Patent US 3,955,072

An apparatus for automatically aligning a semiconductor wafer with a mask in the manufacture of integrated circuit devices is disclosed. The mask and wafer are each provided with alignment patterns, the alignment pattern on the wafer cooperating with the alignment pattern on the mask in a unique visual manner to signify alignment. A scanning mechanism is provided for automatically scanning the alignment pattern areas and producing output signals indicative of the relative positions of the alignment patterns on the wafer and mask. Logic circuitry is provided for operating in response to any misalignment represented by the scan output signals to compute formulae which are utilized to produce control signals for driving motor drive mechanisms to produce relative movement between the mask and wafer to bring them into alignment. Several separate alignment cycles are provided, if needed, for zeroing in on finalized alignment. A tolerance selection control circuit is provided for permitting a variation in final alignment tolerance.