JP2021084044A - Ultrapure water production system and water quality management method thereof - Google Patents

Abstract

To provide a water quality management method of an ultrapure water production system which when there occurs the problem that metal concentration of ultrapure water does not meet required specifications at a use point, enables the location of the occurrence of the abnormality causing the problem to be easily identified.SOLUTION: There is provided a water quality management method of an ultrapure water production system which includes: a preliminary pure water tank; ion exchange equipment; ultrafiltration membrane equipment; an ultrapure water transfer line connected to the ultrafiltration membrane equipment and transferring ultrapure water toward a use point; and a return line branching from the ultrapure water transfer line and returning a part of the ultrapure water to the preliminary pure water tank. The water quality management method of the ultrapure water production system includes an analysis step of analyzing metal concentration in water at the outlet port of the ion exchange equipment, in water flowing a position which is downstream side of the ultrafiltration membrane equipment and upstream side of the branch point of the return line of the ultrapure water transfer line, and in water flowing in the return line, each of the analysis being performed by a concentration method.SELECTED DRAWING: Figure 1

Description

The present invention relates to an ultrapure water production apparatus and a water quality control method thereof.

Ultrapure water from which impurities are highly removed is used in many applications such as water for cleaning silicon wafers in a semiconductor manufacturing process. Ultrapure water generally treats raw water (industrial water, city water, well water, etc.) with a pretreatment system as needed, and sequentially with a primary pure water system and a secondary pure water system (subsystem). Manufactured by

In Patent Document 1, in an ultrapure water production apparatus, a branch line for sampling is provided in a supply line for supplying ultrapure water to a point of use (use point), and ultrapure water is sampled from the branch line for sampling to check the water quality. It is stated that it should be done. This branch line is provided with a valve whose wetted part is made of fluororesin. In Patent Document 2, in order to collect a sample for analysis of ultrapure water supplied to a use point without causing contamination caused by the valve, metal elution is provided in the wetted portion of the metal valve. It is disclosed that a reduced surface treatment is applied. Patent Document 3 discloses an impurity concentration analysis method capable of continuously analyzing the concentration of impurities in ultrapure water so that a change in concentration in a fluid can be accurately monitored.

Japanese Unexamined Patent Publication No. 2006-105349 Japanese Unexamined Patent Publication No. 2008-128375 Japanese Unexamined Patent Publication No. 2001-153855

As disclosed in these documents, the impurity concentration of the produced ultrapure water is measured for water quality control in the ultrapure water production apparatus. However, it is not easy to identify the location of the abnormality that causes the impurity concentration when the impurity concentration does not satisfy the required specifications at the point of use only by controlling the water quality of the produced ultrapure water. In particular, regarding the metal concentration in ultrapure water, the required specifications are becoming more stringent, and there is an increasing need for a technique for easily identifying the location where an abnormality occurs when the metal concentration does not satisfy the required specifications.

An object of the present invention is an ultrapure water production apparatus and its water quality control, which makes it easy to identify the location of an abnormality that causes an abnormality when the metal concentration of ultrapure water does not satisfy the required specifications at the point of use. To provide a method.

According to one aspect of the invention
An ultrapure water supply line connected to a primary pure water tank, an ion exchange device, an ultrafiltration membrane device, and the ultrafiltration membrane device to send ultrapure water toward a point of use, and ultrapure water. It is a water quality control method for ultrapure water production equipment that includes a return line that branches off from the water supply line and returns part of the ultrapure water to the primary pure water tank.
The water at the outlet of the ion exchange device, the water flowing downstream of the ultrafiltration membrane device and upstream from the branch point of the return line of the ultrapure water feed line, and the metal of the water flowing through the return line. A water quality control method is provided, which comprises an analysis step of analyzing each concentration using a concentration method.

According to another aspect of the invention
An ultrapure water supply line connected to a primary pure water tank, an ion exchange device, an ultrafiltration membrane device, and the ultrafiltration membrane device to send ultrapure water toward a point of use, and ultrapure water. An ultrapure water production device that includes a return line that branches off from the water supply line and returns part of the ultrapure water to the primary pure water tank.
Further, water at the outlet of the ion exchange device, water flowing downstream of the ultrafiltration membrane device and upstream from the branch point of the return line of the ultrapure water liquid supply line, and water flowing through the return line. An ultrapure water production apparatus is provided, which comprises an analytical means for analyzing each of the metal concentrations of the above using a concentration method.

According to the present invention, when the metal concentration of ultrapure water does not satisfy the required specifications at the point of use, it is easy to identify the location of the abnormality that causes the ultrapure water production apparatus and its water quality control. A method can be provided.

It is a process flow diagram which shows the schematic configuration example of the ultrapure water production apparatus. It is a schematic diagram which shows the schematic structure of the test apparatus used in the reference example.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto. In the present specification, unless otherwise specified, the terms "upstream" and "downstream" mean upstream and downstream in the flow direction of the water to be treated, respectively.

FIG. 1 shows a schematic configuration example of the ultrapure water production apparatus 1 according to one aspect of the present invention. The ultrapure water production apparatus 1 includes a primary pure water tank 2, an ultraviolet oxidizing apparatus 3, an ion exchange apparatus 4, and an ultrafiltration membrane apparatus 5. These constitute the secondary pure water system (subsystem) of the ultrapure water production equipment, and the primary pure water produced by the primary pure water system (not shown) is processed in this order to produce ultrapure water. , Supply ultrapure water to youth points. The resistivity of ultrapure water (25 ° C.) is, for example, more than 15 MΩ · cm, and in some cases more than 18 MΩ · cm. The resistivity of the primary pure water is lower than that of ultrapure water, for example, 0.1 to 15 MΩ · cm.

Primary pure water is appropriately supplied from the primary pure water system to the primary pure water tank 2 via the line L1, and the primary pure water is stored as water to be treated. The water to be treated stored in the primary pure water tank 2 is supplied to the ultraviolet oxidizing device 3 via the line L2 connecting the primary pure water tank 2 and the ultraviolet oxidizing device 3. Here, the water to be treated is irradiated with ultraviolet rays, and organic substances in the water to be treated are decomposed. The water to be treated extracted from the ultraviolet oxidizing device 3 is supplied to the ion exchange device 4 via the line L3 connecting the ultraviolet oxidizing device 3 and the ion exchange device 4. Here, metal ions and the like in the water to be treated are removed by the ion exchange treatment. The water to be treated (water at the outlet of the ion exchange device 4) extracted from the ion exchange device 4 via the line L4 connecting the ion exchange device 4 and the ultrafiltration membrane device 5 becomes the ultrafiltration membrane device 5. Be supplied. Here, the fine particles in the water to be treated are removed. From the ultrafiltration membrane device 5, the water to be treated (water at the outlet of the ultrafiltration membrane device) that has passed through the ultrafiltration membrane is extracted to the line L5 as ultrapure water. The line L5 is an ultrapure water feeding line that feeds ultrapure water toward the use point, and connects the permeated water outlet of the ultrafiltration membrane device 5 to the use point. Although not shown, concentrated water (water to be treated that has not permeated the ultrafiltration membrane) can be discharged from the ultrafiltration membrane device 5.

At the branch point 9, the return line L6 for returning a part of the ultrapure water to the primary pure water tank branches from the ultrapure water supply line L5. The line L6 is connected to the primary pure water tank 2. A part of the water flowing upstream from the branch point 9 of the ultrapure water supply line L5 is supplied to the use point, and the remaining part is returned to the primary pure water tank 2 via the return line L6.

If necessary, a device other than the device shown in FIG. 1 can be used. For example, a pump for sending the water to be treated and a heat exchanger for controlling the temperature of the water to be treated can be provided between the primary pure water tank 2 and the ultraviolet oxidizing device 3 (line L2). .. Further, a membrane degassing device for removing oxygen can be provided between the ion exchange device 4 and the ultrafiltration membrane device 5 (line L4).

Equipment known in the field of ultrapure water production can be appropriately used for each apparatus constituting the ultrapure water production apparatus including the pretreatment system, the primary pure water system and the secondary pure water system. For example, as the ion exchange device 4, a non-regenerative mixed bed type ion exchange resin tower (cartridge polisher) can be used. The ultrafiltration membrane device 5 includes, for example, an appropriate hollow fiber membrane module in the housing. For example, non-metal materials (resins) such as polyvinyl chloride (PVC) and polyvinylidene fluoride (PVDF) can be used for lines L4, L5, and L6 in order to prevent metal elution.

At the branch point 6, the sampling line L11 branches from the line L4. At the branch point 7, the sampling line L12 branches from the line L5. The branch point 7 is located on the upstream side of the branch point 9. At the branch point 8, the sampling line L13 branches from the line L6. Water flowing to the sampling lines L11, L12, and L13 at the outlet water of the ion exchange device and the water flowing downstream of the ultrafiltration membrane device 5 and upstream from the branch point 9 of the ultrapure water feeding line L5 (ultrafiltration membrane). A sample for metal analysis of the water flowing through the device outlet water) and the return line is sampled. For example, when the membrane degassing device is provided on the line L4, the membrane degassing device can be provided downstream of the branch point 6. In this case, a separate sampling line can be provided downstream of the membrane degassing device and upstream of the ultrafiltration membrane device 5 to perform metal analysis. This makes it possible to separate and evaluate the dirt from the membrane deaerator and the dirt from the ultrafiltration membrane.

Sampling lines L11, L12 and L13 are provided with valves 11, 12 and 13, respectively, and analytical means 14, 15 and 16 are connected downstream of the valves 11, 12 and 13. On-off valves can be used as the valves 11, 12 and 13. These valves can be open during sampling and closed when no sampling is in progress.

Analytical means 14, 15 and 16 are metal for ion exchange device outlet water, water flowing upstream from the branch point of the return line of the ultrapure water supply line (ultrafiltration membrane device outlet water), and water flowing through the return line. It is used in the analysis process to analyze each concentration. The metal to be analyzed in the analysis step is not particularly limited, but is one or more selected from the group consisting of, for example, Na, K, Ca, Mg, Fe, Cu, Al, Zn, Ni, Cr, and Pb. .. For example, Na and Ca may elute from ion exchange resins, Al, Cr, Fe, Ni and Cu from metal members, and Zn from ultrafiltration membranes.

For example, for at least one of the metals analyzed in the analysis step, typically for all the metals analyzed in the analysis step, the metal concentration (normal value) of ultrapure water is 1 ng / L or less. Therefore, from the viewpoint of accurate detection of metal concentration abnormality, the lower limit of quantification of the metal concentration in the analysis step is preferably 0.1 ng / L or less, more preferably 0.01 ng / L or less. Further, if the lower limit of quantification of the metal concentration in the analysis step is about 1 pg / L, the metal concentration can be quantitatively analyzed to a level of 1/1000 of 1 ng / L. Therefore, the lower limit of quantification of the metal concentration in the analysis step may be 1 pg / L or more. When analyzing only one kind of metal in the analysis step, the lower limit of quantification here means the lower limit of quantification of the metal. When analyzing a plurality of kinds of metals in the analysis step, it is preferable that the lower limit of quantification is in the above range for at least one of the plurality of kinds of metals to be analyzed, but the lower limit of quantification for all the metals is in the above range. It is more preferable to be in.

In recent years, semiconductor factories have demanded water quality management at a level lower than ng / L. According to IRDS (International Technology Roadmap for Semiconductors), the required water quality for metals in ultrapure water is 1 ng / L, but in reality, it may be necessary to analyze at a level of 1/1000 of the required water quality. .. In order to perform a more accurate quantitative analysis of a trace amount of metal, it is preferable to prevent the metal from elution from the valve into the sample water. Therefore, it is preferable that at least the wetted portions of the valves 11, 12 and 13 provided in the sampling line are made of non-metal, and it is more preferable that the entire of these valves is made of non-metal. The non-metallic material used for the valve is typically a resin, especially a fluororesin. Examples of the fluororesin include PVDF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxyalkane), FEP (ethylene tetrafluoride / propylene hexafluoride copolymer resin), and PCTFE (trifluoroethylene). Ethylene fluoride), ETFE (ethylene tetrafluoride / ethylene copolymer resin) and the like can be used.

In the analysis step, after concentrating the metal in the sample water, the metal concentration in the sample water (or concentrate) is measured using a metal concentration measuring device, for example, an inductively coupled plasma mass spectrometer (ICP-MS). Can be done. As the concentration method, for example, a method in which a metal in the sample water is captured by an ion adsorption membrane and the captured metal is eluted using an eluent such as an acid can be adopted. As a concentration method, there is a heat concentration method (concentration by heating sample water) in addition to the ion adsorption membrane concentration method, but the ion adsorption membrane concentration method is preferable for clean concentration at a high magnification. The concentration ratio of the concentration operation can be appropriately determined. Instead of the ion adsorption membrane, an ion exchanger made of a monolithic resin may be used. When an ion exchanger made of a monolithic resin is used, the differential pressure applied to the ion exchanger is smaller than that of the ion adsorption membrane method, so that water can pass through the ion exchanger at high SV (space velocity), and the required time is required. It can be shortened. In addition to the above, a method known in the field of quantitative analysis of metals in ultrapure water can be appropriately adopted for the analysis step (including the concentration operation).

Analytical means include a metal concentration measuring device. When performing a concentration operation, the analytical means further include a concentration means. The concentrating means includes, for example, an ion adsorption membrane as described above, or an ion exchanger made of a monolithic resin. In FIG. 1, analysis means 14, 15 and 16 are provided separately for each sampling line L11, L12 and L13, but this is not necessarily the case. For example, the concentrating means can be provided separately for each sampling line to concentrate each sample water, and each concentrating solution can be analyzed by a common measuring device.

In the sampling lines L11, L12, L13 and the analysis means 14, 15, 16, for the members other than the valves 11, 12 and 13, a non-metal material (resin) may be appropriately used as the material of the portion in contact with the sample water. Can be done.

If the metal concentration of ultrapure water does not meet the required specifications at the point of use, that is, if there is an abnormality in water quality, the water flowing upstream from the branch point 9 of the ion exchange device outlet water and the ultrapure water supply line L5 ( The location of the abnormality can be easily identified based on the information that the metal concentrations of the ultrafiltration membrane device outlet water) and the water flowing through the return line each meet the required specifications. An example of a specific method for the ultrapure water production apparatus shown in FIG. 1 will be described below. Table 1 shows an example of cases divided according to whether the metal concentration of the sampled water of the lines L11, L12 and L13 is judged to be "○" (normal) or "x" (abnormal). Here, each water has a metal concentration of 0.1 ng / L or less in a normal state, and "○" (normal) when the metal concentration of each water is 0.1 ng / L or less, and more than 0.1 ng / L. It shall be judged as "x" (abnormal). In each case, it is assumed that the metal concentration of water is more than 0.1 ng / L at the point of use.

Case 1 is a case where there is an abnormality in water quality at the point of use, but no abnormality is observed in any of the sample waters. In this case, the cause of the water quality abnormality can be presumed to be inside the use point.

Case 2 is a case where no abnormality is found in the sample water of the lines L11 and L12, but an abnormality is found in the sample water of the line L13. In this case, it can be estimated that the cause of the water quality abnormality is the piping from the branch point 7 to the branch point 9.

Case 3 is a case where no abnormality is found in the sample water of the line L11, but an abnormality is found in the sample water of the lines L12 and L13. In this case, it can be estimated that the cause of the water quality abnormality is upstream from the branch point 7 and downstream from the branch point 6, particularly the ultrafiltration membrane device 5.

Case 4 is a case where an abnormality is found in the sample water of the lines L11, L12 and L13. In this case, it can be estimated that the cause of the water quality abnormality is upstream from the branch point 6, particularly the ion exchange device 4.

[Reference example]
Hereinafter, the case where a metal (SUS316) valve is provided in the sampling line and the case where a non-metal valve whose part in contact with the fluid (sample water) is made of fluororesin (PFA or PTFE) is provided. An example in which the metal concentration (metal ion concentration) of the sample water is examined by concentrated analysis of the sample water will be described. As shown in FIG. 2, two branch pipes 21 are provided in the main pipe 20. An on-off valve 22 made entirely of metal was connected to one branch pipe, and an on-off valve 23 made entirely of non-metal was connected to the other branch pipe. The connector 24 was screwed into the outlet of each valve, and the tube 25 was connected to the connector. A concentrator 26 provided with a porous ion adsorption membrane was connected to each tube 25. At least the part of the above member and device (excluding the on-off valve) in contact with the sample water was made of non-metal.

The on-off valves 22 and 23 were opened to supply sample water to the main pipe 20, about 2000 L of sample water was passed through the ion adsorption membrane provided in the concentrator 26, and the metal in the sample water was captured by the ion adsorption membrane. Then, 100 ml of 2N nitric acid diluted with high-purity nitric acid (trade name: TAMAPURE AA-100) manufactured by Tama Chemical Co., Ltd. was used to elute the metal from the ion adsorption membrane. The amount of metal in the obtained eluate was measured by ICP-MS. Since the concentration ratio is 2000 / 0.1 = 20000 times, the metal concentration in the sample water was determined from the value obtained by dividing the amount of metal (ng) in the eluent by the concentration ratio.

The results are shown in Table 2. Compared with the case where the metal on-off valve 22 was used, the case where the non-metal on-off valve 23 was used had a lower or equivalent metal concentration.

According to Table 2, for example, for Ni, the amount contaminated by the metal valve is about 0.03 ng / L. Therefore, when a metal valve is used for the sampling line, the analysis value of the metal analysis may include such an error. It is easy to eliminate such an error by using a non-metal valve. As a result, it becomes easier to identify the abnormal part. In addition, if a metal valve is used, the metal may be eluted, making it difficult to evaluate the metal concentration of ultrapure water at a low concentration. However, using a non-metallic valve in ultrapure water It is possible to evaluate the metal concentration at a low concentration.

1 Ultrapure water production equipment 2 Primary pure water tank 3 Ultraviolet oxidation equipment 4 Ion exchange equipment 5 Ultrafiltration membrane equipment 6, 7, 8, 9 Branch points 11, 12, 13 Valves 14, 15, 16 Analytical means 20 Main piping 21 Branch pipe 22 Metal valve 23 Non-metal valve 24 Non-metal connector 25 Non-metal tube 26 Concentrator

Claims (7)

An ultrapure water supply line connected to a primary pure water tank, an ion exchange device, an ultrafiltration membrane device, and the ultrafiltration membrane device to send ultrapure water toward a point of use, and ultrapure water. It is a water quality control method for ultrapure water production equipment that includes a return line that branches off from the water supply line and returns part of the ultrapure water to the primary pure water tank.
The water at the outlet of the ion exchange device, the water flowing downstream of the ultrafiltration membrane device and upstream from the branch point of the return line of the ultrapure water feed line, and the metal of the water flowing through the return line. A water quality control method comprising an analysis step of analyzing each concentration using a concentration method. The ultrapure water production apparatus includes water at the outlet of the ion exchange apparatus, water flowing downstream of the ultrafiltration membrane apparatus and upstream of the branch point of the return line of the ultrapure water supply line, and It has a sampling line that samples each of the water flowing through the return line.
The water quality control method according to claim 1, wherein each of the sampling lines includes a valve whose wetted part is made of non-metal at least. The metal according to claim 1 or 2, wherein the metal to be analyzed in the analysis step is at least one selected from the group consisting of Na, K, Ca, Mg, Fe, Cu, Al, Zn, Ni, Cr and Pb. Water quality management method. The water quality control method according to any one of claims 1 to 3, wherein the metal concentration of the ultrapure water is 1 ng / L or less for at least one of the metals analyzed in the analysis step. The water quality control method according to any one of claims 1 to 4, wherein the lower limit of quantification of the metal concentration is 0.1 ng / L or less for at least one of the metals analyzed in the analysis step. The water quality management method according to claim 5, wherein the lower limit of quantification is 0.01 ng / L or less. An ultrapure water supply line connected to a primary pure water tank, an ion exchange device, an ultrafiltration membrane device, and the ultrafiltration membrane device to send ultrapure water toward a point of use, and ultrapure water. An ultrapure water production device that includes a return line that branches off from the water supply line and returns part of the ultrapure water to the primary pure water tank.
Further, water at the outlet of the ion exchange device, water flowing downstream of the ultrafiltration membrane device and upstream from the branch point of the return line of the ultrapure water liquid supply line, and water flowing through the return line. An ultrapure water production apparatus comprising an analytical means for analyzing the metal concentration of each of the above using a concentration method.

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