JP6417734B2 - Ultrapure water production method - Google Patents

Description

  The present invention relates to an ultrapure water manufacturing method, and more particularly to an ultrapure water manufacturing method suitable for cleaning electronic component members in the semiconductor manufacturing industry or the like.

  In recent years, with the development of semiconductor manufacturing processes, impurities (fine particles) in water (ultra-pure water) for cleaning semiconductor substrates and the like are strictly managed. According to the International Semiconductor Technology Roadmap (ITRS), it is said that a guaranteed value <1000 particles / L (control value <100 particles / L) with a particle diameter> 11.9 nm is required in 2019.

  Conventionally, ultrapure water used as semiconductor cleaning water is treated with raw water (industrial water, city water, well water, etc.) using an ultrapure water production system consisting of a pretreatment system, primary pure water system and subsystems. (See, for example, Patent Document 1).

  In a pretreatment system comprising agglomeration, pressurized flotation (precipitation), filtration device, etc., suspended substances and colloidal substances in raw water are removed. Primary pure water system equipped with reverse osmosis (RO) membrane separation device, deaeration device and ion exchange device (mixed bed type, 2 bed 3 tower type or 4 bed 5 tower type) removes ions and organic components in raw water. Do. The RO membrane separation apparatus removes ionic and colloidal total organic oxygen (TOC) in addition to removing salts. In the ion exchange device, in addition to removing salts, the TOC component adsorbed or ion exchanged by the ion exchange resin is removed. In the degassing device (nitrogen degassing or vacuum degassing), the dissolved oxygen is removed.

In a subsystem including a heat exchanger, a low-pressure ultraviolet (UV) oxidizer, a mixed bed ion exchanger, and an ultrafiltration (UF) membrane separator, the purity of water is further increased to ultrapure water. In the low-pressure UV oxidizer, TOC is decomposed into an organic acid and further to CO ₂ by ultraviolet rays having a wavelength of 185 nm emitted from a low-pressure UV lamp. The decomposed organic acid and CO ₂ are removed by a subsequent ion exchange resin. In the UF membrane separation apparatus, the fine particles are removed and the outflow particles of the ion exchange resin are also removed.

  Thus, conventionally, a nanometer-sized fine particle removal process has been performed by installing a fine particle removal film such as a UF film at the end of the subsystem. In addition, a mini-subsystem is installed as a point-of-use polisher just before the cleaning machine for semiconductor / electronic material cleaning, and a particle removal film is installed at the last stage, or a particle removal film is installed just before the nozzle in the washing machine. A method for efficiently removing fine particles having a size has been studied.

  The UF membrane as the fine particle removal membrane used in the subsystem preferably has a pore size smaller than the fine particle size, but there are innumerable pores on the UF membrane surface, and the pore size varies. . Therefore, the fine particles having a particle diameter of about 10 nm could not be completely removed.

  In order to increase the fine particle removal rate of the fine particle removal film, a technique of providing two stages of fine particle removal films in a subsystem is known. For example, FIGS. A configuration in which a UF membrane device and an ion exchange group-modified microfiltration (MF) membrane device are installed in this order in series is disclosed at the last stage. However, this configuration has a problem that the exchange base is detached from the ion exchange group-modified MF membrane device to become a fine particle source. In addition, the pore size of the MF membrane is on the order of submicron, which is larger than the pore size of the UF membrane, and it is difficult to manage fine particles (particle size> 10 nm) at a level of 1000 particles / L or less.

  FIG. 4A of Patent Document 3 discloses a configuration in which an RO membrane device is provided after the UF membrane device at the end of the secondary pure water device. Since the RO membrane has a smaller pore size than the UF membrane, it is theoretically possible to increase the removal rate of the fine particles. However, since the RO membrane has a low cleanliness as a module and may generate fine particles such as dust from the potting material, it is not suitable as a fine particle removal membrane provided at the end of the subsystem.

  Patent Document 4 discloses a configuration in which a secondary pure water device is provided with a UF membrane device and an anion adsorption membrane device having a pore diameter of 500 to 5000 mm. A hollow fiber membrane having a pore size of 0.02 μm, a porosity of 60%, and a film thickness of 0.35 mm is used as the anion adsorption membrane. Although this anion adsorption membrane can highly remove silica, it is useful for producing ultrapure water. The required level of fine particles could not be removed.

  Patent Document 5 discloses a configuration in which a prefilter for blocking particles having a particle size of 10 μm or more is provided in front of a UF or MF membrane device used as a separation membrane module for producing ultrapure water. This pre-filter is for preventing impurities having a particle diameter of 10 μm or more from colliding with the UF or MF film and causing damage to the film. Fine particles having a particle diameter of less than 10 μm are not removed. Further, in the final stage UF or MF membrane, fine particle leakage to the subsequent stage accompanying the accumulation of fine particles is considered, and there is a possibility that the water quality at the point of use may be lowered.

JP 2010-196591 A JP 2004-283710 A JP 2003-190951 A Japanese Patent Laid-Open No. 10-216721 JP-A-4-338221

  This invention is made | formed in view of the above situation, and makes it a subject to provide the ultrapure water manufacturing method which can manufacture a highly purified ultrapure water with a high fine particle removal rate.

  As a result of intensive studies to solve the above problems, the inventors of the present invention have a pore size distribution in the UF membrane, and in the case of removing fine particles having the same size as the pore size or smaller than the pore size, the same as in the MF membrane. In addition to the MF membrane, not only the MF membrane but also the UF membrane cannot completely remove fine particles with a particle size of 10 nm, but by lowering the permeation flux (Flux) of the fine particle removal membrane, It has been found that the accumulation of fine particles on the film surface can be alleviated and the fine particle removal rate as a module can be improved, and the present invention has been completed based on this finding.

  That is, the method for producing ultrapure water of the present invention comprises a step of producing primary pure water in a primary pure water system, and a step of producing ultrapure water by treating primary pure water in a subsystem to produce ultrapure water. And having a permeation flux of 0.1 to 0.35 m / Hr of the fine particle removal membrane device. It is characterized by doing.

  In this invention, it is preferable that the fine particle concentration of the water supply to the said fine particle removal film apparatus is 1000 pieces / mL or less.

  In the present invention, it is preferable that the fine particle removal film device is installed at the last stage of the subsystem.

  In the present invention, the fine particle removal membrane device is preferably an ultrafiltration membrane device or a microfiltration membrane device.

In the present invention, it is preferable that at least one water treatment device is installed between the pump installed in the subsystem and the particulate removal membrane device. The water treatment device is preferably at least one of an ion exchange device, a deaeration device, a UV oxidizer, and an H ₂ O ₂ removal device.

  According to the present invention, since the permeation flux of the fine particle removal membrane device is 0.1 to 0.35 m / Hr, the accumulation of fine particles on the membrane surface is alleviated, the fine particle removal rate is increased, and high purity ultrapure water is used. Can be manufactured.

  Further, by setting the fine particle concentration of the water supplied to the fine particle removal membrane device to 1000 particles / mL or less, the treated water particle concentration can be controlled to 1 particle / mL or less.

Also, by installing at least one water treatment unit between the pump installed in the subsystem and the particulate removal membrane device, the particulates generated at the sliding part of the pump can reach the particulate removal membrane device. Can be prevented. In particular, the water treatment unit installed between the pump and the particulate removal membrane device is at least one of an ion exchange device, a deaeration device, a UV oxidizer, and an H ₂ O ₂ removal device, The fine particle concentration in the water can be effectively reduced by the fine particle adsorption effect of these units.

It is the schematic of the ultrapure water manufacturing apparatus which concerns on embodiment of this invention. FIG. 3 is an experimental schematic diagram of Experimental Example 1. It is a graph which shows the relationship between a permeation flux and a particle removal rate. It is the schematic of the ultrapure water subsystem used in Example 1. FIG.

  Hereinafter, embodiments of the present invention will be described in detail.

  The ultrapure water production apparatus in FIG. 1 includes a pretreatment system 1, a primary pure water system 2, and a subsystem 3.

  In the pretreatment system 1 including agglomeration, pressurized flotation (precipitation), a filtration device, and the like, the suspended substances and colloidal substances in the raw water are removed. In the primary pure water system 2 equipped with a reverse osmosis (RO) membrane separation device, a deaeration device, and an ion exchange device (mixed bed type, 2 bed 3 tower type or 4 bed 5 tower type), removal of ions and organic components in the raw water I do. The RO membrane separation apparatus removes ionic and colloidal TOC in addition to removing salts. In the ion exchange device, in addition to removing salts, the TOC component adsorbed or ion exchanged by the ion exchange resin is removed. In the degassing device (nitrogen degassing or vacuum degassing), the dissolved oxygen is removed.

  The primary pure water thus obtained (usually pure water having a TOC concentration of 2 ppb or less) is converted into a sub tank 11, a pump P, a heat exchanger 12, a UV oxidation device 13, a catalytic oxidative substance decomposition device 14, Water is sequentially passed through the deaeration device 15, the mixed bed type ion exchange device (deionization device) 16 and the fine particle separation membrane device 17, and the obtained ultrapure water is sent to the use point 18.

As the UV oxidation device 13, a UV oxidation device that irradiates UV having a wavelength near 185 nm, which is used in an ultrapure water production device, for example, a UV oxidation device using a low-pressure mercury lamp is used. This UV oxidation apparatus 13, primary pure water TOC is organic acid, further is decomposed into CO _2.

The catalytic oxidizing substance decomposing apparatus 14 efficiently decomposes and removes H ₂ O ₂ and other oxidizing substances generated in the UV oxidizing apparatus 13 by the catalyst. Examples of the oxidant decomposition catalyst of the catalytic oxidant decomposition apparatus 14 include noble metal catalysts known as redox catalysts, such as palladium (Pd) compounds such as metal palladium, palladium oxide, and palladium hydroxide, or platinum (Pt). Is used.

As the degassing device 15, a vacuum degassing device, a nitrogen degassing device, or a membrane degassing device is used. By this deaeration device 15, dissolved oxygen (DO) and CO _{2 in} the water are efficiently removed.

  The mixed bed ion exchange device 16 removes cations and anions in the water, thereby increasing the purity of the water.

  As the fine particle separation membrane device 17, a UF membrane separation device or an MF membrane separation device can be used. However, a UF membrane separator having a fractional molecular weight of 400 to 10,000, preferably 400 to 8,000 can be suitably used. If the molecular weight cut off is too large, particles having a particle diameter of about 10 nm cannot be removed sufficiently. If the molecular weight cut off is too small, the power (pressure) for obtaining a sufficient permeation flux becomes too large. It is. Here, the molecular weight cut-off is sucrose (340), raffinose (590), vitamin B12 (1360), Bacitrancin (1410), insulin (5700), myoglobin (17000), pepsin (35000), albumin (66000), etc. Using a marker molecule such as polypeptide or protein, dead-end filtration is performed, and the molecular weight at which the blocking rate is 90% is calculated from the relationship between the molecular weight and the blocking rate. The fine particle separation membrane device 17 removes fine particles in water, such as outflow fine particles of the ion exchange resin from the mixed bed ion exchange device 16.

  In the present invention, by setting the permeation flux of the particulate separation membrane device 17 to a low value of 0.3 m / Hr or less, particulate accumulation on the membrane surface is alleviated and a high particulate removal rate is realized. The permeation flux of the fine particle separation membrane device 17 is preferably 0.1 to 0.35 m / Hr, particularly preferably 0.2 to 0.33 m / Hr, and more preferably 0.25 to 0.3 m / Hr.

  Normally, the hollow fiber type UF membrane has a permeation flux of about 0 in order to make the differential pressure on the inner and outer surfaces of the hollow fiber sufficiently lower than 0.18 MPa, which is a limit pressure at which the hollow fiber is crushed, and to secure a large flow rate. Used as 5 m / Hr. On the other hand, in the present invention, by setting the permeation flux to 2/3 or less of that during normal use, fine particles with an order of 10 nm can be efficiently removed, and the fine particle removal rate can be improved.

  In order to manage the water treated by the fine particle separation membrane device 17 to 1000 particles / L (1 piece / mL) or less of fine particles having a particle diameter of 10 nm or more, the fine particle concentration of water introduced into the fine particle separation membrane device 17 is It is preferable to make it 1000 pieces / mL or less.

  In the subsystem 3, the pump P may be further installed not only between the sub tank 11 and the heat exchanger 12 but also between other units. Since a rotating machine such as a pump can generate fine particles from the sliding portion, the pump P is not provided at a position other than the front stage of the fine particle separation membrane device 17 (between the mixed bed ion exchange device 16 and the fine particle separation membrane device 17). It is preferable to install. At least one unit (UV oxidation device 13, catalytic oxidizing substance decomposition device 14, degassing device 15, ion exchange device 16) is installed between the pump P and the fine particle separation membrane device 17, so that the pump The generated fine particles are removed, and the fine particle concentration of water introduced into the fine particle separation membrane device 17 can be reduced.

[Experimental Example 1]
Ultrapure water spiked (added) with Au colloidal particles was passed through the UF membrane module while changing the permeation flux, and the relationship between the permeation flux and the particulate removal rate of the UF membrane module was determined. That is, ultrapure water in which Au colloidal particles having a particle diameter of 10 nm (manufactured by BB International) were added so that the concentration of Au colloidal particles was 1 × 10 ⁹ particles / mL was obtained, as shown in FIG. Supplied from the bottom of the UF membrane module, and treated water was discharged from the top. The amount of concentrated water in the UF membrane module was set at about 5% of the amount of water supplied, and the concentrated water was discharged. The amount of water supplied to the UF membrane module was changed to change the permeation flux of the UF membrane, the concentration of Au colloid particles in the treated water in each permeation flux was measured, and the colloid particle removal rate was calculated. An inductively coupled plasma mass spectrometer (ICP-MS) was used for the analysis of Au colloid particle concentration. The colloid particle removal rate was calculated by dividing the Au colloid particle concentration in the treated water by the Au colloid particle concentration in the feed water. The results are shown in FIG.

  From FIG. 3, it was found that the smaller the permeation flux, the higher the Au colloidal particle removal rate, and that the permeation flux was 99.9% or more at 0.3 m / Hr or less.

  Next, using the following formula, the UF membrane water supply allowable fine particle concentration necessary for managing fine particles having a particle diameter of 10 nm to 1000 / L = 1 / mL or less in the UF membrane treated water was calculated.

In the above formula, C ₀ is the fine particle concentration [number / mL] in the UF membrane feed water, C is the fine particle concentration [number / mL] in the UF membrane treated water, Re is the fine particle removal rate [%] in the UF membrane, and B is The number of fine particles generated from the UF membrane material itself [number / mL].

Substituting 99.9% for the fine particle removal rate Re (removal rate when the permeation flux is 0.3 m / Hr or less) obtained from the results shown in FIG. the relationship between the particle concentration C ₀ and UF membrane treated water particle concentration C shown in Table 1 below.

  From Table 1, even when the fine particle removal rate of the UF membrane is 99.9%, in order to make the UF membrane treated water fine particle concentration 1 mL / mL or less, the UF membrane water supply fine particle concentration is set to 1000 particles / mL or less. I found it necessary.

[Example 1]
The primary pure water is separated from the sub tank 21 of the ultra pure water subsystem 20 shown in FIG. 4, the first pump 22, the heat exchanger 23, the UV oxidizer 24, the H ₂ O ₂ separation catalyst tower 25, the second pump 26, and degassed. Water was sequentially passed through the membrane device 27, the ion exchange resin tower 28, and the UF membrane device 29, and the obtained ultrapure water was sent to the use point 30. Primary pure water is obtained by treating industrial water as raw water with a pretreatment system and a primary pure water system, and has a TOC concentration of 10 to 20 ppb. The first pump 22, the heat exchanger 23, the UV oxidizer 24, the H ₂ O ₂ separation catalyst tower 25, the second pump 26, the degassing membrane device 27, the ion exchange resin tower 28, and the UF membrane device 29. Sample water was collected from the outlet side (# 1 to # 8) and analyzed for the concentration of fine particles having a particle diameter of 10 nm. The fine particle concentration was calculated by filtering a predetermined amount of sample water through a filter, counting the number of fine particles captured by the filter while observing with an electron microscope, and dividing the detected value by the amount of filtered water. The calculation results are shown in Table 2 below.

As shown in Table 2, many fine particles were confirmed at the first pump outlet (# 1) and the second pump outlet (# 5), and there was almost no change in the fine particle concentration at the heat exchanger outlet (# 2). From this result, it was confirmed that fine particles were generated from the sliding part of the pump, and the heat exchanger hardly affected the increase or decrease of the fine particles. On the other hand, in the UV oxidizer, the H ₂ O ₂ decomposition catalyst tower, the degassing membrane apparatus, and the ion exchange resin tower, the fine particle concentration decreased before and after that. This is presumably because the fine particle concentration is reduced by the fine particle adsorption effect of these devices. From this result, in order to reduce the concentration of fine particles in the feed water of the UF membrane (particle removal membrane) device, it was recognized that the pump should be installed at a location other than just before the UF membrane device.

DESCRIPTION OF SYMBOLS 11 Subtank 12 Heat exchanger 13 UV oxidation apparatus 14 Catalytic oxidative substance decomposition apparatus 15 Deaeration apparatus 16 Mixed bed type ion exchange apparatus 17 Fine particle separation membrane apparatus 18 Use point

Claims (4)

Producing primary pure water with a primary pure water system;
An ultrapure water production process in which primary pure water is processed by a subsystem to produce ultrapure water;
Have
In the ultrapure water production method in which fine particle removal processing is performed by the fine particle removal membrane device at the subsystem or later stage thereof,
The fine particle concentration of water supplied to the fine particle removal membrane device is 1000 / mL or less,
The particle size of the fine particles is 10 nm or more,
The fine particle removal membrane device is an ultrafiltration membrane device having a molecular weight cut-off of 400 to 10,000.
The ultrafiltration membrane device has a permeation flux of 0.3 m / Hr or less and a particle removal rate of 10 nm and a particle size of 99.9% or more.
Ultrapure water producing method characterized by the flux of the ultrafiltration membrane apparatus to 0.25-0.3 m / Hr.   2. The method for producing ultrapure water according to claim 1, wherein the particulate removal membrane device is installed at the last stage of the subsystem.   3. The method for producing ultrapure water according to claim 1, wherein at least one water treatment device is installed between a pump installed in the subsystem and the particulate removal membrane device. 4. The method for producing ultrapure water according to claim 3, wherein the water treatment device is at least one of an ion exchange device, a deaeration device, a UV oxidizer, and an H ₂ O ₂ removal device.

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