A projection lens for imaging a pattern arranged in an object plane onto an image
plane using electromagnetic radiation from the extreme-ultraviolet (EUV) spectral
region has several imaging mirrors between its object plane and image plane that
define an optical axis of the projection lens and have reflective coatings. At
least one of those mirrors has a graded reflective coating that has a film-thickness
gradient that is rotationally symmetric with respect to a coating axis, where that
coating axis is acentrically arranged with respect to the optical axis of the projection
lens. Providing at least one acentric, graded, reflective coating allows designing
projection lenses that allow highly uniform field illumination, combined with high
total transmittance.
