Electrical characterization of n-channel MOSFETs with oxynitride gate dielectric formed by Low-Pressure Rapid Thermal Chemical Vapor Deposition

Abstract

This study reports on n-channel MOS transistors using very thin oxynitride gate dielectrics deposited by Low-Pressure Rapid Thermal Chemiical Vapor Deposition (LPRTCVD). The threshold voltage, the transconductance, the fast and slow trap densities, the low field mobility and its reduction factors have been investigated as a function of the nitrogen concentration in the film. The threshold voltage was found to decrease linearly with the nitrogen concentration, primarily because of the increase of the positive insulator charge density. At the same time, it has been shown that the quadratic mobility reduction factor is lower for a LPRTCVD oxynitride (and nearly constant with the nitrogen concentration) in comparison to a thermal oxide. From this high field mobility attenuation, a lower transconductance is then expected for oxynitride-based transistors. Finally, we have shown that the presence of nitrogen in the oxide seems to induce more donor than acceptor traps at the oxynitride-silicon interface.