| 摘要 |
An apparatus and method for detecting defects in a substrate, including the periphery of the substrate, by the use of an image pickup device which sequentially scans the substrate along each of a plurality of vertically displaced horizontal lines for equal horizontal scanning periods. The analog output of the pickup device is coded to provide a binary coded signal having a polarity determined by the amount of light reflected from the substrate at each incremental portion of the scanning periods. The binary coded signal is shifted for a first interval which is less than the horizontal scanning period to obtain a first shifted output, and then further shifted for a second interval, measured from the end of the first interval, which is equal to the horizontal scanning period to obtain a second shifted output. The polarities of the first and second shifted outputs are compared in a comparator, the presence of a defect in the substrate being indicated when the first and second shifted outputs have predetermined opposite polarities at a given instant of time followed by a reversal in the polarities of each of the first and second shifted outputs.
|
