Apparatus for determining the optimum position of an object with respect to a focal point of a focused beam of radiation. The apparatus has a resolution limit and includes a radiation source, a lens for focusing the beam of radiation on the object, and a reticle interposed between the radiation source...http://www.google.com/patents/US5856053?utm_source=gb-gplus-sharePatent US5856053 - Method for estimating optimum position of a wafer for forming image patterns thereon
