Patent ID: 8025475

Claim:
A wafer transfer apparatus that transfers a wafer at least between a transfer chamber and at least one first chamber connected to the transfer chamber via a gate valve, said wafer transfer apparatus comprising: a transfer arm provided in the transfer chamber to load and unload the wafer to and from the first chamber; an aligner, having a rotary stage and an aligning sensor, configured to rotate the wafer by the rotary stage with the aligning sensor sensing a circumference of the wafer and so as to adjust an orientation of the wafer based on a sensing signal of the aligning sensor, before the transfer arm transfers the wafer from the transfer chamber to the first chamber: at least one wafer detection sensor provided to detect whether or not the wafer held by the transfer arm is passing across a light path of the detection sensor when the transfer arm moves to load the wafer into the first chamber, wherein one wafer detection sensor is provided for detecting passage of the wafer being loaded into each first chamber; position data acquiring means that acquires position data of the transfer arm based on an amount of driving of the transfer arm; a storage unit that stores reference position data corresponding to a reference position of the wafer mounted on the transfer arm; wafer diameter determining means that determines an actual diameter of the wafer based on a detection signal of the aligning sensor; and calculation means that determines, based on the position data acquired by the position data acquiring means and a result of judgment of the wafer detection sensor, position data of the transfer arm at a point of time at which the wafer starts passing across the light path of the wafer detection sensor, and position data of the transfer arm at a point of time at which the wafer completes passing across the light path, and then calculates an amount of positional deviation of a center of the wafer based on those position data of the transfer arm thus determined, the reference position data and the actual diameter of the wafer.