Patent ID: 6043502
Filing Date: 2000-03-28
Classification: H01L

Abstract:
An apparatus for sensing an insertion state of a wafer disposed in a slot of a wafer cassette, comprising:a stage supporting the wafer cassette;a light beam source positioned on one side of the wafer cassette;a photo-detector positioned on another side of the wafer cassette in a light path opposing the light beam source for receiving a light beam emanating from the light beam source, the photo-detector generating a position signal of a discrete level as long as it does not receive the beam of light from the light source, and the stage being movable relative to both the light beam source and the photo-detector;a timer operatively connected to said photo-detector so as to generate a pulse signal only after a predetermined time period has elapsed from a time when the position signal is generated; anda position determining mechanism operatively connected to said photo-detector and to said timer so as to receive said position signal and said pulse signal therefrom, respectively, said position determining mechanism generating a decision signal, indicative of a wafer being incorrectly loaded in the slot of the wafer cassette, when the pulse signal and the position signal are received simultaneously.