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Apparatus and method for generating partially coherent illumination for photolithography

United States Patent

July 17, 2001
View the Complete Patent at the US Patent & Trademark Office
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The present invention introduces a novel scatter plate into the optical path of source light used for illuminating a replicated object. The scatter plate has been designed to interrupt a focused, incoming light beam by introducing between about 8 to 24 diffraction zones blazed onto the surface of the scatter plate which intercept the light and redirect it to a like number of different positions in the condenser entrance pupil each of which is determined by the relative orientation and the spatial frequency of the diffraction grating in each of the several zones. Light falling onto the scatter plate, therefore, generates a plurality of unphased sources of illumination as seen by the back half of the optical system. The system comprises a high brightness source, such as a laser, creating light which is taken up by a beam forming optic which focuses the incoming light into a condenser which in turn, focuses light into a field lens creating Kohler illumination image of the source in a camera entrance pupil. The light passing through the field lens illuminates a mask which interrupts the source light as either a positive or negative image of the object to be replicated. Light passing by the mask is focused into the entrance pupil of the lithographic camera creating an image of the mask onto a receptive media.
Sweatt; William C. (Albuquerque, NM)
Sandia Corporation (Livermore, CA)
09/ 300,809
April 27, 1999
STATEMENT OF GOVERNMENT INTEREST This invention was made with Government support under contract DE-AC04-94AL85000 awarded by the U.S. Department of Energy to Sandia Corporation. The Government has certain rights in this invention.