Wafer positioning apparatus

DETAILED DESCRIPTION Accordingly, a general object of the present invention is to provide a wafer positioning apparatus in which the disadvantages of prior such apparatus are eliminated.
A more specific object of the present invention is to provide a compact wafer positioning apparatus.
Another object of the present invention is to provide a wafer positioning apparatus in which the wafer can be positioned without detecting the orientation flat portion thereof.
Therefore, the apparatus is not limited in use to a particular type of wafer.
The above objects of the present invention are achieved by a wafer positioning apparatus which includes first, second and third optical position detectors for detecting a circumference portion of a wafer, the first to third optical position detectors being arranged on a circumference of a circle having a diameter identical to that of the wafer, a transportation robot for holding the waver and moving the held wafer with respect to the first to third optical position detectors, and a control circuit for controlling the transportation robot in accordance with output signals of the first to third optical position detectors so that all of the first to third optical position detectors detect the circumference portion of the wafer at the same time.
It is preferable to provide a fourth optical position detector for detecting the circumference portion of the wafer.
The fourth optical position detector is arranged on the circumference of the circle having the diameter identical to that of the wafer.
The use of the four optical position detectors makes it possible to correctly position the wafer irrespective of the position of an orientation flat portion of the wafer.
Other objects, features and advantages of the present invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings.