Determination of Band Alignment of Hafnium Silicon Oxynitride/Silicon (HfSiON/Si) Structures using Electron Spectroscopy

We investigated the band alignment of hafnium silicon oxynitride (HfSiON) on Si, using reflection electron energy loss spectroscopy (REELS) and X-ray electron spectroscopy (XPS). REELS was found to be effective for determining the bandgap energy of high- k materials. In HfSiON films, although the bandgap ( E g ), energy barrier of electrons (Δ E c ) and holes (Δ E v ) decreased abruptly at high nitrogen concentration, they retained values as large as 1 eV. The bandgap narrowing can be ascribed to Hf–N formation inside HfSiON films. We speculate that HfSiON films are formed by insulating trihafnium tetranitride (Hf 3 N 4 ) or its pseudo-alloy (Hf 3 N 4 ) x (HfO 2 ) 1- x as short-range order in the material, instead of forming conducting HfN.