Workpiece alignment structure and method

DETAILED DESCRIPTION In accordance with one embodiment of this invention, in a wafer processing apparatus 30 (see FIG.
3) the wafers enter via entry chamber 31A, are transported by a robot arm 14 to various process chambers 31B, 31C, 31D, 31E and exit via exit chamber 31F.
A sensor array 32A (including sensors 42A, 42B, 42C and 42D) in central chamber 33 of apparatus 30 is used to determine the initial geometric center of a wafer 22 while wafer 22 is stationary on robot arm 14.
After the wafer's initial position is determined, an aligner 34A is used to correct any eccentricity (due to an initial shift) of wafer 22.
The eccentricity is corrected by aligner 34A in a single movement of wafer 22.
Optionally after wafer 22 is brought to its centered position, any angular misalignment of wafer 22's characteristic edge shape feature (typically a "flat" portion of the wafer's circular circumference) can also be corrected using limited rotational movement.
After correction of initial shift at aligner 34A, wafer 22 is transferred to the process chamber 31B by robot arm 14 via a handout.
After processing is completed in chamber 31B, wafer 22 is picked up by robot arm 14 in another handout.
Process shifts in the wafer's position due to handouts such as the ones in chamber 31B are detected at sensor array 32B (including sensors 42A1, 42B1, 42C1 and 42D1) and if necessary, corrected by wafer aligner 34B.
Sensor array 22B allows the position of wafer 22 to be determined after each handout from the chambers 31B through 31E in the central chamber 33.
If desired, the position of wafer 22 can be determined using sensor array 32B after wafer 22 is removed from selected ones of chambers 31B through 31E rather than from all of these chambers.
The location of sensor array 32B and wafer aligner 34B is shown outside chamber 31C.
Sensor array 32B and corresponding wafer aligner 34B can be placed outside whichever chamber 31B through 31E requires determination of the location of the wafer 22 most often.
This chamber 31X would be the chamber where the likelihood of a process shift in the position of wafer 22 is highest