Patent ID: 7463422
Filing Date: 2008-12-09
Classification: G02B,G03F

Abstract:
1. An optical system of a projection exposure apparatus, comprising at least one lens that is made of a non-crystalline material and at least one lens that is made of a birefringent crystal, wherein all lenses made of a birefringent crystal have a higher susceptibility factor K LT/LH than the lenses made of a non-crystalline material, wherein K LT/LH is given by with <D>being the mean value of the thickness D of the plurality of lenses and <CA> being the mean value of the clear aperture CA of all lenses of the optical system, wherein the optical system is a projection objective configured to image a mask onto an image plane, and wherein the lens which is closest to the image plane has the highest susceptibility factor K LT/LH .