Wafer position error detection and correction system

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention detect wafer positions as wafers are transported within a semiconductor processing equipment and compensate for wafer misalignments when the wafers are not at or very near their nominal position on the wafer transport robot.
The wafer position error detection and correction system of the present invention preferably determines the error in wafer position and compensates for this error by adjusting the linear and rotational position of the wafer transport robot.
Positional adjustments are made so that the wafer transport robot will transport the wafer to its nominal position either within the wafer storage elevator or within the designated wafer processing chamber.
In a preferred embodiment of the present invention, the wafer position is detected when the wafer is removed from a process chamber or from a wafer cassette.
Wafer positions with respect to the robot blade are preferably detected by determining the position of the wafer when an edge of a slot in the robot blade and an edge of the wafer crosses an optical beam path during retraction of the wafer from either a processing chamber or a wafer cassette.
Positional information derived from these wafer position data points may be compared with predetermined, nominal positional information to determine the extent of the wafer misalignment.
This error information is preferably converted into an error component, and the linear extension and rotational displacement of the wafer transport robot are adjusted accordingly to compensate for the misalignment.
FIG.
1A shows a plan view of a wafer processing system which may accommodate the wafer position error detection and correction system of the present invention.
The wafer processing system of FIG.
1A consists of a number of individual process chambers 6 that can be isolated by closing slit valves 8.
Wafers 10, for example eight inch silicon wafers, undergo a variety of processing steps within the various processing chambers 6