JP3620577B2 - Cleaning method for ultrapure water production system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a cleaning method for an ultrapure water manufacturing system, and more particularly to a cleaning method for an ultrapure water manufacturing system suitably used in a semiconductor manufacturing process.
[0002]
[Prior art]
Conventionally, ultrapure water has been used in cleaning processes in the field of semiconductor manufacturing and the like. This ultrapure water is required not to contain fine particles, organic matter, or inorganic substances that cause cleaning trouble. For example, resistivity: 18.2 MΩ · cm or more, fine particles: 1 piece / mL or less, viable bacteria: 1 piece / L or less, TOC (Total Organic Carbon): 1 ppb or less, Silica: 1 ppb or less, Metals: 1 ppt or less, Ions: 10 ppt or less.
[0003]
The above-mentioned ultrapure water use location (use point) is connected to the ultrapure water production apparatus by piping (flow path), and the remaining ultrapure water not used at this use point is connected to another flow path. Then, the ultrapure water production system is configured as a whole by returning to the ultrapure water production apparatus.
By the way, when the above-described ultrapure water production system is newly constructed or suspended for a long time, the quality of ultrapure water is deteriorated by mixing fine particles in the system. Necessary. In particular, when the above system is newly installed in connection with the construction of a factory, fine particles and dirt (organic matter, etc.) adhere to the inside of the system at the time of construction, so that the cleaning operation is prolonged (for example, one month) and the operation rate of the factory is increased. descend.
[0004]
For this reason, there is a demand for shortening the time from cleaning the ultrapure water production system to obtaining ultrapure water that satisfies the required water quality (vertical startup of the ultrapure water production system). For example, the system is cleaned using warm water or hydrogen peroxide as a cleaning solution. Further, Japanese Patent Laid-Open No. 7-195073 proposes a cleaning technique using alcohol having a large cleaning power instead of the above cleaning liquid.
[0005]
[Problems to be solved by the invention]
However, when washing is performed using warm water or hydrogen peroxide solution, since these do not have a strong detergency, removal of fine particles and dirt adhering to the piping of the system is insufficient.
On the other hand, when alcohol is used for cleaning, it is necessary to make the alcohol relatively high in concentration (about 10 to 80%) in order to sufficiently remove the fine particles. Decrease (increased TOC). And since it takes time to remove such residual alcohol, as a result, it is difficult to perform the cleaning operation in a short time.
[0006]
The present invention solves the above-mentioned problems in the ultrapure water production system, is excellent in cleaning power (removal of fine particles and organic substances), and since the components in the cleaning liquid are less likely to remain, the time required for cleaning is short, The purpose is to provide an ultrapure water production system capable of vertical startup of water production equipment.
[0007]
[Means for Solving the Problems]
In order to achieve the above-described object, a cleaning method for an ultrapure water production system according to the present invention as set forth in claim 1 includes: concentrations at least part of the ultrapure water production system formed by connecting the fine particles adhering to at least in part by static electricity can be separated by hydrophilic, an aqueous solution of tetraalkyl ammonium salt, or tetra, It is characterized by washing with a basic washing solution which is an aqueous alkylammonium hydroxide solution .
[0009]
DETAILED DESCRIPTION OF THE INVENTION
As shown in FIG. 1, an ultrapure water production system 1 to which cleaning is performed according to the present invention includes an ultrapure water production apparatus 2, a use point 4 of ultrapure water, and a flow path 6a of ultrapure water connecting them. , 6b. Then, the ultrapure water produced by the ultrapure water production apparatus 2 is sent to the use point 4 through the flow path 6a, and a part of the ultrapure water is used at the use point. The circulation system which returns to the ultrapure water manufacturing apparatus 2 via this is comprised.
[0010]
The ultrapure water production apparatus 2 includes at least an ultraviolet oxidation apparatus 2a and an ultrafiltration membrane apparatus 2b, and after treating the primary pure water 10 described later with the ultraviolet oxidation apparatus 2a to remove organic matter, the ultrafiltration membrane apparatus By removing fine particles in 2b, for example, ultrapure water that satisfies the above-mentioned required water quality is produced. The primary pure water 10 is obtained by treating raw water with, for example, a reverse osmosis membrane, sequentially performing treatment with acidic and basic ion exchange resins, and further performing a reverse osmosis membrane treatment.
[0011]
In the embodiment shown in FIG. 1, a tank 21 that stores primary pure water 10 and unused ultrapure water returned from the use point 4 is disposed on the entry side of the ultrapure water production apparatus 2. . Then, after the temperature of the ultrapure water accommodated in the tank 21 is adjusted by the heat exchanger 23 via the pump 22, the ultrapure water is processed by the ultraviolet oxidizer 2 a and further processed by the ion exchange resin tower 24. Final processing is performed by the filtration membrane device 2b. In addition to these, a reverse osmosis membrane and other membrane treatment devices (not shown) may be appropriately incorporated into the ultrapure water production device 2.
[0012]
The use point 4 indicates a place where ultrapure water is used, and may include pipes, nozzles, and the like as appropriate in addition to a cleaning device (cleaning tank) 4a for cleaning an object (for example, a semiconductor). Note that the ultrapure water used at the use point 4 is appropriately collected as drainage. The ultrapure water flow paths 6a and 6b connecting the ultrapure water production apparatus 2 and the use point 4 are basically composed of pipes and tubes. In the present invention, tanks, pumps, joints, In addition, a channel including a valve and other equipment is also referred to as a flow path. The material used for the channels 6a and 6b may be any material that does not elute into ultrapure water. For example, PVC (polyvinyl chloride), PPS (polyphenylene sulfite), PVDF (polyvinyl difluoride) FRP (fiber reinforced plastic), PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer), stainless steel and the like can be used.
[0013]
Now, the basic cleaning liquid 8 is used for cleaning the ultrapure water production system described above. The cleaning mechanism with such a base is not clear, but in general, the fine particles are attached to the piping of the system by an electrostatic force, and the fine particles are hydrophilized (ionized) by the base or basic salt in the cleaning liquid, and from the adhesion interface. It is considered to be peeled off. In particular, when a nitrogen atom having an unshared electron pair including reduction compound, greater cleaning action of the above.
[0014]
The peeling / removal action described above is sufficiently exerted even when the concentration of the base (or basic salt) contained in the basic cleaning liquid 8 is low (for example, several hundred ppm). Therefore, the concentration of the cleaning liquid can be reduced. Therefore, the ratio of the cleaning liquid component remaining in the system is reduced, and an increase in TOC due to this component is also suppressed. As a result, the cleaning operation can be completed in a short time, and the ultrapure water production system can be started up vertically.
[0015]
The basic cleaning solution 8 can be used, for example, an aqueous solution of te tiger alkylammonium salt, a tetraalkylammonium hydroxide aqueous solution or the like. It is particularly preferable to use an aqueous tetramethylammonium hydroxide (TMAH) solution. In addition, when using TMAH aqueous solution, it is preferable that the density | concentration shall be 10-100 ppm. If the concentration of TMAH is less than the above range, the cleaning power (removability of fine particles and organic matter) is not sufficient, and if the concentration of TMAH exceeds the above range, the cleaning power is saturated and a large amount of TMAH remains after cleaning. It is. More preferably, the TMAH concentration is 40-60 ppm.
[0016]
The temperature of the cleaning liquid is not particularly limited, but it is preferable in terms of cleaning power to be as high as possible within the range not exceeding the heat resistance temperature of the members and pipes constituting the ultrapure water production system, and more specifically, It is good to set it as 20-100 degreeC. For example, when PVC having a heat resistant temperature of about 45 ° C. is used as a member, the temperature of the cleaning liquid is about 40 ° C., and in the case of PVDF having a heat resistant temperature of about 80 ° C., the temperature of the cleaning liquid is 75 to 80 ° C. or lower. Good. Further, when stainless steel is used as a member, it can be washed at a temperature of about 100 ° C.
[0017]
As a specific cleaning method, for example, the basic cleaning liquid 8 may be introduced into the system of the ultrapure water production system, and the entire system may be cleaned in accordance with a normal ultrapure water circulation flow. Moreover, you may wash | clean the one part (for example, ultrafiltration membrane apparatus 2b) of the said system separately. The cleaning time is not particularly limited. For example, the cleaning liquid may be appropriately circulated so that the cleaning liquid flows in the system for several hours. After cleaning, the cleaning liquid is discharged from a blow pipe or the like, and then normal ultrapure water is introduced into the system to remove the remaining cleaning liquid. The waste water containing the cleaning liquid may be adsorbed with, for example, a weakly acidic cation exchange resin.
[0018]
【Example】
Examples, Comparative Examples 1 and 2
1. Cleaning of the ultrapure water production system The ultrapure water production system shown in FIG. 1 was newly established and the following cleaning was performed.
First, after containing the aqueous solution 8 containing 50 ppm of tetramethylammonium hydroxide (TMAH) in the inlet side tank 21 of the ultrapure water production apparatus 2, the pump 22 sends the solution to the heat exchanger 23 to adjust the temperature to 40 ° C. The system was cleaned by circulating the TMAH aqueous solution 8 in the order of the ultrapure water production apparatus 2, the flow path 6a, the use point 4, and the flow path 6b (circulation cleaning time: 1 hour). However, the ion exchange resin tower 24 was not washed, and the TMAH aqueous solution 8 was bypassed via the bypass channel 30.
Next, the TMAH aqueous solution 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 leave the TMAH aqueous solution remaining in the system. 8 was removed. The waste water containing the cleaning liquid was passed through a weakly acidic cation exchange resin to adsorb TMAH.
[0019]
2. Evaluation of detergency After the above-described washing was completed, normal operation was performed, and the change over time in the quality of ultrapure water at use point 4 was investigated. The amount of fine particles in the ultrapure water was obtained by filtering a certain amount of ultrapure water with a filter, and counting fine particles (particle size of 0.05 μm or more) trapped on the filter with a scanning electron microscope. Moreover, TOC in ultrapure water was measured by an ultraviolet oxidation-resistance detection method.
[0020]
The above results are shown in FIGS. The broken line in each figure shows the water quality required for normal ultrapure water.
For comparison, after cleaning the ultrapure water production system in the same manner as described above except that the cleaning liquid was replaced with warm water at 40 ° C., the water quality at the point of use was similarly investigated. This is referred to as Comparative Example 1. Further, Comparative Example 2 was obtained by replacing the cleaning liquid with 50 ppm isopropyl alcohol (IPA).
[0021]
As is clear from FIG. 2, in the example, the time required for the number of fine particles to reach the required water quality (less than 1 / mL) after cleaning of the ultrapure water production system is extremely short (less than half a day), and the fine particle removal capability is improved. Are better. On the other hand, in Comparative Examples 1 and 2, it takes 4 to 5 days or more to obtain the required water quality, and the ability to remove fine particles is low.
In addition, as apparent from FIG. 3, in the example, it takes one day until the TOC reaches the required water quality (1 ppb or less) after washing, and the organic matter removal ability is excellent. On the other hand, in Comparative Examples 1 and 2, it takes 6 to 7 days or more to obtain the required water quality, and the organic matter removing ability is low.
[0022]
【The invention's effect】
As is apparent from the above description, according to the present invention, the ability to remove fine particles and organic matter is superior to the conventional ultrapure water production system cleaning method. It can be removed and removed quickly. Furthermore, since the cleaning liquid has a low concentration, it is unlikely that the components in the cleaning liquid remain after the cleaning to increase the TOC.
[0023]
As a result, the cleaning operation can be performed in a short time as a whole, and the vertical startup 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 the change over time in the number of fine particles in ultrapure water after cleaning by the ultrapure water production system.
FIG. 3 is a graph showing a change with time of TOC in 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 device 2a Ultraviolet oxidation device 2b Ultrafiltration membrane device 4 (Ultrapure water) use points 6a, 6b (Ultrapure water) flow path 8 TMAH aqueous solution (basic cleaning solution)

Claims (4)

Ultrapure water production system, the point of use of ultrapure water, and at least a portion of the ultrapure water production system consisting of the ultrapure water production system and the flow path of the ultra-pure water for connecting the use point, the static electricity Washing with a basic cleaning solution which is an aqueous solution of tetraalkylammonium salt or an aqueous solution of tetraalkylammonium hydroxide at a concentration capable of hydrophilizing and peeling off the fine particles adhering to at least a part. Cleaning method for ultrapure water production system. The method for cleaning an ultrapure water production system according to claim 1, wherein the concentration of the basic cleaning liquid is several hundred ppm. The method for cleaning an ultrapure water production system according to claim 1 , wherein the tetraalkylammonium hydroxide aqueous solution is a tetramethylammonium hydroxide aqueous solution . The tetramethylammonium hydroxide aqueous solution has a concentration of 10 to 100. ppm The method for cleaning an ultrapure water production system according to claim 3.

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