Temperature dependence of chemical states and band alignments in ultrathin HfOxNy/Si gate stacks

Abstract

The chemical states and band alignments of HfOxNy films on Si substrates as a function of post-thermal treatment were systematically investigated. Analysis of N1s spectra reveals that there are four components in N chemical states, which are assigned to the N–Hf, N ≡ Si, Si2 = N–O and N–O bonds. The N–O bond is very unstable upon annealing as compared with the N–Hf, N ≡ Si and Si2 = N–O bonds. The relationship between band alignments and chemical states in the HfOxNy/Si stack upon annealing is also studied. It is found that the conduction-band offset shows no obvious change upon annealing, while the band gap and the valence-band offset increase with the increase in the annealing temperature, which is mainly due to the reduction in the N–O bond during the annealing process. With the values of band gap and band offsets of the HfOxNy film, the energy-band alignments of the HfOxNy/Si stack as a function of post-deposition annealing were constructed.