Patent ID: 7869138
Filing Date: 2011-01-11
Classification: B82Y,G02B,G03F,G21K

Abstract:
1. A projection objective, comprising: an object plane in which an object field is formed, an entry pupil and an exit pupil, a mirrored entry pupil in a mirrored entry pupil plane obtained by mirroring the entry pupil at the object plane, an image plane, an optical axis, at least a first mirror and a second mirror, wherein the projection objective has a negative back focus of the entry pupil, and wherein a principal ray originating from a central point of the object field traverses the objective from the object plane to the image plane and intersects the optical axis in at least one point of intersection, wherein each individual point of intersection has along the optical axis a respective first distance A 1 from the object plane and the mirrored entry pupil plane has a second distance A 2 from the object plane, wherein A 2 is less than A 1 , and wherein the exit pupil is a non-obscured exit pupil.