Optimizing signal-to-noise ratio in optical imaging of defects on unpatterned wafers

Abstract

A system for optical imaging of defects on unpatterned wafers that includes an illumination module, relay optics, a segmented polarizer, and a detector. The illumination module is configured to produce a polarized light beam incident on a selectable area of an unpatterned wafer. The relay optics is configured to collect and guide, radiation scattered off the area, onto the polarizer. The detector is configured to sense scattered radiation passed through the polarizer. The polarizer includes at least four polarizer segments, such that (i) boundary lines, separating the polarizer segments, are curved outwards relative to a plane, perpendicular to the segmented polarizer, unless the boundary line is on the perpendicular plane, and (ii) when the area comprises a typical defect, a signal-to-noise ratio of scattered radiation, passed through the polarizer segments, is increased as compared to when utilizing a linear polarizer.