JP3771684B2 - Ultrapure water production method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrapure water production method for producing ultrapure water used in semiconductor production and the like, and more particularly to an ultrapure water production method capable of improving water quality maintenance and maintainability.
[0002]
[Prior art]
In the process of producing ultrapure water used for cleaning the surface of a semiconductor wafer, microorganisms blocked by the filtration membrane live on the filtration membrane, and metabolites of the microorganisms pass through the filtration membrane and become super When mixed in pure water, the metabolite will adversely affect the characteristics of the semiconductor wafer, and microorganisms that live in the pipes up to the use point will proliferate in the long term, so the microorganisms are sterilized in the ultrapure water production process. There is a need.
[0003]
As a conventional example of sterilizing microorganisms on ultrapure water or on a filtration membrane, the ultrapure water production apparatus is temporarily stopped, and hot water of 80 to 90 ° C. is passed from the filtration membrane path of the ultrapure water production apparatus to the use point. Sterilize and remove microorganisms stuck to the surface of the filtration membrane through circulation or stagnation, or remove hydrogen peroxide (H ₂ O ₂ ) into the filtration membrane path of the ultrapure water production apparatus. Some have sterilized and removed microorganisms adhered to the surface of the filtration membrane through circulation or stagnation.
[0004]
[Problems to be solved by the invention]
However, in each of the above-mentioned conventional examples, since the ultrapure water production apparatus is temporarily stopped and the sterilization treatment of the microorganism is performed, the production of ultrapure water is stopped, and the semiconductor wafer production process continues to the ultrapure water production process. When implemented in this manner, there is a problem that the production of semiconductor wafers must be stopped.
[0005]
In addition, the facility manager must periodically sample the ultrapure water or filtered water produced to investigate the habitation state of the microorganisms, which increases the management cost.
[0006]
In particular, when hydrogen peroxide (H ₂ O ₂ ) is used, since the hydrogen peroxide (H ₂ O ₂ ) is a strong oxidizing agent, hydrogen peroxide (H ₂ O after sterilization of microorganisms) is used. ₂ ) It is necessary to store the waste liquid in a pit, decompose hydrogen peroxide (H ₂ O ₂ ) with a degrading enzyme such as catalase, and dispose of the waste liquid.
[0007]
The present invention solves the above-mentioned problems, and an object of the present invention is to reliably sterilize microorganisms blocked by the filtration membrane by injecting ozone into the water to be filtered, and to provide a downstream ultrapure water line. In addition to improving the production efficiency of ultrapure water by sterilizing microorganisms without suspending the ultrapure water production system, the resident of microorganisms in ultrapure water or filtered water by the facility manager is improved. It is intended to provide a method for producing ultrapure water that can reduce the management cost by omitting the state investigation and can eliminate the waste liquid treatment after sterilization of microorganisms.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, an ultrapure water production method according to the present invention includes a first step of decomposing organic matter and residual ozone by irradiating primary pure water with ultraviolet rays , and an ion exchange resin after the first step. A second step of removing ions in the water by a polisher step, a third step of injecting ozone at an ozone injection concentration of 3 ppm or less after the second step, and a polyvinylidene fluoride after the third step. A fourth step of performing a final filtration step of the ultrapure water production step using a microfiltration membrane or an ultrafiltration membrane made of an ozone-resistant membrane composed of a ride (PVDF), and an ultra-fine produced in the fourth step And a fifth step of dispensing pure ultrapure water to the first step while distributing pure water according to use .
[0009]
With the above configuration, ozone can act on microorganisms in the water to be filtered supplied to the filtration membrane so that the microorganisms can be sterilized in a short time easily and reliably. The sterilized microorganisms lose their ecological function and become organic matter ( And is removed from the ultrapure water production path by the filtration membrane in the same manner as the fine particles.
[0010]
Thereby, since living microorganisms do not live on the filtration membrane, the metabolite of microorganisms does not mix in ultrapure water, and the quality of the manufactured ultrapure water can be maintained at a high level.
[0011]
Further, when an ozone resistant membrane is used as the microfiltration membrane or the ultrafiltration membrane, the amount of filtered water in the microfiltration membrane module or the ultrafiltration membrane module is not reduced by ozone, and the microfiltration membrane module or the ultrafiltration membrane The lifetime of the module can be improved.
[0012]
Further, since ozone or oxygen added to the water to be filtered before filtration is decomposed or removed after filtration, it is not adversely affected by ozone when the produced ultrapure water is used. As in the example, waste liquid treatment after sterilization of microorganisms is not necessary, so that the cost can be reduced.
[0013]
In addition, when ozone is added to the water to be filtered before filtration to sterilize microorganisms blocked by the filtration membrane without stopping the ultrapure water production device, and continuously produce ultrapure water For example, the following effects can be obtained. In other words, since the sterilization of microorganisms can be performed continuously without stopping the ultrapure water production process, it is not necessary to stop the semiconductor production line, improving the production efficiency of the semiconductor, The management cost can be reduced by omitting the investigation of the state of habitation of microorganisms in pure water or filtered water.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the ultrapure water production method according to the present invention will be specifically described with reference to the drawings. FIG. 1 is a diagram showing the processing steps of the first embodiment of the ultrapure water manufacturing method according to the present invention, and FIG. 2 is a diagram showing the processing steps of the second embodiment of the ultrapure water manufacturing method according to the present invention.
[0015]
First, the process of 1st Embodiment of the ultrapure water manufacturing method based on this invention is demonstrated using FIG. In FIG. 1, raw water 1 such as river water, lake water, groundwater, etc. is a flocculation process shown in Step S1 of FIG. It is purified and clarified by the device.
[0016]
In step S2 of FIG. 1, by a reverse osmosis filtration process using a reverse osmosis membrane (RO), small substances that are not excluded by the coagulation sedimentation method, microfiltration membrane or ultrafiltration membrane of step S1, specifically, ions and organic substances Exclude. And the ion in water is removed by the ion exchange resin of step S3, and the primary pure water 2 is produced | generated in step S4.
[0017]
The generated primary pure water 2 reacts with water in the primary pure water 2 by irradiating with ultraviolet rays (UV) having a wavelength of 185 nm in step S5 to generate OH radicals (hydroxy radicals). This OH radical (hydroxy radical) oxidizes and decomposes organic substances present in the primary pure water. Further, residual ozone (O ₃ ) injected and circulated, which will be described later, is also decomposed. Further, in step S6, ions in water are removed by the ion exchange resin, and a polisher process is performed.
[0018]
Ion exchange resins used in the step S6, if the ozone (O ₃₎ is included in the water, because the feature by the strong oxidizing action of the ozone (O ₃₎ is deteriorated, at step S5, advance ozone (O ₃ ) The decomposition step of ₃ ) is performed to decompose ozone (O ₃ ) in the water, and the maintenance of the ion exchange resin used in step S6 is ensured.
[0019]
Step S7 is an ozone (O ₃ ) injection process. In step S6, ions are removed by a polisher, and ozone (O ₃ ) is injected into water having a resistivity of 18.3 MΩ · cm. For ozone (O ₃ ), purified oxygen gas or air is usually ionized by a silent discharge method to generate ozone (O ₃ ) gas, and the generated ozone (O ₃ ) gas is used with a porous diffuser or the like. And finely poured into water. Microorganisms are sterilized by this ozone injection.
[0020]
In step S7, the sterilizing action of the microorganism is proportional to the product of the injection concentration C of the injected ozone (O ₃ ) and the time T. Therefore, as described later, it is preferable to continuously inject ozone (O ₃ ) continuously. In this case, the injection concentration C of ozone (O ₃ ) may be low. In this case, ozone (O ₃ ) ₃ ) The injection concentration C is preferably 1 ppm or less. Further, when ozone (O ₃ ) is injected intermittently at a predetermined timing, the ozone (O ₃ ) injection concentration C is preferably 3 ppm or less.
[0021]
Step S8 is a filtration process by the final stage filter of the ultrapure water production process in which a microfiltration membrane module or an ultrafiltration membrane module having an ozone resistance membrane having ozone resistance is installed. Microorganisms sterilized by injecting ozone into the water to be filtered are supplemented by the ozone resistant membrane. Since the sterilized microorganisms lose their ecological function and become organic matter (trash), they can be removed to the outside from the ultrapure water production path in the same way as fine particles.
[0022]
The ozone resistant membrane is a hollow fiber membrane made of an organic ozone resistant material such as a fluororesin. When the ozone-resistant membrane is made of polyvinylidene fluoride (PVDF), it is excellent in ozone (O ₃ ) resistance, and the pore diameter controllability of the hollow fiber membrane and the reliability (sharpness) of the pore size distribution. It is preferable because it is excellent. Also, the hollow fiber membrane adhesive and the like are preferably ozone-resistant such as silicone resins.
[0023]
Although ceramic membranes are resistant to ozone, they are not preferred because they are expensive and fragile, and metal ions from the ceramic membrane flow out into the filtered water.
[0024]
Normally, the ozone (O ₃ ) injected in step S7 is self-decomposed and reduced to oxygen (O ₂ ) in about 15 minutes, but in this embodiment, the generated ultrapure water 4 is distributed according to the application. In the vicinity of the use point 3 to be used (step S9), that is, when the dissolved oxygen concentration is particularly restricted, a deoxygenation and deozonization process shown in step S10 is provided. An ozone / oxygen decomposition / removal step for decomposing or removing residual ozone (O ₃ ) or oxygen (O ₂ ) is performed.
[0025]
Thereby, the ozone / oxygen decomposition / removal step of injecting hydrogen gas using platinum or palladium-based catalyst in step S10 according to the use application of the ultrapure water 4 taken out through the use point 3 in step S9. The ozone (O ₃ ) or oxygen (O ₂ ) remaining in the filtered water is decomposed or removed by performing a deoxygenation and deozone process to become, for example, a semiconductor wafer using the generated ultrapure water 4 When cleaning the surface, the strong oxidizing action of ozone (O ₃ ) does not adversely affect the semiconductor wafer.
[0026]
Step S4 → Step S5 → Step S6 → Step S7 → Step S8 → Step S9 → Step S4 in FIG. 1 is a circulation processing step, and the primary pure water 2 obtained by filtering the raw water 1 by the steps S1 to S3. Is carried out from the use point 3 in step S9 to the outside as ultrapure water 4, 5, 6,..., 20,. Is mixed with the primary pure water 2 in step S4 and continuously circulated through the circulation process.
[0027]
According to the above configuration, using the ozone resistant membrane provided in the microfiltration membrane module or the ultrafiltration membrane module that is the final stage filter in step S8, the predetermined amount is added to the filtered water before filtration by the ozone injection step in step S7. By injecting ozone (O ₃ ) by a predetermined amount during the period of time, microorganisms blocked by the ozone resistant film are sterilized without stopping the ultrapure water production apparatus, and continuous ultrapure water 4-20 Can be manufactured. Further, the ultrapure water at the point of use 3 which is an ultrapure water circulation line is also sterilized with ozone (O ₃ ) and returns to the primary pure water 2 in step S4.
[0028]
A specific example when ultrapure water is produced in the above configuration will be described in detail.
[0029]
[Example 1]
As the ozone resistant membrane module used in Step S8, a 3 inch diameter and 1 meter long module using a hollow fiber membrane made of polyvinylidene fluoride (PVDF) and having an average pore diameter of 0.05 μm is used, and 3 m ³ / hr. In Step S7, ozone (O ₃ ) with an ozone concentration of 0.3 ppm was continuously injected at all times for one year, and then the microorganisms that lived in the ultrapure water 20 at the use point 3 in Step S9 As a result of measurement, 0 microorganisms / 1000 ml, that is, no resident microorganisms were detected.
[0030]
According to this result, it is not necessary to temporarily stop the ultrapure water production apparatus and perform the sterilization treatment of microorganisms as in the conventional example, so the ultrapure water production is continuously performed without being temporarily stopped. I can do it.
[0031]
In addition, it is not necessary for the facility manager to periodically sample the ultrapure water or filtered water produced to investigate the state of microbial habitat, thereby reducing the management cost.
[0032]
[Comparative Example 1]
As a comparative example, three modules having a diameter of 3 inches and a length of 1 m using a hollow fiber membrane made of polyacrylonitrile (PAN) and having a cut off molecular weight (CMW) of 13,000 are used. The ultrapure water production apparatus is temporarily stopped every 4 months (3 times a year) with a filtered water amount of 3 m ³ / hr, and microorganisms are sterilized with hydrogen peroxide (H ₂ O ₂ ). After operating for a year, the microorganisms inhabiting before performing the hydrogen peroxide sterilization with the ultrapure water 20 at the use point 3 in step S9 were measured, and the inhabiting microorganisms were 10 / 100ml to 40 / 100ml. Detected in range.
[0033]
[Comparative Example 2]
As a comparative example, made of polysulfone (PS), fractionation molecular weight (CMW; cut off molecular weight) length 3 inches in diameter using a hollow fiber membrane 10,000 using modules of 1 m, 3m ³ / Hr filtered water volume every 4 months (3 times a year), ultrapure water production equipment is temporarily stopped, heat sterilized at 80-90 ° C, operated for 1 year, and then the use of step S9 The inhabiting microorganisms before the heat sterilization were measured with the ultrapure water 5 of point 3, and the inhabiting microorganisms were detected in the range of 5/100 ml to 20/100 ml.
[0034]
[Example 2]
As the ozone resistant membrane module used in step S8, a hollow fiber membrane made of polyvinylidene fluoride (PVDF) having a cut off molecular weight (CMW) of 100,000 is 3 inches in diameter and 1 m in length. Three modules are used, and ozone (O ₃ ) with an ozone concentration of 3 ppm in step S7 is injected at a flow rate of 3 m ³ / hr at a rate of 3 ppm once a day for 10 minutes. Every three months, the use of step S9 When the microorganisms that inhabit at point 3 were measured, the number of inhabiting microorganisms was 0/1000 ml, that is, no inhabiting microorganisms were detected.
[0035]
According to the result of Example 2, as in Example 1, it is not necessary to temporarily stop the ultrapure water production apparatus and execute the sterilization treatment of microorganisms as in the conventional example. Can be manufactured.
[0036]
In addition, it is not necessary for the facility manager to periodically sample the ultrapure water or filtered water produced to investigate the state of microbial habitat, thereby reducing the management cost.
[0037]
Next, 2nd Embodiment of the ultrapure water manufacturing method based on this invention is described using FIG. In this embodiment, a deoxygenation and deozonization process similar to that in step S10 shown in FIG. 1 is provided on the upstream side in the vicinity of the use point 3 in step S9 in the first embodiment shown in FIG. 1 (step S9 in FIG. 2). ₂ ), the ozone / oxygen decomposition / removal process for decomposing or removing ozone (O ₃ ) or oxygen (O ₂ ) remaining in the filtered water after the filtration is performed at once in step S9 of FIG. . Therefore, the deoxygenation and deozone processes are not provided on the downstream side in the vicinity of each use port of the use point 3 (step S10) in FIG.
[0038]
With the above configuration, the filtered water filtered by the ozone resistant membrane module in step S8 in FIG. 2 is all ozone / oxygen decomposition / injection of hydrogen gas using platinum or palladium based catalyst in step S9. After performing deoxygenation and deozone processes as the removal process to decompose or remove ozone (O ₃ ) or oxygen (O ₂ ) remaining in the filtered water, ultrapure water 4 to 4 through use point 3 in step S10 20 is taken out. Thus, as in the first embodiment, when the generated ultrapure water 4 is used, for example, when the surface of the semiconductor wafer is cleaned, the strong oxidizing action of ozone (O ₃ ) adversely affects the semiconductor wafer. There is no such thing.
[0039]
Step S4 → Step S5 → Step S6 → Step S7 → Step S8 → Step S9 → Step S10 → Step S4 in FIG. 2 is also a circulation processing step as in the first embodiment, and the steps S1 to S3 The primary pure water 2 obtained by filtering the raw water 1 is taken out as ultrapure water 4, 5,..., 20 from the use point 3 in step S10 by performing the above-described steps S5 to S9. Unused ultrapure water is mixed with the primary pure water 2 in step S4 and continuously circulated through the circulation process.
[0040]
According to the above configuration, as in the first embodiment, the ozone injection process in step S7 is performed using the ozone resistant membrane provided in the microfiltration membrane module or the ultrafiltration membrane module that is the final filter in step S8. Thus, by injecting ozone (O ₃ ) by a predetermined amount into water at a predetermined time, microorganisms can be sterilized and removed with an ozone resistant film without stopping the ultrapure water production apparatus. The ultrapure water that has not been used at the use point 3 returns to the primary pure water 2 in step S4 and circulates through the ultrapure water circulation line.
[0041]
Other configurations are the same as those of the first embodiment, and the same effects as described above can be obtained.
[0042]
【The invention's effect】
Since the present invention has the above-described configuration and action, the microorganisms contained in the primary pure water can be sterilized in a short time, easily and reliably by applying ozone to the microorganisms. High quality of pure water can be maintained.
[0043]
In addition, since ozone or oxygen added to the water to be filtered before filtration is decomposed / removed after filtration in the final filtration step, there is no adverse effect of ozone when using the manufactured ultrapure water. In addition, unlike the conventional example, waste liquid treatment after sterilization of microorganisms is not required, so that the cost can be reduced.
[0044]
Further, in the present invention, it is not necessary to temporarily stop the ultrapure water production apparatus as in the conventional example to carry out the sterilization treatment of microorganisms. Efficiency can be improved. In addition, for example, when the semiconductor wafer manufacturing process is continuously performed in the ultrapure water manufacturing process, the production efficiency of the semiconductor wafer does not decrease.
[0045]
In addition, it is not necessary for the facility manager to periodically sample the ultrapure water or filtered water produced to investigate the state of microbial habitat, thereby reducing the management cost.
[Brief description of the drawings]
FIG. 1 is a diagram showing processing steps of a first embodiment of a method for producing ultrapure water according to the present invention.
FIG. 2 is a diagram showing processing steps of a second embodiment of the method for producing ultrapure water according to the present invention.
[Explanation of symbols]
1 ... Raw water 2 ... Primary pure water 3 ... Use points 4, 5, 20 ... Ultra pure water

Claims (1)

A first step of decomposing organic matter and residual ozone by subjecting primary pure water to ultraviolet irradiation ;
After the first step, a second step of removing ions in water by a polisher step with an ion exchange resin ;
A third step of injecting ozone at an ozone injection concentration of 3 ppm or less after the second step ;
After the third step, a fourth step of performing a final filtration step of an ultrapure water production step using a microfiltration membrane or an ultrafiltration membrane made of an ozone resistant membrane composed of polyvinylidene fluoride (PVDF) ;
A fifth step of distributing the ultrapure water generated in the fourth step according to the use, and supplying unused ultrapure water to the first step ;
A method for producing ultrapure water , comprising :

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