Patent ID: 7929115
Filing Date: 2011-04-19
Classification: G02B,G03F

Abstract:
1. An objective comprising: a plurality of optical elements having optical surfaces arranged to be capable of imaging an object surface of the objective onto an image surface of the objective with ultraviolet radiation having an operating wavelength 155 nm≦λ a low absorption antireflection coating having at least one layer of dielectric material, wherein: the radiation beam includes a plurality of rays incident on the optical surfaces with a plurality of respective angles of incidence, AOI, defining, for each location on an optical surface, a local maximum angle of incidence, AOI for each optical surface the global maximum angle of incidence, AOI at least one of the optical elements is a lens element having at least one lens surface having a surface shape and a surface position such that the global maximum angle of incidence, AOI the local range of angles of incidence, ΔAOI, for the at least one of the optical elements is equal to or less than the critical angle Ac for all locations on the lens surface; the low absorption antireflection coating is a graded antireflection coating; the low absorption antireflection coating is applied to the at least one lens surface; a geometrical layer thickness of the at least one layer of the antireflection coating varies as a function of the location of the at least one lens surface such that, for each location on the at least one lens surface, the antireflection coating is effective to reduce reflection in the respective local range of angles of incidence; and the objective is configured to be used as a projection objective of a microlithography projection exposure apparatus.