Lithographic apparatus comprising an electrical discharge generator and method for cleaning an element of a lithographic apparatus

摘要

A method for cleaning elements of a lithographic apparatus, for example optical elements such as a collector mirror, includes providing a gas containing nitrogen; generating nitrogen radicals from at least part of the gas, thereby forming a radical containing gas; and providing at least part of the radical containing gas to the one or more elements of the apparatus. A lithographic apparatus includes a source and an optical element, and an electrical discharge generator arranged to generate a radio frequency discharge.