Patent ID: 7330279

Claim:
A method of selecting a profile model and selecting parameters of the profile model for use in optical metrology of structures in a wafer, the method comprising: a) setting one or more termination criteria; b) setting one or more parameter selection criteria; c) selecting a profile model for use in optical metrology of a structure in a wafer, the profile model having a set of geometric parameters associated with dimensions of the structure; d) selecting a set of optimization parameters for the profile model using one or more input measured diffraction signals and the one or more parameter selection criteria, wherein the set of optimization parameters is converted from the set of geometric parameters, and wherein the number of optimization parameters within the set of optimization parameters is less than the number of geometric parameters within the set of geometric parameters; e) testing the selected profile model and the set of optimization parameters against the one or more termination criteria; and f) performing the steps c, d, and e until the one or more termination criteria are met.