Method of and device for detecting micro-scratches

Abstract

A method and device detect for the presence of defects, namely micro-scratches, in the surface of a wafer. Light is projected onto a medium at the surface of the wafer, at an angle at which light is not reflected by another layer that may be located under the medium. Light reflected by the surface of the wafer is converted into an electrical signal but any light scattered by the surface is excluded as much as possible from contributing to the formation of the signal. The electric signal corresponds to the intensity of the light reflected from the surface of the wafer. As the light is scanned across the wafer, the values of the electric signal are compared to yield a determination of whether defects are present in the medium. Because the light projected onto the surface of the wafer will be scattered by defects such as micro-scratches, the wafer can be successfully monitored for the existence of such micro-scratches. In particular, defects including micro-scratches formed in the medium can be detected regardless of the structure underlying the medium, such as a pattern layer.