In the manufacture of semiconductor devices, it is of critical importance to know the thickness and material properties of various dielectric and semiconducting thin films. Although there are many techniques for measuring these films, the most commonly used are reflection spectrophotometry [1,2] and ellipsometry [3]. In the former method, the normal- incidence reflectivity is measured as a function of wavelength. The shape of the reflectivity spectrum is then analyzed using the Fresnel equations to determine the thickness of the film. In some cases, the refractive index can also be determined provided that the dispersion of the optical constants are well known. The latter method consists of reflecting a beam of known polarization off the sample surface at an oblique angle. The film thickness, and in some cases the refractive index, can be determined from the change in polarization experienced upon reflection.