Patent ID: 6744522
Filing Date: 2004-06-01
Classification: G01B

Abstract:
A method for measuring an optical thickness of a test object, the method comprising:(a) interfering a first optical wavefront from the test object and a second optical wavefront from a reference surface to produce an interference signal, (b) for a selected location on the test object, obtaining an interference pattern of the test object at a first wavelength &lgr;1; (c) for the selected location, calculating a first estimate of the optical thickness from the interference pattern recorded at wavelength &lgr;1; (d) for the selected location obtaining an interference pattern of the test object at a second wavelength &lgr;2; (e) for the selected location, calculating a second estimate of the optical thickness from the interference pattern recorded at wavelength &lgr;2; and (f) for the selected location, calculating a third estimate of the optical thickness by combining the first and second estimates of optical thickness.