Fiducial-Filtering Automatic Wafer Centering Process and Associated System

A system for automatic wafer centering, comprising:

• an array of sensors, each sensor within the array of sensors configured to detect when an edge of a wafer passes by the sensor;
• and
• a controller configured to receive data indicating a position of a wafer handling component of a robot as the wafer handling component is moved with a wafer held on the wafer handling component, the controller configured to receive signals from the array of sensors as the wafer is moved through the array of sensors, the signals indicating when the edge of the wafer passes by a particular sensor of the array of sensors,
• the controller configured to determine a number (N) of detected wafer edge locations, each detected wafer edge location defined by a set of coordinates (x, y) in a coordinate system of the wafer handling component at which any sensor of the array of sensors detects the edge of the wafer,
• the controller configured to determine an estimated wafer offset that substantially minimizes a performance index value for each unique set of (N−1) of the number (N) of detected wafer edge locations, the estimated wafer offset defined as a vector extending from a center of the coordinate system of the wafer handling component to an estimated center location of the wafer, each unique set of (N−1) of the number (N) of detected wafer edge locations having a corresponding estimated wafer offset and a corresponding performance index value,
• the controller configured to identify a final wafer offset as the estimated wafer offset corresponding to the unique set of (N−1) of the number (N) of detected wafer edge locations that has a smallest corresponding performance index value,
• the controller configured to use the final wafer offset to direct the robot to center the wafer at a target station.

A method for automatic wafer centering, comprising:

• acquiring a number (N) of detected wafer edge locations, each detected wafer edge location defined by a set of coordinates (x, y) in a coordinate system of a wafer handling component;
• determining a minimized performance index value for each unique set of (N−1) of the number (N) of detected wafer edge locations, wherein the minimized performance index value has an associated estimated wafer offset that corresponds to a center of a circle that is best fit to a corresponding unique set of (N−1) of the number (N) of detected wafer edge locations within the coordinate system of the wafer handling component;
• determining a smallest minimized performance index value for the number (N) of detected wafer edge locations;
• and
• using the smallest minimized performance index value and its associated wafer offset to center the wafer at a target station.