Cleaning method and associated illumination source metrology apparatus

Abstract

An assembly comprises a space configured for placing a medium to receive a first radiation for generating a second radiation. In operation, the second radiation propagates coaxially with the first radiation after the medium. The assembly further comprises an optical element after the medium for transmitting or reflecting the first radiation with a surface area. The assembly is configured such that, in operation, a cleaning gas is in contact with the surface area. A reactive medium is generated from at least a part of the cleaning gas by the second radiation for removing a contamination from the surface area.

Dependencies are inferred from the claim text.