A laboratory step and repeat wafer exposure camera is described. It includes a simple automatic alignment system on every chip based on bright field illumination and dark field intensity detection. Maximum intensity of the dark field light flux corresponds to mask and wafer alignment. The masks are prealigned on a jig borer. The focusing and leveling are accomplished by reading three air gauges and correcting the wafer height accordingly.
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J. Wilczyńskí (1979) studied this question.