PLASMA-DEPOSITED SILICON-NITRIDE ON ULTRATHIN SILICON-OXIDE FILMS INVESTIGATED BY INFRARED GRAZING INTERNAL-REFLECTION SPECTROSCOPY

Ultrathin silicon nitride films of 0.4-4.0 nm thickness prepared by remote plasma-enhanced chemical-vapor deposition (RPECVD) and direct plasma-enhanced CVD (DPECVD), respectively, are investigated by infrared grazing internal reflection spectroscopy. The ultrathin silicon nitride films are deposited on top of a 1.3 nm silicon oxide film thermally grown on crystalline silicon. From the spectra it is concluded that the vibrational properties of the 1.3 nm silicon oxide layer have strongly changed after deposition of a thin DPECVD silicon nitride film. The infrared spectra are analyzes by simulating the measured spectra with a dielectric function model that accounts for the amorphous film structure. An analytic formula for this dielectric function model is derived.