Device for positioning a semi-conductor wafer

摘要

A device for detecting a position of an edge of a disk-like workpiece having an outer periphery whose shape includes a portion bearing positional information related to the workpiece, the device including a system for rotationally moving the workpiece; an illuminating system; and a photodetecting system; wherein the illuminating system and the photodetecting system are disposed so as to sandwich therebetween an outer peripheral portion of the workpiece when it is rotationally moved by the moving system and wherein the illuminating system projects, toward the photodetecting system, a light beam having an elongated shape in cross-section.