Contaminant particles within lithographic apparatuses may be deposited onlo surfaces of sensitive components such as reflectors, causing their performance to decline over time. For example, in extreme ultra-violet (EUV) lithographic apparatuses, contaminant particles may be droplets of liquid metal (e.g. tin, Sn) which have leaked into the lithographic apparatus from the EUV source. Alternatively, contaminant particles may be particles that have been removed from surfaces of components during cleaning operations. Further alternatively, contaminant particles may be atoms or molecules that have been etched away from surface by EUV-induced plasma.
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