JP7555184B2 - Ultrapure water production equipment and water quality control method - Google Patents

Description

The present invention relates to an ultrapure water production apparatus and a method for managing water quality therewith.

Ultrapure water, from which impurities have been highly removed, is used for many purposes, such as water for washing silicon wafers in the semiconductor manufacturing process. Ultrapure water is generally produced by treating raw water (industrial water, city water, well water, etc.) in a pretreatment system as necessary, and then sequentially treating it in a primary pure water system and a secondary pure water system (subsystem).

Patent Document 1 describes an ultrapure water production apparatus in which a sampling branch line is provided in a supply line for supplying ultrapure water to a use point, and ultrapure water is sampled from the branch line to confirm the water quality. This branch line is provided with a valve whose liquid-contacting part is made of fluororesin. Patent Document 2 discloses that a surface treatment is applied to the liquid-contacting part of a metallic valve to reduce metal elution in order to collect samples for analysis of the ultrapure water supplied to the use point without causing contamination due to the valve. Patent Document 3 discloses an impurity concentration analysis method that continuously analyzes the concentration of impurities in ultrapure water, enabling concentration changes in the fluid to be monitored with high accuracy.

JP 2006-105349 A JP 2008-128375 A JP 2001-153855 A

As disclosed in these documents, the impurity concentration of the produced ultrapure water is measured to control the water quality in ultrapure water production equipment. However, simply managing the quality of the produced ultrapure water does not make it easy to identify the location of the abnormality that causes the impurity concentration to no longer satisfy the required specifications at the point of use. In particular, with regard to the metal concentration in ultrapure water, the required specifications are becoming more stringent, and there is a growing need for technology that can easily identify the location of the abnormality when the metal concentration no longer satisfies the required specifications.

The object of the present invention is to provide an ultrapure water production system and a method for managing the water quality thereof that can easily identify the location of an abnormality that causes the metal concentration of ultrapure water at the point of use to no longer satisfy the required specifications.

According to one aspect of the present invention,
A water quality control method for an ultrapure water production system including a primary pure water tank, an ion exchange device, an ultrafiltration membrane device, an ultrapure water delivery line connected to the ultrafiltration membrane device and delivering ultrapure water to a point of use, and a return line branching off from the ultrapure water delivery line and returning a portion of the ultrapure water to the primary pure water tank, comprising:
The present invention provides a water quality control method, which comprises an analysis step of analyzing, using a concentration method, the metal concentrations of the water at the outlet of the ion exchange device, the water flowing downstream of the ultrafiltration membrane device and upstream of the branching point of the return line of the ultrapure water supply line, and the water flowing through the return line.

According to another aspect of the present invention,
An ultrapure water producing apparatus including a primary pure water tank, an ion exchange device, an ultrafiltration membrane device, an ultrapure water delivery line connected to the ultrafiltration membrane device and delivering ultrapure water to a point of use, and a return line branching off from the ultrapure water delivery line and returning a portion of the ultrapure water to the primary pure water tank,
Furthermore, an ultrapure water producing apparatus is provided, which is characterized by including an analytical means for analyzing the metal concentrations of the water at the outlet of the ion exchange device, the water flowing downstream of the ultrafiltration membrane device and upstream of the branching point of the return line of the ultrapure water delivery line, and the water flowing through the return line, each using a concentration method.

The present invention provides an ultrapure water production system and a water quality management method that can easily identify the location of an abnormality that causes the metal concentration of ultrapure water at the point of use to no longer satisfy the required specifications.

1 is a process flow diagram showing a schematic configuration example of an ultrapure water production apparatus. FIG. 2 is a schematic diagram showing a schematic configuration of a test device used in a reference example.

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

Figure 1 shows an example of the schematic configuration of an ultrapure water production apparatus 1 according to one embodiment of the present invention. The ultrapure water production apparatus 1 has a primary pure water tank 2, an ultraviolet oxidation device 3, an ion exchange device 4, and an ultrafiltration membrane device 5. These constitute a secondary pure water system (subsystem) of the ultrapure water production apparatus, and the primary pure water produced in the primary pure water system (not shown) is treated in this order to produce ultrapure water, which is then supplied to a point of use. The resistivity of the ultrapure water (at 25°C) is, for example, greater than 15 MΩ·cm, and in some cases, greater than 18 MΩ·cm. The resistivity of the primary pure water is lower than that of ultrapure water, and is, for example, 0.1 to 15 MΩ·cm.

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

A return line L6 branches off from the ultrapure water supply line L5 at branch point 9, returning a portion of the ultrapure water to the primary pure water tank. Line L6 is connected to the primary pure water tank 2. A portion of the water flowing upstream of branch point 9 on the ultrapure water supply line L5 is supplied to the use point, and the remaining portion is returned to the primary pure water tank 2 via the return line L6.

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

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

At branch point 6, sampling line L11 branches off from line L4. At branch point 7, sampling line L12 branches off from line L5. Branch point 7 is located upstream of branch point 9. At branch point 8, sampling line L13 branches off from line L6. At sampling lines L11, L12, and L13, samples for metal analysis are taken from the ion exchanger outlet water, the water flowing downstream of ultrafiltration membrane device 5 and upstream of branch point 9 of ultrapure water supply line L5 (ultrafiltration membrane device outlet water), and the water flowing through the return line. For example, when a membrane degassing device is provided on line L4, the membrane degassing device can be provided downstream of 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 degassing device 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 valves 11, 12 and 13. On-off valves can be used as valves 11, 12 and 13. These valves can be opened during sampling and closed when sampling is not performed.

The analytical means 14, 15, and 16 are used in an analysis process that analyzes the metal concentrations of the ion exchange device outlet water, the water flowing upstream of the branch point of the return line of the ultrapure water supply line (ultrafiltration membrane device outlet water), and the water flowing through the return line. The metals analyzed in the analysis process are not particularly limited, but are, for example, one or more selected from the group consisting of Na, K, Ca, Mg, Fe, Cu, Al, Zn, Ni, Cr, and Pb. For example, Na and Ca may be eluted from the ion exchange resin, Al, Cr, Fe, Ni, and Cu from the metal member, and Zn from the ultrafiltration membrane.

For example, for at least one of the metals analyzed in the analysis process, typically for all of the metals analyzed in the analysis process, the metal concentration (normal value) in the ultrapure water is 1 ng/L or less. Therefore, from the viewpoint of accurate detection of abnormal metal concentrations, the quantitative lower limit of the metal concentration in the analysis process is preferably 0.1 ng/L or less, more preferably 0.01 ng/L or less. Furthermore, if the quantitative lower limit of the metal concentration in the analysis process is about 1 pg/L, the metal concentration can be quantitatively analyzed to a level of 1/1000 of 1 ng/L. Therefore, the quantitative lower limit of the metal concentration in the analysis process may be 1 pg/L or more. Note that, when only one type of metal is analyzed in the analysis process, the quantitative lower limit here means the quantitative lower limit of that metal. When multiple types of metals are analyzed in the analysis process, it is preferable that the quantitative lower limit of at least one of the multiple types of metals to be analyzed is in the above range, but it is more preferable that the quantitative lower limit of all of the metals is in the above range.

In recent years, semiconductor factories have been demanding water quality management at a level even lower than ng/L. According to the 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 perform analysis at a level of 1/1000 of the required water quality. In order to quantitatively analyze trace amounts of metals more accurately, it is preferable to prevent metals from eluting from the valves into the sample water. For this reason, it is preferable that at least the liquid-contacting parts of the valves 11, 12, and 13 installed in the sampling line are made of nonmetal, and it is more preferable that the entire valves are made of nonmetal. The nonmetallic material used for the valves is typically resin, particularly fluororesin. Examples of fluororesins that can be used include PVDF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxyalkane), FEP (tetrafluoroethylene-hexafluoropropylene copolymer resin), PCTFE (trifluorochloroethylene), and ETFE (tetrafluoroethylene-ethylene copolymer resin).

In the analysis step, the metals in the sample water are concentrated, and then the metal concentration in the sample water (or concentrated liquid) can be measured using a metal concentration measuring device, such as an inductively coupled plasma mass spectrometer (ICP-MS). For example, a method of capturing the metals in the sample water with an ion adsorption membrane and eluting the captured metals with an eluent such as an acid can be used as the concentration method. In addition to the ion adsorption membrane concentration method, there is also a heating concentration method (heating the sample water to concentrate), but the ion adsorption membrane concentration method is preferable for high-magnification and clean concentration. 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 in the ion adsorption membrane method, so water can be passed through the ion exchanger at a high SV (space velocity), and the required time 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 in the analysis step (including the concentration operation).

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

In addition, for the sampling lines L11, L12, L13 and the analysis means 14, 15, 16, as well as for components other than the valves 11, 12, and 13, non-metallic materials (resins) can be used as appropriate for the materials of the parts that come into contact with the sample water.

If the metal concentration of the ultrapure water at the point of use does not meet the required specifications, i.e., if there is an abnormality in the water quality, the location of the abnormality can be easily identified based on information on whether the metal concentrations of the ion exchanger outlet water, the water flowing upstream of the branch point 9 of the ultrapure water supply line L5 (ultrafiltration membrane device outlet water), and the water flowing through the return line each meet the required specifications. A specific example of the method for the ultrapure water production system shown in Figure 1 is described below. Table 1 shows examples of cases divided according to whether the metal concentrations of the sampled water on lines L11, L12, and L13 are judged to be "○" (normal) or "×" (abnormal). Here, each water has a metal concentration of 0.1 ng/L or less under normal conditions, and if the metal concentration of each water is 0.1 ng/L or less, it is judged to be "○" (normal), and if it is more than 0.1 ng/L, it is judged to be "×" (abnormal). In all cases, the metal concentration of the water at the point of use is assumed to be more than 0.1 ng/L.

Case 1 is when there is a water quality abnormality at the use point, but no abnormality is found in any of the sampled water. In this case, it can be assumed that the cause of the water quality abnormality is inside the use point.

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

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

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

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

The on-off valves 22 and 23 were opened to supply sample water to the main pipe 20, and approximately 2000 L of sample water was passed through the ion adsorption membrane of the concentrator 26, capturing the metals in the sample water on the ion adsorption membrane. The metals were then eluted from the ion adsorption membrane using 100 ml of 2N nitric acid diluted with high-purity nitric acid (product name: TAMAPURE AA-100) manufactured by Tama Chemical Co., Ltd. The amount of metal in the resulting eluate was measured by ICP-MS. Since the concentration ratio was 2000/0.1 = 20,000 times, the metal concentration in the sample water was calculated by dividing the amount of metal (ng) in the eluate by the concentration ratio.

The results are shown in Table 2. When the non-metallic on-off valve 23 was used, the metal concentrations were lower or equivalent compared to when the metallic on-off valve 22 was used.

According to Table 2, for example, the contamination level of Ni due to metallic valves is about 0.03 ng/L. Therefore, if metallic valves are used in the sampling line, the analytical values of the metal analysis may contain an error of this level. If non-metallic valves are used, it is easy to eliminate such errors. As a result, it becomes easier to identify abnormalities. In addition, if metallic valves are used, metals may dissolve, making it difficult to evaluate the metal concentration in ultrapure water at low concentrations, but if non-metallic valves are used, it becomes possible to evaluate the metal concentration in ultrapure water at low concentrations.

REFERENCE SIGNS LIST 1 Ultrapure water production apparatus 2 Primary pure water tank 3 Ultraviolet oxidation apparatus 4 Ion exchange apparatus 5 Ultrafiltration membrane apparatus 6, 7, 8, 9 Branch points 11, 12, 13 Valves 14, 15, 16 Analyzing means 20 Main pipe 21 Branch pipe 22 Metal valve 23 Nonmetal valve 24 Nonmetal connector 25 Nonmetal tube 26 Concentration apparatus

Claims (7)

A water quality control method for an ultrapure water production system including a primary pure water tank, an ion exchange device, an ultrafiltration membrane device, an ultrapure water delivery line connected to the ultrafiltration membrane device and delivering ultrapure water to a point of use, and a return line branching off from the ultrapure water delivery line and returning a portion of the ultrapure water to the primary pure water tank, comprising:
A water quality management method comprising an analysis step of analyzing, using a concentration method, the metal concentrations of the water at the outlet of the ion exchange device, the water flowing downstream of the ultrafiltration membrane device and upstream of the branching point of the return line of the ultrapure water delivery line, and the water flowing through the return line. the ultrapure water production apparatus has sampling lines for sampling water at an outlet of the ion exchange device, water flowing downstream of the ultrafiltration membrane device and upstream of a branch point of a return line of the ultrapure water delivery line, and water flowing through the return line,
The water quality control method according to claim 1 , wherein each of the sampling lines is provided with a valve having at least a liquid-contacting portion made of a non-metallic material. The water quality management method according to claim 1 or 2, wherein the metal 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. The water quality management method according to any one of claims 1 to 3, wherein the ultrapure water has a metal concentration of 1 ng/L or less for at least one of the metals analyzed in the analysis step. The water quality management method according to any one of claims 1 to 4, wherein the lower limit of quantification of the metal concentration for at least one of the metals analyzed in the analysis step is 0.1 ng/L or less. 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 producing apparatus including a primary pure water tank, an ion exchange device, an ultrafiltration membrane device, an ultrapure water delivery line connected to the ultrafiltration membrane device and delivering ultrapure water to a point of use, and a return line branching off from the ultrapure water delivery line and returning a portion of the ultrapure water to the primary pure water tank,
The ultrapure water producing apparatus further comprises an analytical means for analyzing the metal concentrations of the water at the outlet of the ion exchange device, the water flowing downstream of the ultrafiltration membrane device and upstream of the branch point of the return line of the ultrapure water delivery line, and the water flowing through the return line, each using a concentration method.

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