Patent ID: 8902406

Claim:
A projection objective configured to image a pattern in an object plane into an image plane along a radiation path, the projection objective comprising: a plurality of mirrors between the object plane and the image plane, the plurality of mirrors being configured so that, during use of the projection objective, each of the plurality of mirrors is irradiated at an incident angle range characteristic for the mirror, wherein: a mirror of the plurality of mirrors has a largest incident angle range; the mirror having the largest incident angle range comprises a graded reflective coating supported and a substrate which supports the graded reflective coating; the graded reflective coating has a contour line defining a constant thickness of the graded reflective coating in a mirror plane parallel to the image plane; the contour line is elliptical with unequal major and minor axes, parabolic or hyperbolic; and the projection objective is configured to be used with EUV radiation.