Patent ID: 6795202
Filing Date: 2004-09-21
Classification: H01L

Abstract:
A wafer processing apparatus adapted to detect a wafer on each shelf of a rack having shelves on which wafers can be placed provided in a pod, the wafer processing apparatus comprising:moving means that can be moved along said shelves of the rack by driving means; a first transmissive sensor movable along the shelves of said rack by said moving means and including a first emitter and a first detector that are disposed in such a way as to be opposed to each other, said first emitter and said first detector being arranged in such a way that when said first transmissive sensor is moved along the shelves of the rack, in the case that a wafer is present on a shelf of the rack, light emitted from said first emitter toward said first detector is blocked by the wafer, and in the case that a wafer is not present on a shelf, light emitted from said first emitter is allowed to pass to said first detector; a second transmissive sensor including a second emitter and a second detector opposed to said second emitter, said second transmissive sensor being movable along the shelves of said rack with said moving means; a dog disposed between said second emitter and said second detector and having index means that can pass or block light emitted from said second emitter toward said second detector when said second transmissive sensor is moved along the shelves of said rack; and a computing means for performing determination of the number of the wafer(s) placed on a shelf of said rack by comparing a wafer thickness obtained by calculating a ratio of duration time of a first signal from said first transmissive sensor corresponding to the wafer(s) and duration time of a second signal from said second sensor corresponding to said index means and a threshold value that has been set in advance in accordance with the wafer thickness and the number of wafers.