Patent ID: 6991895

Claim:
A method for image formation, comprising: providing an imaging system with a source plane, an object plane, a pupil plane, and an image plane, and having a variable numerical aperture; providing around said image plane a substrate equipped with image-recording media; providing around said object plane a mask having a pattern consisting of first and second arrays of polygons; providing around said source plane first and second illumination of low σ(size); locating said first illumination at a position on said source plane corresponding to position −b 1 /2+b 2 /2 or b 1 /2−b 2 /2 on said pupil plane, and setting said numerical aperture to a first value NA 1 such that |b 1 /2+b 2 /2|<NA 1 <|3b 1 /2−b 2 /2|, then exposing said substrate through said imaging system thereby forming a first image; then locating said second illumination at a position on said source plane corresponding to position b 1 /2+b 2 /2 or −b 1 /2−b 2 /2 on said pupil plane, and setting said numerical aperture to a second value NA 2 such that |b 1 /2+b 2 /2|<NA 2 <|3b 1 /2−b 2 /2|, then exposing said substrate through said imaging system thereby forming a second image that is superimposed on said first image.