It is clear that 193nm lithography photoresists and scanner optical components, as well as masks, are far more sensitive to airborne molecular contaminants (AMC) than those used in earlier lithography generations. However, even older equipment can be significantly affected by AMC. Additionally, although a fab may have AMC levels under control, excursions in the ambient environment or tool pressure differentials may impact process and equipment and, over time, may result in a significant effect on lithographic illumination power or uniformity. Therefore, accurate, reliable, real-time AMC measurements at scanner manufacturer specification levels are the natural direction for monitoring critical environments. This article discusses various real- time monitors, their advantages and limitations, and proposes strategies and applications for each.
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