Optical gain approach for enhancement of overlay and...

Optics: measuring and testing – By alignment in lateral direction

Reexamination Certificate

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C356S401000, C356S508000, C382S151000

Reexamination Certificate

active

07602491

ABSTRACT:
A resultant image of a grating target may be obtained by dividing an image of the target into first and second portions and optically modifying the first and/or second portion such that a final image formed from their combination is characterized by a Moiré pattern. The resultant image may be analyzed to determine a shift in the grating target from a shift in the Moiré pattern. Optical alignment apparatus may include a first beam splitter, an image transformation element optically coupled to the first beam splitter, and a second beam splitter. The first beam splitter divides an image of a grating target into first and second portions. The second beam splitter combines the first portion and the second portion. The image transformation element optically modifies the first and/or second portion such that a final image formed from their combination is characterized by a Moiré pattern.

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U.S. Appl. No. 60/914,295, filed Apr. 26, 2007.
International Search Report and Written Opinion of the International Searchign Authority for the International application No. PCT/US2008/061318 dated Aug. 4, 2008, 9 page.

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