Patent ID: 7400699

Claim:
An illumination system for lithography with wavelengths of ≦193 nm comprising: (a) a first optical element, which is divided into first raster elements and lies in a first plane, wherein said first plane defines an x-direction and a y-direction, wherein said first raster elements each has an x-dimension and a y-dimension with an aspect ratio, and wherein at least two of said first raster elements have aspect ratios of different magnitudes; and (b) a second optical element, which is divided into second raster elements, wherein each of said second raster elements is in a light path from a corresponding one of said first raster elements, wherein the illumination system defines a field, wherein said field is illuminated in an object plane of the illumination system, and wherein at least some of said second raster elements have an anamorphotic optical effect, which is selected such that an aspect ratio of images of said first raster elements is substantially the same in said object plane, independent of said aspect ratio of said first raster elements.