The Identification and Suppression of Defects Responsible for Electrical Hysteresis in Metal-Nitride-Silicon Capacitors

An attempt was made to correlate the hysteresis in high frequency capacitance-voltage (C-V) measurements on metal-nitride-silicon (MNS) capacitors and spin density measured by electron spin resonance (ESR) spectrometry on a series of silicon-rich and nitrogen-rich silicon nitride films deposited by plasma enhanced chemical vapor deposition (PECVD). We found that the hysteresis Δ V H in the C-V characteristics can be divided into Δ V +, which corresponds to negative charge trapping, and Δ V -, which corresponds to positive charge trapping. A one-to-one correlation was found between Δ V + and the spin density attributed to the silicon dangling bond. However, Δ V - was nearly constant even though the spin density changed by two orders of magnitude. Nevertheless, Δ V - was found to be significantly reduced by an ammonia plasma treatment of the silicon substrate before the silicon nitride deposition. These observations support the hypothesis that besides the silicon dangling bond, which can be suppressed by using nitrogen-rich films instead of silicon-rich films, there is another important type of defect probably at the nitride-silicon interface, which can be suppressed by an appropriate ammonia plasma treatment.