Abstract: An interferometer forms a pair of projected sub-beams by decomposing a single coherent, linearly-polarized beam. These sub-beams are focussed by an objective lens onto a pair of test spots on a test surface. The reflections of these sub-beams are recombined to form an elliptically polarized return beam, which is broken into return sub-beams of opposing polarities in a polarizing beam splitter. The intensities of these return sub-beams are used to calculate a difference in height between the two test spots. When these test spots are aligned along a path of relative motion with the test surface, the resulting differences in height are added to form an accumulative profile of the test surface.
Type:
Grant
Filed:
September 23, 1996
Date of Patent:
July 21, 1998
Assignee:
International Business Machines Corporation