Invited Paper Novel Chemistry For High Quality, Low Hydrogen PECVD Silicon Nitride Films

Abstract

We present a low temperature (<300°C) plasma deposition process to prepare novel fluorine-containing silicon nitride films (p-SiN:F1 using SiH4-NF-N2 discharge mixtures at 14 MHz RF applied frequency. The deposition rate can be extremely high, up to 1600 A/min. p-SiN:F has electrical properties (dielectric constant, breakdown strength, resistivity, etc.) which compare favorably with high temperature CVD silicon nitride. By controlling the feed chemistry and physical variables of the discharge, a wide variety of film compositions are achieved. Two classes of films were identified as stable or unstable to air exposure and the instability of the films correlated with the atom fraction of fluorine initially incorporated. The results obtained from IR, AES, and RBS measurements show that low hydrogen-containing films are produced by the introduction of fluorine in the silicon nitride films. More importantly, the concentration of Si-H is extremely low because strong Si-F bonding replaces relatively weak Si-H bonds that satisfy free Si orbitals in conventional plasma nitride, and the hydrogen remaining in the film is present as stable N-H bonds. We believe this substitution of silicon-bound hydrogen, caused by the gas phase and surface-driven reactions, is a reason for superior film properties. The mechanism for this novel discharge chemistry is discussed.