OPTIMIZATION METHOD FOR AN OBJECTIVE WITH FLUORIDE CRYSTAL LENSES AND OBJECTIVE WITH FLUORIDE CRYSTAL LENSES

摘要

The invention relates to a numerical optimization method for determining optical data of an objective (1), more particularly a projection objective for a microlithography projection exposure facility, wherein an optimization function is minimized with said optimization method. According to the inventive optimization method, the disturbing influence of intrinsic birefringence of lenses (L101-L130) that are made of fluoride crystal material and have a cubic crystal structure is reduced by considering at least one birefringence image error in the optimization function, which is determined on the basis of the tracing of a beam (7) through a fluoride crystal lens and which only depends on the geometric parameters of the beam, insofar as it is dependent upon the parameters of said beam. Objectives (1) in which both optical retardation and optical retardation asymmetry are corrected are produced with said numerical optimization method. The objectives have several homogenous groups (HG1-HG7) in which the optical retardation asymmetry is corrected.