Patent ID: 7515282

Claim:
A method of modeling a profile of a structure having a region with a spatially varying property using an optical metrology model, wherein the optical metrology model is to be used to determine the profile of the structure using optical metrology when the structure is formed on a wafer, the method comprising: defining a set of profile parameters for the optical metrology model to characterize the profile of the structure; defining a set of layers for a portion of the optical metrology model that corresponds to the substrate region of the structure with the spatially varying property, wherein the spatially varying property is a property of the substrate region, each layer having a defined height and width; for each layer, defining a mathematic function that varies across at least a portion of the width of the layer to characterize the spatially varying property within a corresponding layer in the substrate region of the structure, wherein the mathematical function characterizes the variation of the spatially varying property in a first direction and a second direction within the corresponding layer in the substrate region of the structure, and wherein the first and second directions are perpendicular; defining the optical metrology model using the mathematical function; and storing the optical metrology model.