A method of detecting positions of first and second marks, at least one of the first and second marks being associated with a substrate, and exposing the substrate to a pattern. The method includes steps of sensing an image of the first and second marks, an image of the first mark and an image of the...http://www.google.es/patents/US7672000?utm_source=gb-gplus-sharePatente US7672000 - Position detecting method and apparatus
