Noise-reduction metrology models

A system for using Noise-Reduced (N-R) data to examine a semiconductor wafer, the system comprising:

• a wafer alignment means configured for aligning a reference wafer in a first metrology tool, the reference wafer having a first target structure at a first site, the wafer alignment means comprising a platform subsystem, an alignment subsystem coupled to the platform subsystem, and an alignment sensor coupled to the alignment subsystem;
• one or more collection subsystems configured for 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;
• and
• a controller configured for 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, for obtaining simulation data for the reference wafer, the simulation data having simulated accuracy data associated therewith, for 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 for identifying the first target structure using the simulation data when the first accuracy data is not more accurate than the simulated accuracy data.

A non-transitory computer-readable medium containing computer-executable instructions for performing a Noise-Reduction (N-R) procedure, the method comprising instructions for:

• aligning a reference wafer in a first metrology tool, the reference wafer comprising 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.