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Ultrapure water, also known as "UPW" or "high-purity water", is water that has been purified to uncommonly stringent specifications. Ultrapure water is a commonly used term in the semiconductor industry to emphasize the fact that the water is treated to the highest levels of purity for all contaminant types, including: organic and inorganic compounds; dissolved and particulate matter; volatile and non-volatile, reactive and inert; hydrophilic and hydrophobic; and dissolved gases. UPW and commonly used term deionized (DI) water are not the same. In addition to the fact that UPW has organic particles and dissolved gases removed, a typical UPW system has three stages: a pretreatment stage to produce purified water, a primary stage to further purify the water, and a polishing stage, the most expensive part of the treatment process.〔The polishing stage is a set of treatment steps and is usually a recirculation and distribution system, continuously treating and recirculating the purified water in order to maintain stable high purity quality of supplied water. Traditionally the resistivity of water serves as an indication of the level of purity of UPW. Deionized (DI) water may have a purity of at least one million ohms-centimeter or one Mohm∙cm. Typical UPW quality is at the theoretical maximum of water resistivity (18.18 Mohm∙cm at 25 °C). Therefore the term has acquired measurable standards that further define both advancing needs and advancing technology in ultrapure water production.〕 A number of organizations and groups develop and publish standards associated with the production of UPW. For microelectronics and power, they include Semiconductor Equipment and Materials International (SEMI) (microelectronics and photovoltaic), American Society for Testing and Materials International (ASTM International) (semiconductor, power), Electric Power Research Institute (EPRI) (power), American Society of Mechanical Engineers(ASME) (power), and International Association for the Properties of Water and Steam (IAPWS) (power). Pharmaceutical plants follow water quality standards as developed by pharmacopeias, of which three examples are the United States Pharmacopeia, European Pharmacopeia, and Japanese Pharmacopeia. The most widely used requirements for UPW quality are documented by ASTM D5127 "Standard Guide for Ultra-Pure Water Used in the Electronics and Semiconductor Industries"〔(ASTM D5127 ) Standard Guide for Ultra-Pure Water Used in the Electronics and Semiconductor Industries〕 and SEMI F63 "Guide for ultrapure water used in semiconductor processing".〔(SEMI F63 ) Guide for Ultrapure Water Used in Semiconductor Processing〕 ==Sources and control== Bacteria, particles, organic and inorganic sources of contamination vary depending on a number of factors including the feed water to make UPW as well as the selection of the piping materials to convey it. Bacteria are typically reported in colony-forming units (CFU) per volume of UPW. Particles use number per volume of UPW. Total organic carbon (TOC), metallic contaminates, and anionic contaminates are measured in dimensionless terms of parts per notation, such as ppm, ppb, ppt and ppq. Bacteria have been referred to as one of the most obstinate in this list to control.〔Mittlemann MW and Geesey GC,"Biofouling of Industrial Water Systems: A Problem Solving Approach", Water Micro Associates, 1987〕 Techniques that help in minimizing bacterial colony growth within UPW streams include occasional chemical or steam sanitization (which is common in the pharmaceutical industry), ultrafiltration (found in some pharmaceutical, but mostly semiconductor industries), ozonation and optimization of piping system designs that promote the use of Reynolds Number criteria for minimum flow〔Libman S, "Use of Reynolds Number as a Criteria for Design of High-Purity Water Systems", Ultrapure Water, October 2006〕 along with minimization of dead legs. In modern advanced UPW systems positive (higher than zero) bacteria counts are typically observed in the newly constructed facilities. This issue is effectively addressed by sanitization using ozone or hydrogen peroxide. With proper design of the polishing and distribution system no positive bacteria counts are typically detected throughout the life cycle of the UPW system. Particles in UPW are the bane of the semiconductor industry, causing defects in sensitive photolithographic processes that define nanometer sized features. In other industries their effects can range from a nuisance to life-threatening defects. Particles can be controlled by use of filtration and ultrafiltration. Sources can include bacterial fragments, the sloughing of the component walls within the conduit’s wetted stream and also the cleanliness of the jointing processes used to build the piping system. Total organic carbon in ultra pure water can contribute to bacterial proliferation by providing nutrients, can substitute as a carbide for another chemical species in a sensitive thermal process, react in unwanted ways with biochemical reactions in bioprocessing and, in severe cases, leave unwanted residues on production parts. TOC can come from the feed water used to produce UPW, from the components used to convey the UPW (additives in the manufacturing piping products or extrusion aides and mold release agents), from subsequent manufacturing and cleaning operations of piping systems or from dirty pipes, fittings and valves. Metallic and anionic contamination in UPW systems can shut down enzymatic processes in bioprocessing, corrode equipment in the electrical power generation industry and result in either short or long-term failure of electronic components in semiconductor chips and photovoltaic cells. Its sources are similar to those of TOC's. Depending on the level of purity needed, detection of these contaminants can range from simple conductivity (electrolytic) readings to sophisticated instrumentation such as ion chromatography (IC), atomic absorption spectroscopy (AA) and inductively coupled plasma mass spectrometry (ICP-MS). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ultrapure water」の詳細全文を読む スポンサード リンク
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