Optics: measuring and testing – By polarized light examination – With light attenuation
Patent
1998-04-07
1999-11-09
Font, Frank G.
Optics: measuring and testing
By polarized light examination
With light attenuation
356385, G01B 1100
Patent
active
059824921
ABSTRACT:
The center of a semiconductor wafer relative to a rotation axis of a spindle carrying the wafer is detected by turning the spindle while a line source of optical radiation is directed at the wafer. A CCD linear optical detector array extending along a line between the spindle axis to a point beyond the wafer periphery effectively detects the amount of optical energy intercepted by the wafer. The source is turned on for a predetermined duration and the detector is read out in response to a shaft encoder detecting that the spindle has moved to each of many predetermined angles. A microprocessor responsive to the optical detector determines the length of the line each time the detector turns on by deriving an indication of the amount of optical energy accumulated by the CCD array each time the detector turns on. The microprocessor combines the determined line length indications to detect the workpiece center relative to the spindle axis.
REFERENCES:
patent: 5644400 (1997-07-01), Mundt
patent: 5825913 (1998-10-01), Rostami et al.
U.S. application No. 08/654,321, Huynh, filed Mar. 29, 1996.
Bond Robert J.
Oppenheimer Carl
Quaratiello Mark
Font Frank G.
Lam Research Corporation
Nguyen Tu T.
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