Patent ID: 6980281
Filing Date: 2005-12-27
Classification: G03F

Abstract:
1. A lithographic apparatus comprising: a beam processing system for providing a beam of radiation along a beam path to a substrate, said beam processing system including at least one optical element that reflects or transmits radiation of said beam along said beam path; an aperture screen with an opening for permitting the passing of said beam; and a handling unit arranged to move said aperture screen to and from a position in said beam path for blocking out a portion of said beam from a remainder of said beam, said aperture screen having a test surface that is located adjacent said opening and arranged to receive at least a part of said portion of said beam that is blocked out from said remainder of said beam when said aperture screen is at said position, said test surface being made of a material that is sensitive, under influence of radiation from said beam, to chemical alterations that also affect said optical element under influence of radiation from said beam.