Patent ID: 8041450

Claim:
A semiconductor substrate processing apparatus, comprising: a substrate handling chamber; a first pair of position sensors each comprising: a light beam emitter configured to emit a beam of light; and a receiver configured to receive the light beam; and a substrate transfer robot within the handling chamber, the robot comprising: an elongated end effector having a distal end and a proximal end, the end effector configured to pick up and hold a semiconductor substrate at the distal end such that the substrate has a same expected position with respect to the end effector every time the substrate is picked up and held by the end effector; and a robot actuator configured to move the end effector within the handling chamber to transfer substrates among a plurality of substrate stations; wherein the end effector has a length such that it is possible for an edge of a substrate held in the expected position by the end effector to partially block a light beam emitted from the emitter of one of the position sensors, while the proximal end of the end effector partially blocks a light beam emitted from the emitter of the other position sensor.