Patent ID: 8736831

Claim:
A system configured to inspect a substrate, comprising: an illumination subsystem configured to direct light to the substrate, wherein patterned features are formed on an upper surface of the substrate; an objective configured to collect light scattered from the substrate; an optical element positioned in a path of the light collected by the objective, wherein the optical element is configured to direct light scattered from the patterned features into a first direction and other scattered light into a second direction; a detector configured to generate output responsive to only the light directed into the second direction; an additional detector configured to generate output responsive to only the light directed into the first direction; and a processor configured to detect defects on the substrate using the output, wherein the processor is further configured to use the output generated by the additional detector to determine diffraction from the patterned features and to adjust the optical element based on the diffraction to direct substantially all of the light scattered from the patterned features into the first direction and to direct any other undesirable scattered light into the first direction.