Browse Prior Art Database

Cavity Detector for Semiconductor Wafers

IP.com Disclosure Number: IPCOM000039909D
Original Publication Date: 1987-Aug-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Batchelder, JS: AUTHOR

Abstract

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.

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Cavity Detector for Semiconductor Wafers

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. If a number of grazing angle detectors collect the light scattered from the surface, a pot hole would thus be indicated if no detector saw a scatter signal when the light spot was incident on that particular region of the surface. This technique can be implemented with any normally incident illuminating scanner wherein coincident detection is used. The signal from each grazing angle detector is thresholded, and then all of the thresholded signals are logical ORed together. The complement of this signal indicates a pot hole.

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