Abstract: A method for characterizing line width roughness of printed features is provided. A wafer having thereon a plurality of gratings formed within a test key region is prepared. The wafer is transferred to a spectroscopic ellipsometry tool having a light source, a detector and a computer. A polarized light beam emanated from the light source is directed onto the gratings. Spectrum data of reflected light is measured and recorded. The spectrum data is compared to a library linked to the computer in real time. The library contains a plurality of contact-hole model based spectra created by incorporating parameter values that describes the line width roughness. The spectrum data is matched with the contact-hole model based spectra, thereby determining the parameter values.