Cavity Detector for Semiconductor Wafers
Original Publication Date: 1987-Aug-01
Included in the Prior Art Database: 2005-Feb-01
Indentation defects, such as cracks, pits, pot holes, scratches etc., on smooth or rough surfaces can be detected with normally incident illumination and coincident detection at or near an oblique grazing angle. When a light spot is scanned across a rough surface, the surface roughness generates light scatter. At near grazing angles, the intensity of that scatter will be approximately proportional to the square of the average roughness under the spot. Asperities or features that protrude above the average level of the surface can then be identified from the coincident detection of the scattered light. However, if the light spot crosses a region that is everywhere lower than the average level of the surface, as might be the case for a pit, scratch, pothole, or crack, no scatter would be detected at the grazing angles.