Stage rotation system to improve edge measurements

摘要

A method for operating an optical measurement system is disclosed which permits measurements to be made more uniformly in regions close the edge of a wafer. The optical measurement system includes a probe beam which is focused to an elliptically shaped spot on the surface of the wafer. Improved measurements near the wafer's edge are obtained by rotating the wafer with respect to the measurement spot to insure that the short axis of the ellipse is perpendicular to the wafer edge.