Optical inspection of wafer bevels using multiple light sources

Abstract

Optical inspection of the surface of a substrate may take place in a factory interface where an aligner rotates the substrate to identify an alignment mark. While rotating, light may also be reflected off the surface of the substrate and captured by to identify defects or other variations on the substrate surface. However, the edge of the substrate often includes a bevel, and light directed at the edge of the substrate does not reflect off the bevel into the camera uniformly. Therefore, multiple light sources may be used simultaneously. For example, one light source may be directed perpendicularly at the edge of the bevel while another light source is directed at the bevel edge and configured such that light reflects off of the bevel into the camera. This provides an image with uniform lighting that can be more effectively used to identify defects on the edge of the substrate.

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