Development of a double sided stitching interferometer for wafer characterization

A 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 sided Fizeau interferometer with which the front side and the back side flatness of a wafer are measured simultaneously. Both flatness maps are used to derive the wafer thickness variation. Field distortion of the optical system, alignment errors and the thickness variations of the reference cavity are compensated by self-calibrating techniques in order to achieve a measurement uncertainty in the order of several nanometers.