Ellipsometric Method for the Determination of All the Optical Parameters of the System of an Isotropic Nonabsorbing Film on an Isotropic Absorbing Substrate Optical Constants of Silicon*

Abstract

From a series of ellipsometric measurements it is now possible to obtain uniquely all of the optical parameters of the system; absorbing substrate+nonabsorbing surface film. The method utilizes the fact that the reflectance of such a system at normal incidence remains essentially constant for a small but finite range of surface-film thicknesses. Furthermore, it hinges on the fact that the ellipsometric parameters Δ and ψ, measured on different film thicknesses grown on the same sample, are compatible with only one choice of the complex refractive index n2+ik2 of the substrate and the refractive index n1 of the film. Measurements on chemically etched samples of silicon yield n2 = 4.052 and k2 = 0.029, in agreement with the results of earlier workers. Measurements on cleaved samples of silicon, on the other hand, reveal that the true values are n2 = 4.140±0.02 and k2 = 0.034±0.01 for 5461 Å.