Patent ID: 7072049

Claim:
A method of modeling wafer structure profile, the method comprising: a) determining one or more termination criteria; b) determining whether a wafer structure includes at least one layer having three or more materials along a line within the at least one layer; c) creating an optical metrology model, wherein three or more materials are incorporated in the model of the at least one layer having three or more materials; d) obtaining a set of diffraction signals converted from a set of diffraction beams measured off of the wafer; e) simulating a set of diffraction signals using the optical metrology model; f) determining if the one or more termination criteria are met by using the set of simulated diffraction signals and the set of diffraction signals converted from the set of diffraction beams measured off of the wafer; and g) if the one or more termination criteria are not met, modifying the optical metrology model and repeating steps e) and f) until the one or more termination criteria are met.