Characterization of thin-film amorphous semiconductors using spectroscopicellipsometry

Spectroscopic ellipsometry (SE) has been used to routinely characterize amo rphous silicon nitride and diamond thin films. Since SE measurements do not yield quantities of interest directly, the SE data must first be fit to a model to obtain useful parameters such as film thickness and optical functi ons. The Tauc-Lorentz (TL) model for the optical functions of amorphous mat erials [Appl. Phys. Lett. 69, 371/373, 2137 (1996)] has been shown to be ve ry useful in interpreting these SE results. A four-parameter model is usual ly sufficient to describe the optical functions of the thin film to the acc uracy of the ellipsometer. One of these parameters, the band gap E-g, corre lates with other mechanical and chemical properties of the film, such as th e silicon-to-nitrogen ratio in silicon nitride films, and to the sp(3)-bond ed carbon fraction and the hardness of amorphous carbon films. (C) 2000 Els evier Science B.V. All rights reserved.