Bias-voltage application in a hard x-ray photoelectron spectroscopic study of the interface states at oxide/Si(100) interfaces

The energy distribution of the interface states in the Si band-gap at an ultrathin oxide/Si(100) interface was investigated using a bias-voltage application in hard x-ray photoelectron spectroscopy. For the SiO₂/Si interface, interface states were observed near the mid-gap, whereas the interface states for the SiON/Si interface increased around the mid-gap and new states formed near the conduction band minimum (CBM) and valence band maximum (VBM) compared to the case of the SiO₂/Si interface. Moreover, the interface state density increased with the nitrogen concentration in the oxide, but the spectral shape was independent of the nitrogen concentration. The N1s spectra indicated that the N-O species at the SiON/Si interface induced inhomogeneous interface sites. Because inhomogeneity might break or weaken bonds at the SiON/Si interface, the density of broken bonds (the mid-gap states) and weakened bonds (the states near VBM and CBM) at the interface increased as the number of inhomogeneous sites increased.