Patent ID: 7679721
Filing Date: 2010-03-16
Classification: G02B,G03F

Abstract:
1. A projection objective of a microlithographic projection exposure apparatus for imaging a reticle that can be arranged in an object plane of the projection objective onto an image plane, comprising: a) a first lens which is the penultimate curved optical element on the image side, has a concave surface on the image side and contains a first intrinsically birefringent crystal which has a first orientation of the crystal axes, and b) a second lens which is the last curved optical element on the image side, has a convex surface on the object side and contains a second intrinsically birefringent crystal, which has a second orientation of the crystal axes that can be described by rotating the first orientation of the crystal axes about a symmetry axis of the first lens, wherein the first and second orientations of the crystal axes are selected so that an intrinsic birefringence due to the first crystal, together with an intrinsic birefringence due to the second crystal, leads in total to at least approximately axisymmetric distribution of the overall birefringence, and wherein the concave surface of the first lens is spherical, the convex surface of the second lens is spherical, and the concave surface of the first lens and the convex surface of the second lens have at least approximately the same centre of curvature.