Patent ID: 6072581
Filing Date: 2000-06-06
Classification: G01B

Abstract:
A geometrically-desensitized interferometer for profiling a test object surface, said interferometer comprising:(A) a light generator spaced from the test object surface in a Z direction;(B) an optical assembly which is disposed between said light generator and the test object surface and which is configured to 1) divide light received from said light generator into first and second impinging beams which a) propagate in two different directions, b) impinge upon the test object surface, and c) generate first and second reflected beams from the test object surface and 2) recombine said first and second reflected beams propagating from the test object surface to form an interference pattern which is representative of a characteristic of the test object surface;(C) an imaging device which is disposed on a common side of said optical assembly with said light generator and which has an aperture arranged to receive light transmitted through said optical assembly by said light generator and reflected back through said optical assembly by the test object surface, whereinsaid optical assembly is spaced from the test object surface by a distance H' in the Z direction that places the test object surface in or closely adjacent to an optimum metrology plane in which said first and second reflected beams originate at the same location on said test object surface but at different incident angles, whereinsaid optical assembly is configured to steer stray light beams away from said aperture of said imaging device while at least essentially minimizing phase offset, and whereinphase offset is an optical phase difference proportional to the difference in optical path length of said first and second reflected beams.