Method for producing ultrapure water

Abstract

To produce ultrapure water from which boron has been fully removed, for example, in a clean room.SOLUTION: An ultrapure water production system includes: a primary pure water tank 20 which is in communication with outside air and reserves primary pure water; and a subsystem 30 which is connected with the primary pure water tank 20 and produces ultrapure water. An unused part of the ultrapure water produced in the subsystem 30 circulates into the primary pure water tank 20. The subsystem 30 includes: a boron removal device 33 filled with a boron selective resin; and a non-regenerative ion exchange device 35 which is provided downward of the boron removal device.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention ,nine relates to a method for producing ultrapure water at within a lean room In the law .

Background Art

[0002] As a system that can easily produce ultrapure water in laboratories of research institutions, for example, there are pure water production devices described in Patent Document 1 and Patent Document 2. The pure water production device described in Patent Document 1 includes a primary pure water system that generates primary pure water from supply water, a primary pure water tank that stores the primary pure water, a subsystem (secondary pure water system) that generates ultrapure water when the primary pure water is supplied from the primary pure water tank, and a water sampling dispenser that is used for sampling ultrapure water when the ultrapure water is supplied from the subsystem. The subsystem includes an ultraviolet oxidation device to which the primary pure water is supplied from the primary pure water tank, and a non-regenerative ion exchange device provided downstream of the ultraviolet oxidation device. In the subsystem, the ultrapure water that is not supplied to the water sampling dispenser circulates back to the primary pure water tank, and thus circulation purification is performed. The pure water production device disclosed in Patent Document 1 is configured such that the primary pure water system and the subsystem are housed in the same housing and the primary pure water tank can be arranged adjacent to this housing, and as a desktop-type device, it can be placed on an experimental bench or the like. In the pure water production device disclosed in Patent Document 2, the pipe through which the pure water circulates in the subsystem is extended to the water sampling dispenser, and the water sampling dispenser is also incorporated into the pure water circulation system in the subsystem.

[0003] When using ultrapure water in fields related to semiconductor device manufacturing, it is required to reduce the boron concentration in the ultrapure water as much as possible. Patent Document 3 discloses that, in order to obtain ultrapure water with a high degree of boron removal over a long period of time, an ion exchange device is provided in the primary pure water system of an ultrapure water production system, which is filled with a mixture of a boron-adsorbing resin and a strongly basic anion exchange resin. Similarly, Patent Document 4 discloses that, in order to obtain ultrapure water with reduced boron concentration while suppressing the effect of the elution of TOC (Total Organic Carbon) components from the boron-selective ion exchange resin on the subsystem of the ultrapure water production system, an ion exchange device is provided in the primary pure water system of an ultrapure water production system, in which a boron-selective ion exchange resin is placed on the supply side of the water to be treated and an ion exchange resin other than the boron-selective ion exchange resin is filled on the discharge side.

[0004] Generally, the manufacturing and research of semiconductor devices are conducted in cleanrooms. In cleanrooms, a clean environment is maintained by constantly filtering the air using HEPA filters (High Efficiency Particulate Air High Filters) or ULPA filters (Ultra Low Penetration Air Filters) to remove airborne particles (e.g., dust and dirt). A HEPA filter is an air filter that, at its rated airflow, has a particle collection efficiency of 99.97% or higher for particles with a diameter of 0.3 μm, while a ULPA filter is an air filter that, at its rated airflow, has a particle collection efficiency of 99.9995% or higher for particles with a diameter of 0.15 μm. Glass filters are often used as the filter medium in HEPA and ULPA filters. Non-Patent Literature 1 states that the boron concentration in the air inside a cleanroom is higher than that in the outdoor atmosphere, and that this boron is presumed to originate from the ULPA filter. As an example, Non-Patent Literature 1 states that the boron concentration in the outdoor atmosphere is 17 ng / m³. 3 When the boron concentration in the air inside the cleanroom was 130 ng / m³, 3 It states that this was the case. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2018-202293 [Patent Document 2] Japanese Patent Publication No. 2020-6295 [Patent Document 3] Japanese Patent Publication No. 2016-47496 [Patent Document 4] Japanese Patent Publication No. 2018-86619 [Non-patent literature]

[0006] [Non-Patent Document 1] Technical News: Analysis of Trace Substances in Cleanroom Air TN045 [online], Sumika Analysis Center Co., Ltd., [Accessed January 20, 2022], Internet<URL: https: / / www.scas.co.jp / technical-informations / technical-news / pdf / tn045.pdf> [Overview of the project] [Problems that the invention aims to solve]

[0007] When ultrapure water is produced by placing an apparatus such as the one shown in Patent Document 1 or Patent Document 2 inside a cleanroom, the boron concentration in the resulting ultrapure water may not decrease sufficiently.

[0008] The objective of the present invention is, Inside the cleanroom Ultrapure water that can produce ultrapure water from which boron has been sufficiently removed. of Manufacturing method Law The purpose is to provide. [Means for solving the problem]

[0009] The inventors investigated the phenomenon of increased boron concentration in ultrapure water produced in a cleanroom and obtained the following findings. Specifically, the liquid level in the primary pure water tank installed in the subsystem of an ultrapure water production system fluctuates depending on the amount of ultrapure water actually used at the point of use and the amount of primary pure water supplied to the tank. In a large ultrapure water production system, nitrogen gas (N2) purging is performed, so the space above the liquid level in the primary pure water tank is filled with nitrogen gas. However, in a small ultrapure water production system such as a tabletop type, the primary pure water tank is in contact with the outside air via an air vent filter, and as the liquid level in the primary pure water tank fluctuates, air from outside the tank enters the primary pure water tank via the air vent filter. If a small ultrapure water production system is installed in a cleanroom, boron components contained in the air inside the cleanroom enter the primary pure water tank and dissolve in the pure water in the primary pure water tank, causing an increase in the boron concentration in the ultrapure water obtained in the subsystem. Since the ultrapure water circulates within the subsystem, the boron concentration increases further over time. Since boron is introduced into the subsystem in the primary pure water tank, the boron concentration in the ultrapure water does not decrease even if boron removal treatment is performed in the primary pure water system.

[0010] Based on the above findings, the inventors have completed the present invention. That is, the ultrapure water of the present invention. of manufacturing method teeth, A method for producing ultrapure water by installing an ultrapure water production system in a cleanroom, wherein the ultrapure water production system is connected via an air vent filter. The system comprises a primary pure water tank that communicates with the outside air and stores primary pure water, and a subsystem connected to the primary pure water tank that produces ultrapure water. The ultrapure water produced in the subsystem that is not used is circulated back to the primary pure water tank. death, subsystem teeth The system includes a boron removal device filled with boron-selective resin, and a non-regenerative ion exchange device located downstream of the boron removal device. The air vent filter is a filter that allows boron components in the outside air to pass through, and is composed of nonwoven fabric and / or activated carbon. . [Effects of the Invention]

[0012] According to the present invention, a cleanroom insideUltra-pure water with sufficient boron removal can be produced.

Brief Description of the Drawings

[0013] [Figure 1] It is a flowchart showing a system for producing ultra-pure water according to an embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0014] Next, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 shows a system for producing ultra-pure water according to an embodiment of the present invention. This ultra-pure water production system is, for example, a desktop-type system suitable for use in a clean room or the like. Here, the clean room as referred to herein means a "room designed, constructed, and operated to control the inflow, generation, and retention of particles, which is classified by class according to the floating particle number concentration" as defined in JIS B9920-1;2019. The clean room in which the ultra-pure water production system of the present embodiment is preferably used is, for example, a clean room belonging to Class 1 to Class 8 in the air cleanliness class defined by the ISO 14644-1 standard.

[0015] The illustrated ultra-pure water production system is roughly divided into a primary pure water system 10 that produces primary pure water by supplying supply water such as tap water, a primary pure water tank 20 that stores the primary pure water produced by the primary pure water system 10, and a subsystem (secondary pure water system) 30 that is connected to the primary pure water tank and produces ultra-pure water. The ultra-pure water produced by the subsystem 30 is supplied to a water sampling dispenser 60 used for sampling ultra-pure water.

[0016] The primary pure water system includes a pretreatment unit 11 that performs pretreatment on the supply water by means of an activated carbon device, a filter, etc., a pump (P) 12 that feeds the supply water treated by the pretreatment unit 11, a reverse osmosis membrane device (RO) 13 provided on the secondary side of the pump 12, and an electro-deionization water production device (EDI (Electrodeionization) device) 14 that is supplied with the permeate water of the reverse osmosis membrane device 13 and performs desalination treatment on this permeate water. The treated water obtained by performing desalination treatment in the electro-deionization water production device 14 is primary pure water, which is stored in the primary pure water tank 20. The concentrated water discharged from the reverse osmosis membrane device 13 is discharged to the outside as drainage.

[0017] A]]A communication pipe 21 is attached to the primary pure water tank 20 to communicate the space above the liquid level inside the tank with the outside air so that the pressure of the liquid level inside the tank becomes atmospheric pressure. The outside air mentioned here refers to the air outside the primary pure water tank 20. If the primary pure water tank 20 is arranged in a clean room, it refers to the air in the clean room, not the outdoor atmosphere. An air vent filter 22 is provided in the communication pipe 21 to prevent particles in the outside air from entering the primary pure water tank 20. The air vent filter 22 is composed of, for example, a non-woven fabric made of polypropylene for dust prevention, activated carbon for adsorbing and removing volatile organic substances, and soda lime for absorbing and removing carbon dioxide. The boron component contained more in the air in the clean room than in the outdoor air is not removed by the air vent filter 22. Also, ionic components other than carbonic acid are not removed by the air vent filter 22.

[0018] Subsystem 30 produces ultrapure water by further purifying the primary pure water supplied from the primary pure water tank 20. By circulating the ultrapure water that is not used at the point of use back into the primary pure water tank 20, it is possible to produce ultrapure water of even higher purity. As mentioned above, since the primary pure water tank 20 is in contact with the outside air, it is unavoidable that boron components contained in the outside air will mix with the pure water in the tank. Therefore, in the ultrapure water production system of this embodiment, in order to obtain ultrapure water from which boron has been sufficiently removed, subsystem 30 is equipped with a boron removal device 33 filled with boron-selective resin. In addition, since there is a risk that ionic components may be introduced into the system via the air vent filter 22 of the primary pure water tank 20, subsystem 30 is also provided with a non-regenerative ion exchange device (CP) 35, also called a cartridge polisher.

[0019] The boron-selective resin packed into the boron removal device 33 is a chelate resin having a boron-selective polyhydric alcohol group (e.g., N-methylglucamine group) as a functional group instead of the ion exchange group in an anion exchange resin, and selectively adsorbs and removes boron components. Examples of boron-selective resins include Organo's Orlite® X-U653J, Organo's Ambersep IRA743, and Mitsubishi Chemical's Diaion® CRB03. It is preferable to use a boron-selective resin that has a low amount of TOC component elution. Specifically, pure water with a space velocity (SV) of 50 to 200 h -1 When water is passed through the boron-selective resin, it is preferable to use a boron-selective resin in which the increase in TOC concentration after water passage is less than 1 ppb compared to before water passage. Although boron components can also be removed by general strong basic anion exchange resins that are not boron-selective resins, in water boron exists in the form of boric acid, which is an extremely weak acid. Therefore, when a general strong basic anion exchange resin is used to remove boron components, the strong basic anion exchange resin will break down prematurely with respect to the boron components, and the boron components will leak into the treated water.

[0020] Boron-selective resins exhibit significant leaching of TOC components, particularly in the initial stages of water flow, as well as some leaching of metal components. It is also known that the presence of carbon dioxide reduces the boron removal rate in boron-selective resins. A typical subsystem for ultrapure water production includes an ultraviolet oxidation device that decomposes and removes TOC components by ultraviolet oxidation treatment, and a non-regenerative ion exchange device located downstream of the ultraviolet oxidation device to adsorb and remove metal components and carbon dioxide components generated by the ultraviolet oxidation device. Therefore, in subsystem 30 of this embodiment, it is preferable to provide an ultraviolet oxidation device 34 downstream of the boron removal device 33, and a non-regenerative ion exchange device 35 downstream of the ultraviolet oxidation device 34.

[0021] Therefore, in this embodiment, subsystem 30 includes a pump (P) 31 connected to the outlet of the primary pure water tank 20 to supply primary pure water from the primary pure water tank 20, a flow meter (FI) 32 connected to the secondary side (i.e., outlet) of the pump 31, a boron removal device (B) 33 to which primary pure water is supplied via the flow meter 32, an ultraviolet oxidation device (UV) 34 connected to the outlet of the boron removal device 33, and a non-regenerative ion exchange device 35 (CP) connected to the outlet of the ultraviolet oxidation device 34. Ultrapure water flows out from the outlet of the non-regenerative ion exchange device 35. In this embodiment, since piping for circulation purification is provided extending from subsystem 30 to the water sampling dispenser 60, the ultrapure water flowing out from the non-regenerative ion exchange device 35 is sent to the circulation outlet 42 of subsystem 30 via the supply piping 41. The subsystem 30 is provided with a circulation inlet 43 that receives ultrapure water returning from the water sampling dispenser 60. The ultrapure water returning from the water sampling dispenser 60 is circulated to the primary pure water tank 20 via a circulation pipe 44 connected to the circulation inlet 43. A relief valve 45 is provided in the circulation pipe 44.

[0022] Next, the water sampling dispenser 60 will be described. The water sampling dispenser 60 is placed in a location easily accessible to the user on a laboratory bench or similar surface, so that the user can easily sample ultrapure water into a container such as a beaker. For this reason, the water sampling dispenser 60 may be located slightly away from the subsystem 30. The water sampling dispenser 60 has an inlet 61 for receiving ultrapure water and an outlet 62 for returning unused ultrapure water to the subsystem 30. The inlet 61 is connected to the circulation outlet 42 of the subsystem 30 by piping 51, and the outlet 62 is connected to the circulation inlet 43 by piping 52. The inlet 61 and outlet 62 are connected at a connection point 63 by piping inside the water sampling dispenser 60. A pipe 64 extends from this connection point 63, and a nozzle 65 for discharging ultrapure water is provided at the end of the pipe 64. A solenoid valve 66 is provided on the pipe 64 to control the discharge of ultrapure water from the nozzle 65.

[0023] When the pump 31 is operated in subsystem 30, the primary pure water in the primary pure water tank 30 passes sequentially through the boron removal device 33, the ultraviolet oxidation device 34, and the non-regenerative ion exchange device 35, removing boron, TOC, and ionic components from the primary pure water. This produces ultrapure water. The ultrapure water is supplied from the circulation outlet 42 to the water sampling dispenser 60, returns to the circulation inlet 43 of subsystem 30 via the connection point 63 in the water sampling dispenser 60, and circulates back to the primary pure water tank 20 via the circulation piping 44. A relief valve 45 is provided in the circulation piping 44, so that the pressure of the ultrapure water in the water sampling dispenser 60 is kept constant. When the solenoid valve 66 is opened in this state, the ultrapure water flows from the connection point 63 through the piping 64 to the nozzle 65, and the ultrapure water is discharged from the nozzle 65. Therefore, by operating the solenoid valve 66, the user can collect ultrapure water from which boron has been sufficiently removed. [Examples]

[0024] The present invention will be described in more detail below with reference to examples and comparative examples.

[0025] [Example 1] The ultrapure water production system shown in Figure 1, excluding the primary pure water system 10, was assembled and installed in a cleanroom that meets the ISO 14644-1 Class 6 (i.e., Class 1000) standard. In this cleanroom, a HEPA filter is used to remove suspended particles. Organo's Orlite (registered trademark X-U653J) was used as the boron-selective resin to fill the boron removal device 33, and Organo's ion exchange resin ESP-2 was used in the non-regenerative ion exchange device 35. The air vent filter 22 installed in the primary pure water tank 20 was composed of polypropylene nonwoven fabric, activated carbon, and soda lime.

[0026] The subsystem 30 was operated by supplying ultrapure water with controlled boron concentration to the primary pure water tank 20, and the ultrapure water was continuously circulated within the subsystem 30. As a result, the boron concentration in the outlet water of the non-regenerative ion exchange unit 35 was 0.1 ppt one month after the start of operation and 0.1 ppt three months after the start of operation.

[0027] [Comparative Example 1] An apparatus identical to that in Example 1 was assembled, except that it lacked the boron removal device 33, and this apparatus was operated in the same manner as in Example 1. As a result, the boron concentration in the outlet water of the non-regenerative ion exchange device 35 was 0.3 ppt one month after the start of operation, and 1.3 ppt three months after the start of operation.

[0028] From the above, it has been found that, according to the ultrapure water production system based on the present invention, even when ultrapure water is produced in a clean room over a long period of time, ultrapure water with boron sufficiently removed can be obtained. [Explanation of Symbols]

[0029] 10. Primary Pure Water System 11 Pre-processing section 13 Reverse osmosis membrane device (RO) 14. Electrical Deionized Water Production System (EDI) 20 Primary pure water tank 21 Communication pipe 22 Air vent filters 30 subsystems 33 Boron removal device (B) 34. Ultraviolet Oxidation Equipment (UV) 35 Non-regenerative ion exchange device (CP) 41 Supply piping 44 Circulation piping 45 Relief valve 60 water dispensers 65 nozzles 66 Solenoid valve

Claims

1. A method for producing ultrapure water by installing an ultrapure water production system in a clean room, The ultrapure water production system comprises a primary pure water tank that stores primary pure water and communicates with the outside air via an air vent filter, and a subsystem that is connected to the primary pure water tank and produces ultrapure water. The ultrapure water produced in the subsystem that is not used is circulated to the primary pure water tank. The subsystem comprises a boron removal device filled with a boron-selective resin, and a non-regenerative ion exchange device located downstream of the boron removal device. A method for producing ultrapure water, wherein the air vent filter is a filter that allows boron components in the outside air to pass through, and is composed of a nonwoven fabric and / or activated carbon.

2. The manufacturing method according to claim 1, wherein in the subsystem, an ultraviolet oxidation device is provided downstream of the boron removal device and upstream of the non-regenerative ion exchange device.

3. The manufacturing method according to claim 1 or 2, wherein the ultrapure water production system comprises a primary pure water system that generates primary pure water from feed water, and the primary pure water generated by the primary pure water system is supplied to the primary pure water tank.

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