Patent ID: 7463351

Claim:
An optical system for detecting defects on a wafer surface, the wafer surface having at least one pattern, the system comprising: a source of light to produce a beam; optics directing the beam along a path terminating at the wafer surface, the path comprising at least a terminal portion, said terminal portion defining a line substantially perpendicular to the wafer surface, and said beam impinging onto the wafer, producing an illuminated spot thereon; an array of detectors for detecting light; an ellipsoidal mirrored surface, said mirrored surface and the detector array having an axis of symmetry about the line substantially perpendicular to the wafer surface, said mirrored surface defining an input aperture positioned proximate to the wafer surface to receive scattered light therethrough from the wafer surface; said mirrored surface further defining an exit aperture and being substantially rotationally symmetric about said axis of symmetry, so that the mirrored surface reflects and focuses rotationally symmetrically about said axis of symmetry light that passes through the input aperture to the detector array; said exit aperture being located opposite to the input aperture; and at least one filter located between said exit aperture and said detector array, and a controller adapted to selectively switch individual detectors from the array on or off in synchronization with rotation of the wafer, the at least one filter and controller configured to facilitate the generation of data indicative of scattered light substantially other than scattered light corresponding to the at least one pattern.