Patent ID: 7523021

Claim:
A method of obtaining a weighting function to enhance measured diffraction signals used in optical metrology, the method comprising: obtaining a set of measured diffraction signals, wherein the set of measured diffraction signal was measured from a single site on a wafer using a photometric device; defining a first weighting function based on noise that exists in the measured diffraction signal, wherein defining the first weighting function comprises: generating a noise profile based on the set of measured diffraction signals; defining a noise envelope based on the noise profile; and defining the first weighting function based on the noise envelope; defining a second weighting function based on accuracy of the measured diffraction signal; defining a third weighting function based on sensitivity of the measured diffraction signal; defining a fourth weighting function based on one or more of the first, second, and third weighting functions; and generating an enhanced measured diffraction signal by multiplying another measured diffraction signal and a fifth weighting function, wherein the fifth weighting function is defined using the first weighting function, second weighting function, third weighting function, or fourth weighting function, and wherein the enhanced measured diffraction signal is used to determine a characteristic of a feature on a wafer using optical metrology.