JP2002052324A - Method for washing ultrapure water production system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a washing method for a production system of ultrapure water, which is excellent especially in removal of biofilm and leaves little residue of a washing liquid, and in which the starting time of an ultrapure water production apparatus is minimized. SOLUTION: When at least some of an ultrapure water production system comprising an ultrapure water production apparatus, a use point of the ultrapure water and the flow path of the ultrapure water which connects the above ultrapure water production apparatus and the above use point is washed, the above fine particles are removed in such a way that the biofilm formed on the contacting surface with at least some of the above ultrapure water is brought into contact with a basic solution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for cleaning an ultrapure water production system, and more particularly to a method for cleaning an ultrapure water production system suitably used in a semiconductor production process.

[0002]

2. Description of the Related Art Conventionally, ultrapure water has been used in a cleaning process in the field of semiconductor manufacturing and the like. This ultrapure water is required to be free of fine particles, organic substances and inorganic substances that cause cleaning troubles. For example, resistivity: 18.2 MΩ · c
m or more, fine particles: 1 / mL or less, viable bacteria: 1 / L or less,
The required water quality is such that TOC (Total Organic Carbon): 1 μg / L or less, silica: 1 μg / L or less, metals: 1 ng / L or less, and ions: 10 ng / L or less.

[0003] The above-mentioned use place (use point) of the ultrapure water is connected to the ultrapure water production apparatus by a pipe (flow path), and the remaining ultrapure water not used at this use point is separated into another. A circulation system is formed by returning to the ultrapure water production device via the flow path, and an ultrapure water production system is configured as a whole. By the way, when the above ultrapure water production system is operated for a long period of time, due to the effect of microbes present in the ultrapure water, traces of ultrapure water such as piping in the production equipment and incidental facilities at the point of use. On the surface in contact with bacteria, adherents consisting of bacterial cells (including both live and dead bacteria) and bacterial production substances (hereinafter referred to as "biofilm")
Is inevitably formed.

[0004] In addition, even in a newly installed device, there is a case where bacteria adhere to the inside during the construction process and a biofilm is formed in the same manner as described above. If the biofilm thus formed comes off during the operation of the apparatus, the quality of the ultrapure water is significantly reduced. Therefore, it is necessary to appropriately clean the system and remove the biofilm.

[0005] Therefore, conventionally, sterilization and cleaning of the ultrapure water production system have been performed using a hydrogen peroxide solution or hot water.

[0006]

However, when sterilization and washing are performed using a hydrogen peroxide solution, sterilization is possible, but the effect of removing the biofilm adhered to the inside of the pipe or the like is not sufficient. Hard to say. Therefore, in order to completely remove the biofilm using the hydrogen peroxide solution, it is necessary to make the concentration of the hydrogen peroxide solution high at 1 to 2% and to carry out the washing frequently. However, when such washing is performed, there is a possibility that the hydrogen peroxide solution remains in the system after the washing and the water quality is reduced, and a time for removing such residual hydrogen peroxide solution is required,
As a result, it becomes difficult to perform the cleaning operation in a short time.

On the other hand, when hot water is used, it is necessary to raise the temperature to about 90 ° C., which may cause deterioration of the constituent materials and may not provide a sufficient effect. . The present invention solves the above-described problems in the ultrapure water production system, does not deteriorate the components of the system, has excellent biofilm removal ability, and has a small amount of components in the cleaning liquid, so that the time required for cleaning is small. It is an object of the present invention to provide an ultrapure water production system capable of shortening the production time.

[0008]

In order to achieve the above-mentioned object, a method for cleaning an ultrapure water production system according to the present invention comprises an ultrapure water production apparatus, an ultrapure water use point, and the ultrapure water production. A method for cleaning an ultrapure water production system comprising an ultrapure water flow path connecting an apparatus and the use point, wherein a biofilm formed on at least a part of the contact surface with the ultrapure water is used as a base. It is characterized in that it is dissolved by contacting with a neutral solution.

In the above structure, an aqueous solution of ammonia or tetramethylammonium hydroxide (TMAH) is preferably used as the basic solution.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, an ultrapure water production system 1 to be cleaned according to the present invention has an ultrapure water production apparatus (secondary pure water apparatus) 2 and a point of use of ultrapure water. 4,
And ultrapure water flow paths 6a and 6b connecting them. Then, the ultrapure water produced by the ultrapure water production apparatus 2 is sent to the use point 4 via the flow path 6a, and a part of the ultrapure water is used at the use point. And returns to the ultrapure water production apparatus 2 through the circulating system.

The ultrapure water production apparatus 2 includes at least an ultraviolet oxidation apparatus 2a and an ultrafiltration membrane apparatus 2b.
The ultrapure water which satisfies the above-mentioned required water quality, for example, is produced by removing the organic matter by treating the next pure water 10 with the ultraviolet oxidation device 2a and then removing the fine particles with the ultrafiltration membrane device 2b. The primary pure water 10 is obtained by treating raw water with, for example, a reverse osmosis membrane, sequentially performing treatment with an acidic and basic ion exchange resin, and further performing a reverse osmosis membrane treatment.

In the embodiment shown in FIG. 1, a tank 21 for storing the primary pure water 10 and unused ultrapure water returned from the use point 4 is provided at the inlet of the ultrapure water producing apparatus 2.
Is arranged. Then, the ultrapure water contained in the tank 21 is temperature-controlled by the heat exchanger 23 via the pump 22, then processed by the above-described ultraviolet oxidizing apparatus 2 a, further processed by the ion-exchange resin tower 24, The final treatment is performed in the filtration membrane device 2b. In addition to this, a reverse osmosis membrane or another membrane treatment device (not shown) may be appropriately incorporated in the ultrapure water production device 2.

The use point 4 indicates a place where ultrapure water is used. The use point 4 may include, in addition to a cleaning device (cleaning tank) 4a for cleaning an object (for example, a semiconductor), a pipe, a nozzle, and the like. The ultrapure water used at use point 4 is
Collected as wastewater as appropriate. The ultrapure water flow paths 6a and 6b connecting the ultrapure water production apparatus 2 and the point of use 4 basically consist of pipes and tubes, but in the present invention, tanks, pumps, fittings, The flow path is also referred to as the one including valves and other equipment. The material used for the flow paths 6a and 6b may be any material that does not elute its components into ultrapure water. For example, PVC (polyvinyl chloride), PPS (polyphenylene sulfide), PVD
F (polyvinyl difluoride), FRP (fiber reinforced plastic), PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer), stainless steel, or the like can be used.

In the cleaning method of the present invention, the biofilm adhered to a system component such as a pipe in the above system is dissolved and removed. Then, as a specific means for dissolving, a chemical for dissolving a protein constituting the biofilm, specifically, a basic solution is brought into contact. The basic solution is not particularly limited, and examples thereof include aqueous solutions of ammonia, tetramethylammonium hydroxide (TMAH), sodium hydroxide, potassium hydroxide, and the like. Among them, an aqueous solution of ammonia and TMAH is preferable.

When ammonia is used, its pH is preferably set to 7-14, especially 9-11. Further, these concentrations are preferably 5 to 500 mg / L in the case of ammonia, for example. If the concentration of ammonia is less than the above range, the dissolving power is not sufficient,
Conversely, if it exceeds the above range, the dissolving power is saturated and a large amount of ammonia remains after washing. More preferred ammonia concentration is 50-100 mg
/ L.

On the other hand, when TMAH is used, its p
H is 7 to 14 as in the case of ammonia, particularly 9 to
Preferably, it is set to 11. The concentration is 5-500 mg /
L, more preferably in the range of 50 to 100 mg / L. If the concentration of TMAH is less than the above range, the dissolving power is not sufficient, and if it exceeds the above range, the dissolving power is saturated and a large amount of TMAH remains after washing.

The temperature of the cleaning liquid is not particularly limited, but it is advantageous in terms of detergency to make the temperature as high as possible within a range not exceeding the heat-resistant temperature of the members and piping constituting the ultrapure water production system. Specifically, the temperature is preferably set to 20 to 100 ° C. For example, the temperature of the cleaning solution may be about 40 ° C. when PVC having a heat-resistant temperature of about 45 ° C. is used, and the temperature of the cleaning liquid may be 75 ° C. to 80 ° C. for PVDF whose heat-resistant temperature is about 80 ° C. . Furthermore, when stainless steel is used as a member, it can be washed at a temperature of about 100 ° C.

When cleaning the ultrapure water production system with these cleaning liquids, a specific method is as follows. As shown in FIG.
1 is mixed with the pure water in 1 or the ultrapure water circulating in the system, and the cleaning liquid 8 adjusted so that the pH and the concentration are within the above-mentioned ranges is used to clean the entire system according to the normal circulation flow of ultrapure water. do it. At this time, the flow rate of the cleaning liquid is 1.0 m / sec or more, and further, 1.2 to 2.0 m
/ Sec is preferable.

When the cleaning liquid 8 comes into contact with the biofilm attached to the system, the biofilm is dissolved, and the physical force due to the flow of the cleaning liquid is applied to the dissolved biofilm. Is more easily removed and removed. Further, as another method, in a state where the cleaning agent is filled in the cleaning portion of the ultrapure water production system, for example, a micro vibration is applied to the cleaning liquid by ultrasonic waves or the like, and a physical force is applied to the biofilm by the cleaning liquid. Methods for peeling and removing can be given.

The above-mentioned stripping / removing action is sufficiently exerted even when the concentration of the basic solution contained in the cleaning liquid 8 is low (for example, several tens mg / L). Therefore, the concentration of the cleaning liquid can be reduced. Therefore, the ratio of the components of the cleaning liquid remaining in the system is reduced, and the TOC due to the components is prevented from increasing. as a result,
The washing operation can be completed in a short time, and the vertical start-up of the ultrapure water production system becomes possible.

The cleaning time is not particularly limited. For example, the cleaning liquid may be appropriately circulated so that the cleaning liquid flows through the system for several hours, preferably about 0.5 to 3 hours. After washing,
The cleaning liquid is discharged from a blow pipe or the like, and then ordinary ultrapure water is introduced into the system to remove the remaining cleaning liquid. The wastewater containing the cleaning liquid may be subjected to, for example, an adsorption treatment with a weakly acidic cation exchange resin.

Further, individual devices such as the ultrafiltration membrane device 2b and the ultraviolet oxidation device 2a, a part of the piping, and a part of the system such as a piping joint may be individually washed.
In this case, the cleaning liquid may be injected just before the part to be cleaned and an outlet for the cleaning liquid may be provided immediately after the part to be cleaned, and the cleaning liquid may be supplied for a certain period of time, or vibration may be applied in a state where the cleaning liquid is filled.

[0023]

Example <Example 1> 1. Cleaning of Ultrapure Water Production System The ultrapure water production system shown in FIG. 1 was newly installed, and the following cleaning was performed. First, ammonia water was gradually added to the inlet tank 21 of the ultrapure water production apparatus 2, and the pH was gradually increased from pH6 to pH1.
While raising to 1, the flow rate is 1.5 m by the pump 22.
6 hours after the start of the addition of the aqueous ammonia, the pH of the cleaning solution is 11, and the ammonia concentration is 70 mg / L.
Therefore, the cleaning solution was circulated at the same flow rate for another 30 minutes to clean the system. However, the ion exchange resin tower 24 was not washed, and the washing liquid 8 was bypassed through the bypass channel 30. Next, the cleaning liquid 8 is discharged from a blow pipe (not shown), the primary pure water 10 is supplied to the inlet tank 21, and the obtained ultrapure water is appropriately circulated in the system to remove the cleaning liquid 8 remaining in the system. Discharged. The discharged cleaning liquid 8 was neutralized.

2. Evaluation of detergency As well as continuously monitoring the biofilm peeling effect in the above-mentioned cleaning process with a fine particle measuring instrument installed in the liquid,
The degree of the peeling of the biofilm was examined by capturing it on a filter having a particle size of 0.45 μm and counting the number of bacteria in the filter. The results are shown in FIG. Further, a change in water quality during the chemical replacement process with pure water after the cleaning operation, that is, a rise in specific resistivity was measured. The TOC in ultrapure water is
Measured by UV oxidation-resistivity detection method
showed that.

<Example 2> A TMAH aqueous solution was gradually added to the inlet tank 21 of the system as the cleaning liquid 8,
While gradually increasing the pH to 12 from
After 6 hours from the start of the addition of the TMAH aqueous solution, the pH of the washing solution was adjusted to 12, TM
When the AH concentration reached 100 mg / L, the system was cleaned in the same manner as in Example 1 except that the cleaning solution was circulated at the same flow rate for another 30 minutes, and the same evaluation test was performed. 2 and FIG.

<Embodiment 3> As the cleaning liquid 8, sodium hydroxide at pH 11 and concentration 4
0 mg / L was added, the system was washed in the same manner as in Example 1, and the time-dependent change in water quality was measured in the same manner. The results are shown in FIG. 2 and FIG. The washing solution was used in the same manner as in Examples 1 and 2, and 6
After an hour, the pH and the concentration were adjusted to 11 and 40 mg / L, respectively.

<Comparative Example 1> The ultrapure water production system was cleaned in the same manner as in Example 1 except that the cleaning liquid 8 was replaced with a hydrogen peroxide solution (H ₂ O ₂ ). The same evaluation test was performed, and the results are shown in FIGS. The hydrogen peroxide solution was added so that the concentration became 1% in 6 hours from the start of the addition. As is clear from FIG. 2, in Examples 1 to 3, the number of bacteria rapidly increased about 5 hours after the start of cleaning of the ultrapure water production system, and the capture of biofilm was promoted. confirmed. On the other hand, in Comparative Example 1, the biofilm was hardly captured even after the elapse of 7 hours, indicating that the cleaning effect was low.

Further, as is apparent from FIG.
In Nos. To 3, the rise of the resistivity in the chemical replacement process with pure water after washing was steep, and the required water quality was reached in about one and a half hours, and it was confirmed that the washing operation could be performed in a short time. . On the other hand, in Comparative Example 1, it was found that the rise of the resistivity was slow, and it took about twice as long to reach the required water quality.

When Examples 1, 2 and 3 are compared,
It was confirmed that the ammonia water and TMAH of Examples 1 and 2 were superior to the sodium hydroxide of Example 3 in both the cleaning effect and the cleaning time.

[0030]

As apparent from the above description, according to the present invention, the biofilm removal ability is superior to that of the conventional ultrapure water production system cleaning method.・ Can be removed. Further, since a sufficient effect can be exhibited with a low-concentration cleaning liquid, the rise of the specific resistivity after cleaning is sharp, and the cleaning liquid does not remain.

As a result, the cleaning operation can be performed in a short time as a whole, and the vertical start-up of the ultrapure water production system becomes possible.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a cleaning flow of an ultrapure water production system according to the present invention.

FIG. 2 is a graph showing a time-dependent change in the number of viable bacteria in a biofilm captured by a filter in a washing process of the ultrapure water production system.

FIG. 3 is a graph showing a change over time in the resistivity of ultrapure water after cleaning of the ultrapure water production system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ultrapure water production system 2 Ultrapure water production apparatus 2a Ultraviolet oxidization apparatus 2b Ultrafiltration membrane apparatus 4 Use point 6a, 6b (ultrapure water) flow path 8 Cleaning liquid

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C02F 1/50 510 C02F 1/50 531J 531 532C 532 532D B08B 9/06

Claims (2)

[Claims] 1. A method for cleaning an ultrapure water production system comprising an ultrapure water production apparatus, an ultrapure water use point, and an ultrapure water flow path connecting the ultrapure water production apparatus and the use point. A method for cleaning an ultrapure water production system, wherein a biofilm formed on at least a part of a contact surface with the ultrapure water is brought into contact with a basic solution. 2. The cleaning method according to claim 1, wherein the basic solution is aqueous ammonia or an aqueous solution of tetramethylammonium hydroxide.