Patent ID: 8441613

Claim:
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 radiation having an operating wavelength forming a radiation beam; and a low absorption coating having at least one layer of 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 MAX , a local minimum angle of incidence, AOI MIN , and a local range of angles of incidence, ΔAOI=AOI MAX -AOI MIN ; for each optical surface the global maximum angle of incidence, AOI MAXG is the maximum angle of incidence occurring on the respective optical surface; at least one of the optical elements is a first element having a first surface having a surface shape and a surface position such that the global maximum angle of incidence, AOI MAXG , exceeds a critical angle A C and the global maximum angle of incidence, AOI MAXG , exceeds an angle of 40°; 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 A C for all locations on the first surface; the low absorption coating is a graded coating; the low absorption coating is applied to the first surface; a geometrical layer thickness of the at least one layer of the coating varies as a function of the location of the first surface; and the objective is configured to be used as a projection objective of a microlithography projection exposure apparatus.