In an optical projection system for use in projection printing of masks to wafers, comprising an illumination system including a light source and a mask positioned in the optical path of the illumination system, an optical phase structure is positioned in the optical path between the light source and...http://www.google.com.au/patents/US5624773?utm_source=gb-gplus-sharePatent US5624773 - Resolution-enhancing optical phase structure for a projection illumination system
Resolution-enhancing optical phase structure for a projection illumination ...
