The Use of POU Particle Measurements in High-Purity Water Applications
By Bill Shade
Deionized (DI) water is used extensively in electronics manufacturing. In semiconductor manufacturing it is used for cleaning and etching wafers. DI water is also used in chemical mechanical planarization (CMP) processes and the critical immersion lithography process. Up to 1,000 gallons of water is needed to process a single 300-millimeter (mm) wafer. Because DI water is used in many critical process steps and directly contacts the wafer, controlling its contaminants is critical to maintaining high yields. On-line monitoring of particle levels is a common method of controlling contamination in DI water systems. While these systems do a superior job of treating and filtering the water, the output needs to be monitored in the unlikely event there is a problem with the system. Particles can occur due to issues with the piping, ion exchange (IX) beds, pumps, and or filters. At the same time, DI water management systems are being offered for local treatment of DI water just prior to the point of use (POU) in critical process steps. Filters for particle removal are part of these local DI water management systems. Therefore, it may be desirable to monitor these locations as well to prevent process issues; however, cost effective monitoring solutions will be required.
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