DIRECT AERIAL IMAGE MEASUREMENT AS A METHOD OF TESTING HIGH NUMERICALAPERTURE MICROLITHOGRAPHIC LENSES

A method for testing high numerical aperture (NA) microlithographic le nses using direct aeriel image measurements has been developed. By mea suring contrast versus focus for dense line/space patterns, this syste m can quantify the amount of astigmatism, distortion, field curvature, and spherical aberration produced by a lens under test. Experimental results show high correlation with more traditional lens testing metho ds such as transmissive interferometry and evaluating exposed resist p atterns. The lens used in these experiments is an 0.53 NA, 248 nm obje ctive designed for imaging 0.35 mum features over a 31 mm diam field.