| 摘要 |
In a wafer thickness measuring apparatus and a method thereof, detection values are obtained from a sample piece (for example, a wafer chip) at a plurality of measurement points thereon by first and second detectors for absolute measurement of distances, and at the same time, measurement values of the fluctuations, for relative measurement of distances, are obtained by the optical heterodyne interferometer, and those measurement values are memorized as a plurality of measurement data being related with those measurement values. When measuring the thickness of a wafer, the measurements are performed at measurement points on the wafer which has a front surface and a reverse surface in height lying within the height of the sample piece, on which such a correspondence is obtained, thereby obtaining the detection values of the first and second detectors. Searching conversely from those detection values by referring the correspondence data, the respective detection values are converted into the data of the relative fluctuations therefrom upon the basis of the thickness of the sample piece, thereby obtaining the relative amounts of fluctuation in positions (i.e., the distances) upon the basis of the thickness of the sample piece, respectively. Then, by conducting addition and/or subtraction of the fluctuation amount on the front surface and the reverse surface from the thickness of the sample piece as a reference, it is possible to calculate out the thickness of the wafer to be measured.
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