Patent ID: 7408622

Claim:
An illumination system for a microlithographic projection exposure apparatus, comprising: a light source for generating projection light, a masking arrangement for masking a reticle, a masking objective for imaging the masking arrangement on the reticle, and a polarizer that is arranged in the masking objective and polarizes transiting projection light linearly in at least one direction, wherein the polarizer comprises a plurality of polarizer elements each including two polarization-selective beam splitting layers arranged at an angle to one another, the beam splitting layers being arranged at an angle to a plane which is disposed at least approximately perpendicularly to an optical axis of the masking objective, and wherein a scattering element is arranged between the two beam splitting layers in such a way that at least a part of the light reflected by one beam splitting layer passes through the scattering element and is scattered therein before impinging on the other beam splitting layer.