JPH09253639A - Ultrapure water making apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrapure water making apparatus enhanced in the removal ratio of TOC in a secondary pure water system. SOLUTION: An ultraviolet oxidizing device 16 and the degassing device 14 provided on the upstream side thereof to remove dissolved nitrogen in water to be treated are arranged in a secondary pure water system C. By this constitution, almost all of ultraviolet irradiation energy is effectively utilized in the oxidative decomposition of TOC in the ultraviolet oxidizing device 16. An oxygen or ozone adding device 26 adding oxygen gas and/or ozone gas to water to be treated is arranged between the degassing device 14 and the ultraviolet oxidizing device 16. As a result, TOC decomposition efficiency in the ultraviolet oxidizing apparatus 16 is further enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for producing ultrapure water (including pure water) used for cleaning silicon wafers in the semiconductor industry. More specifically, the TOC removal rate in a secondary pure water system will be described. The present invention relates to an ultrapure water production system with improved performance.

[0002]

2. Description of the Related Art In general, an apparatus for producing ultrapure water used for cleaning silicon wafers includes a primary pure water system into which treated water from a pretreatment system is introduced and a treated water from the primary pure water system. The secondary pure water system (subsystem) to be introduced is provided. The primary deionized water system is composed of an ion exchange device, a reverse osmosis membrane device, a degassing device, an ultraviolet sterilization device, etc., and removes most of the impurities such as fine particles, ionic components, organic substances and colloidal components contained in the water to be treated. To remove. The secondary deionized water system is composed of a treated water introduction tank of the primary deionized water system, an ultraviolet oxidizer, a cartridge polisher (non-regenerative mixed bed ion exchange device), an ultrafiltration membrane device, etc. It removes traces of impurities that remain in the treated water of the system. In the secondary pure water system, continuous circulation operation is performed, and a part of the obtained ultrapure water is sent to the point of use and the rest is circulated in the tank. The wastewater of ultrapure water used at the point of use is sent to the recovery system for reuse.

With the recent increase in the integration of semiconductor devices,
The required water quality for ultrapure water for wafer cleaning has become extremely severe. In particular, dissolved oxygen forms a natural oxide film on the wafer surface in a short time, which causes deterioration of device characteristics and a reduction in yield. Therefore, ultra pure water for wafer cleaning is required to have a dissolved oxygen concentration as low as possible. Therefore, in an apparatus for producing ultrapure water for wafer cleaning, a deoxidizer such as a vacuum degassing tower, a membrane degassing apparatus, or a nitrogen aeration apparatus is generally used in the primary pure water system for the purpose of reducing the dissolved oxygen concentration. The system is installed in the system, and nitrogen is sealed in the tank at the inlet of the secondary pure water system (the treated water introduction tank of the primary pure water system) to remove dissolved oxygen in the water to be treated by the primary pure water system. In addition, oxygen is prevented from being dissolved in water at the time of transition from the primary pure water system to the secondary pure water system. However, even in this case, a very small amount of dissolved oxygen usually remains in the water to be treated in the secondary pure water system.

[0004]

As the degree of integration of semiconductor devices is improved, ultra pure water for wafer cleaning is required to have a concentration of organic substances (organic carbon: TOC) as low as possible. Currently, TOC is removed by removing most of it with an ion exchange device or reverse osmosis membrane device of the primary pure water system, and then oxidatively decomposing the rest into an organic acid or carbonic acid with an ultraviolet oxidation device of the secondary pure water system. The organic acid and carbonic acid produced are removed by the cartridge polisher in the subsequent stage. Therefore, in order to reduce the TOC concentration in ultrapure water to an extremely small amount, it is necessary that TOC be almost completely decomposed by the ultraviolet oxidizer of the secondary pure water system.

Therefore, the present inventors have decided to use TOC in ultrapure water.
For the purpose of reducing the concentration, a study was conducted to enhance the TOC decomposition efficiency in the ultraviolet oxidizer of the secondary pure water system. In the process, the ultraviolet radiant energy of the secondary pure water system in the conventional ultrapure water production system does not sufficiently contribute to the decomposition of TOC and the satisfactory decomposition efficiency is not obtained. Found out.

That is, in the conventional ultrapure water production system, 1
Since a deoxidizer is installed in the secondary deionized water system and nitrogen is sealed in the tank at the inlet of the secondary deionized water system, inside the tank (if a nitrogen aeration device is used as the deoxidizing device, inside the device) A large amount of nitrogen gas is dissolved in water, and dissolved nitrogen is present at a high concentration in the inflow water to the ultraviolet oxidizer of the secondary pure water system. Due to this dissolved nitrogen, the TOC in the ultraviolet oxidizer is increased. It was discovered that the decomposition efficiency decreases.

The reason for this is that the decomposition of TOC in the ultraviolet oxidizer of the secondary deionized water system causes the generation of hydroxy radicals (.OH) and hydrogen peroxide from water upon irradiation with ultraviolet rays (wavelength 185 nm). Radicals and hydrogen peroxide oxidize TOC, but when dissolved nitrogen is present in the water to be treated, part of the ultraviolet radiation energy is due to the reaction between dissolved nitrogen and residual dissolved oxygen, nitrous acid and nitric acid. It is thought that this is because the amount of ultraviolet radiation energy that is consumed in the production of methane and is used for the original purpose of oxidative decomposition of TOC decreases.

The present invention has been made in view of the above circumstances, and in the ultraviolet oxidizer of the secondary pure water system, a part of the ultraviolet irradiation energy is converted into nitrous acid or nitric acid by the reaction between dissolved nitrogen and residual dissolved oxygen. By suppressing consumption of the UV irradiation energy so that almost all of the UV irradiation energy is effectively used for the oxidative decomposition of TOC, the TOC decomposition efficiency in the UV oxidizer is increased to improve the TOC removal rate. It is an object of the present invention to provide a device for producing ultrapure water.

[0009]

In order to achieve the above object, the present invention is an ultrapure water production system comprising a primary pure water system and a secondary pure water system, which comprises an ultraviolet oxidizer and There is provided an ultrapure water production system characterized in that a degassing device existing upstream and for removing dissolved nitrogen in water to be treated is installed in a secondary pure water system.

In the present invention, in the secondary pure water system, the degassing device for removing dissolved nitrogen is installed upstream of the ultraviolet oxidation device, so that the concentration of dissolved nitrogen in the inflow water to the ultraviolet oxidation device is reduced. Therefore, in the ultraviolet oxidation device, it is possible to suppress a part of the ultraviolet irradiation energy from being consumed by the reaction between dissolved nitrogen and dissolved oxygen. Therefore, almost all of the ultraviolet irradiation energy is effectively used for the oxidative decomposition of TOC, and the TOC decomposition efficiency becomes high. In this case, the tank existing at the inlet of the secondary pure water system is filled with nitrogen, and even if a large amount of nitrogen is dissolved in the water in this tank, the degassing device is installed on the downstream side of the tank. As a result, the concentration of dissolved nitrogen in the water flowing into the ultraviolet oxidation device can be reduced and the TOC decomposition efficiency can be increased.

In the present invention, as the degassing device installed in the secondary pure water system, at least one that removes dissolved nitrogen in the water to be treated is used. As such a degassing device, the dissolved nitrogen concentration in the water to be treated is 1 ppm or less,
It is particularly preferable to reduce it to 0.1 ppm or less. When a degasser that removes dissolved nitrogen and dissolved oxygen in the water to be treated is used, the degasser can reduce both the dissolved nitrogen concentration and the dissolved oxygen concentration in the treated water. Therefore, it is possible to omit the installation of the deoxidizer in the primary pure water system and the filling of the tank at the inlet of the secondary pure water system with nitrogen. As such a degassing device, one that reduces the dissolved nitrogen concentration in the water to be treated to the above concentration and the dissolved oxygen concentration to 0.5 ppm or less, particularly 0.05 ppm or less is preferable.

The type of degassing device is not limited, and a vacuum degassing tower, a heating degassing device, or the like can be used, but it is preferable to use a membrane degassing device in terms of downsizing of equipment.
The membrane degassing device allows the water to be treated to flow into one of the chambers partitioned by the gas permeable membrane and decompresses the other chamber,
It is an apparatus for transferring the gas contained in the water to be treated to the other chamber through the gas permeable film and removing it.

The degasser may be installed at any position upstream of the ultraviolet oxidizer in the secondary deionized water system, but nitrogen is redissolved in water between the degasser and the ultraviolet oxidizer. It is necessary not to. In this respect, it is preferable to be immediately before the ultraviolet oxidation device, since nitrogen is unlikely to dissolve in water between the degassing device and the ultraviolet oxidation device. In addition, at the entrance of the secondary pure water system 1
When the treated water introduction tank of the next pure water system is filled with nitrogen, the installation position of the degassing device is the downstream side of the tank.

The UV oxidizer may be of any type such as a circulation type or a dipping type, and it is suitable to use the circulation type oxidizer in terms of processing efficiency. Further, as an ultraviolet oxidation device, a wavelength of 185
A conventional one equipped with a low-pressure mercury lamp that emits ultraviolet rays of nm and 254 nm can be used. In addition,
It is suitable to install a cartridge polisher after the ultraviolet oxidation device to remove the organic acid and carbonic acid generated by the decomposition of TOC.

In the present invention, an oxygen or ozone addition device for adding oxygen gas and / or ozone gas to the water to be treated can be installed between the degassing device and the ultraviolet oxidation device. It is possible to further improve the TOC decomposition efficiency. That is, in a deaerator such as a membrane deaerator or a vacuum deaerator, dissolved oxygen is usually removed together with dissolved nitrogen, but in an ultraviolet oxidation device, it is better that dissolved oxygen exists in the water to be treated. Hydroxyl radicals and hydrogen peroxide are easily generated by UV irradiation with a wavelength of 185 nm, and when dissolved ozone is present, hydroxyl radicals and hydrogen peroxide are also generated by UV irradiation with a wavelength of 254 nm, so they are dissolved in the water to be treated. The presence of oxygen and / or dissolved ozone improves the TOC decomposition efficiency as compared to the case where oxygen and dissolved ozone are not present. Therefore, when the oxygen or ozone addition device is installed and oxygen gas and / or ozone gas is added to the water to be treated between the degassing device and the ultraviolet oxidation device after removing the dissolved nitrogen and dissolved oxygen, particularly ozone gas If added,
It becomes possible to greatly improve the TOC decomposition efficiency,
Even if the TOC concentration in the water to be treated is high, the TOC can be removed almost completely.

The configuration of the oxygen or ozone addition device is not particularly limited, and any device such as a gas permeable membrane device and an aeration device can be used. However, using the gas permeable membrane device makes gas addition efficiency and equipment compactification. Is preferable in terms of. The gas permeable membrane device supplies the gas to be added (oxygen gas or ozone-containing gas) to one of the chambers partitioned by the gas permeable membrane, and supplies the gas to the other chamber to gas the gas. It is a device that dissolves in the water to be treated through a permeable membrane.

When oxygen gas is added to the water to be treated by an oxygen or ozone addition device, the dissolved oxygen concentration is 0.5.
It is preferable to add it so that the concentration of dissolved ozone is 0.1 to 2 ppm.
It is preferable to add it so as to be 1 ppm. As a result, it is possible to prevent dissolved oxygen and dissolved ozone from remaining unnecessarily in the ultrapure water obtained by the secondary pure water system. When adding an ozone-containing gas with an oxygen or ozone adding device, it is appropriate to use an ozone-containing gas that uses oxygen as a raw material as the ozone-containing gas, and use an ozone-containing gas that uses air as a raw material. If the gas contains nitrogen and nitrogen is added to the water to be treated, the object of the present invention may not be achieved.

The ultrapure water production system of the present invention comprises a primary pure water system and a secondary pure water system in which the degassing device and the ultraviolet oxidation device described above are installed. Any can be used as. For example, for a primary pure water system, a two-bed, three-column type ion exchange device, a reverse osmosis membrane device, a degassing device, an ultraviolet sterilizer,
It is possible to install a regenerative mixed bed type ion exchanger,
The treated water introduction tank of the primary pure water system, the cartridge polisher, the ultrafiltration membrane device, the low pressure reverse osmosis membrane device and the like can be installed in the secondary pure water system.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] FIG. 1 is a flowchart showing a first embodiment of the ultrapure water production system according to the present invention. In this apparatus, A is a pretreatment system, B is a primary pure water system, and C is a secondary pure water system. The pretreatment system A is provided with a coagulating sedimentation device, a filtration device, an activated carbon tower, etc., and mainly removes suspended substances in the raw water 2, and then supplies the treated water to the primary pure water system B. In the primary pure water system B, 4 is a two-bed, three-column type ion exchange device equipped with a cation tower, a decarboxylation tower, and an anion tower, 6 is a tank, 8 is a reverse osmosis membrane device, and 10 is a regenerative mixed bed. 1 shows a type ion exchange device. The treated water of the primary pure water system B is supplied to the secondary pure water system C. In the secondary pure water system C, 12 is a treated water introduction tank of the primary pure water system, 14 is a membrane degassing device (degassing device) for removing dissolved nitrogen and dissolved oxygen in the water to be treated, and 16 is a circulation type ultraviolet ray. An oxidizer, 18 is a cartridge polisher, and 20 is an ultrafiltration membrane device. In the secondary pure water system C, continuous circulation operation is performed, and a part of the obtained ultrapure water is used at the use point 2
4 and the rest is circulated to the tank 12.
The waste water of ultrapure water used at the point of use (cleaning waste water after cleaning the wafer and the like) is sent to a recovery system (not shown) for reuse.

In this apparatus, the membrane deaerator 14 removes the dissolved nitrogen and dissolved oxygen in the water to be treated, and the treated water having a reduced dissolved nitrogen concentration and dissolved oxygen concentration is treated with the ultraviolet oxidation device 1.
6. In this device, 2
Since the dissolved oxygen is removed by the membrane deaerator 14 of the secondary pure water system C, the primary pure water system B is not equipped with a deoxidizer, and the tank 12 of the secondary pure water system C is not installed. Nitrogen is not included.

[Second Embodiment] FIG. 2 is a flow chart showing a second embodiment of the ultrapure water production system according to the present invention. This apparatus is the same as the apparatus of the first embodiment except that the degasser 14 and the ultraviolet oxidizer 16 of the secondary pure water system C are used.
And a gas permeable membrane device (oxygen or ozone addition device) for adding oxygen gas and / or ozone gas to the water to be treated 2
6 is installed and the other points are the same as those of the first embodiment, and therefore, the same components as those of the apparatus of FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

In this apparatus, after removing the dissolved nitrogen and dissolved oxygen in the water to be treated by the membrane degassing apparatus 14, by adding oxygen gas and / or ozone gas to the water to be treated by the gas permeable membrane apparatus 26, Dissolved nitrogen concentration is reduced, and treated water containing dissolved oxygen and / or dissolved ozone is supplied to the ultraviolet oxidation device 16.

[Third Embodiment] FIG. 3 is a flow chart showing a third embodiment of the ultrapure water production system according to the present invention. In this apparatus, a vacuum degassing tower 28 is installed between the reverse osmosis membrane apparatus 8 of the primary pure water system B and the regenerative mixed bed type ion exchange apparatus 10 in the apparatus of the first embodiment. Since the tank 12 of the next pure water system C is filled with nitrogen and the other points are the same as those of the first embodiment, the same reference numerals are given to the same components as those of the apparatus of FIG. The description is omitted.

In the present apparatus, the dissolved oxygen in the water to be treated is removed by the vacuum degassing tower 28, and then the dissolved nitrogen in the water to be treated is removed by the membrane deaerator 14 to obtain the dissolved nitrogen concentration and the dissolved oxygen concentration. Oxidizer 1 for reducing treated water
6. In this device, a large amount of nitrogen is dissolved in water in the tank 12 of the secondary pure water system, but the dissolved nitrogen can be removed by the membrane degassing device 14.

[0025]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples. The effects of the present invention were confirmed by performing the following tests using the apparatus shown in FIGS. The apparatus of FIG. 4 is a conventional ultrapure water production apparatus,
The apparatus is the same as that of the third embodiment except that no membrane degassing device is installed between the tank 12 and the ultraviolet oxidation device 16.

In the apparatus shown in FIGS. 1 to 4, the following were used as the membrane degassing apparatus 14, the ultraviolet oxidation apparatus 16 and the gas permeable membrane apparatus 26. Membrane deaerator: Dainippon Ink and Chemicals MJ-520P was used as a gas permeable membrane. Vacuum degree is 25 torr
r. Ultraviolet oxidizer: A distribution type ultraviolet oxidizer manufactured by Chiyoda Kousaku Co., Ltd., which was equipped with a low-pressure mercury lamp that emits ultraviolet rays having wavelengths of 185 nm and 254 nm, was used. The ultraviolet irradiation amount was 0.35 kW · h / m ³ . Gas permeable membrane apparatus: The same MJ-520P as the membrane degassing apparatus was used as the gas permeable membrane.

In the following examples and comparative examples, TO
The C removal rate was calculated by the following formula. The TOC concentration in the inflow water of the ultraviolet oxidation device 16 was 18 to 20 ppb. TOC removal rate (%) = [(AB) / A] × 100 A: TOC concentration in the inflow water of the ultraviolet oxidation device 16 B: TOC concentration in the outflow water of the cartridge polisher 18

[Example 1] Ultrapure water was produced using the apparatus shown in FIG. As a result, the dissolved nitrogen concentration in the inflow water to the ultraviolet oxidation device 16 was 1 ppm or less, and the dissolved oxygen concentration was 5 ppm.
The removal rate was 0 ppb and the TOC removal rate was 90%.

Example 2 Ultrapure water was produced using the apparatus shown in FIG. In this case, oxygen gas was added to the water to be treated from the gas permeable membrane device 26 so that the dissolved oxygen concentration in the water to be treated was 1 ppm. As a result, the ultraviolet oxidation device 1
Dissolved nitrogen concentration in the water flowing into 6 is less than 1 ppm, TOC
The removal rate was 95%. Compared with Example 1, the TOC removal rate was improved because the amount of dissolved oxygen was larger than that in Example 1 in the water to be treated, so that hydroxyl radicals and hydrogen peroxide were easily generated by irradiation with ultraviolet light having a wavelength of 185 nm. This is because it is generated.

Example 3 Ultrapure water was produced using the apparatus shown in FIG. In this case, ozone-containing oxygen gas was added to the water to be treated from the gas permeable membrane device 26 so that the dissolved ozone concentration in the water to be treated was 0.5 ppm. as a result,
Dissolved nitrogen concentration in the inflow water to the ultraviolet oxidation device 16 is 1p
pm or less, the TOC removal rate was 98%. Compared with Example 2, the TOC removal rate was improved not only by the presence of dissolved ozone but by the wavelength of 185 nm as well as by the wavelength of 25.
This is because hydroxyl radicals and hydrogen peroxide are also generated by 4 nm ultraviolet irradiation.

[Comparative Example] Ultrapure water was produced using the apparatus shown in FIG. As a result, the dissolved nitrogen concentration in the inflow water to the ultraviolet oxidation device 16 was 17 ppm or more, and the TOC removal rate was 8
It was 5%, and the TOC removal rate was inferior to that of the device of the present invention.

[0032]

INDUSTRIAL APPLICABILITY The ultrapure water production system of the present invention has an excellent TOC removal effect because almost all of the ultraviolet irradiation energy is effectively utilized for the oxidative decomposition of TOC in the ultraviolet oxidation system of the secondary pure water system. .

[Brief description of drawings]

FIG. 1 is a flowchart showing a first embodiment example of an ultrapure water production system according to the present invention.

FIG. 2 is a flow diagram showing a second embodiment of an ultrapure water production system according to the present invention.

FIG. 3 is a flow chart showing a third embodiment of the ultrapure water production system according to the present invention.

FIG. 4 is a flow chart showing an example of a conventional ultrapure water production system.

[Explanation of symbols]

 A Pretreatment system B Primary pure water system C Secondary pure water system 12 Tank 14 Membrane degasser (degasser) 16 UV oxidizer 26 Gas permeable membrane device (oxygen or ozone addition device)

Claims (5)

[Claims] 1. An ultrapure water production apparatus comprising a primary pure water system and a secondary pure water system, which removes dissolved nitrogen in the water to be treated, which is located on the upstream side of the ultraviolet oxidation device. An ultrapure water production system characterized in that a degasser is installed in a secondary pure water system. 2. A device located at the inlet of the secondary pure water system
The ultrapure water production system according to claim 1, wherein the treated water introduction tank of the next pure water system is filled with nitrogen, and a degassing device is installed on the downstream side of the tank. 3. The degassing device is a membrane degassing device.
Or the ultrapure water production system described in 2. 4. Between the degasser and the ultraviolet oxidizer,
The ultrapure water production system according to claim 1, 2 or 3, wherein an oxygen or ozone addition device for adding oxygen gas and / or ozone gas to the water to be treated is installed. 5. The ultrapure water production system according to claim 4, wherein the oxygen or ozone addition device is a gas permeable membrane device.