JPH0779994B2 - Ultrapure water production method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing ultrapure water, and more particularly to a method for producing ultrapure water by a distillation method.

[Conventional technology]

High-purity water (ultra-pure water) containing as few impurities as possible is required for the semiconductor manufacturing process and the pharmaceutical manufacturing. Especially in the LSI cleaning process, a large amount of ultrapure water is used. The purity of this ultrapure water has a great influence on the yield of products, and even higher purity water is required for cleaning highly integrated LSI (1M, 4M bits) these days.

The conventional ultrapure water production system uses environmental technology Vol 14, No. 4 (198
5), 353 to 358, it is composed of various filtration membranes, ion exchange towers, germicidal lamps, deaerators, etc.
FIG. 5 shows a schematic diagram of a conventional ultrapure water production system. The raw water is subjected to pretreatment steps such as coagulation sedimentation-filtration-microfiltration, and then sent to the reverse osmosis step (RO) to remove most of dissolved organic components and 90 to 99% of inorganic salts contained in the raw water. It Further, this permeated water is decarbonated through the degassing tower and sent to the ion exchange resin step. The ion exchange tower is a two-bed type and a mixed-bed type regeneration system, in which salt is completely removed in this process. Normally, primary pure water with a specific resistance of 10 MΩ · cm or more is obtained here and then stored in a pure water tank. To be done. Primary pure water is
It is treated with a mixed bed type ion exchange resin (Polysia), and after further removing impurities completely, microorganisms are removed by an ultraviolet sterilization step, and fine particles and dead bacteria remaining in an ultrafiltration step (UF) are removed, It becomes ultrapure water.

Further, as shown in Japanese Patent Laid-Open No. 61-230703, a pure water producing apparatus using a hydrophobic porous membrane has been proposed. In this device, one side partitioned by a hydrophobic porous membrane that allows liquid vapor to pass therethrough but does not allow the liquid itself to pass is used as a raw material passage, and a cooling plate is provided on the other side to provide the cooling plate and the hydrophobic porous film. Is a condensing chamber, and the outside of the cooling plate is a cooling water passage, and a separation membrane unit configured to condense the vapor that has passed through the porous membrane from the raw liquid passage with a condensate, and a heat tank having a heater. At least, and introduce a stock solution such as tap water into the cooling water passage of the separation membrane unit, further introduce the stock solution passing through the cooling water passage to the heat tank, the high temperature stock solution heated in the heat tank Is piped so as to lead to the stock solution passage of the separation membrane unit.

[Problems to be solved by the invention]

The above-mentioned conventional technology is composed of many elemental devices such as various filtration membranes, ion exchange resins, and germicidal lamps, and in order to improve the water quality of the generated ultrapure water, it is inevitable that each elemental device has a level up.
Even in the current system, for example, with regard to the membrane module, there are no defects on the surface of the membrane that has a separation function, the seal between the raw solution and the permeate side is perfect, and there is no liquid retention part in the module. There are many requirements such as that it can be sufficiently washed and bacteria do not proliferate, and there are few elution components from the module, and a special grade is used for ultrapure water. However, in order to prevent bacterial growth in the module, cleaning by regular flushing and sterilization by chemicals are necessary. Even in the desalting process with ion-exchange resin, a method to prevent impurities from being mixed in from outside during regeneration is adopted, and a non-regenerated type of the final stage polyurethane uses a sufficiently purified high-purity resin. Are taken into consideration.

As described above, in the conventional ultrapure water production technique, there are problems such as a considerable amount of maintenance required to maintain the water quality, and elution due to the large number of elemental devices, and deterioration of the water quality due to the stagnant portion.

In addition, in the conventional pure water production system using a hydrophobic membrane, there is a special de-CO ₂ de-T
Since no OC device was installed, it was not possible to create a level of water quality that could be used for cleaning LSIs.

An object of the present invention is to eliminate the above-mentioned drawbacks by using a high temperature ultrapure water which is said to be capable of producing higher purity water with a simple device having less elemental equipment and at the same time having higher cleaning power. It is to provide a method for producing ultrapure water for the next generation, which can also be produced.

[Means for Solving Problems] The present invention generates steam from raw water outside a clean room that separates the point of use of ultrapure water from the outside, and transfers the steam in a vapor phase state into the clean room, It is condensed by a condenser installed near the point of use and equipped with a hydrophobic porous membrane.

[Action]

A steam generator such as a boiler is installed outside the clean room, and it is transferred to the condenser in the clean room in the state of steam and returned to water by the condenser near the point of use. A hydrophobic porous membrane is arranged in the condenser, and the steam is filtered by the membrane immediately before being condensed to separate mist (droplets) entrained in the steam. By doing so, only high-purity water vapor is condensed, and ultrapure water is generated.

Usually, tap water or water subjected to reverse osmosis treatment contains a large amount of various inorganic substances, ions, organic substances, and microorganisms. In the case of a phase change such as membrane distillation, non-volatile substances such as inorganic substances, microorganisms, and high boiling organic substances are easily removed, but volatile substances such as carbon dioxide gas components and low boiling organic substances are easily removed. Can hardly be removed. Therefore, it is necessary to install a CO ₂ removal and TOC removal unit in the previous stage to remove volatile substances that cannot be removed in the previous stage of membrane distillation. Therefore, the steam generator installed outside the clean room is first divided into _two parts, the volatile substances are removed by the CO ₂ removal and TOC removal parts by the heating method and the oxidation method in the previous stage, and then the steam generation part is installed. Steam is produced. Since the volatile components have been removed in the previous stage, the impurities mixed in the water vapor are only mist (droplets) entrained. This water vapor is sent to the condenser installed in the clean room. The condenser has a hydrophobic porous membrane and a cooling surface, and the sent steam is filtered through the membrane to remove mist entrained therein, and only pure steam is condensed to produce ultrapure water.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows the basic flow of the present invention. Raw water such as city water is pretreated by RO etc. to prevent scale from adhering to the inside of the steam generator. The pretreated water enters the steam generator. The water vapor from which volatile substances have been removed is sent to the clean room as water vapor in a clean pipe,
After entering the condenser near the point of use and removing the mist in the water vapor by the hydrophobic porous membrane in the condenser, it is condensed and produced in ultrapure water.

FIG. 2 shows an example of the outline of the steam generator. The pretreated raw water 20 enters the CO ₂ removal and TOC removal section 21, and is boiled by the heater 23 to remove CO ₂ and TOC components together with steam.
Although heating is performed directly in this embodiment, a method such as flash evaporation can also be used. This steam 24 is used in the next steam generation unit 22.
It becomes a steam generation heat source, and the condensed water is discharged outside the system as a drain 27. De CO _2, raw water removed CO ₂ and TOC components in de TOC section 21 is sent to the flow rate adjusting valve 26 as the steam generator 22. The raw water becomes steam here and is sent to the clean room through the pipe 25. A pre-heater 28 is installed to adjust the amount of heat.

FIG. 3 shows an outline of the condenser. The water vapor sent from the pipe 25 passes through the membrane module 31 having the hydrophobic porous membrane 33 and is separated from the accompanying mist. Here, the material of the hydrophobic porous film 33 is polytetrafluoroethylene, polypropylene, polyethylene or the like. The vapor separated from the mist is condensed on the cooling surface 34 cooled by the cooling water 33 in the condensing section 32, and is taken out as ultrapure water 35. According to the present embodiment, high-purity ultrapure water containing very few impurities other than water can be taken out at a high temperature. The specific resistance of water that has passed through the membrane module 31 is 18 MΩ · cm or more, fine particles (0.1 μm · piece / piece) are 100 or less, and microorganisms (piece / piece) are 10 or less.
Below, the organic matter (ppb) was 10 or less.

FIG. 4 shows an outline of a heat recovery type condenser. The above method has an insufficient structure in terms of effective heat recovery. Therefore, as shown in FIG. The steam sent from the pipe 25 is filtered by the membrane module 31, then sent to the first tower 42, and cooled by the raw water 41 in the first tower 42 to become ultrapure water. This raw water 41 is sent from a steam generator outside the clean room. At the same time, the raw water in the first tower 42 evaporates, the water vapor is filtered by the hydrophobic porous material 46, and then the cooling water 44 in the second tower 43.
Is condensed and becomes ultrapure water 45. According to this method, since heat can be recovered, the cost of produced water can be reduced. In this example, two stages of condensation are shown, but 3
It doesn't matter even if it is 4 steps or 4 steps.

In FIG. 1, the condenser is used to condense water and use it as ultrapure water. However, if cleaning with water vapor rather than LSI with water is effective, the cooling surface 34
By removing (Fig. 3), clean water vapor can be taken.

〔The invention's effect〕

According to the present invention, a volatile component which is a problem in an ordinary distillation apparatus is removed by a steam generator, and entrained mist is removed by a hydrophobic porous membrane of a condenser. It becomes possible to produce ultrapure water.
Further, since the contamination such as elution during the transfer of ultrapure water, which has been a problem in the past, can be prevented by filtering and condensing immediately before the point of use, a water quality higher than that in the past can be obtained. Further, since the temperature of the generated water is high, it becomes high-temperature ultrapure water as it is, which is more effective for cleaning wafers and the like.

[Brief description of drawings]

FIG. 1 is a schematic flow chart of the present invention, FIG. 2 is a schematic configuration diagram of a steam generator, FIG. 3 is a schematic configuration diagram of a condenser, and FIG. 4 is a schematic configuration diagram of a heat recovery type condenser. FIG. 5 is a schematic view showing a conventional ultrapure water production process. 20 ...... raw water, 21 ...... de CO ₂ removal TOC section, 22 ...... steam generating unit, 25 ...... pipe, 31 ...... membrane modules, 32 ...... condensing unit,
33 ... Hydrophobic porous membrane, 34 ... Cooling surface, 35 ... Ultrapure water.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuya Ehara 4026 Kuji Town, Hitachi City, Hitachi, Ibaraki Prefecture, Hitachi Research Institute, Ltd. Hitachi Research Laboratory (72) Inventor Takayoshi Hashiyoshi 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi, Ltd.

Claims (2)

[Claims] 1. A method of producing steam from raw water outside a clean room that separates the point of use of ultrapure water from the outside, transferring this steam in the gas phase state into the clean room, and installing a hydrophobic porous material near the point of use. A method for producing ultrapure water, which comprises condensing with a condenser equipped with a membrane. 2. A method for producing ultrapure water according to claim 1, wherein carbon dioxide gas and organic substances in the raw water are removed, and then steam is generated from the raw water.