Patent ID: 6483572
Filing Date: 2002-11-19
Classification: G03F

Abstract:
In a lithographic alignment system, a method for correcting misalignments resulting from environmental effects on a lens which are unrelated to stage position, the method comprising:positioning said lens for projecting images therethrough from an object plane to an image plane; providing a reticle in said object plane, said reticle having a working pattern and a first pair of fiducial marks positioned outside of said working pattern; illuminating said fiducial marks and projecting images thereof through said lens; using a device for reflecting said images projected through said lens, reflecting said images to a detector; detecting said reflected images by said detector in a plane which is a reflection of said image plane; using a feedback system, operatively associating said detector with said reticle; and aligning the reticle based on said associating in a manner misalignment caused by environmental effects on said lens can be detected and corrected.