WO2025229831A1 - Method of at-startup washing of ultrapure-water production apparatus - Google Patents

Abstract

This method of at-startup washing of a ultrapure-water production apparatus provided with a subsystem having an ion exchange device is characterized in that, as regards components utilized on the later-stage side of the ion exchange device, components for which the ratio of liquid-contact area (m²) per single component to water pass rate (m³/h) of the relevant component in the ultrapure-water production apparatus (liquid-contact area per unit ultrapure-water flow rate) is 1,0×10^-6m²/(m³/h) or greater are washed in advance with water or chemicals and thereafter placed in the ultrapure-water production apparatus.

Description

Cleaning method for ultrapure water production equipment when starting up

The present invention relates to a cleaning method for ultrapure water production equipment when it is started up, i.e., when it begins operation.

The point at which ultrapure water is used (use point) in a semiconductor manufacturing plant or similar facility is connected to the ultrapure water production system via an ultrapure water supply pipe, and any remaining ultrapure water not used at this use point is returned to the ultrapure water production system's sub-tank via an unused ultrapure water return pipe.

Traditionally, when installing, expanding, modifying, or maintaining an ultrapure water production system, dust and other fine particles in the air, particles contained in water such as iron rust, and even shavings generated during the manufacturing process (hereinafter collectively referred to as "fine particles") are introduced into the system and removed by cleaning when the system is started up.

Preventing initial contamination of ultrapure water production equipment depends largely on the water quality at start-up. In particular, contamination on the secondary side of the ion exchange unit has a significant impact on the quality of the ultrapure water produced, so managing the cleanliness of this part is extremely important.

Conventionally, to clean an ultrapure water production system, the components that make up the system are assembled to complete the ultrapure water production system, and then either the area where the components are assembled or the entire system is cleaned with ultrapure water, or ultrapure water containing TMAH (tetramethylammonium hydroxide) or hydrogen peroxide as needed (see, for example, Patent Document 1).

Patent Document 2 describes a method for starting up an ultrapure water production system, in which the impurity concentration in the feedwater is specified when installing an ultrafiltration membrane (UF membrane), and water flow is started when the concentration falls below the standard value.

Patent Document 3 discloses a method for cleaning ultrapure water production equipment and point-of-use piping using an alkaline solution and sterilized water. This method is effective for removing fine particles from the system, sterilizing the system, and reducing metals, but since it involves cleaning actual equipment, it is a large-scale cleaning process that takes several days.

Japanese Patent Application Laid-Open No. 2000-317413 Japanese Patent Application Laid-Open No. 2022-187148 Patent No. 5287713

The objective of the present invention is to provide a cleaning method for ultrapure water production equipment during startup that shortens the startup time of the equipment and enables the rapid production of high-purity ultrapure water.

The present invention is as follows:

[1] A cleaning method for starting up an ultrapure water production system equipped with a subsystem having an ion exchange device, comprising:
This cleaning method for ultrapure water production equipment at the start-up of an ultrapure water production equipment is characterized in that, for components used in the downstream side of the ion exchange equipment, the ratio of the liquid contact area (m ² ) of a single component to the water flow rate (m ³ /h) of said component in the ultrapure water production equipment (liquid contact area per unit ultrapure water flow rate) is 1.0 × 10 ^-6 m ² /(m ³ /h) or more, is pre-cleaned with water or a chemical solution and then installed in the ultrapure water production equipment.

[2] A cleaning method for the start-up of the ultrapure water production system of [1], in which the components are cleaned by immersing or running them in one or more of the following: pure water, warm pure water, acidic chemicals, alkaline chemicals, and oxidizing chemicals for at least one hour.

[3] A cleaning method for ultrapure water production equipment during startup according to [1] or [2], wherein the component is at least one of a treated water strainer, resin catcher, piping, valves, pumps, degassing membranes, dissolving membranes, UF membranes, gaskets, sampling valves, sampling tubes, and heat exchangers of an ion exchange device.

In the present invention, among the components of an ultrapure water production system, those with a liquid contact area per unit ultrapure water flow rate of 1.0 × 10 ^-6 m ² /(m ³ /h) or more are pre-cleaned with water or chemicals before being installed in the ultrapure water production system. This allows high-purity ultrapure water to be obtained quickly even when starting up an ultrapure water production system that requires water quality of sub-ng/L.

According to one aspect of the present invention, it is possible to omit the large-scale chemical cleaning process that is performed after pre-cleaned components are installed in the ultrapure water production system, thereby shortening the trial operation process. However, a large-scale chemical cleaning process may also be performed.

Even when expanding or maintaining ultrapure water production equipment, by pre-cleaning the above components as described above and then incorporating them into the ultrapure water production equipment, it becomes possible to use high-purity ultrapure water quickly.

In one aspect of the present invention, by cleaning the above-mentioned components using chemical cleaning, it is possible to reduce the number of chemical cleaning processes in the entire ultrapure water production system and shorten the start-up period. However, it is also possible to carry out a large-scale chemical cleaning process.

FIG. 1 is a flow diagram of a subsystem of an ultrapure water production system. 10 is a graph showing experimental results.

The ultrapure water production system that is the subject of this invention comprises a primary pure water production system and a subsystem (secondary pure water production system). Furthermore, a pretreatment device is typically installed upstream of this primary pure water production system.

In the pretreatment equipment, the raw water is subjected to pretreatment such as filtration, coagulation and sedimentation, and microfiltration membranes, mainly to remove suspended solids. This pretreatment usually reduces the number of particles in the water to ¹⁰³ particles/mL or less.

Primary pure water production equipment is equipped with a reverse osmosis (RO) membrane separation device, a degassing device, a regenerative ion exchange device (mixed-bed or four-bed, five-tower type, etc.), an electric deionization device, an ultraviolet (UV) irradiation oxidation device or other oxidation device, and is used to remove most of the electrolytes, fine particles, live bacteria, etc. from the pretreated water. Primary pure water production equipment is composed of, for example, a heat exchanger, two or more RO devices, a mixed-bed ion exchange device, and a degassing device.

The subsystem consists of a water supply pump, a cooling heat exchanger, a low-pressure ultraviolet oxidation device, a non-regenerative mixed-bed ion exchange device, and a membrane filtration device such as an ultrafiltration (UF) membrane separator or a microfiltration (MF) membrane separator, but may also be equipped with a membrane degasser, an RO membrane separator, an electrodeionization device, etc. In the subsystem, the TOC components in the water are oxidatively decomposed using the low-pressure ultraviolet oxidation device, and the oxidative decomposition products are removed using the mixed-bed ion exchange device in the subsequent stage.

Figure 1 is a system diagram showing an example of a subsystem of such an ultrapure water production system.

The primary pure water produced in the primary pure water production system is pumped from sub-tank (primary pure water tank) 1 by pump 2 and processed through low-pressure ultraviolet oxidation device (UV device) 3, ion exchange device 4, pump 5, piping 6, degassing device 7, piping 8, and ultrafiltration (UF) device 9.

In the low-pressure ultraviolet oxidation device 3, TOC is decomposed into organic acids and further _CO2 using 185 nm ultraviolet light emitted from a low-pressure ultraviolet lamp. The organic matter and _CO2 produced by the decomposition are removed in the downstream ion exchange device 4 and degassing device 7. In the UF (ultrafiltration) device 9, fine particles are removed, as well as particles effluent from the ion exchange resin.

The ultrapure water produced in this subsystem is sent to the use point 11 via the ultrapure water supply pipe 10, and unused ultrapure water is returned to the subtank 1 via the return pipe 12.

In Figure 1, pipe 21 branches off from pipe 8, which sends water from degassing membrane device 7 to UF device 9. A portion of the degassed water is introduced into preheater 22 via pipe 21 and preheated. After passing through pipe 23 and heater 24, it is further heated and sent to point of use 28 via pipe 25, UF device 26, and pipe 27. Unused ultrapure water from point of use 28 is sent to preheater 22 via return pipe 29. Excess ultrapure water from preheater 22 is returned to subtank 1 via return pipe 30.

A sampling valve 10a is provided on the piping 10, allowing sample water to be introduced into the analysis device 16 via sampling piping 15. Sample water is also sampled from the piping 27 via sampling valve 27a and sampling piping 31, cooled in sampling cooler 32, and then introduced into the analysis device 16 via piping 33.

After the new construction or expansion of this subsystem is completed, the ultrapure water production equipment is operated to produce ultrapure water. Of the components incorporated into the subsystem during this new construction or expansion, those located at the ion exchange unit or downstream (but up to the point of use) and with a liquid contact area per unit ultrapure water flow rate of 1.0 x 10 ^-6 m ² /(m ³ /h) or more per component are pre-cleaned (hereinafter sometimes referred to as pre-cleaning).

Such components include the strainer and resin catcher of the ion exchange unit 4, the pump 5, the degassing unit 7, the UF unit 9, the piping 10, the sampling valves 10a and 27a, the preheater 22, the heater 24, the UF unit 26, the piping 6, 8, 10, 21, 23, 25, 27, and 31, the sampling piping 15, 31, and 33, the various valves and gaskets installed on these piping, and the sampling cooler 32.

The pre-cleaning may be one or more of the following: cleaning with pure water (resistivity of 5 MΩcm or more, preferably 18 MΩcm or more), cleaning with warm pure water (30°C or more, preferably 40 to 75°C), cleaning with an acidic chemical aqueous solution (nitric acid or the like, preferably with a concentration of 0.1% or more), cleaning with an alkaline chemical aqueous solution (choline hydroxide or the like, preferably with a pH > 10.5), cleaning with an oxidizing chemical aqueous solution (H ₂ O ₂ or the like, preferably with a concentration of 0.1% or more, particularly 0.1 to 2%). Pure water or ultrapure water is preferred as the water for preparing the chemical aqueous solution.

Pre-cleaning is preferably carried out until the amount of eluted fine particles and soluble components from the component is reduced to less than half. After the initial cleaning has been carried out and the required time and elution process from the component have been determined, pre-cleaning can be carried out by specifying the cleaning time without checking the amount of elution. It is usually preferable to perform pre-cleaning by immersion or pouring for at least one hour, for example, one to three hours.

Stainless steel components are particularly effective as materials for components to be pre-cleaned, but this is not limited to this, and non-ferrous materials such as fluororesin components and other plastic materials are also acceptable.

[Example 1, Comparative Examples 1 and 2]
An example of cleaning the strainer (made of SUS) of the ion exchange resin device of the subsystem will be described.

This strainer is cylindrical, measuring φ114.3 mm and L373 mm, with multiple slits on its circumferential side. There are four slits, each 0.2 mm wide. The liquid contact area per strainer, ignoring the slits, is 0.29 ^m2 . The water flow rate per strainer is 14.5 ^m3 /h, and the liquid contact area per unit ultrapure water flow rate is 2.0 x ^{10-2 m2} /( ^m3 /h). This value is greater than the reference value of 1.0 x ^{10-6 m2} /( ^m3 /h).

In Example 1, the strainer was immersed in 1% H ₂ O ₂ (ultrapure water containing hydrogen peroxide) for 2 hours for cleaning, and then incorporated into the ion exchange device.

In Example 2, this strainer was washed with 1 L/hr of ultrapure water for 5 days and then installed in the ion exchange device.

In Comparative Example 1, the strainer was installed in the ion exchange device without being cleaned at all.

The ion exchange resin and other components of the ion exchange device, such as the casing, other than the strainer, were washed with ultrapure water in the same manner as above. The ion exchange resin used was a mixed resin of anion exchange resin and cation exchange resin (1,160 L).

Ultrapure water was passed through each ion exchanger at SV=50 hr ⁻¹ and the Fe concentration in the effluent was measured. The results are shown in FIG.

As shown in Figure 1, in Comparative Example 1, it took more than eight days for the Fe concentration to fall below 1 ng/L, whereas in Examples 1 and 2, it fell below 1 ng/L in three days.

Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications are possible within the scope of the invention.
This application is based on Japanese Patent Application No. 2024-073854, filed on April 30, 2024, the entire contents of which are incorporated by reference.

REFERENCE SIGNS LIST 1 Subtank 3 Ultraviolet oxidation device 4 Ion exchange device 7 Degasser 9, 26 UF device 11, 28 Point of use 16 Analytical device 22 Preheater 24 Heater 32 Sampling cooler

Claims (4)

1. A method for cleaning an ultrapure water production system equipped with a subsystem having an ion exchange device at the time of startup, comprising:
This cleaning method for ultrapure water production equipment at the start-up of an ultrapure water production equipment is characterized in that, for components used in the downstream side of the ion exchange equipment, the ratio of the liquid contact area (m ² ) of a single component to the water flow rate (m ³ /h) of said component in the ultrapure water production equipment (liquid contact area per unit ultrapure water flow rate) is 1.0 × 10 ^-6 m ² /(m ³ /h) or more, is pre-cleaned with water or a chemical solution and then installed in the ultrapure water production equipment. The cleaning method for starting up the ultrapure water production system of claim 1, in which the components are cleaned by immersing or running them in one or more of pure water, warm pure water, acidic chemicals, alkaline chemicals, and oxidizing chemicals for at least one hour. A cleaning method for starting up the ultrapure water production system of claim 1, in which the components are immersed in hydrogen peroxide solution having a concentration of 0.1% or more for at least one hour for cleaning. 4. The method for cleaning an ultrapure water production system during startup according to any one of claims 1 to 3, wherein the component is at least one of a treated water strainer, a resin catcher, a piping, a valve, a pump, a degassing membrane, a dissolving membrane, a UF membrane, a gasket, a sampling valve, a sampling tube, and a heat exchanger of an ion exchange system.