Interferometric thickness measurement of free form silicon wafers

摘要

A relatively low cost pre-prototype measurement machine for measuring the geometry of double side polished wafers has been developed. The measurement principle is based on a scanning double side Fizeau interferometer with which the front side flatness and the back side flatness of a wafer is measured simultaneously. Both flatness maps are used to calculate the wafer thickness variation. The influence of lens aberrations, alignment errors and flatness errors of reference flats is compensated for by self-calibrating software compensation techniques.