Abstract

The present invention includes a system for monitoring surface structures on a planar surface utilizing a radiation source emitting a beam. The planar surface has various surface structure types, including a plurality of grooves therein which intersect at various angles which are equal to or less than a predetermined maximum angle. The system includes an apparatus for directing the beam to the planar surface along an optical axis perpendicular to the planar surface resulting in radiation being scattered from the planar surface and a reference beam being specularly reflected from the planar surface. The system also includes detector responsive to radiation scattered from the planar surface. This detector produces a first signal representative thereof. Also provided is a spatial filter for filtering radiation scattered from the planar surface to allow only radiation from at least selected one of the plurality of surface structure types to reach the detector responsive to radiation scattered from the planar surface. The system may also include a detector responsive to the reference beam, producing a second signal in response to the reference beam and a circuit for producing a final signal from the first signal and the second signal.