Patent Document ID: 9869543
Application ID: 14184295
Patent Flag: 1

Claim One:
1. A method of reducing algorithmic inaccuracy in scatterometry overlay (SCOL) metrology, comprising: designing a SCOL target on a sample, the SCOL target including two or more cells, comprising: at least one first segmented target structure on a first layer of the sample segmented with a coarse pitch and a first fine pitch; and at least one second segmented target structure on a second layer of the sample segmented with the coarse pitch and a second fine pitch, wherein the two or more cells include two or more predetermined offsets between the corresponding at least one first segmented target structure and the at least one second segmented target structure, wherein an overlay signal associated with measured diffraction modes from the two or more cells is indicative of an overlay offset between the first layer and the second layer of the sample, wherein the overlay signal is a periodic function of the overlay offset and is represented by a sum of oscillatory frequencies of different orders; selecting the values of the coarse pitch, the first fine pitch, and the second fine pitch to limit, within a specified inaccuracy requirement, an algorithmic error in determining the overlay offset by limiting oscillation frequencies having an order higher than a predetermined cutoff order; providing the designed SCOL target on the sample; measuring one or more diffraction modes from the two or more cells of the SCOL target with a detector to generate the overlay signal; calculating a value of the overlay offset based on the measured overlay signal; correcting for the algorithmic error associated with oscillation frequencies of the overlay signal higher than a predetermined cutoff order; and updating the value of the overlay offset based on the correction.