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 monitoring for 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.