To provide a highly sensitive spectroscopic scatterometer.

Before the diffraction from a diffracting structure on a semiconductor wafer, if necessary, the film thickness and the index of refraction of films located under the structure are first measured using a spectroscopic reflectometer or spectroscopic ellipsometer. A rigorous model is then used to calculate intensity or ellipsometric signatures of the diffracting structure. The diffracting structure is then measured using a spectroscopic scatterometer using polarized and broadband radiation to obtain the intensity or ellipsometric signatures of the diffracting structure. The signatures are then matched with the signatures in the database to determine the grating shape parameters of the structure.