Patent ID: 6772084
Filing Date: 2004-08-03
Classification: G01N,G03F

Abstract:
A method of obtaining overlay measurements for a semiconductor wafer, the method comprising:forming a periodic grating on the wafer having: a first set of gratings, wherein the first set of gratings are formed on the wafer using a first mask, and a second set of gratings, wherein the second set of gratings are formed on the wafer using a second mask, wherein the first and second sets of gratings are intended to be formed on the wafer with an intended asymmetrical alignment when the first mask and second mask are in alignment; selecting a wavelength; measuring a diffraction signal of the first and second sets of gratings after the first and second sets of gratings are formed on the wafer using the selected wavelength; and determining a misalignment between the first and second sets of gratings formed on the wafer based on the measured diffraction signal.