Method for correcting position measurements for optical errors and method for determining mask writer errors

Abstract

A method for correcting optical errors occurring in coordinates of positions of a plurality of targets measured via an imaging system comprising a field of view. The plurality of targets includes a first array of targets and a second array of targets overlapping the first array of targets, and a portion of the plurality of targets are outside of the field of view. The method broadly includes the following steps: a) placing the first array of targets in the field of view of the imaging system; b) measuring coordinates of each target within the first array of targets repeatedly via the imaging system; c) placing the second array of targets in the field of view of the imaging system; d) measuring coordinates of each target within the second array of targets repeatedly via the imaging system; e) determining an alignment function from the measurement results of step b, step d, or steps b and d, the alignment function being a function of coordinates of the field of view of the imaging system and giving an additive correction for optical errors of the coordinates of positions of the plurality of targets measured by the imaging system; f) correcting the coordinates of the positions of the plurality of targets measured by the imaging system by adding the respective value of the alignment function at the field-of-view coordinates at which the coordinates of the position of the respective target were measured; and, g) obtaining a final result for the position of each target of the plurality of targets by averaging over the corrected coordinates found in step f for the respective target at each relative position of the plurality of targets and field of view of the imaging system.