DISSIMILAR SUPERIMPOSED GRATING PRECISION ALIGNMENT AND GAP MEASUREMENT SYSTEMS

摘要

A substrate having a diffraction grating of a first periodicity formed thereon, a mask having a diffraction grating of a second periodicity formed thereon, the mask and substrate being positioned such that the respective mask and substrate gratings are generally parallel opposing one another on the mask and substrate, means for providing collimated coherent light directed so as to impinge on the mask and substrate gratings, and means for separately collecting, recombining, and detecting the intensity of at least a first given order of diffracted light beams as respectively diffracted by the mask and substrate gratings.