Patent ID: RE42338

Claim:
A lithographic projection apparatus, comprising: an illumination system constructed and arranged to supply a projection beam of radiation; a first object table provided with a first object holder constructed and arranged to hold a mask; a second object table provided with a second object holder constructed and arranged to hold a substrate; a projection system constructed and arranged to utilize said radiation to image an irradiated portion of the mask onto a target portion of the substrate; and at least one of said illumination system and projection system having an optical element with a surface on which radiation is incident and a capping layer covering said surface, said capping layer being formed of a relatively inert material, wherein said relatively inert material is selected from the group consisting of: diamond-like carbon, Ru, Rh, TiN, MgF 2 , LiF, C 2 F 4 and compounds and alloys thereof , wherein the optical element is configured to reflect the incident radiation .