Patent ID: 7465590

Claim:
A method comprising: performing a first measurement of a sample having at least a first layer and a second layer that is under the first layer; processing the sample to at least partially remove the first layer; performing a second measurement of the sample after processing; modeling the sample with a first pair of linked models, the first pair of linked models comprising a first model of the pre-processed sample and a second model of the post-processed sample, wherein the first layer of the first model and the first layer of the second model are independent variables and the second layer of the first model and the second layer of the second model are constrained to have the same parameters; modeling the sample with a second pair of linked models, the second pair of linked models comprising a third model of the pre-processed sample and a fourth model of the post-processed sample, wherein the first layer of the third model is an independent variable, the first layer of the fourth model has a thickness of zero, the second layer of the third model and the second layer of the fourth model are independent variables; using the first measurement, the second measurement, the first model, the second model, the third model, and the fourth model to determine at least one desired parameter of the post-processed sample; and reporting the results of the determined at least one desired parameter of the post-processed sample.