Patent ID: 8004656

Claim:
An illumination system for a microlithographic projection exposure step-and-scan apparatus, comprising: a light source, a first optical raster element that extends in or in close proximity of a first pupil plane of the illumination system and includes a plurality of first substructures that increase the geometrical optical flux of the system in a first direction, said first direction being at least substantially perpendicular to a scan direction of the projection exposure apparatus, and a second optical raster element that extends in or in close proximity of a second pupil plane of the illumination system, which is not necessarily different from the first pupil plane, and includes a plurality of second substructures that further increase the geometrical optical flux of the system in the first direction and increase the geometrical optical flux of the system in a second direction that is at least substantially parallel to the scan direction, wherein the first optical raster element and the second optical raster element cause an intensity distribution in a reticle plane along the second direction that has a slope with smooth transitions between a zero intensity level and a top intensity level, and wherein the slope has a Gaussian shape.