JP2868645B

A wafer conveyor apparatus which moves a wafer moving device which moves wafers housed in a wafer cassette and performs conveyance the wafers, comprises a first arm provided with a light emitting device, a second arm provided with a light receiving device that detects light emitted from the light emitting device, and a wafer detector that has a judgment device for judging the presence or absence or a housing status of a wafer inside a wafer cassette on the basis of the output information of the light receiving device. In addition, the first arm provided to a conveyor platform and having the light emitting device provided at its distal end and the second arm provided to the conveyor platform and having the light receiving device provided at its distal end, are moved and positioned above and below an outside of an outer peripheral side of the wafer, and the first arm and the second arm are moved in a direction of the thickness of the wafer, light is irradiated from the light emitting device and the light is detected by the light receiving device to measure an apparent thickness of the wafer. Then, the apparent thickness of the wafer as obtained by measurement is compared with an actual thickness of the wafer and an inclination of a housed wafer is detected, and depending upon a detected inclination of the wafer, the wafer is either moved, the housing of the wafer corrected, or alarm processing is performed.