| 摘要 |
PURPOSE:To make it possible to detect the existence of a wafer with good precison and in a non-contact state by a method wherein light-projecting means, which respectively irradiate on optical beam and irradiate a pair of optical beams in total, and light-receiving means, which receive reflected lights from incident points to output a significant conversion electrical signal to show the existence of the wafer, are provided at respective two points, the distances between which respectively become longer than the distance between both ends in the peripheral direction of the noncircular contour part of the wafer. CONSTITUTION:Optical beams on the side of radiation, which irradiate the peripheral edge part of a wafer 10 which is an existence detecting object, are set in two beams. Respective radiant light beams BR-1 and BR-2 are each obtained from individual projectors 61 and 62 for exclusive use to each beam, while the radiant light beams are set in such a way that a distance L1 between the incident points of the radiant light beams becomes longer than a distance L2 between both ends of a noncircular contour part 11 at points where the radiant light beams are incided in the peripheral edge part of the wafer 10. In case any of the radiant light beams BR-1 and BR-2 is incided in the circular contour part of the wafer 10, it is reflected in the direction of a reflection angle thetaC equal to an angle of incidence thetaC. For this, separate and independent light-receiving devices 71 and 72 are respectively arranged in these paths. Accordingly, the reflected light beams are respective by detected by the light-receiving devices 71 and 72 and output of a significant quantity of converted electricity is produced, for example. |
