Patent ID: 7508488

Claim:
A projection exposure system for imaging a structure onto a substrate, the projection exposure system comprising: a projection optical system having an object plane and an image plane, wherein at least one first location in the object plane is imaged into a corresponding second location in the image plane, and wherein a first optical path length between the first location and the second location is of a first length; a measuring light source for generating measuring light having a coherence length which is less than half of the first length; an optical delay system providing a first beam path and a second beam path for light traversing the optical delay system, wherein a difference between an optical path length of the first beam path and an optical path length of the second beam path is adjustable and of a second length, wherein the second length is adjustable to be substantially equal to two times the first length; and a detector for detecting a light intensity; wherein the projection exposure system comprises an interferometer system including the measuring light source, the projection optical system, the optical delay system and the detector, wherein the measuring light source, the projection optical system, the optical delay system and the detector are arranged such that measuring light having traversed the projection optical system and measuring light having traversed the optical delay system is incident on the detector.