Patent ID: 8442659

Claim:
A wafer treatment apparatus comprising: a plurality of upwardly opening tanks; a robot operable to move a wafer cassette from one tank to another tank; the robot comprising a first support, a carriage slidably mounted to the first support for upward and downward motion, an upright shaft rotatably coupled to the carriage for pivoting about a longitudinal axis of the shaft and relative to the carriage between plural positions, the shaft being supported by the carriage for upward and downward movement with the upward and downward motion of the carriage, a shaft elevator coupled to the carriage and operable to raise and lower the carriage to thereby raise and lower the shaft, a shaft rotator coupled to the shaft and operable to pivot the shaft from one position to another position, a cassette support arm coupled to an upper end portion of the shaft and a wafer cassette holder carried by the cassette support arm and projecting downwardly from the wafer cassette arm at a location spaced from the shaft; the robot also comprising a shaft position sensor, the shaft position sensor comprising a target with a target surface mounted to the shaft and a sensor spaced from the target surface and operable to provide at least one analog output signal corresponding to the distance from the target surface to the sensor, the target being configured to vary the distance from the target surface to the sensor depending upon the rotational position of the shaft such that the at least one analog output signal also corresponds to the rotational position of the shaft; a controller comprising a first input coupled to the sensor for receiving a signal corresponding to the at least one analog output signal and a command input for receiving a command signal indicating a rotational position to which the shaft is to be moved, the controller being coupled to the shaft elevator so as to cause the shaft elevator to move the carriage upwardly to raise the shaft upwardly, to raise the cassette support arm upwardly, and to raise the cassette holder upwardly to lift a cassette supported by the cassette holder upwardly to a position above a first of said tanks from which the cassette holder can be pivoted from a first location above the first tank to the rotational position indicated by the command signal, the shaft rotator being responsive to a signal corresponding to the command signal to pivot the shaft to the rotational position indicated by the command signal; wherein if the rotational position indicated by the command signal is above a second tank into which the cassette is to be immersed to treat wafers supported by the cassette holder, the controller is operable to control the shaft elevator to lower the carriage such that a cassette supported by the cassette holder is lowered into the second tank.