Sample positioning system to improve edge measurements

摘要

Systems and methods for operating an optical measurement system are disclosed which permit measurements to be made more uniformly in regions close the edge of a sample, such as a wafer. An optical measurement system can include a probe beam that is focused to an elliptically shaped spot on the surface of the sample. Improved measurements near the edge of the sample can be obtained by rotating the wafer with respect to the measurement spot to ensure that the short axis of the ellipse is perpendicular to the wafer edge.