Patent ID: 7489386

Claim:
A system for projecting a pattern from a mask onto a substrate comprising: a radiation source to emit a light beam in the extreme ultraviolet wavelength range; a mask to reflect a patterned light beam and comprising absorbent and reflective structure elements arranged to form the pattern; a collector mirror and an illumination optical system forming a first part of a beam path to direct the light beam onto the mask; a projection optical system comprising an arrangement of reflective mirrors forming a second part of the beam path to focus the patterned light beam from the mask onto a substrate and image the pattern on the substrate; and an optical element arranged in the beam path and located a distance from any conjugate plane associated with the mask, the optical element comprising at least two regions having different degrees of reflection or transmission, wherein a first region is assigned to a first position on at least one of the mask and the collector mirror and a second region is assigned to a second different position on at least one of the mask and the collector mirror in accordance with the beam path.