Effect of metal work function on conduction current in silicon nitride films after exposure to ultraviolet illumination

Abstract

We investigated the influence of the work function of metal gate electrodes on the current component induced by exposing silicon nitride-silicon oxide double-layer films to high-energy ultraviolet (UV) illumination. Prior to UV exposure, the conduction current under negative gate bias through an aluminum-nitride-oxide-silicon structure was larger than that through a mercury-nitride-oxide-silicon structure. In these structures under negative gate bias, it has been considered that electrons injected from the metal electrodes into the nitride films dominate the conduction current. Hence, the experimental result can be explained by the notion that the probability of electron injection into the nitride film from the aluminum electrode is higher than that from the mercury electrode because of the difference of the work function between the two kinds of metals. After UV exposure, the conduction current under negative gate bias through both the structures were almost identical to each other. This result reveals that the current component after exposure to UV illumination is dominated by charge carriers generated in the bulk of the nitride film.