Patent ID: 7526749
Filing Date: 2009-04-28
Classification: G03F,H01L

Abstract:
1. A method for generating a calibration curve for use in an overlay measurement, the method comprising: printing a first array of targets on a wafer; calculating a target asymmetry parameter value for each of the targets in the array of targets; generating a first calibration curve including the calculated target asymmetry parameter values, wherein a center of symmetry of the first calibration curve corresponds to a zero overlay; printing a second array of targets on a wafer, wherein a-pitch of the first array of targets is different from a pitch of the second array of targets; generating a second calibration curve including the calculated target asymmetry parameter values for the second array of targets, wherein a center of symmetry of the second calibration curve corresponds to a zero overlay; measuring a distance between the respective centers of symmetry for the first and second calibration curves; and calculating an overlay value based on the distance between the respective centers of symmetry of the first and second calibration curves and a ratio of pitch difference between the first and the second arrays of targets to either the first or the second array pitch.