Process for identifying defects in a substrate having non-uniform surface properties

摘要

A surface inspection method of the invention includes scanning an inspection surface taking surface measurements. Determinations of various noise levels in the surface are made based on variations in the surface measurements. A dynamic threshold is then determined. The dynamic threshold adapts to the noise levels in the inspection surface to provide a varying threshold that can provide areas of high and low defect sensitivity on the same inspection surface. Defects are then identified by comparing surface measurements with the dynamic threshold. Additionally, the invention includes a surface inspection method that uses signal-to-noise ratios to identify defects. Such a method scans an inspection surface to obtain surface measurements. Noise levels associated with the inspection surface are then determined. Signal-to-noise ratios are determined for the surface measurements. The signal-to-noise ratios are compared with a signal-to-noise ratio threshold value. Defects are identified based on the comparisons of the signal-to-noise ratio of the surface measurements with the signal-to-noise ratio threshold value.