Effect of incorporated nitrogen on the band alignment of ultrathin silicon-oxynitride films as a function of the plasma nitridation conditions

The effects of plasma nitridation conditions, including substrate temperature (room temperature or high temperature) and plasma source gas (N₂ or NH₃), on the energy band characteristics and the chemical states of ultrathin SiON films was studied by using reflection electron energy loss spectroscopy (REELS) and X-ray photoelectron spectroscopy (XPS). The depth profile of nitrogen incorporated in the SiON films as a function of the above conditions was examined using mediumenergy ion scattering (MEIS). The decrease in the band gap caused by nitridation was enhanced to a greater extent at high substrate temperature and by using a N₂ plasma. The profile for N incorporation indicated that the change in band gap was directly related to the quantity of N in the SiON film. These characteristics are strongly related to the chemical state of the occupied N 2p state in SiON.