JPH11323579A - Humidity controlling method in clean room - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a humidity controlling method in a clean room by which corrosion in pipings and devices in a vapor and condensed water system can be prevented by using a neutralizing amine having a cyclic structure as a treating agent for boiler condensed water, by which contamination of a silicon wafer due to amines when humidifying vapor from a boiler is introduced into the clean room, and by which problems of products due to the contamination can be avoided. SOLUTION: A neutralizing amine having a cyclic structure such as morpholine and cyclohexylamine is used as a treating agent for a boiler condensed water. The obtd. boiler vapor is used to humidify a clean room. Especially, in the case of using neutral amines having plural cyclic structure with different partition ratios (such as an amine having 0.01 to 2 partition ratio and an amine having >2 partition ratio), it is advantageous for the corrosion preventing effect and economy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of adjusting the humidity in a clean room by supplying humidifying boiler steam to a clean room (clean room), and more particularly to a method for controlling the humidity in a clean room using humidifying boiler steam. The present invention relates to a method for adjusting humidity in a clean room, which makes it possible to minimize boiler steam and condensate system piping and equipment while minimizing contamination of wafers and the like.

[0002]

2. Description of the Related Art Metal materials such as carbon steel used for steam / condensation system piping of a boiler are corroded by the action of oxygen or carbon dioxide contained in the steam / condensation system. In particular, carbon dioxide (carbon dioxide) generated by thermal decomposition of the M-alkaliness component (bicarbonate) contained in the feedwater in the boiler is condensed when the vapor (gas phase) condenses. ), Which causes severe corrosion of the metal by lowering the pH of the condensate, which is the main cause of corrosion of the steam / condensate piping.

Conventionally, as a method for preventing such metal corrosion due to carbon dioxide gas, a method of decarboxylation of condensed water using an ion exchange device or a degassing device, and a method of decondensing with a neutralizing amine. A method of adjusting the pH of water and a method of preventing metal corrosion due to carbon dioxide gas by forming a water-repellent protective film on the metal surface using a long-chain aliphatic amine (film-forming amine) have been performed. Among these methods,
A method using a neutralizing amine is widely used from the viewpoint of anticorrosion effect and economy.

[0004]

In the case of using a neutralizing amine to protect the steam / condensation system of a boiler, the boiler steam contains a considerable amount of the neutralizing amine. When used in a food processing process or a precision device production process in which the quality (purity) of which quality is required, there is a concern that it may lead to product contamination. Especially,
If boiler steam is used as humidifying steam in a clean room handling silicon wafers, such as in the manufacture of silicon wafers and semiconductors, the adhesion of neutralizing amine to the silicon wafers may cause product defects. There is a problem that there is.

[0005] The present invention has been made in view of such problems,
Humidity in the clean room taking into account minimizing contamination of the silicon wafers and other neutralizing amines in the clean room that uses the boiler steam for humidification, as well as corrosion protection of the boiler steam and the condensing system piping and equipment. The purpose is to establish an adjustment method.

[0006]

The present invention is characterized in that a humidifying boiler vapor is supplied to a clean room by using a neutralizing amine having at least one cyclic structure as a condensing agent for a boiler. It is intended to provide a method of adjusting humidity in a clean room.

Hereinafter, the present invention will be described in detail. The present inventors have found that among various neutralizing amines treated as boiler steam and condensate treatment agents (condensation treatment agents), there is a great difference in the adsorptivity to silicon wafers depending on the type thereof.
We have found that cyclic amines such as morpholine and cyclohexylamine have lower adsorbability (adsorption amount) on silicon wafers than alkanolamines such as monoethanolamine and aminomethylpropanol. The reason why the alkanolamines such as monoethanolamine and aminomethylpropanol have a high adsorptivity (adsorption amount) to a silicon wafer is not necessarily clear, but it is considered that one reason is that hydroxyl groups (OH) are contained. .

On the other hand, in terms of an efficient method of preventing corrosion of piping and equipment of a steam / condensate system (particularly a liquid phase portion) of a general boiler, carbon dioxide which is a main factor of corrosion is efficiently neutralized, and steam is condensed. -Neutralizing amines exhibiting a distribution behavior close to carbon dioxide (partition ratio: 2.1 to 10) (having a large distribution ratio) in order to control the pH suitable for corrosion prevention of the entire condensate system [for example, Cyclohexylamine (partition ratio: 2.1 to
10)] and neutralizing amines [e.g., monoethanolamine, aminomethylpropanol, morpholine (partition ratio: 0.2 to
1.5)] can be used in combination with the anti-corrosion effect and economy of the entire steam / condensation system (reduction of the amount of amine added)
It is effective from the point of view. That is, neutralization of carbon dioxide in the terminal piping system is performed by a neutralizing amine having a large distribution ratio (exceeding a distribution ratio of 2), and neutralization of carbon dioxide in a system near the boiler is reduced by a small distribution ratio ( Distribution ratio 0.01-2)
The role of the two types of neutralizing amines can be shared by performing with a neutralizing amine having the above. When using one type of neutralizing amine, the larger of the minimum required injection amount for each of the above two systems As compared with the case where it is necessary to use the minimum required injection amount or more, a high anticorrosive effect can be secured with a small injection amount.

As is apparent from the above description, the present invention provides a method for adjusting humidity in a clean room using a humidifying boiler vapor, which reduces the effect of adhesion of an amine to a silicon wafer or the like and provides efficient corrosion protection. As a method for realizing, a method using an amine having a cyclic structure as a neutralizing amine is provided,
By using a combination of neutralizing amines having multiple cyclic structures with different distribution ratios, more effective anticorrosion effect and economical efficiency (reduction of amine addition) for the entire steam / condensation system It provides a method that can be used.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail, but the present invention is not limited to these embodiments.

Examples of the neutralizing amine having a cyclic structure which can be used in the present invention include morpholine, cyclohexylamine, N-methylmorpholine, N-ethylmorpholine, piperazine, benzylamine and the like. Among them, morpholine and cyclohexylamine are particularly preferable in view of properties and stability.

These neutralizing amines having a cyclic structure can achieve the object of the present invention even when used alone. However, as is apparent from the above, a plurality of neutralizing amines having different distribution ratios are used. It is preferable to use a neutralizing amine having a cyclic structure in combination. In the case of the present invention, the above-mentioned alkanolamines such as monoethanolamine and aminomethylpropanol have a high adsorptivity to a silicon wafer, so that their use is avoided. That is, as a neutralizing amine having a cyclic structure, the distribution ratio is 0.01 to
Preferably, at least one neutralizing amine having a partition ratio of 0.1 to 2 and at least one neutralizing amine having a partition ratio of 2 to 2 are used in combination. More preferably, more than one neutralizing amine is used in combination.
More preferably, a combination of cyclohexylamine and morpholine is used.

The "partition ratio" mentioned here is simply the ratio of the concentration of the solute in the gas phase (vapor) and the liquid phase (water) when the gas phase (water) is in equilibrium (in the gas phase). Concentration of solute / concentration of solute in liquid phase). For details, refer to “Boiler Water Management <Basic and Actual>,” edited by the Japan Boiler Association (issued in 1984).
It is described on page 58. That is, in the case of the present invention, the distribution ratio is a boiler pressure of 10 kgf / cm ² or less and the temperature of the liquid phase is from room temperature to 185 ° C., wherein “partition ratio = neutralizing amine concentration in steam / condensate in condensed water” Neutralizing amine concentration ".

The neutralizing amine having a cyclic structure used as a condensing anticorrosive in the present invention is mixed with boiler feed water and injected into the boiler, or directly injected into the boiler or into the steam system depending on the amount of steam generated. By doing so, it is possible to effectively prevent corrosion of steam and condensate piping and equipment, and when supplied to a clean room as boiler steam for humidification, the amount of adsorption to silicon wafers etc. is small, and product Failure can be prevented from occurring.

The amount of the neutralizing amine having a cyclic structure to be added at this time varies considerably depending on the type of the neutralizing amine, the concentration of bicarbonate ion in the feed water, the material of the pipes, the recovery rate of the condensate, and the like. In general, it is as follows. That is,
(1) In the case of pure water supply, 1 to 10 mg of amine is injected per 1 liter (L) of water supply. (2) In the case of soft water supply, 10 to 100 mg of amine is injected in 1 L of water supply. Therefore, the injection amount of a general neutralizing amine is:
That is, 1 to 100 mg / L.

As a typical example of combining a plurality of neutralizing amines having cyclic structures having different distribution ratios, for example, when morpholine and cyclohexylamine are used, the weight ratio of the two is determined by the total amount of both, Although it varies considerably depending on the bicarbonate ion concentration in the medium, the material of the pipe and the like, the recovery rate of condensed water, etc., generally, morpholine: cyclohexylamine = 10: 1 to 1:10, preferably 5: 1 to 1 1: 5. In this case, an example of a typical addition injection amount is about 15 mg / L of morpholine and about 10 mg / L of cyclohexylamine, and the weight ratio of both is about 3: 2.

The neutralizing amine having a cyclic structure as a condensing anticorrosive to be injected into the boiler may be used in combination with, for example, a known oxygen scavenger, a cleaning agent and other various additives. For example, as a deoxidizer, sodium sulfite, glucose, tannic acid or the like (for example, about 10 to 100 mg / L with respect to feed water), and as a cleaning agent, tripotassium phosphate or the like (for example, with respect to feed water) 10-100
mg / L) and potassium hydroxide or the like as an alkali agent (for example, about 5 to 100 mg / L with respect to feed water).

[0018]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto.

EXAMPLE 1 Morpholine and cyclohexylamine as a neutralizing amine having a cyclic structure and monoethanolamine as an alkanolamine were used for supplying water to a boiler which generates boiler steam used for indoor humidity control in a semiconductor manufacturing clean room. Addition of appropriate amounts of aminomethylpropanol and diethylaminoethanol (comparative example) in the range of 10 to 30 ppm neutralizes carbon dioxide in the boiler steam with each of the above amines and prevents corrosion of steam / condensate piping and equipment can do. The concentration of the added amine was adjusted to the minimum concentration at which the desired anticorrosive effect of the piping was obtained. Compared with the above-mentioned alkanolamines conventionally used as neutralizing amines and the long-chain aliphatic amines used as filming amines, the neutralizing amines having a cyclic structure used in this example are more suitable for silicon. By using the method of the present invention, because it has the property of hardly adsorbing on the silicon oxide surface,
In particular, it was possible to reduce the amount of neutralizing amine adsorbed from indoor air humidity-adjusted by boiler vapor on silicon wafers used in a semiconductor manufacturing clean room. As a result, the effects of improving the accuracy of the semiconductor device manufacturing process and improving the yield have been observed.

An experiment for comparing the amount of amine adsorbed on the silicon wafer surface in the boiler vapor by the type of neutralizing amine (this example and a comparative example) was performed as follows. FIG. 1 shows an outline of the experimental apparatus.

In the water supply tank 1, an appropriate amount of various neutralizing amines is added to soft water having a quality as shown in Table 1, and the resulting water is fed to the test boiler 2 as a water supply by the pump P.
The test boiler 2 generated steam. The steam pressure in the test boiler 2 is 10 kgf / cm ² , and the steam generation amount is 3.
0 kg / h, blow rate was 10%. This vapor (including the neutralizing amine) was mixed with a certain amount of air sent from the air cylinder 3 and cooled in the cooler 4. The resulting humidity-adjusted air is sent into a silicon wafer chamber 5 (corresponding to a clean room) and brought into contact with a silicon wafer 7 (diameter 6 inches, hydrophilic), and then a collection liquid tank 6 initially containing pure water. And passed out of the system. The experiment was performed for 24 hours, and the amount of amine adsorbed on the silicon wafer 7 was measured. The neutralizing amine concentration of the humidity-adjusted air (gas phase) in the silicon wafer chamber 5 can be calculated from the air flow rate and the neutralizing amine concentration in the collected liquid in the collected liquid tank 6 after the experiment. . In this case, by adjusting the neutralizing amine concentration in the feed water, the neutralizing amine concentration in the gas phase was adjusted to be around 500 ppb.

[0022]

[Table 1]

Table 2 shows the experimental results. The alkanolamines monoethanolamine, aminomethylpropanol, and diethylaminoethanol were adsorbed in large amounts on the silicon wafer, whereas the cyclohexylamine and morpholine amines having a cyclic structure were hardly adsorbed on the silicon wafer, It can be seen that the amount of adsorption on the wafer could be suppressed to 1/3 to 1/5 of that of alkanolamine.

[0024]

[Table 2]

The following method was used to measure the amount of neutralizing amine adsorbed on the silicon wafer. After the experiment, the silicon wafer 7 was taken out of the silicon wafer chamber 5 and immersed in a glass cell filled with 80 ml of pure water for 30 minutes. Almost all the neutralizing amine adsorbed on the silicon wafer by this immersion was dissolved in pure water (confirmed). The amount of the neutralizing amine adsorbed on the silicon wafer was determined by measuring the amine concentration in the obtained solution by ion chromatography.

Example 2 In this example, morpholine and cyclohexylamine as neutralizing amines having a cyclic structure were used alone for supplying water to a boiler that generates boiler steam used for adjusting indoor humidity in a semiconductor manufacturing clean room. A comparison was made between the case where it was added and the case where it was mixed and added. As the latter case, the following experiment was carried out for two cases of morpholine 15 mg + cyclohexylamine 15 mg (weight ratio = 1: 1) and morpholine 20 mg + cyclohexylamine 10 mg (weight ratio = 2: 1). According to the method of mixing and using a plurality of neutralizing amines having different distribution ratios according to the present embodiment, by using a neutralizing amine having a cyclic structure, the silicon wafer is removed from the indoor air humidity-adjusted by boiler steam. In addition to being able to reduce the amount of neutralizing amine adsorbed on the surface, the use of a mixture of two or more neutralizing amines with different distribution ratios has the effect of using steam and condensate piping and equipment throughout the entire system. Can be anticorrosive. In the method of adding only one type of neutralizing amine, the corrosion prevention effect differs depending on the location of the steam / condensation system piping and equipment. It was necessary to adjust the addition injection amount. On the other hand, according to the method of mixing and using a plurality of neutralizing amines having different distribution ratios in the present embodiment, since the anticorrosion effect is almost constant without being substantially different depending on the location of the piping, it can be applied to the boiler water supply. Even if the injection concentration of the neutralizing amine is set lower than usual, it is possible to obtain a sufficient anticorrosion effect over the steam / condensation system piping and the entire equipment. The amount of adsorption of the neutralizing amine could be further reduced.

An experiment for comparing the difference in the anticorrosion effect by the above-described method for preparing a neutralizing amine (single or mixed) was carried out.
The procedure was as follows. Using an experimental apparatus as shown in FIG. 2, the condensation rate of the vapor containing the neutralizing amine generated from the autoclave 12 was changed to 10%, 50%, and 90%. The corrosion prevention effect of the neutralizing amine was examined by measuring the corrosion rate of the test piece.

In the water supply tank 11, an appropriate amount of various neutralizing amines and 25 mg / L of potassium hydroxide are added to soft water having the quality shown in Table 1 in Example 1, and the water is supplied to the autoclave 12 as a pump. , And steam was generated by the autoclave 12. The steam pressure of the autoclave 12 was 10 kgf / cm ² , the amount of generated steam was 3.0 kg / h, and the blow rate was 10%. After the steam (including the neutralizing amine) is cooled to an appropriate temperature by the cooler 13, the steam is introduced into the corrosion evaluation tank 14, and the pressure in the tank and the discharge amount of the steam are varied to condense the steam. The rate was adjusted. And the condensation rate is 10%, 50%,
By setting it to 90%, the tip, middle, and end of the steam / condensate system pipe are reproduced, and in each case, the pH of the liquid phase and the mild steel test piece 15 (1.
0 × 30 × 50mm) corrosion rate (mg / dm ² · da)
The anticorrosion effect was evaluated by measuring y).
The experimental period was two weeks.

Table 3 shows the experimental results. When the neutralizing amine was used alone, the corrosion rate varied considerably with changes in the condensation rate. On the other hand, it was found that when two kinds of neutralizing amines having different distribution ratios (morpholine and cyclohexylamine) were used in combination, a low corrosion rate was always exhibited irrespective of the fluctuation of the condensation rate. This is presumably because when two kinds of neutralizing amines having different distribution ratios are used in combination, the pH of the condensate is almost always constant without depending on the condensation rate.

[0030]

[Table 3]

The corrosion rate was determined according to the following equation (1).

[0032]

(Equation 1)

[0033]

According to the present invention, by using a neutralizing amine having a cyclic structure as a condensing agent for a boiler, corrosion of piping and equipment of a steam / condensing system is prevented, and humidity is controlled by boiler steam. It is possible to reduce the amount of neutralizing amine adsorbed on the silicon wafer in the cleaned clean room, and to eliminate defects of the product due to the adhesion of the amine.

When a plurality of neutralizing amines having different distribution ratios are combined and used as a condensing agent for a boiler,
The condensate can be maintained at a high pH, and not only can the condensate piping and equipment be effectively protected from corrosion throughout the system, but also the neutralization of silicon wafers in clean rooms using humidifying boiler steam. Amine contamination can also be minimized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an experimental apparatus for examining the amount of amine in a boiler vapor adsorbed on a silicon wafer surface in Example 1.

FIG. 2 is a configuration diagram of an experimental apparatus for examining a corrosion rate of a test piece during condensate in Example 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Water supply tank 2 Test boiler 3 Air cylinder 4 Cooler 5 Silicon wafer chamber 6 Collection liquid tank 7 Silicon wafer 11 Water supply tank 12 Autoclave 13 Cooler 14 Corrosion evaluation tank 15 Test piece

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Sachiko Yanagi 25-1, Ekimae Honmachi, Kawasaki-ku, Kawasaki-ku, Kanagawa Prefecture Inside Toshiba Microelectronics Corporation (72) Inventor Makoto Horiike 1-2-8 Shinsuna, Koto-ku, Tokyo Olga (72) Inventor Yoshiaki Shibata 1-2-8 Shinsuna, Koto-ku, Tokyo Organo Corporation

Claims (3)

[Claims] 1. A method for adjusting humidity in a clean room, comprising supplying a humidifying boiler vapor to a clean room using a neutralizing amine having at least one cyclic structure as a condensing agent for the boiler. 2. The neutralizing amine having a cyclic structure includes at least one neutralizing amine having a distribution ratio of 0.01 to 2 and at least one neutralizing amine having a distribution ratio of more than 2, preferably a distribution ratio of 2. The method for adjusting humidity in a clean room according to claim 1, wherein at least one kind of neutralizing amine of 0.1 to 2 and at least one kind of neutralizing amine exceeding a distribution ratio of 2 are used. 3. The method for adjusting humidity in a clean room according to claim 1, wherein morpholine and / or cyclohexylamine is used as the neutralizing amine having a cyclic structure.