JP5320665B2 - Ultrapure water production apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrapure water manufacturing apparatus capable of manufacturing high-purity ultrapure water which can adjust cavitation force when an arbitrary fixed-concentration gas less than a saturation concentration is solved by a simple apparatus and simple operation to use as cleaning water of ultrasonic cleaning, and to provide a method. <P>SOLUTION: When raw water is demineralized and deaerated to manufacture primary pure water in a primary pure water system A, the primary pure water obtained in the primary pure water system A and secondary pure water circulated from a use point are sealed with nitrogen gas and stored in a secondary pure water storage tank 11, the secondary pure water obtained from the secondary pure water storage tank 11 and different in nitrogen concentration is deaerated in a membrane deaeration apparatus 14 to remove nitrogen, and deaerated water is loaded with gas to dissolve gas in a gas dissolving apparatus 16, a gas flow rate supplied to the gas dissolving apparatus 16 is controlled at a predetermined flow rate by a gas flow rate control apparatus 17 to manufacture ultrapure water. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a method and apparatus for producing ultrapure water used for washing water or the like in an electronic component production process, and more particularly to an apparatus for producing ultrapure water having a constant gas concentration suitable for washing water for ultrasonic cleaning of semiconductor devices and It is about the method.

  In semiconductor devices such as IC and LSI, liquid crystal devices, and other electronic component manufacturing processes, semiconductor devices such as semiconductor substrates and glass substrates, and semiconductor devices in which a layer structure of diffusion layers, electrodes, coating layers, etc. are formed on these substrates, To clean products such as liquid crystal devices, high-purity ultrapure water is used as cleaning water. Ultrapure water used as such washing water has been required to have high-purity water quality according to the product grade (high integration). Conventional required water quality items for washing water include resistivity, the number of fine particles, the number of viable bacteria, TOC (Total Organic Carbon), heavy metals, ions, silica, dissolved oxygen concentration, and the like.

  Among these required water qualities, when fine particles, viable bacteria, etc. adhere to the surface of the silicon wafer, problems such as disconnection due to exposure failure mainly occur. In addition, TOC, which is a component that dissolves in water, becomes an obstacle due to film formation, and heavy metals and ions affect the electrical properties of silicon wafers. And since dissolved oxygen forms a natural oxide film on the silicon surface, changes electrical characteristics, and changes the characteristics of semiconductor products, it is important to reduce these concentrations.

  For this reason, high-purity ultrapure water used as cleaning water is generally desalted from industrial water, etc., with ion exchange resin, etc. in primary pure water systems, and if necessary, passes through steps such as deoxygenation treatment and membrane treatment. Water is produced, and the primary pure water obtained by the primary pure water production system is produced as ultrapure water through steps such as UV treatment, ion exchange treatment and membrane treatment in the secondary pure water system. The ultrapure water produced in this way is supplied to the point of use and used as cleaning water, etc., but the secondary pure water system avoids a drop in purity due to impurities brought in from the vessel wall, outside air, etc. Is recycled as secondary pure water.

  By the way, the conventional cleaning method for electronic components has mainly been a method of cleaning with ultrapure water after cleaning with a highly concentrated acid or alkali (for example, hydrofluoric acid, sulfuric acid, ammonia water, etc.). However, as semiconductor devices (elements) have been miniaturized, ultrasonic cleaning using cleaning water that does not contain high-concentration chemicals is effective in the future cleaning of semiconductor device products. Specifically, gas, for example, various gases with different properties (hydrogen, oxygen, nitrogen, ozone, etc.) are dissolved, and if necessary, cleaning water in which a small amount of chemicals such as acid and alkali are dissolved and ultrasonic waves are used in combination. There is a way to wash.

  The ultrasonic cleaning is a method in which ultrasonic waves are irradiated in the cleaning water, cavitation is generated by dissolved gas in the cleaning water, and cleaning is performed by the physical force. Cavitation becomes stronger as the dissolved concentration of gas increases, and the cleaning effect increases. However, semiconductor products having a fine layer structure are often broken by cavitation. Since the relationship between cavitation and destruction of semiconductor products varies depending on the product, it is necessary to adjust the gas dissolution concentration in ultrapure water used as cleaning water to an arbitrary predetermined concentration to control the cavitation force.

  Gas-dissolved ultrapure water used in place of conventional high-concentration chemicals is called “functional cleaning water” and is often used by installing a small device in the vicinity of each cleaning device. Nitrogen-dissolved water is suitable for rinsing water used for finishing cleaning after chemical cleaning, but when manufacturing ultrapure water in which gas is dissolved by installing a small device for each cleaning device, It is difficult to adjust the density.

  In a conventional ultrapure water production system, primary pure water or ultrapure water is produced through deaeration and deoxygenation processes. Carbon dioxide gas in a pure water storage tank for storing such primary pure water or ultrapure water is used. In order to prevent resistivity drop due to dissolution, nitrogen gas is introduced into the pure water storage tank to seal the primary pure water or ultrapure water against the air. Nitrogen gas is dissolved. However, since nitrogen gas is only introduced so as to cover the surface of the pure water storage tank, the concentration of dissolved nitrogen is not controlled, and the entire nitrogen concentration in the pure water storage tank is not uniform. For this reason, the nitrogen concentration of pure water taken out from the pure water storage tank is not constant.

  As a method of dissolving gas in ultrapure water at a predetermined concentration, Patent Document 1 (Japanese Patent Laid-Open No. 2000-197815) discloses ultrapure water saturated with nitrogen when producing oxygen-dissolved water for producing ozone water. The method of dissolving oxygen corresponding to the vacant capacity of the gas is shown by evacuating the gas, creating a vacant space in the gas dissolving capacity, and dissolving and saturating the oxygen in the oxygen dissolving apparatus. . However, Patent Document 1 does not show that the gas is dissolved at a constant concentration less than the saturation concentration.

In the method of Patent Document 1, since gas (nitrogen + oxygen) is finally dissolved at a saturated concentration, when such gas-dissolved water is used as cleaning water for ultrasonic cleaning, cavitation becomes strong and fine. There is a possibility that the semiconductor product having the layer structure portion is destroyed. When primary pure water is used as a raw material, nitrogen gas is only introduced so as to cover the water surface of the water tank, and the nitrogen concentration of primary pure water is not constant. In order to produce ultrapure water in which a gas having an arbitrary constant concentration less than 1 is dissolved, it is necessary to make a nitrogen-dissolved water having a saturated concentration once. Even in this case, the gas cannot be dissolved at a constant concentration less than the saturation concentration.
JP 2000-197815 A

  The object of the present invention is to dissolve a gas having an arbitrary constant concentration less than the saturation concentration with a simple apparatus and operation, and to adjust the cavitation force when used as cleaning water for ultrasonic cleaning. It is to provide an ultrapure water production apparatus and method capable of producing pure water.

The present invention is the following ultrapure water production apparatus and method.
(1) a primary pure water system for producing primary pure water by desalting and degassing raw water;
A secondary pure water storage tank for storing primary pure water obtained from the primary pure water system and secondary pure water circulated from the use point by sealing with nitrogen gas;
A degassing device for degassing secondary pure water having different nitrogen concentrations obtained from the secondary pure water storage tank and removing nitrogen to a nitrogen concentration of 0.5 mg / L or less;
A gas dissolving device that dissolves gas by adding gas to degassed water, and the gas flow rate supplied to the gas dissolving device is controlled to a predetermined flow rate to obtain the dissolved gas concentration calculated by the following equation [1] And a secondary pure water system that supplies the obtained ultrapure water to the point of use.
The degassing device is a membrane degassing device;
The apparatus for producing ultrapure water, wherein the gas dissolving apparatus is an apparatus for dissolving gas through a membrane.
Dissolved gas concentration (mg / L) = [gas flow rate (mL / min) × molecular weight (g / mol)] / [22.4 (L / mol) × water flow rate (L / min)] (1)
(In the equation [1], “gas dissolved concentration” is the gas dissolved concentration in secondary pure water, “gas flow rate” is the gas flow rate supplied to the gas dissolving device, and “molecular weight” is the gas flow rate supplied to the gas dissolving device. (Molecular weight, “flow rate” is the flow rate of degassed treated water supplied to the gas dissolving device.)
(2) The apparatus according to (1), wherein the gas pressure supplied to the gas dissolving apparatus is constant.
(3) The apparatus according to (1) or (2), wherein the gas flow rate control device detects the gas concentration of the dissolved gas and performs feedback control so that the detected gas concentration becomes a constant value. .
(4) The apparatus according to any one of (1) to (3), wherein the gas to be dissolved is nitrogen.
(5) In the primary pure water system, raw water is desalted and degassed to produce primary pure water,
Primary pure water obtained by the primary pure water system and secondary pure water circulating from the use point are stored in a secondary pure water storage tank sealed with nitrogen gas,
A degassing step of degassing secondary pure water with different nitrogen concentrations obtained from the secondary pure water storage tank to remove nitrogen to a nitrogen concentration of 0.5 mg / L or less;
The gas dissolution process for adding gas to the degassed water to dissolve the gas, and the gas flow rate to be supplied to the gas dissolution apparatus are controlled to a predetermined flow rate for the dissolved gas concentration calculated by the following equation [1] In a secondary pure water system including a gas flow rate control step, an ultrapure water production method for producing ultrapure water in which a gas having an arbitrary constant concentration less than a saturated concentration is dissolved and supplying it to a use point,
The degassing step is degassed by a membrane degassing device,
The method for producing ultrapure water characterized in that the gas dissolving step dissolves gas through a membrane.
Dissolved gas concentration (mg / L) = [gas flow rate (mL / min) × molecular weight (g / mol)] / [22.4 (L / mol) × water flow rate (L / min)] (1)
(In the equation [1], “gas dissolved concentration” is the gas dissolved concentration in secondary pure water, “gas flow rate” is the gas flow rate supplied to the gas dissolving device, and “molecular weight” is the gas flow rate supplied to the gas dissolving device. (Molecular weight, “flow rate” is the flow rate of degassed treated water supplied to the gas dissolving device.)
(6) The method according to (5) above, wherein the gas pressure supplied to the gas dissolving step is constant.
(7) The method according to (5) or (6), wherein the gas flow rate control step detects the gas concentration of the dissolved gas and performs feedback control so that the detected gas concentration becomes a constant value. .
(8) The method according to any one of (5) to (7), wherein the gas to be dissolved is nitrogen.

  The ultrapure water produced in the present invention is ultrapure water in which a gas having an arbitrary constant concentration less than the saturation concentration is dissolved. Ultrapure water used for cleaning water or the like in an electronic component manufacturing process, particularly, ultrapure water of a semiconductor device. Although it is suitable for the ultrapure water used for the sonic cleaning water, it may be used for other purposes.

  In the apparatus and method for producing ultrapure water in the present invention, as in the case of production of general ultrapure water, in the primary pure water system, raw water is desalted and degassed to produce primary pure water. Primary pure water obtained from the water system and secondary pure water circulating from the point of use are stored in a secondary pure water storage tank sealed with nitrogen gas, and the nitrogen concentration obtained from the secondary pure water storage tank is different. Ultrapure water is produced by processing secondary pure water in the secondary pure water system and supplied to the use point.

  As the primary pure water system, general apparatuses and methods can be adopted. Such a primary pure water production system is configured to install a demineralizer and a deaerator, demineralize with the demineralizer, and deaerate with the deaerator. As the desalting apparatus, a desalting apparatus such as an ion exchange apparatus including a cation exchange resin and an anion exchange resin or a reverse osmosis apparatus including a reverse osmosis (RO) membrane can be used. As an ion exchange device, in addition to a device that is filled with a cation exchange resin and an anion exchange resin and regenerates with a regenerant such as acid or alkali, a device that regenerates by energization can be adopted. But you can. As the degassing device, a vacuum degassing device, a membrane degassing device, or the like can be adopted. In addition, when a high-purity water quality is required, a system that removes impurities through steps such as deoxygenation treatment and membrane treatment is preferable. A pretreatment device such as an activated carbon tower can be provided before the desalination device, deaeration device, or the like.

  In order to produce primary pure water in such a primary pure water system, raw water is pretreated in a pretreatment device such as an activated carbon tower if necessary, then desalted with a desalinator, deaerated with a deaerator, If necessary, high-purity primary pure water is produced by removing impurities through steps such as deoxygenation treatment and membrane treatment. The primary pure water produced in this way is supplied to the secondary pure water system. In the secondary pure water system, a large amount of secondary pure water circulates from the point of use.

  The secondary pure water storage tank for storing the primary pure water obtained in the primary pure water system and the secondary pure water circulating from the use point is in a state of mixing the primary pure water and the secondary pure water circulating from the use point, It is configured to be sealed and stored with nitrogen gas. The primary pure water obtained by desalting and degassing the raw water and the secondary pure water circulating from the point of use are in a degassed state. Nitrogen gas can be introduced and sealed, but nitrogen gas may be blown into the stored pure water. When nitrogen gas is introduced and sealed so as to cover the surface of the secondary pure water storage tank, the nitrogen gas dissolves in pure water near the water surface, but does not dissolve in the internal pure water, and stores secondary pure water. The total nitrogen concentration in the tank is not uniform. In this case, the concentration of nitrogen is not controlled, and the nitrogen concentration of pure water taken out from the secondary pure water storage tank changes with a change in the water level in the secondary pure water storage tank, and does not become a constant concentration.

  In the secondary pure water system, the primary pure water produced by the primary pure water system is mixed with the secondary pure water circulated from the use point and stored in the secondary pure water storage tank. High purity by removing organic substances from secondary pure water by UV treatment equipment (low pressure UV oxidation equipment) and removing other impurities by desalting equipment, UF membrane separator etc. if necessary Configured to be This configuration is the same as that of the conventional secondary pure water system, and the same apparatus as the conventional one is adopted and the same operation as the conventional one is performed.

  In the present invention, the secondary pure water system is further provided with a deaeration device so that the secondary pure water is deaerated to remove nitrogen. Further, by providing a gas dissolving device, the gas is added to the degassed treated water to dissolve the gas. Furthermore, by providing a gas flow rate control device, the gas flow rate supplied to the gas dissolving device is controlled to a predetermined flow rate.

  In the secondary pure water storage tank, nitrogen gas for sealing is introduced so as to cover the water surface of the water storage tank, so when the secondary pure water is extracted from the secondary pure water storage tank, the secondary pure water is Nitrogen concentration in water changes. If secondary pure water with a varying nitrogen concentration obtained from the secondary pure water storage tank is used for ultrasonic cleaning as it is, the cavitation force also changes, the ultrasonic cleaning effect changes, and the cavitation force becomes excessive, Damage to electronic equipment such as semiconductor products also occurs.

  In the present invention, in order to make the cavitation force constant, deaeration by a deaeration device and gas dissolution by a gas dissolution device are performed in the secondary pure water system, and at this time, the gas flow rate control device sets the gas flow rate to a predetermined flow rate. By controlling, a gas having an arbitrary constant concentration less than the saturation concentration is dissolved, and high-purity ultrapure water capable of adjusting the cavitation force when used as cleaning water for ultrasonic cleaning is manufactured.

  In Patent Document 1, ultrapure water saturated with nitrogen is degassed to create a space in the gas dissolution capacity, and oxygen is dissolved and saturated in the oxygen dissolution apparatus to reduce the gas dissolution capacity. Since the corresponding oxygen is dissolved and the gas finally reaches a saturated concentration, the cavitation force becomes excessive.In the present invention, the primary pure water is deaerated without being saturated with nitrogen, and a gas having a concentration less than the saturated concentration is obtained. Since it melt | dissolves, it becomes possible to melt | dissolve the gas of arbitrary fixed concentrations less than saturation concentration, and to adjust a cavitation force to an appropriate value.

The degassing device used in the secondary pure water system of the present invention degass the primary pure water whose nitrogen concentration varies to make the nitrogen concentration 0.5 mg / L or less . Although the nitrogen concentration of the secondary pure water taken out from the secondary pure water storage tank is not constant and changes, nitrogen is removed from the pure water whose nitrogen concentration changes in this way, and the nitrogen concentration after deaeration is reduced to 0. 0. When the concentration is 5 mg / L or less , the concentration of the dissolved gas can be made constant only by controlling the flow rate of the gas supplied to the gas dissolving device thereafter to a predetermined flow rate. If you are a nitrogen concentration after degassing to less than 0.5mg / L, the degassing operation is simplified. A membrane deaerator is used as such a deaerator.

The gas dissolving apparatus used in the secondary pure water system of the present invention is to add ultra-pure water in which a gas having an arbitrary constant concentration less than the saturated concentration is dissolved by adding the gas to the degassed treated water and dissolving the gas. belongs to. As such a gas dissolving apparatus, an apparatus for dissolving a gas through a membrane is used . The gas to be dissolved is preferably nitrogen, but other gases may be dissolved depending on the purpose.

  A membrane degassing device or a device that dissolves gas through a membrane is equipped with a gas permeable membrane, that is, a gas permeable thin film that does not allow liquid to permeate, and gas flows on one side of the gas permeable membrane and liquid flows on the opposite side. Those which are permeated to the side and dissolved are preferred. The configuration of the apparatus can be the same as that of an apparatus generally used as a membrane separation apparatus such as a UF apparatus.

  As the gas permeable membrane, polypropylene membrane, polydimethylsiloxane membrane, polycarbonate-polydimethylsiloxane block copolymer membrane, polyvinylphenol-polydimethylsiloxane-polysulfone block copolymer membrane, poly (4-methylpentene-1) membrane, There are poly (2,6-dimethylphenylene oxide) membranes, polytetrafluoroethylene membranes, etc., all of which can be used for membrane deaerators and devices for dissolving gas through the membranes. Good.

  As a membrane degassing device or a device for dissolving gas through the membrane, a device in which such a gas permeable membrane is formed in a module can be used. The module can be the same as that of a module of a device generally used as a membrane separation device such as a UF device, such as a tubular membrane module, a planar membrane module, a spiral membrane module, and a hollow fiber membrane module. A thread membrane module is preferred.

The deaerator is configured to remove nitrogen and other gases dissolved in pure water by supplying pure water to be degassed to one side of the gas permeable membrane and suctioning from the opposite side. . The pressure of the pure water side to be degassed is 300～500KPa, pressure of the suction side -80 to-100 kPa, the nitrogen concentration of the pure water that has been deaerated is less 0.5 mg / L. When a hollow fiber membrane module is used, it is preferable that pure water to be deaerated is supplied to the outside of the hollow fiber membrane and sucked from the inside.

  The gas dissolving device supplies degassed pure water to one side of the gas permeable membrane, and supplies a gas such as nitrogen gas to the opposite side, thereby allowing the gas to flow into pure water to an arbitrary constant concentration less than the saturated concentration. Configured to dissolve. The deaerated pure water can be supplied at a normal supply pressure, and the dissolved gas can be supplied from a cylinder in a pressurized state and dissolved. When using a hollow fiber membrane module, it is preferable to supply degassed pure water to the outside of the hollow fiber membrane and supply gas to the inside.

The gas flow rate control device is configured to control the flow rate of the gas such as nitrogen gas supplied to the gas dissolving device to a predetermined flow rate for obtaining the dissolved gas concentration calculated by the above equation [1]. Since the degassed water by the deaerator has a constant nitrogen concentration, when a gas such as nitrogen gas is supplied at a constant pressure, the amount of dissolved gas becomes constant, and any constant concentration less than the saturation concentration. It can be dissolved in the gas concentration and the cavitation force can be adjusted to an appropriate value. In particular, by setting the nitrogen concentration of the deaerated pure water to 0.5 mg / L or less, the gas is easily dissolved to a constant gas concentration without any special operation. In this case, it is preferable to control the gas pressure to be constant. As such a gas flow rate control device, the gas concentration of the dissolved water may be detected and feedback control may be further performed so that the detected gas concentration becomes a constant value. It is set as the structure which can supply the fixed fixed amount of gas. In this case, gas Dissolved concentrations of secondary pure water can be calculated by the following [1] wherein the desired type of gas by (1) formula, once the passing water, by adjusting the gas flow rate, the two It can be set arbitrarily dissolved gas concentration of the following pure water.
Dissolved gas concentration (mg / L) = [gas flow rate (mL / min) × molecular weight (g / mol)] / [22.4 (L / mol) × water flow rate (L / min)] (1)
(In the equation [1], “gas dissolved concentration” is the gas dissolved concentration in secondary pure water, “gas flow rate” is the gas flow rate supplied to the gas dissolving device, and “molecular weight” is the gas flow rate supplied to the gas dissolving device. (Molecular weight, “flow rate” is the flow rate of degassed treated water supplied to the gas dissolving device.)

  In the ultrapure water production method of the present invention using the above ultrapure water production apparatus, first, primary water is produced by desalting and degassing raw water in a primary pure water system. At this time, the raw water is pretreated in a pretreatment device such as an activated carbon tower if necessary, then desalted with a desalting device, deaerated with a degassing device, and further subjected to impurities such as deoxygenation treatment and membrane treatment if necessary. Is removed to produce high purity primary pure water.

  The primary pure water obtained in the primary pure water system and the secondary pure water circulated from the use point are introduced into the secondary pure water storage tank, sealed with nitrogen gas and stored. Since the primary pure water obtained by desalting and degassing the raw water and the secondary pure water circulating from the use point are in a deaerated state, by introducing nitrogen gas into the gas phase part of the storage tank and sealing it, Prevent air intrusion and dissolution. When nitrogen gas is introduced and sealed so as to cover the surface of the secondary pure water storage tank, the nitrogen gas dissolves in the secondary pure water near the water surface, but does not dissolve in the internal pure water, and does not dissolve in the secondary pure water. The total nitrogen concentration in the water storage tank is not uniform. In this case, the nitrogen concentration of the secondary pure water taken out from the secondary pure water storage tank changes with the change of the water level in the secondary pure water storage tank, and does not become a constant concentration.

  For this reason, in the deaeration process, secondary pure water obtained from the secondary pure water storage tank is degassed by a deaeration device such as a membrane deaeration device to remove nitrogen, and a constant concentration less than the saturation concentration is obtained. Use gas concentration. In the gas dissolving step, the gas is dissolved in the gas dissolving device by adding the gas to the degassed water. At this time, in the gas flow rate control step, the gas flow rate control device controls the gas flow rate supplied to the gas dissolving device to a predetermined flow rate. Thereby, in the secondary pure water system, ultrapure water in which a gas having an arbitrary constant concentration less than the saturation concentration is dissolved is produced.

  The ultrapure water produced in this way is sent to a use point and used for cleaning water or the like in the electronic component production process. Since the above-mentioned ultrapure water dissolves a gas having an arbitrary constant concentration less than the saturation concentration, even when used as cleaning water for ultrasonic cleaning of semiconductor devices, the cavitation force is adjusted to an appropriate value and is fine. A semiconductor product having a layer structure is not destroyed. Most of the ultrapure water sent to the point of use is circulated directly to the secondary pure water storage tank. Wastewater used as wash water at the point of use can be returned to the treatment process of the primary deionized water system according to the degree of contamination, but can be treated with a secondary deionized deionized water storage tank. It can also be returned to.

According to the present invention, primary pure water is produced by desalting and degassing raw water in the primary pure water system, and secondary pure water circulated from the primary pure water obtained from the primary pure water system and the point of use is secondary. The pure water storage tank is sealed with nitrogen gas and stored. In the secondary pure water system, the secondary pure water obtained from the secondary pure water storage tank is degassed to remove nitrogen from the nitrogen concentration of 0.5 mg / When the gas is added to the degassed treated water and dissolved in the degassed treated water, the gas flow rate supplied to the gas dissolving device is a predetermined concentration for calculating the dissolved gas concentration calculated by the above equation [1] . Since the flow rate is controlled, it is possible to adjust the cavitation force when using it as a cleaning water for ultrasonic cleaning by dissolving a gas with an arbitrary constant concentration less than the saturated concentration by simple equipment and operation. To produce pure ultrapure water Can.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a flowchart showing an ultrapure water production apparatus and method according to an embodiment of the present invention. In FIG. 1, A is a primary pure water production system, which is an activated carbon tank 1, an intermediate water tank 2, an RO membrane device 3, a vacuum degassing device 4, a first ion exchange device 5, a second ion exchange device 6, and a primary pure water tank. 7. The activated carbon tank 1 is provided as a pretreatment device. The RO membrane device 3, the first ion exchange device 5, and the second ion exchange device 6 are provided as a desalting device, and are configured to remove nonionic substances such as organic substances. The first ion exchange device 5 is an electric regeneration type continuous ion exchange device, and is configured to remove a large amount of ionic substances. The second ion exchange device 6 is a non-regenerative large-sized ion exchange device and is configured to remove residual ionic substances. The vacuum deaerator 4 is configured to remove oxygen gas as well as general gas such as carbon dioxide gas. The primary pure water tank 7 is configured to store primary pure water sealed with nitrogen gas.

B is a secondary pure water system (subsystem), which is a secondary pure water tank 11, a pump P, a heat exchanger 12, a UV oxidizer 13, a membrane deaerator 14, a suction device 15, a gas dissolving device 16, and a gas flow rate control. The apparatus 17, the ion exchange apparatus 18, and the UF membrane apparatus 19 are configured. The secondary pure water tank 11 is configured to store the primary pure water and the secondary pure water circulating from the use point by sealing with nitrogen gas. The heat exchanger 12 is configured to cool the secondary pure water. The UV oxidizer 13 is configured to irradiate low pressure UV (ultraviolet rays) to oxidize and sterilize organic substances contained in a trace amount. The membrane degassing device 14 includes a gas permeable membrane, and by sucking from the suction device 15, secondary pure water having different nitrogen concentrations obtained from the secondary pure water tank 11 is degassed through the gas permeable membrane to remove nitrogen. Is configured to do. The gas dissolving device 16 includes a gas permeable membrane, and is configured to add nitrogen gas to the degassed treated water through the gas permeable membrane and dissolve it. The gas flow rate control device 17 is configured to control the flow rate of the nitrogen gas supplied to the gas dissolving device 16 to a predetermined flow rate set in advance. At this time, the dissolved nitrogen concentration meter N dissolves the dissolved nitrogen gas in the dissolved water. The nitrogen concentration is measured, and the signal is input to the gas flow rate control device 17 to control the nitrogen concentration. The ion exchanger 18 is a non-regenerative ion exchanger and is configured to remove residual ionic substances. The UF membrane device 19 is configured to remove residual nonionic substances by UF membrane separation.

  Reference numeral 10 denotes a use point, that is, a place where ultrapure water is used, where ultrapure water is used as cleaning water in the manufacturing process of electronic components, and where it is used as cleaning water for ultrasonic cleaning of semiconductor devices. included. Secondary pure water that has not been used at the use point 10 is configured to circulate in the secondary pure water tank 11. On the other hand, the cleaning waste water is returned to the activated carbon tank 1, the RO membrane device 3, the primary pure water tank 7, etc. of the primary pure water production system A and regenerated depending on the concentration of the pollutant.

  In the ultrapure water production apparatus of FIG. 1, ultrapure water is produced as follows. First, primary pure water is produced by the primary pure water system A. Here, raw water such as industrial water is supplied from the line L1, activated carbon treatment is performed in the activated carbon tank 1, and it is sent from the line L2 to the intermediate water tank 2 for storage. . The stored water in the intermediate water tank 2 is sent from the line L3 to the RO membrane device 3 for RO membrane separation, sent from the line L4 to the vacuum degasser 4 for deaeration and deoxygenation, and the first ion exchange device from the line L5. 5 and further sent from the line L6 to the second ion exchange device 6 for desalting by cation exchange and anion exchange. Then, it sends to the primary pure water tank 7 from the line L7 and stores it. The primary pure water tank 7 is sealed by introducing nitrogen gas from the line L8. The primary pure water of the primary pure water tank 7 is sent from the line L9 to a general pure water supply destination such as a boiler, and a part of the primary pure water is sent from the line L11 to the secondary pure water tank 11 of the secondary pure water system B. It is done.

  The method for producing ultrapure water in the secondary pure water system B introduces primary pure water from the line L11 to the secondary pure water tank 11 and circulates unused ultrapure water from the line L12 at the use point 10 to obtain secondary pure water. Is circulated in the secondary pure water tank 11, and nitrogen gas is introduced into the secondary pure water tank 11 from the line L13 to perform sealing. The secondary pure water in the secondary pure water tank 11 is sent to the heat exchanger 12 by the pump P, and the heat absorbed at the use point 10 is recovered. And it sends to the UV oxidation apparatus 13 from the line L16, and low-pressure UV (ultraviolet rays) is irradiated, the organic substance contained in a trace amount is oxidized, decomposed | disassembled and disinfected.

The UV-oxidized water is sent from the line L17 to the membrane deaerator 14 and sucked by the suction device 15 from the line L18, thereby degassing the secondary pure water obtained from the secondary pure water tank 11 having different nitrogen concentrations. At this time, nitrogen in the secondary pure water is removed through the gas permeable membrane and discharged out of the system from the line L19. As a result, the secondary pure water is deaerated to a nitrogen concentration of 0.5 mg / L or less . The degassed water is sent from the line L20 to the gas dissolving device 16, and the nitrogen gas sent from the line L21 is set by the gas flow rate control device 17 so as to obtain a gas dissolved concentration calculated by the equation [1]. The flow rate is controlled to the above flow rate and sent from the line L22 to the gas dissolving device 16, and nitrogen gas is added to the degassed treated water to dissolve the gas to an arbitrary constant concentration less than the saturated concentration. At this time, the dissolved nitrogen concentration meter N measures the dissolved nitrogen concentration in the nitrogen gas dissolved water, and inputs the signal to the gas flow rate control device 17 to control the nitrogen concentration to be corrected . The gas-dissolved water is sent from the line L23 to the ion exchange device 18 to remove residual ionic substances by non-regenerative ion exchange. The ion-exchanged water is sent from the line L24 to the UF membrane device 19, and ultrapure water is produced by removing the remaining fine particles by UF membrane separation.

  The ultrapure water is sent from the line L25 to the use point 10 and used for cleaning water in the electronic component manufacturing process. Ultrapure water dissolves a gas with a certain concentration less than the saturation concentration and adjusts the cavitation force when used as cleaning water for ultrasonic cleaning, so it is used as cleaning water for ultrasonic cleaning of semiconductor devices. Even in this case, the cavitation force is adjusted to an appropriate value, and the semiconductor product having a fine layer structure is not destroyed. Unused ultrapure water at the use point 10 is circulated from the line L12 to the secondary pure water tank 11 as circulating secondary pure water, and reused as raw water for producing ultrapure water in the secondary pure water system B.

  Examples of the present invention and comparative examples will be described below.

[Comparative Example 1]
In the ultrapure water production apparatus of FIG. 1, nitrogen gas is introduced and sealed at 5 kPa into the gas phase of the primary pure water tank 7 and the secondary pure water tank 11, respectively, and the membrane deaerator 14 and gas of the secondary pure water system B are sealed. By bypassing the dissolving device 16 and flowing primary pure water, secondary pure water treatment was performed to produce ultrapure water. At this time, the water flow rate is 1 m 3 / Hr. FIG. 2 shows the change with time of the dissolved nitrogen concentration of ultrapure water produced as described above.

[Example 1]:
In Comparative Example 1, secondary pure water was flowed through the membrane degassing device 14 and the gas dissolving device 16 of the secondary pure water system B to perform secondary pure water treatment to produce ultrapure water. The membrane deaerator 14 is equipped with a 4 inch diameter deaeration membrane module with a hollow fiber membrane made of polypropylene (inner diameter 200 μm, outer diameter 300 μm) and sucked from the inside of the hollow fiber membrane to −97 kPa by the suction device 15. Thus, the secondary pure water having different nitrogen concentrations obtained from the secondary pure water tank 11 was degassed to a nitrogen concentration of 0.5 mg / L or less. The gas dissolving device 16 is equipped with a deaeration membrane module having a diameter of 4 inches equipped with a hollow fiber membrane made of polypropylene (inner diameter: 200 μm, outer diameter: 300 μm), and a dissolved nitrogen concentration meter N (M-3610 / 511, manufactured by Hack). The dissolved nitrogen concentration is measured, and the gas flow rate is controlled by a gas flow rate control device 17 (mass flow controller, manufactured by Lintec Co., Ltd.) while the nitrogen gas is pressurized from a cylinder to a nitrogen gas flow rate of 220 mL / min. Supplied and dissolved through the hollow fiber membrane. At this time, the water flow rate is 1 m 3 / Hr. FIG. 2 shows the change with time of the dissolved nitrogen concentration of ultrapure water produced as described above.

[Example 2]:
In Example 1, it melt | dissolved by changing the nitrogen gas flow rate of the gas flow control apparatus 17 to 170 mL / min. FIG. 2 shows the change with time of the dissolved nitrogen concentration of ultrapure water produced as described above.

  From the above results, the nitrogen concentration in the ultrapure water of Comparative Example 1 treated with the conventional system varied from 8 to 14 mg / L, whereas the ultrapure water of Examples 1 and 2 treated with the improved system fluctuated. Ultrapure water with an arbitrary constant value with a width of 0.5 mg / L or less and a nitrogen concentration below the saturation concentration was obtained. Thus, it can be seen that by adding the degassing and gas dissolving functions, nitrogen-dissolved water having a desired concentration can be obtained even when the nitrogen concentration varies.

  It is used in a method and apparatus for producing ultrapure water used for cleaning water in electronic component manufacturing processes, in particular, a method and apparatus for producing ultrapure water having a certain gas concentration suitable for cleaning water for ultrasonic cleaning of semiconductor devices. The

The flowchart which shows the pure water manufacturing method and apparatus of embodiment. It is a graph which shows the dissolved nitrogen concentration in implementation.

Explanation of symbols

A Primary pure water system B Secondary pure water system 1 Activated carbon tank 2 Intermediate water tank 3 RO membrane device 4 Vacuum degassing device 5 First ion exchange device 6 Second ion exchange device 7 Pure water tank 10 Use point 11 Primary pure water tank 12 Heat Exchanger 13 UV oxidation device 14 Membrane deaeration device 15 Suction device 16 Gas dissolution device 17 Gas flow rate control device 18 Ion exchange device 19 UF membrane device P Pump N Dissolved nitrogen concentration meter

Claims (8)

A primary pure water system for producing primary pure water by desalting and degassing raw water;
A secondary pure water storage tank for storing primary pure water obtained from the primary pure water system and secondary pure water circulated from the use point by sealing with nitrogen gas;
A degassing device for degassing secondary pure water having different nitrogen concentrations obtained from the secondary pure water storage tank and removing nitrogen to a nitrogen concentration of 0.5 mg / L or less;
A gas dissolving device that dissolves gas by adding gas to degassed water, and the gas flow rate supplied to the gas dissolving device is controlled to a predetermined flow rate to obtain the dissolved gas concentration calculated by the following equation [1] And a secondary pure water system that supplies the obtained ultrapure water to the point of use.
The degassing device is a membrane degassing device;
The apparatus for producing ultrapure water, wherein the gas dissolving apparatus is an apparatus for dissolving gas through a membrane.
Dissolved gas concentration (mg / L) = [gas flow rate (mL / min) × molecular weight (g / mol)] / [22.4 (L / mol) × water flow rate (L / min)] (1)
(In the equation [1], “gas dissolved concentration” is the gas dissolved concentration in secondary pure water, “gas flow rate” is the gas flow rate supplied to the gas dissolving device, and “molecular weight” is the gas flow rate supplied to the gas dissolving device. (Molecular weight, “flow rate” is the flow rate of degassed treated water supplied to the gas dissolving device.)   The apparatus according to claim 1, wherein the gas pressure supplied to the gas dissolving apparatus is constant.   The apparatus according to claim 1 or 2, wherein the gas flow rate control device detects the gas concentration of the dissolved gas and performs feedback control so that the detected gas concentration becomes a constant value.   4. An apparatus according to claim 1, wherein the gas to be dissolved is nitrogen. In the primary pure water system, raw water is desalted and degassed to produce primary pure water,
Primary pure water obtained by the primary pure water system and secondary pure water circulating from the use point are stored in a secondary pure water storage tank sealed with nitrogen gas,
A degassing step of degassing secondary pure water with different nitrogen concentrations obtained from the secondary pure water storage tank to remove nitrogen to a nitrogen concentration of 0.5 mg / L or less;
The gas dissolution process for adding gas to the degassed water to dissolve the gas, and the gas flow rate to be supplied to the gas dissolution apparatus are controlled to a predetermined flow rate for the dissolved gas concentration calculated by the following equation [1] In a secondary pure water system including a gas flow rate control step, an ultrapure water production method for producing ultrapure water in which a gas having an arbitrary constant concentration less than a saturated concentration is dissolved and supplying it to a use point,
The degassing step is degassed by a membrane degassing device,
The method for producing ultrapure water characterized in that the gas dissolving step dissolves gas through a membrane.
Dissolved gas concentration (mg / L) = [gas flow rate (mL / min) × molecular weight (g / mol)] / [22.4 (L / mol) × water flow rate (L / min)] (1)
(In the equation [1], “gas dissolved concentration” is the gas dissolved concentration in secondary pure water, “gas flow rate” is the gas flow rate supplied to the gas dissolving device, and “molecular weight” is the gas flow rate supplied to the gas dissolving device. (Molecular weight, “water flow rate” is the flow rate of degassed treated water supplied to the gas dissolving device.)   6. The method according to claim 5, wherein the gas pressure supplied to the gas dissolving step is constant.   The method according to claim 5 or 6, wherein the gas flow rate control step detects the gas concentration of the dissolved gas and performs feedback control so that the detected gas concentration becomes a constant value.   The method according to any one of claims 5 to 7, wherein the gas to be dissolved is nitrogen.

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