The method of measuring the relative between submicron lithographic features on a wafer having thereon a reference characteristic associated with a reference submicron grating structure of periodicity p.sub.1 onto which there may be cast from a reticle the image of a projected submicron grating structure...http://www.google.de/patents/US5216257?utm_source=gb-gplus-sharePatent US5216257 - Method and apparatus for alignment and overlay of submicron lithographic features
