Patent ID: 7742177

Claim:
A method of processing a wafer comprising: aligning a reference wafer in a first metrology tool, the reference wafer having a first target structure at a first site; obtaining a first set of measured diffraction signals, each measured diffraction signal being measured from the first site on the reference wafer using a first set of sensor pixels in a first sensor; performing a first noise-reduction procedure to generate first noise-reduced data for the first sensor based on the first set of measured diffraction signals, the first noise-reduced data having first accuracy data associated therewith; obtaining simulation data for the reference wafer, the simulation data having simulated accuracy data associated therewith; identifying the first target structure using the first noise-reduced data when the first accuracy data is more accurate than the simulated accuracy data; and identifying the first target structure using the simulation data when the first accuracy data is not more accurate than the simulated accuracy data.