Mask aligner with a wafer position detecting device

Claim 1

A wafer position detecting apparatus, comprising: projection optical means for exposing a wafer to a circuit pattern of a mask; first illuminating means, disposed adjacent said projection optical means, for illuminating the wafer without using said projection optical means; first photoelectric conversion means, associated with said first illuminating means, for detecting a mark on the wafer; second illuminating means for illuminating the wafer through said projection optical means; second photoelectric conversion means, associated with said second illuminating means, for detecting a mark on the wafer; wafer carrying means movable between a first position where a wafer carried thereon is illuminated by said first illuminating means and a second position where the wafer carried thereon is illuminated by said second illuminating means; and control means including: detecting means for detecting the deviation of the mark on the wafer carried by said carrying means from a predetermined reference position by cooperation with said first illuminating means and said first photoelectric conversion means without aligning the mark on the wafer with the predetermined reference position; and means for moving said carrying means to the second position in accordance with an output from said detecting means indicative of the detected deviation to allow the wafer to be illuminated and detected by said second illuminating means and said second photoelectric conversion means.