Correction of overlay offset between inspection layers in integrated circuits

A first method for determining the offset between the origins of the coordinate systems used for inspection of at least two different defect inspections of a wafer with integrated circuits disposed on it, comprises creating a database containing location data for defects disposed on at least two inspection layers of an integrated circuit wafer; defining maximum offsets for interlayer defects; defining minimum spacings for intralayer defects; for all defects having spacings larger than the minimum spacings searching the database for interlayer defect pairs having offsets smaller than the maximum offsets; calculating an actual offset for each interlayer defect pair; determining whether the actual offsets are randomly distributed; identifying dense zones for the actual offsets if they are not randomly distributed; and developing an estimate of the offset between the origins of the at least two layers and a confidence value for the estimate for said actual offsets. A second method comprises identifying from the database at least one die having a number of defects nd wherein 0