Temperature dependence of chemical states and band alignments in ultrathin HfO _xN _y/Si gate stacks

The chemical states and band alignments of HfO _xN _y 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, NSi, Si ₂=N-O and N-O bonds. The N-O bond is very unstable upon annealing as compared with the N-Hf, NSi and Si ₂=N-O bonds. The relationship between band alignments and chemical states in the HfO _xN _y/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 HfO _xN _y film, the energy-band alignments of the HfO _xN _y/Si stack as a function of post-deposition annealing were constructed.