JP2000246076A - Gas dissolution method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple and highly precise method for controlling the gas concentration of water in which a gas is dissolved and which is to be used for wet washing of electronic materials such as a silicon substrate for semiconductors, a glass substrate for liquid crystals. SOLUTION: This method is for obtaining water in which a gas is dissolved in a desired concentration at a prescribed temperature and a prescribed pressure and is carried out by adjusting the temperature or the pressure of water in which the gas is to be dissolved to be that at which the desired concentration is equal to the saturated concentration and then supplying and dissolving the gas to and in the water until the gas is dissolved to the saturated concentration. Next, the resultant water saturated with the gas at the adjusted temperature or the adjusted pressure is adjusted to be the prescribed temperature or the prescribed pressure to give an unsaturated water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a gas dissolving method. More specifically, the present invention can control the gas concentration of gas-dissolved water used for wet cleaning of electronic materials such as silicon substrates for semiconductors and glass substrates for liquid crystals by a simple method and with high accuracy. It relates to a gas dissolution method.

[0002]

2. Description of the Related Art Removal of fine particles, organic substances, metals, and the like from the surface of electronic materials such as silicon substrates for semiconductors, glass substrates for liquid crystals, and quartz substrates for photomasks is necessary to ensure product quality and yield. Very important. For this purpose, wet cleaning is performed at a high temperature using a concentrated chemical based on hydrogen peroxide, which is a so-called RCA cleaning method, and a mixed solution of ammonia and hydrogen peroxide (APM) or hydrochloric acid and hydrogen peroxide is used. Mixed solution (HPM)
And so on. The use of these cleaning methods reduces the cost of chemical solutions, the cost of ultrapure water for rinsing, the cost of waste liquid treatment, and the cost of air conditioning that exhausts chemical vapors and prepares fresh air. In recent years, the wet cleaning process has been reviewed in order to reduce the burden on the environment such as mass disposal of drugs and emission of exhaust gas. The present inventors previously dissolved a specific gas in ultrapure water,
We have developed a functional wash water that is prepared by adding a trace amount of chemicals as needed, uses a very small amount of chemicals, and exhibits excellent cleaning effects. This functional washing water has been highly evaluated for its resource saving and environmental preservation, and has been used in place of high-concentration chemicals. Examples of the gas used for the functional cleaning water include hydrogen gas, oxygen gas, ozone gas, rare gas, and carbon dioxide gas. The functional cleaning water in which these gases are dissolved has a cleaning effect comparable to that of a conventionally used high-concentration chemical cleaning while maintaining properties close to pure water. In particular, rare gas dissolved water such as hydrogen gas dissolved water, oxygen gas dissolved water, argon, etc.
When used in a washing step using ultrasonic waves, an extremely high effect of removing fine particles is exhibited. In the production of gas-dissolved water, the use of an accurate gas flow controller or the like can provide water with a relatively high concentration of a specific gas dissolved therein with good reproducibility. However, as the use of functional cleaning water in which a specific gas is dissolved has been widespread, a gas dissolving method that can more simply and precisely control the concentration of a dissolved gas has been required.

[0003]

SUMMARY OF THE INVENTION According to the present invention, the gas concentration of gas-dissolved water used for wet cleaning of electronic materials such as silicon substrates for semiconductors and glass substrates for liquid crystals is controlled by a simple method with high accuracy. The purpose of the present invention is to provide a gas dissolving method which can be carried out in the above.

[0004]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventor has adjusted the water for dissolving the gas to a temperature or a pressure at which the desired concentration becomes the saturation concentration, and adjusted the gas. After supplying and dissolving the gas to the saturated concentration, the temperature or pressure of the obtained gas-saturated dissolved water is adjusted again to obtain the unsaturated dissolved water, so that the dissolved gas concentration can be accurately controlled by a simple operation. The inventors have found that the present invention has been achieved, and have completed the present invention based on this finding. That is, the present invention provides (1) a method of obtaining gas-dissolved water having a desired concentration at a predetermined temperature and a predetermined pressure, wherein the water for dissolving the gas is adjusted to a temperature or pressure at which the desired concentration is a saturated concentration. Supplying gas to the water to dissolve the gas to a saturation concentration,
Next, the present invention provides a gas dissolving method in which the obtained gas-saturated dissolved water at the adjusted temperature or the adjusted pressure is adjusted to a predetermined temperature or a predetermined pressure to obtain unsaturated dissolved water.
Further, as a preferred embodiment of the present invention, (2) after heating the ultrapure water to room temperature or higher, dissolve the gas to a saturation concentration at that temperature, and then lower the temperature of the gas-dissolved water to room temperature. (3) The gas dissolving method according to (2), wherein the gas to be dissolved is hydrogen gas, oxygen gas, argon gas, krypton gas or xenon gas, and (4) ultrapure water is retained. The gas dissolving method according to item (1), wherein the gas is dissolved to a saturated concentration at that pressure while maintaining the sealed environment under reduced pressure below normal pressure, and then the environment of the gas-dissolved water is returned to normal pressure, and (5) The gas dissolving method according to (4), wherein the gas to be dissolved is hydrogen gas, oxygen gas, helium gas, neon gas, argon gas, krypton gas or xenon gas.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The gas dissolving method of the present invention is a method for obtaining gas-dissolved water having a desired concentration at a predetermined temperature and a predetermined pressure. Or, after adjusting to a pressure, a gas is supplied to the water to dissolve the gas to a saturated concentration, and then the obtained gas-saturated dissolved water at the adjusted temperature or the adjusted pressure is adjusted to a predetermined temperature or a predetermined pressure. To obtain unsaturated dissolved water. The method of the present invention is used for cleaning the surface of an electronic material such as a silicon substrate for a semiconductor, a glass substrate for a liquid crystal, and a quartz substrate for a photomask to remove fine particles,
It can be suitably used for preparing ultrapure water in which hydrogen gas, oxygen gas, rare gas and the like are dissolved. Since the cleaning power of gas-dissolved water used for cleaning electronic materials, etc., varies depending on the concentration of dissolved gas, it is necessary to strictly control the concentration of dissolved gas in gas-dissolved water in the cleaning process where a constant cleaning effect is always required. There is. Since the amount of gas dissolved in water is uniquely determined by the temperature and pressure, the water in which the gas is dissolved is adjusted to a temperature or pressure at which the desired dissolved gas concentration is saturated, and then the gas is supplied to saturate. Dissolved gas concentration, and then adjusting the obtained gas-saturated dissolved water at the adjusted temperature or the adjusted pressure to a predetermined temperature or a predetermined pressure to obtain a gas-dissolved water whose dissolved gas concentration is strictly controlled. Can be. In the method of the present invention, only the temperature of the water in which the gas is dissolved can be adjusted, only the pressure can be adjusted, or both the temperature and the pressure can be adjusted simultaneously.

In the method of the present invention, the water for dissolving the gas is degassed in advance to reduce the saturation of the dissolved gas,
It is preferable to dissolve the gas after making a space in the gas dissolving capacity. In the present invention, the gas saturation refers to the amount of gas dissolved in water at a temperature of 25.
It is a value obtained by dividing the amount of gas dissolved at 1 ° C. and 1 atm. For example, when water is in equilibrium with a nitrogen gas at a temperature of 25 ° C. and a pressure of 1 atm, the dissolved amount of the nitrogen gas in the water is 17.6 mg / liter. Gas only, dissolved amount 17.6mg
/ Liter of water is 1.0 times, the only gas dissolved in water is nitrogen gas, and the dissolved amount of 8.8 mg / liter of water is 0.5. It is twice. Water in equilibrium with air at a temperature of 25 ° C. and a pressure of 1 atm is dissolved in 13.7 mg / liter of nitrogen gas and 8.1 mg / liter of oxygen gas to become 1.0 times in saturation. Therefore, the degree of saturation of water is 0.2 times when the amount of dissolved gas is set to 2.7 mg / liter of nitrogen gas and 1.6 mg / liter of oxygen gas by degassing. Water with a saturation of 0.5 times
Since there is a space corresponding to the saturation of 0.5 times in the gas dissolving capacity, other gas corresponding to the saturation of 0.5 times can be easily and quickly dissolved. Further, water having a saturation degree of 0.2 times has a saturation degree of 0.8 in the gas dissolving capacity.
Since there is a space equivalent to twice the amount, another gas corresponding to a saturation degree of 0.8 can be easily and rapidly dissolved. In dissolving the gas by the method of the present invention, there is no particular limitation on the method of degassing water, and for example, vacuum degassing, reduced pressure film degassing, and the like can be used. The method for dissolving the gas in water is not particularly limited, and may be, for example, bubbling, dissolution using a gas permeable membrane, or the like.

Since gas-dissolved ultrapure water used as washing water for electronic materials and the like is often used at room temperature, after heating ultrapure water to room temperature or higher, the gas is dissolved to a saturation concentration at that temperature. Then, by lowering the temperature of the gas-dissolved water to room temperature, gas-dissolved water having a desired concentration can be obtained. A method in which water is heated to dissolve the gas to a saturated concentration and then cooled is suitable as a method for obtaining gas-dissolved water having a relatively high concentration. For example, the amount of hydrogen gas dissolved in water is almost constant at a temperature of 50 ° C. or higher, which is 1.4 mg / water.
Since it is liter, the water temperature is raised to 50 ° C. to dissolve the hydrogen gas to the saturation concentration, and then cooled to 25 ° C. to obtain water in which the hydrogen gas is dissolved at about 0.9 times the saturation concentration. it can. Since the amount of oxygen gas dissolved in water at 80 ° C. is 25.1 mg / liter, the water temperature is set at 8 ° C.
The temperature was raised to 0 ° C. to dissolve oxygen gas to a saturation concentration,
By cooling down to ° C., water in which oxygen gas having a saturation concentration of about 0.6 times is dissolved can be obtained. The method in which water is heated to dissolve the gas to the saturation concentration and then cooled can be applied to hydrogen gas, oxygen gas, argon gas, krypton gas, xenon gas, etc., in which the saturation concentration increases as the water temperature decreases. . When the temperature of the water for dissolving the gas is higher than the use temperature of the water for dissolving the gas, the step of heating the water for dissolving the gas can be omitted.

[0008] Since gas-dissolved ultrapure water used as washing water for electronic materials and the like is often used at normal pressure, the sealed environment in which ultrapure water is held is depressurized to a normal pressure or lower, and then gaseous. To the saturation concentration at that pressure,
Next, by returning the environment of the gas-dissolved water to normal pressure, gas-dissolved water having a desired concentration can be obtained. According to the method of dissolving the gas to a saturated concentration by reducing the pressure of water and then returning the gas to a normal pressure, a relatively wide range of the dissolved gas concentration can be selected. That is, the amount of gas dissolved in water in a decompressed state approximately follows Henry's law, and the vapor pressure of water at a temperature of 25 ° C. is 24 mmHg. After dissolving to a saturated concentration, the pressure is returned to normal pressure, whereby water in which a gas having a concentration of about 0.1 times the saturated concentration at normal pressure is dissolved can be obtained.
After dissolving the gas to the saturated concentration at that pressure while maintaining the closed environment where water is held under reduced pressure, the method of returning the environment of the gas-dissolved water to normal pressure is hydrogen gas, oxygen gas, helium gas, It can be applied to almost all gases such as neon gas, argon gas, krypton gas and xenon gas. There is no particular limitation on the method of returning the water in which the gas has been dissolved to the saturated concentration in the closed environment under reduced pressure to normal pressure. It can be transported to a point of use and used for cleaning or the like, or the gas-dissolved water can be sent out of a sealed environment to a storage tank maintained at normal pressure using a pump and temporarily stored.

When the method of the present invention is applied to ultrapure water and the obtained gas-dissolved ultrapure water is used as washing water for electronic materials and the like, the ultrapure water used as raw water has an electrical resistivity at a temperature of 25 ° C. 18 MΩ · cm or more and one organic carbon
0 μg / liter or less, and the metal content is 20 n
g / liter or less, and preferably 10,000 particles / liter or less. When preparing gas-dissolved ultrapure water according to the method of the present invention and using it for cleaning electronic materials and the like, deterioration of water quality due to temperature control or pressure control must be avoided. It is preferable that the member is a member such as a fluororesin which does not cause deterioration of water quality. For example, a plurality of fluororesin tubes are bundled and put in a container, water for dissolving gas is flowed inside or outside the tubes, and a heating medium or a cooling medium is passed or held on the opposite side through the tube wall surface. And the like.
As a medium for heating and cooling, a gas other than a liquid such as water can be applied, but a liquid having a large heat capacity is suitable from the viewpoint of a temperature control effect. According to the method of the present invention, a gas dissolved water whose dissolved gas concentration is strictly controlled by dissolving a specific gas to a saturated concentration in a heated state or a reduced pressure state without using an expensive gas flow rate adjusting device or the like. Can be obtained easily and with good reproducibility.

[0010]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. In the following examples, under normal temperature (25 ° C.) and normal pressure (1 atm), it is less than saturated,
The objective was to produce ultrapure water in which 33 mg / liter of oxygen gas was dissolved, which had a sufficient cleaning effect.
The temperature and pressure at which 33 mg / liter becomes the saturated dissolved concentration of oxygen gas are calculated from known data.
It can be seen that the temperature is 0.83 atm in the case of ° C. and normal temperature. Example 1 Ultrapure water was degassed under reduced pressure using a degassing membrane module, and then degassed using a Teflon heat exchanger.
The mixture was heated to 0 ° C., and dissolved in oxygen gas by bubbling under normal pressure using an excess amount of oxygen gas. Then, after cooling to room temperature again using another Teflon heat exchanger, the gas phase was stored in a storage tank in a nitrogen gas atmosphere. When the dissolved oxygen gas concentration of the oxygen gas-dissolved water was measured using a dissolved oxygen meter, it was 33 mg / liter as intended. A 6-inch diameter silicon wafer whose surface was oxidized with ozone-containing ultrapure water was contaminated with alumina fine powder to prepare a contaminated wafer having alumina fine particles adhered to the surface. Wafer / dust detector [Tokyo Optical Machinery
And the number of fine particles having a diameter of 0.2 μm or more per wafer was 44,000.
Individually adhered. The contaminated wafer was rotated at 500 rpm, and the above-mentioned oxygen gas-dissolved water was subjected to an ultrasonic irradiation nozzle [Pretec, Fine Jet] at a frequency of 1.6 MHz.
Was applied at a flow rate of 700 ml / min while irradiating the ultrasonic wave at an output of 13.5 W, and spin cleaning was performed for 60 seconds. Next, the substrate was rinsed with ultrapure water and dried. The number of particles attached on the wafer surface after drying was measured in the same manner. As a result, the number was 2,520, and the removal rate of the particles was 94.3.
%Met. Example 2 Ultrapure water was subjected to membrane degassing in the same manner as in Example 1, followed by 0.8
It was led to a reduced-pressure closed vessel adjusted to 3 atm, and oxygen gas was dissolved by bubbling in this vessel using an excess amount of oxygen gas. Thereafter, the oxygen gas-dissolved water was introduced into a storage tank maintained at normal pressure in a nitrogen gas atmosphere and stored. When the dissolved oxygen gas concentration of the oxygen gas-dissolved water was measured using a dissolved oxygen meter, it was 33 mg / liter as intended. Using this oxygen gas dissolved water, the contaminated wafer prepared in Example 1 was cleaned in the same manner as in Example 1. The number of the attached fine particles on the wafer surface after drying was 2,650, and the removal rate of the fine particles was 94.0%. Comparative Example 1 A degassing membrane module and a gas-dissolving membrane module were connected, ultrapure water was degassed in a prestage degassing membrane module, and oxygen gas was dissolved by quantitative gas supply in a latter stage gas dissolving membrane module. As a result, oxygen gas dissolved water having a dissolved oxygen gas concentration of 33 mg / liter was prepared. Using this oxygen gas dissolved water, the contaminated wafer prepared in Example 1 was cleaned in the same manner as in Example 1. The number of attached fine particles on the wafer surface after drying was 2,600, and the removal rate of fine particles was 94.
1%. Table 1 shows the results of Examples 1 and 2 and Comparative Example 1.

[0011]

[Table 1]

From the results shown in Table 1, the oxygen gas-dissolved water of Example 1 prepared by dissolving oxygen gas at 40 ° C. and then cooling to room temperature, and dissolving oxygen gas at 0.83 atm and then normal pressure The oxygen gas-dissolved water of Example 2 prepared by reverting to the above has the same cleaning effect as the oxygen gas-dissolved water of Comparative Example 1 prepared using an apparatus in which a degassing membrane module and a gas dissolving membrane module are connected. I understand.

[0013]

According to the gas dissolving method of the present invention, gas dissolved water in which the dissolved concentration of a specific gas is highly controlled can be produced economically without strict control of the gas supply amount. it can.

Claims (1)

[Claims] 1. A method for obtaining gas-dissolved water having a desired concentration at a predetermined temperature and a predetermined pressure, comprising:
After adjusting the temperature or pressure to the desired concentration to a saturated concentration, supplying a gas to the water to dissolve the gas to a saturated concentration,
Next, a gas dissolving method in which the obtained gas-saturated dissolved water at the adjusted temperature or the adjusted pressure is adjusted to a predetermined temperature or a predetermined pressure to obtain unsaturated dissolved water.