A computer-implemented method for determining optical roughness in a semiconductor pattern structure that includes receiving, using a processor, optical responses spectra collected from the semiconductor pattern structure and constructing, using the processor optical critical dimension (OCD) models by using a set of input parameters for each layer of the semiconductor pattern structure. The method further includes calculating, using the processor, theoretical optical responses from a theoretical input generated by the OCD models. In addition, the method provides for comparing, using the processor, the optical responses spectra of the semiconductor pattern structure to the theoretical optical responses to determine output parameters for the optical roughness of the semiconductor pattern structure.