manufacturing process. Also, stainless steel electrodes are subject to severe wear like graphite electrodes, and the cathode side There was a problem that the degree of transition to

[Means for Solving Problems] The present invention has been conceived in view of such a viewpoint, and is a quaternary ammonium salt previously proposed, which is obtained by reacting a trialkylamine with a dialkyl carbonate. The present invention relates to an improvement of the invention using an inorganic acid salt of ammonium, in which a relatively inexpensive nickel electrode is used as an anode and the consumption of the electrode is small, and a high-purity quaternary ammonium hydroxide aqueous solution is produced. The present invention provides a method for producing an aqueous quaternary ammonium hydroxide solution.

That is, the present invention is an electrolysis in which a trialkylamine and a dialkyl carbonate are reacted to synthesize a quaternary ammonium inorganic acid salt, and then a cation exchange membrane is used as a diaphragm, and at least the anode is composed of a nickel electrode. It is a method for producing a quaternary ammonium hydroxide aqueous solution in which a bath is used to electrolyze the inorganic acid salt.

The trialkylamine used in the present invention can preferably include trimethylamine and triethylamine, and the dialkyl carbonate can preferably include dimethyl carbonate and diethyl carbonate. These are preferably methanol or ethanol. A quaternary ammonium inorganic acid salt is produced by reacting in a solvent.

Regarding the reaction conditions for producing the quaternary ammonium inorganic acid salt, the reaction molar ratio of trialkylamine and dialkyl carbonate is 1 mol or more of trialkylamine to 1 mol of dialkyl carbonate, preferably 2 mol or more. The reaction temperature is 100 to 150 ° C., preferably 140 to 150 ° C., the reaction pressure is usually 6.0 to 20 kg / cm ² , and the reaction time is usually 2 hours or longer, preferably 4 hours or longer. For example, 2 mol of trimethylamine for 1 mol of dimethyl carbonate.
When moles are added and the reaction is carried out under the conditions of a reaction temperature of 140 ° C, a reaction pressure of 16 kg / cm ² and a reaction time of 5.5 hours, ditetramethylammonium carbonate with 2 quaternary ammonium ions is synthesized at a ratio of 90% or more. It has been confirmed that

Then, from the reaction product obtained by the above reaction, a reaction solvent such as methyl alcohol, unreacted trialkylamine, dialkyl carbonate or the like is removed by distillation or reduced pressure distillation,
Then, the reaction product is purely dissolved and distilled again or distilled under reduced pressure. It has been confirmed that the reaction product after the distillation treatment does not contain alkyltetraalkylammonium carbonate with one quaternary ammonium.

Then, the above-mentioned reaction product quaternary ammonium inorganic acid salt, specifically ditetraalkylammonium carbonate,
An aqueous solution of tetraalkylammonium hydrogen carbonate or a mixture thereof is supplied to the anode chamber of an electrolytic cell having a cation exchange membrane as a diaphragm, and is electrolyzed even when a DC voltage is applied, and quaternary ammonium ions generated by this electrolysis. Passes through the cation exchange membrane and moves to the cathode chamber, where quaternary ammonium hydroxide is accumulated. At this time, hydrogen is generated at the cathode, and carbon dioxide gas and oxygen are generated at the anode.

In the present invention, a nickel electrode is used for at least the anode among the electrodes used in the electrolytic cell.

The cathode may be any one as long as it is an alkali-resistant electrode, but a stainless electrode or a nickel electrode having excellent alkali resistance is preferably used.

Further, it is preferable to use a fluorocarbon type exchange membrane having excellent durability as the cation exchange membrane, but in the present invention, halogen ions and formate ions which adversely affect the cation exchange membrane are generated during electrolysis. Therefore, inexpensive polystyrene-based or polypropylene-based exchange membranes can also be used.

In electrolysis in the electrolytic cell, an aqueous solution of a quaternary ammonium inorganic acid salt is circulated to the anode chamber and pure water is supplied to the cathode chamber, and the residence time of each liquid in the anode chamber and the cathode chamber is 60. It is preferable to set within 1 second, preferably 1 to 10 seconds, and set the current density within the range of 1 to 50 A / dm ² . At this time, the concentration of the aqueous solution of the inorganic acid salt supplied to the anode chamber is within 60% by weight, preferably 5 to 40% by weight.
It is better to set the value of quaternary ammonium hydroxide to 0.01 to 1.0% by weight only at the start of operation because the electric conductivity of pure water supplied to the anode chamber is low and electrolysis is difficult to occur at the start of operation. It is better to use the one with a certain amount added.

Since the present invention is intended to produce an ultrahigh-purity quaternary ammonium hydroxide aqueous solution, it is of course possible to use a highly purified trialkylamine or dialkyl carbonate as a raw material, or the like. It is desirable to thoroughly wash each member of the electrolytic cell, the storage tank of the circulating fluid, and the like in advance.
Further, it is desirable to seal the electrolytic cell and the storage tank with a high-purity inert gas in order to prevent impurities from entering from the outside of the system.

[Operation] In the present invention, the quaternary ammonium inorganic acid salt synthesized by the reaction of a trialkylamine and a dialkyl carbonate is electrolyzed in an electrolytic cell equipped with an anode composed of a nickel electrode to minimize the consumption of the anode. It is considered that the cation exchange membrane can effectively prevent the trace amount of nickel ions generated by the consumption of the nickel electrode from permeating to the cathode chamber side.

[Examples] Hereinafter, the present invention will be specifically described based on Examples and Comparative Examples.

Example 1 124 g of trimethylamine (about 2.1 mol) was placed in a pressure resistant reactor.
e), 95 g (about 1.05 mole) of dimethyl carbonate and 200 g of methyl alcohol are charged and dissolved, and this is reacted at a reaction temperature of 120 ° C., a reaction pressure of 13 kg / cm ² and a reaction time of 5.5 hours, and the reaction mixture is used as a solvent. Methyl alcohol and unreacted starting materials trimethylamine and dimethyl carbonate were separated and removed by distillation under reduced pressure, and the resulting reaction product was purified to 0.2%.
Dissolved in, and distilled again under reduced pressure to completely remove methyl alcohol and the like remaining in the aqueous solution, and then added pure again to give a quaternary ammonium inorganic acid salt solution having a concentration of 0.65 mole / 2.5.
Got

On the other hand, a nickel electrode was inserted as an anode in the polypropylene anode chamber, and a stainless (SUS304) electrode was inserted as a cathode in the stainless (SUS304) cathode chamber.
An electrolytic cell having a structure in which a fluorocarbon-based ion exchange membrane (Nafion 324 manufactured by DuPont Co., Ltd.) was arranged between these anode chambers was prepared.

The aqueous solution of the quaternary ammonium inorganic acid salt was circulated in the anode chamber of this electrolytic cell under the condition of residence time of 2.5 seconds, and 0.1 g of tetramethylammonium hydroxide aqueous solution was circulated in the cathode chamber under the condition of residence time of 5 seconds. , A voltage of 13 V and a current of about 2.0 A / dm ² applied between the anode and cathode for about 3
After electrolysis for 2 hours, tetramethylammonium hydroxide 1
An aqueous solution in which 75 g was dissolved was prepared.

The anolyte and anolyte were sampled at the start of electrolysis and at regular intervals thereafter, and the nickel concentration was measured by IPC emission spectrometry and flameless atomic absorption spectrometry, and tetramethylammonium hydroxide (TMAH) in the catholyte was used. ) The concentration was measured. The results are shown in Table 1.

Comparative Example 1 Electrolysis was performed under the same conditions as in Example 1 except that tetramethylammonium formate was used as the quaternary ammonium inorganic hydrochloric acid. In Comparative Example 1, about 15 hours after the start of electrolysis, the anolyte was colored deep green, and the nickel electrode used as the anode was significantly corroded and consumed. Therefore, the electrolysis was stopped at this point. The nickel concentration in the anolyte and catholyte and the tetramethylammonium hydroxide (TMAH) concentration in the catholyte measured in the same manner as in Example 1 above
Shown in the table.

Comparative Example 2 Electrolysis was carried out for 32 hours under the same conditions as in Example 1 except that a graphite electrode was used as the anode.

In the case of this Comparative Example 2, the total amount of the anolyte was reduced to 0 every 6 hours.
After filtering with a 2 μm filter, graphite fine particles were collected and dried, and the weight thereof was measured. The results are shown in Table 3.

Comparative Example 3 Electrolysis was performed under the same conditions as in Example 1 except that a stainless (SUS304) electrode was used as the anode. In Comparative Example 3, the iron concentration and chromium concentration in the anolyte and catholyte and the tetramethylammonium hydroxide (TMAH) concentration in the catholyte were measured in the same manner as in Example 1 above. The results are shown in Table 4.

[Effects of the Invention] According to the method of the present invention, a relatively inexpensive nickel electrode can be used as the anode, the consumption of this electrode is small, and impurities such as metal ions which are harmful in the manufacturing process of the semiconductor device are used. In addition to the extremely small amount of graphite, it does not contain graphite fine particles at all, and it does not contain impurities such as halogen ions that cause corrosion problems of storage containers. An aqueous ammonium solution can be produced.

Claims (4)

[Claims] 1. An electrolytic cell in which a trialkylamine and a dialkyl carbonate are reacted to synthesize a quaternary ammonium inorganic acid salt, and then a cation exchange membrane is used as a diaphragm, and at least the anode is composed of a nickel electrode. A method for producing a quaternary ammonium hydroxide aqueous solution, which comprises electrolyzing the above-mentioned inorganic acid salt using. 2. The method for producing a quaternary ammonium hydroxide aqueous solution according to claim 1, wherein the inorganic acid salt is ditetramethylammonium carbonate. 3. The method for producing an aqueous solution of quaternary ammonium hydroxide according to claim 1, wherein the inorganic acid salt is tetramethylammonium hydrogen carbonate. 4. The method for producing an aqueous solution of quaternary ammonium hydroxide according to claim 1, wherein the inorganic hydrochloric acid is a mixture of ditetramethylammonium carbonate and tetramethylammonium hydrogen carbonate.