Patent ID: 6353473
Filing Date: 2002-03-05
Classification: G01B

Abstract:
A wafer thickness measuring apparatus with use of an optical heterodyne interferometer, comprising:a sample piece being positioned corresponding to height of a wafer and inclined at a predetermined angle substantially corresponding to an inclination angle due to bend of said wafer, and having a constant thickness being already known and equivalent to that of said wafer; a first detector for generating a detection signal depending upon a distance from a predetermined reference position facing to a front surface side of said wafer to a position on the front surface of said wafer corresponding to a measurement point of said optical heterodyne interferometer; a second detector for generating a detection signal depending upon a distance from a predetermined reference position facing to a reverse surface side of said wafer to a position on the reverse surface of said wafer corresponding to a measurement point of said optical heterodyne interferometer; a data sampling/memorizing means for measuring fluctuations at a large number of measurement points on the front surface or the reverse surface of said sample piece by means of said optical heterodyne interferometer, and then for memorizing detection values based upon said detection signals of said first and second detectors, which are obtained at said measurement points, depending upon the fluctuation amounts at the respective measurement points; and means for obtaining the respective detection values upon the detection signals of said first and second detectors at arbitrary measurement points on said wafer, a front surface and a reverse surface of which lie within a range of height between the front surface and the reverse surface of said sample piece, and for obtaining said fluctuation amounts corresponding to said detection values which are measured by said optical heterodyne interferometer and memorized in said data sampling/memorizing means from the respective detection values, respectively, thereby calculating out thickness of said wafer upon basis of the respective fluctuation amounts obtained and the thickness of said sample piece.