Patent ID: 8069020

Claim:
A method of relating one or more process parameters of a process to dispersion for use in optical metrology of a structure formed on a semiconductor wafer, the dispersion characterizing optical properties of one or more materials of the structure, the structure having a profile, the profile having profile parameters, the method comprising: fabricating a first wafer using a first set of values for one or more process parameters specifying a process condition of the process in fabricating the structure; measuring a first value of a dispersion from the fabricated first wafer; fabricating a second wafer using a second set of values for the one or more process parameters; measuring a second value of the dispersion from the fabricated second wafer; fabricating a third wafer using a third set of values for the one or more process parameters, wherein the first, second, and third set of values for the one or more process parameters are different from each other; measuring a third value of the dispersion from the fabricated third wafer; defining a dispersion function to relate the one or more process parameters to the dispersion using the first, second, and third set of values for the one or more process parameter and the measured first, second, and third values of the dispersion; generating a simulated diffraction signal, which characterizes the behavior of light diffracted from the structure, using a value of the one or more process parameters, the defined dispersion function, and profile parameters; and storing the simulated diffraction signal; wherein the one or more process parameters are process conditions of the process, the process being a single step of semiconductor fabrication.