Highly Ozonized UPW and Its Impact On Filters
By Jochen Ruth & Gerd Heser
The use of highly ozonized ultrapure water (UPW*) in advanced semiconductor manufacturing processes can replace many chemical additives and is used as a process fluid for specific applications. Thorough knowledge of the compatibility of system components to ozone exposure is necessary to ensure the integrity of components and to avoid contamination of deionized (DI) water and wafer surfaces due to degradation byproducts of ozone attacks— an aging fact (1).
Filtration of ozonized UPW at the point of entry (POE) into tools is obligatory. Unfortunately, only limited data are available to judge chemical and mechanical compatibility of porous polymeric structures such as high-end filter media. Common knowledge and textbook information as well as published investigations (2) are typically restricted to solid materials and static conditions. Transfer of these data to thin, highly porous membranes with huge surface area is very challenging.
Several destructive and non-destructive methods for determining the properties of a filter element during and after use have been evaluated. In cooperation with an OEM for ozone generators, a long-term dynamic test scenario was developed, which was capable of continuously producing a consistent level of > 80 parts per million (ppm) of dissolved ozone in UPW. Two state-of-the art polytetrafluoroethylene (PTFE) filter cartridges (30 nanometer [nm] and 12 nm) were exposed to full flow and outlet concentration of the ozone generator over several months.
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