Contamination control in an EUV light source

Abstract

A method is performed for controlling contamination in a light source. The method includes: obtaining a reference image of an optical element in the light source; obtaining a real-time image of the optical element; comparing the real-time image with the reference image to determine a contamination metric associated with the optical element; and triggering an operation in the light source based on the determined contamination metric to thereby mitigate contamination at the optical element.

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