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Roel Gronheid, IMEC, Lithography Department, Kapeldreef, Leuven, Belgium, & Rida Al-Horr, Dionex Corporation, Sunnyvale, CA, USA

ABSTRACT

This article describes a new technique for in-line purge gas monitoringfor acid contaminants. The technique is applied to the inlet and outlet channels of the active charcoal filters on an ASML PAS5500/1100 193- nm scanner. For this study the focus was on NOx and SOx contaminants. They were observed to fluctuate over time and to be present at high levels (0.5–3 ppb) at the filter inlet. At the outlet, the residual contamination could be measured and the average was found to be ~35 ppt for NO/HONO and ~2 ppt for SOx, corresponding to filtering efficiencies of 98% and 99.8%, respectively.