WAFER PREALIGNMENT APPARATUS, ITS METHOD FOR JUDGING WAFER PRESENCE, METHOD FOR SENSING WAFER EDGE POSITION, COMPUTER-READABLE RECORD MEDIUM WITH RECORDED PROGRAM FOR EXECUTING THIS POSITION SENSING METHOD, APPARATUS FOR SENSING WAFER EDGE POSITION, AND PREALIGNMENT SENSOR

摘要

A prealignment sensor comprising a frame fixed to a base and having a U-shape when viewed from its side. A light source is attached to a lower part of the flame. A convex lens is attached to a lower part of an inside of the frame by which diffused light of the light source is transformed into parallel light. A lens holder is provided for fixing the convex lens to the frame. An optical receiver is attached to an upper part of an inside of the frame by which the parallel light is received and is transformed into an electrical signal. A signal processing circuit is attached to the frame by which the electric signal is transformed into a desired displacement magnitude. The frame is formed of aluminum subjected to sulfuric-acid hard alumite treatment and then to steam sealing.