Profile measurement of silicon wafer by laser autocollimation

This paper describes an angle-probe based scanning system for flatness measurement of silicon wafers. An angle probe is used to scan the wafer surface to get local slopes of the surface without being influenced by the straightness error of the scanning motion. The profile height of the wafer surface can then be obtained from integrating the angle probe output with respect to distance along the scanning direction. A compact and sensitive angle probe utilizing the principle of laser autocollimation was designed and made specifically for the scanning system. The angle probe was confirmed to have a resolution higher than 0.01 arc-seconds. An experimental scanning system was also constructed to measure the surface profile of a 200 mm diameter silicon wafer using the angle probe. Measurements of the cross-sectional profile along a line on the wafer surface were conducted.