JP2000288362A - Cleaning method of filtration membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently remove fine particles sticking to a filter membrane by bringing the filter membrane into contact with gas-dissolved water in which oxygen gas, hydrogen gas, carbonic acid gas, nitrogen gas or a rare gas is dissolved and thereby cleaning the filter membrane. SOLUTION: A nozzle 3 for a bubble jet fluid mixes a gas-dissolved water fed into a water conveying pipe 1 under pressure with gas forced into an air blowing pipe 2 under a high pressure, in the nozzle 3. When the energy of the gas is transferred to the gas-dissolved water, the gas-dissolved water becomes a fine water flow to be ejected to a filter membrane as a high energy water flow from a nozzle outlet 4. In this case, for cleaning the filter membrane, gas-dissolved water in which oxygen gas, hydrogen gas, carbonic acid gas, nitrogen gas or a rare gas is dissolved, is used. Consequently, the number of fine particles residing on a filter membrane is reduced to about 1/10-1/100. Thus it is possible to rapidly and accurately count, for example, the number of fine particles in high-purity water caught by the filter membrane by a low water throughput, when the measurement is performed by identification using a direct microscopic process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for cleaning a filtration membrane. More specifically, the present invention relates to a method for cleaning a filtration membrane capable of efficiently removing fine particles attached to the filtration membrane.

[0002]

2. Description of the Related Art From the surface of electronic materials such as silicon substrates for semiconductors, glass substrates for liquid crystals, and quartz substrates for photomasks,
Removing impurities such as fine particles, organic matter, and metals
It is extremely important to ensure product quality and yield. Very high purity is required for cleaning water and rinsing water used in a cleaning step for removing impurities. If impurities such as fine particles are mixed in the cleaning water or the rinsing water used in these cleaning steps, the impurities cause secondary contamination on a silicon substrate for semiconductors and the like, thereby causing defects. For this reason, ultrapure water used in the washing step needs to be analyzed in advance to check the quality of the water and to be constantly controlled. As a method for measuring particles in ultrapure water,
On-line measurement using a particle monitor that utilizes laser light scattering, and direct microscopy, in which ultrapure water is filtered using a filtration membrane, and fine particles captured on the filtration membrane are measured using a scanning electron microscope. There is. In the case of direct microscopy, the filtration membrane is washed with water of higher purity than the ultrapure water to be measured, or with water added with ammonia, but still remains on the filtration membrane. Since a considerable amount of initial contaminant particles are attached, it is necessary to pass a large amount of ultrapure water in order to identify and measure the particles in ultrapure water, which is extremely wasteful in terms of both the amount of filtered water and the time of water flow. There are many at present.
For this reason, there is a need for a method for cleaning a filtration membrane that can efficiently remove the attached fine particles by cleaning the filtration membrane.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for cleaning a filtration membrane which can efficiently remove fine particles adhering to the filtration membrane.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, by contacting and washing the filtration membrane with gas-dissolved water, the fine particles adhering to the filtration membrane have been obtained. Have been found to be able to be effectively removed, and the present invention has been completed based on this finding. That is, the present invention provides: (1) a method for cleaning a filtration membrane, which comprises contacting the filtration membrane with gas-dissolved water in which oxygen gas, hydrogen gas, carbon dioxide gas, nitrogen gas or rare gas is dissolved, and Is provided. Further, as a preferred embodiment of the present invention, (2) the method for washing a filtration membrane according to (1), wherein the filtration membrane is a filtration membrane used for a filtration treatment of ultrapure water or a high-purity chemical solution; (1) The method for cleaning a filtration membrane according to the above (1), wherein the membrane is a filtration membrane used for measuring the number of fine particles in ultrapure water or a high-purity chemical solution by direct microscopy; (4) oxygen gas, hydrogen gas, In gas dissolved water in which nitrogen gas or rare gas is dissolved,
(1) The method for washing a filtration membrane according to (1), wherein a high-purity alkali is added, (5) upon contact between the filtration membrane and gas-dissolved water,
(1) The method for cleaning a filtration membrane according to the above (1), wherein ultrasonic waves are transmitted to the filtration membrane or the gas-dissolved water, and (6) the method for bringing the gas-dissolved water into contact with the filtration membrane as a cavitation jet fluid or a bubble jet fluid. The washing method of the filtration membrane described in the item 1) can be mentioned.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for cleaning a filtration membrane according to the present invention, the filtration membrane is cleaned by bringing it into contact with gas-dissolved water in which oxygen gas, hydrogen gas, carbon dioxide gas, nitrogen gas or a rare gas is dissolved. . In the method of the present invention, oxygen gas, hydrogen gas,
Gas-dissolved water in which only one of carbon dioxide gas, nitrogen gas and rare gas is dissolved can be used, or gas dissolved in combination of two or more of oxygen gas, hydrogen gas, carbon dioxide gas, nitrogen gas and rare gas Dissolved water can also be used.
There is no particular limitation on the material of the filtration membrane to be washed by the method of the present invention, and examples thereof include organic filtration membranes such as polyester-based, polycarbonate-based, cellulose-based, and fluororesin-based membranes, and inorganic filtration membranes such as aluminum oxide. Can be. There is no particular limitation on the use of the filtration membrane to be washed by the method of the present invention. For example, ultrafiltration membranes or microfiltration membranes used for filtration of ultrapure water or high-purity chemicals, fine particles in ultrapure water or high-purity chemicals A filtration membrane used for measuring the number by direct microscopy, a filtration membrane for measuring turbidity in water, and the like can be given. Among them, the method of the present invention can be particularly suitably used for washing a filtration membrane for measuring the number of fine particles. In order to measure the number of particles such as ultrapure water directly by microscopy, ultrapure water to be measured is passed through a particle capture filter with a removable filter, After capturing the fine particles and passing a predetermined amount of ultrapure water or the like, the filter membrane is removed from the filter, and the number of fine particles on the filter membrane surface is measured using a scanning microscope. By subtracting the number of fine particles on the filtration membrane surface before passing water from the number of fine particles on the filtration membrane surface after passing water, the number of captured fine particles can be grasped. However, if the number of fine particles on the surface of the filtration membrane before the passage of water is large, the measurement becomes difficult and an error is likely to occur. Also,
If the number of trapped fine particles is not larger than the number of fine particles on the filtration membrane surface before water passage, an error is likely to occur, so that a large amount of water must be passed for measurement, and it takes a long time. . The filtration membrane washed by the method of the present invention,
Since the number of fine particles remaining on the filtration membrane surface is small, the number of fine particles captured by a small amount of water can be accurately measured,
The amount of water required for measurement can be reduced, and the required time can be reduced.

[0006] Oxygen gas, hydrogen gas used in the method of the present invention,
The gas-dissolved water in which carbon dioxide gas, nitrogen gas or rare gas is dissolved is preferably water in which these gases are dissolved in ultrapure water. Ultrapure water has an electrical resistivity of 18M at 25 ° C.
Ω · cm or more, organic carbon is preferably 10 μg / liter or less, and fine particles are preferably 10,000 particles / liter or less. In the method of the present invention, the method for producing gas-dissolved water in which oxygen gas, hydrogen gas, carbon dioxide gas, nitrogen gas or a rare gas is dissolved is not particularly limited. For example, these gases can be dissolved by bubbling water. . However, in order to increase the dissolving efficiency of these gases, water must be degassed in advance to reduce the saturation of dissolved gases,
Preferably, the gas to be dissolved is supplied to dissolve.
Here, the gas saturation is a value obtained by dividing the amount of gas dissolved in water by the amount of gas dissolved at a pressure of 0.1 MPa and a temperature of 20 ° C. For example, water has a pressure of 0.1 MPa and a temperature of 2
Water in equilibrium with air at 0 ° C.
Since 4.9 mg / liter and 9.1 mg / liter of oxygen gas are dissolved and the saturation is 1.0 times, the amount of dissolved gas is reduced by degassing to 3.0 mg / liter of nitrogen gas and 1% of oxygen gas. The saturation of water at 0.8 mg / liter is 0.2 times. Water having a saturation degree of 0.2 times has a space corresponding to 0.8 times the saturation degree in the gas dissolution capacity, so that a gas corresponding to 0.8 times the saturation degree can be easily dissolved. . For example, at a pressure of 0.1 MPa and a temperature of 20 ° C., the amount of hydrogen gas dissolved in water is 1.63 mg / liter, so hydrogen gas is dissolved in water having a saturation degree of 0.2 times.
Hydrogen gas dissolved water having a dissolved hydrogen gas concentration of 1.30 mg / liter can be easily produced. The amount dissolved in water at a pressure of 0.1 MPa and a temperature of 20 ° C. was 44.3 mg of oxygen gas /
Liter, carbon dioxide gas 1,710mg / l, nitrogen gas 19.0mg / l, helium 1.56mg / l,
Neon 9.36 mg / L, Argon 60.8 mg / L, Krypton 233 mg / L, Xenon 643
mg / liter, and gas-dissolved water having a degree of saturation corresponding to each dissolved amount can be produced.

In producing gas-dissolved water, there is no particular limitation on the method of degassing water. For example, vacuum degassing, degassing under reduced pressure, and the like can be used. There is no particular limitation on the method of dissolving the gas in degassed water, for example, bubbling,
Dissolution using an ejector or a gas-permeable membrane module can be performed. Among them, it is preferable to use a gas permeable membrane module in multiple stages to remove dissolved gas and dissolve gas. For example, a gas permeable membrane module is provided in two stages, decompression membrane degassing for all dissolved gases is performed using the gas permeable membrane module in the previous stage, and oxygen gas, hydrogen gas, Carbon dioxide gas, nitrogen gas or rare gas can be dissolved. By installing gas permeable membrane modules in two stages and performing decompression membrane degassing and gas dissolution for all dissolved gases in two stages, gas can be almost quantitatively dissolved without wasteful release. can do. In the method of the present invention, high-purity alkali can be added to gas-dissolved water in which oxygen gas, hydrogen gas, nitrogen gas, or rare gas is dissolved. An alkali is added to the gas-dissolved water to adjust the pH to 8 or more, more preferably 9 to
By adjusting to 10, the effect of removing fine particles on the filtration membrane surface and the effect of preventing re-adhesion can be enhanced. The high-purity alkali to be added is not particularly limited, and examples thereof include ammonia, sodium hydroxide, potassium hydroxide, and tetramethylammonium hydroxide (TMAH). Among these, high-purity aqueous ammonia can be suitably used. In the method of the present invention, there is no particular limitation on the method for cleaning the filtration membrane using gaseous water in which oxygen gas, hydrogen gas, carbon dioxide gas, nitrogen gas or a rare gas is dissolved, and, for example, the filtration membrane is hung by a clamp. Batch treatment can be performed by immersing in a washing tank filled with gas-dissolved water, or single-wafer cleaning in which a filter membrane is placed on a loader and gas-dissolved water is poured into the filter membrane for treatment. Can also. It is preferable that the gas-dissolved water in the cleaning tank be in a fluidized state, and it is preferable that the gas-dissolved water be continuously supplied and washed while overflowing. The washing tank can be provided in two or more stages. When gas-dissolved water to which alkali is added is used, it is preferable that the last washing tank be filled with ultrapure water and rinsed. Also in single wafer cleaning, when using gas-dissolved water to which alkali is added, it is preferable to provide a rinsing step after cleaning. In the method of the present invention, ultrasonic waves can be transmitted to the filter membrane or the gas-dissolved water when the filter membrane is washed with the gas-dissolved water. By transmitting the ultrasonic waves, the effect of removing the fine particles on the filtration membrane surface can be enhanced. The frequency of the transmitted ultrasonic wave is not particularly limited, but is preferably 10 kHz to 3 MHz. There is no particular limitation on the method of transmitting ultrasonic waves to the filtration membrane or the gas-dissolved water. For example, a cleaning tank of an ultrasonic cleaner can be filled with gas-dissolved water and the filtration membrane can be immersed, or an ultrasonic oscillator Gas-dissolved water can also be sprayed on the filtration membrane using a nozzle with a gas nozzle.

In the method of the present invention, the gas-dissolved water can be jetted as a jet fluid to the filtration membrane held by the holding tool. The form of the jet fluid is not particularly limited, and examples thereof include a bubble jet fluid and a cavitation jet fluid. FIG. 1 is a sectional view of a nozzle for a bubble jet fluid and a plan view showing a nozzle outlet shape. To the nozzle for the bubble jet fluid, gas-dissolved water is sent to the water supply pipe 1 at high pressure, gas is sent to the air supply pipe 2 at high pressure, and the gas-dissolved water and gas are mixed in the nozzle 3. The energy of the gas is transferred to the gas-dissolved water by the mixing of the gas-dissolved water and the gas, and the gas-dissolved water is turned into a fine water stream, which is jetted from the nozzle outlet 4 as a high-energy water stream to the filtration membrane. The pressure of the gas dissolved water to water in the nozzle is preferably 2 to 10 kg / cm ^2, more preferably 4~7kg / cm ^2. The pressure of the gas air to the nozzle is preferably 2 to 10 kg / cm ^2, more preferably 3~6kg / cm ^2. FIG. 2 is a sectional view of a nozzle for a cavitation jet fluid and a plan view showing a nozzle outlet shape. The nozzle for cavitation jet fluid is a high pressure water pipe 5
And a low-pressure water supply pipe 6, and gas-dissolved water is supplied to each of the water supply pipes. At the nozzle outlet, high-pressure water is sprayed from a small-area opening 7 in the center of the nozzle, and low-pressure water is sprayed from a concentric large-area opening 8 surrounding the periphery.
The flow ratio of high-pressure water to low-pressure water is preferably 5: 1 to 20: 1, more preferably 8: 1 to 15: 1. By providing a difference in the flow rate of high-pressure water and low-pressure water,
A vortex is generated at the interface between the flow of high-pressure water and low-pressure water, and entrains outside air to grow a cavity composed of a gas phase. When the grown cavity is destroyed, a shock wave is generated and is jetted to the filtration membrane as a water flow accompanied by the shock wave. The pressure of the high pressure water is preferably 5 to 100 kg / cm ^2, more preferably 20~80kg / cm ^2. Pressure of low-pressure water is preferably 0.5 to 5 kg / cm ^2, more preferably 1~4kg / cm ^2. According to the filtration membrane cleaning method of the present invention, compared to the conventional cleaning method, by using gas dissolved water in which oxygen gas, hydrogen gas, carbon dioxide gas, nitrogen gas or a rare gas is dissolved, for cleaning the filtration membrane. The number of fine particles remaining on the surface of the filtration membrane can be reduced to 1/10 to 1/100, whereby the filtration membrane can be used for discrimination and counting of the number of fine particles in ultrapure water by direct microscopy. In this case, accurate measurement values can be obtained in a short time with a small amount of water flow.

[0009]

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 examples and comparative examples, the number of attached fine particles is the number of fine particles having a diameter of 0.05 μm or more per one filtration membrane measured by a direct microscopic method. Example 1 Ultrapure water containing dissolved hydrogen gas having a concentration of 1.2 mg / l was used as washing water, and the pore diameter was 0.05 μm and the diameter was 2 μm.
A 5 mm polycarbonate fine particle trapping filtration membrane [New Cripore] was washed. The filter membrane is hung using a clamp, immersed in a 1,000 ml washing tank filled with washing water, and 300 ml / pour of washing water is added.
Washed for 0 minutes. The number of microparticles attached to the filtration membrane was 9.54 × 10 ⁷ before washing, and 1.33 × 10 ⁷ after washing,
The fine particle removal rate was 86.1%. Example 2 The same filtration membrane as that of Example 1 was used by using an ultrasonic cleaner [FINESONIC PT-08M, frequency: 750 ± 100 kHz] as a cleaning tank.
Washing was performed using 2 mg / liter of hydrogen gas-dissolved ultrapure water as washing water. The filtration membrane is hung using a holding tool, immersed in an ultrasonic cleaner filled with cleaning water, and the cleaning water is supplied at 300 ml /
The mixture was poured and washed for 30 minutes while overflowing. The number of fine particles adhering to the filtration membrane was 9.36 × 10 ⁷ before washing, 6.29 × 10 ⁶ after washing, and the particle removal rate was 93.3.
%Met. Example 3 The same filtration membrane as in Example 1 was prepared by using an ultrasonic cleaner [Pretech PT-08M, frequency: 750 ± 100 kHz] as a cleaning tank. Was washed using ultrapure water in which was dissolved as washing water. The filtration membrane is hung using a clamp, immersed in an ultrasonic cleaner filled with washing water, poured with 300 ml / min of washing water, washed for 20 minutes while overflowing, and then ultrasonically filled with ultrapure water. Transfer to the washer,
Ultrapure water was poured at 300 ml / min and rinsed for 10 minutes while overflowing. The number of fine particles attached to the filtration membrane was 9.53 × 10 ⁷ before washing, and 4.55 × 10 ⁵ after washing.
The fine particle removal rate was 99.5%. Example 4 The filtration membrane was washed in the same manner as in Example 1 except that oxygen gas-dissolved ultrapure water having a dissolved oxygen gas concentration of 35 mg / liter was used as the washing water. The number of fine particles attached to the filtration membrane was 9.48 × 10 ⁷ before washing, and 2.23 × 10 ⁷ after washing.
And the fine particle removal rate was 76.5%. Example 5 A filtration membrane was washed in the same manner as in Example 2, except that oxygen gas-dissolved ultrapure water having a dissolved oxygen gas concentration of 35 mg / liter was used as washing water. The number of fine particles adhering to the filtration membrane was 9.18 × 10 ⁷ before washing, and 7.30 × 10 ⁶ after washing.
And the fine particle removal rate was 92.0%. Example 6 The filtration membrane was washed in the same manner as in Example 3 except that ultrapure water in which 35 mg / l of oxygen gas and 1 mg / l of ammonia were dissolved was used as washing water. The number of fine particles adhering to the filtration membrane was 9.55 × 10 ⁷ before washing, 5.69 × 10 ⁵ after washing, and the fine particle removal rate was 99.4%. Example 7 A filtration membrane was washed in the same manner as in Example 1 except that argon-dissolved ultrapure water having a dissolved argon concentration of 30 mg / liter was used as washing water. The number of fine particles attached to the filtration membrane was 8.74 × 10 ⁷ before washing, and 4.25 × 10 ⁷ after washing.
And the fine particle removal rate was 51.4%. Example 8 A filtration membrane was washed in the same manner as in Example 2, except that argon-dissolved ultrapure water having a dissolved argon concentration of 30 mg / liter was used as washing water. The number of fine particles adhering to the filtration membrane was 9.56 × 10 ⁷ before washing, and 1.51 × 10 ⁷ after washing.
And the fine particle removal rate was 84.2%. Example 9 The filtration membrane was washed in the same manner as in Example 3 except that ultrapure water in which 35 mg / l of argon and 1 mg / l of ammonia were dissolved was used as washing water. The number of fine particles adhering to the filtration membrane was 9.59 × 10 ⁷ before washing, 1.61 × 10 ⁶ after washing, and the fine particle removal rate was 98.3%. Comparative Example 1 The filtration membrane was washed in the same manner as in Example 1 except that ultrapure water was used as the washing water. The number of fine particles attached to the filtration membrane was 9.78 × 10 ⁷ before washing, and 6.81 × after washing.
The number was 10 ⁷ , and the fine particle removal rate was 30.4%. Comparative Example 2 The filtration membrane was washed in the same manner as in Example 2 except that ultrapure water was used as the washing water. The number of fine particles attached to the filtration membrane was 8.98 × 10 ⁷ before washing, and 2.53 × after washing.
The number was 10 ⁷ , and the fine particle removal rate was 71.8%. Comparative Example 3 The filtration membrane was washed for 20 minutes in the same manner as in Example 1 using ultrapure water in which 1 mg / liter of ammonia was dissolved, and then rinsed with ultrapure water for 10 minutes. The number of fine particles attached to the filtration membrane was 9.63 x 1 before washing.
0 ^7, after washing is × 10 ⁷ cells 5.72, particulate removal rate was 40.6%. Comparative Example 4 A filtration membrane was washed in the same manner as in Example 3 except that ultrapure water in which 1 mg / liter of ammonia was dissolved was used as washing water. The number of particles attached to the filtration membrane was 9.
The number was 21 × 10 ^{7, the} number after washing was 1.11 × 10 ⁷ , and the fine particle removal rate was 87.9%. Table 1 shows the results of Examples 1 to 9 and Comparative Examples 1 to 4.

[0010]

[Table 1]

As can be seen from Table 1, in the examples using ultrapure water in which hydrogen gas, oxygen gas or argon is dissolved as cleaning water, the results are higher than in the comparative example using ultrapure water as cleaning water. Fine particles adhering to the filtration membrane were removed at the removal rate. Further, in any of hydrogen gas-dissolved ultrapure water, oxygen gas-dissolved ultrapure water, and argon-dissolved ultrapure water, the fine particle removal rate is higher when ultrasonic waves are transmitted than when ultrasonic waves are not transmitted. Is getting higher. Further, when ammonia is added to these gas-dissolved waters, the fine particle removal rate is further improved.

[0012]

According to the method for cleaning a filtration membrane of the present invention, fine particles adhering to the filtration membrane can be removed by a simple treatment at a high removal rate and cleaned. When the filtration membrane cleaned by the method of the present invention is used for identifying and measuring fine particles in ultrapure water, correct measurement results can be obtained in a small amount of water and in a short time.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view and a plan view of a nozzle for a bubble jet fluid.

FIG. 2 is a sectional view and a plan view of a nozzle for a cavitation jet fluid.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Water supply pipe 2 Air supply pipe 3 Nozzle 4 Nozzle outlet 5 High pressure water supply pipe 6 Low pressure water supply pipe 7 Small area opening 8 Large area opening

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D006 GA06 GA07 KC07 KC16 KC19 KC20 KD17 LA08 MA03 MA22 MC03 MC11 MC28 MC48 MC49 PA01 PB02 PB20 PB70 PC02

Claims (1)

[Claims] 1. A method for cleaning a filtration membrane, comprising contacting the filtration membrane with a gas-dissolved water in which an oxygen gas, a hydrogen gas, a carbon dioxide gas, a nitrogen gas or a rare gas is dissolved to clean the filtration membrane.