Method and system for evaluating an object that has a repetitive pattern

摘要

A method for evaluating placement errors within a lithographic mask, the method includes: providing or receiving a reference result that represents a distance between a reference pair of points of a reference element; measuring, for each pair of points out of multiple pairs of points that are associated with multiple spaced apart elements of the lithographic mask, the distance between the pair of points to provide multiple measurement results; wherein differences between a measurement result and the reference result are indicative of relative placement errors; and determining relative placement errors in response to relationships between the reference result and each of the measurement results.