Non-stoichiometry effects in the XPS spectra of HfN films

Abstract XPS spectra for HfN x films made by bias magnetron sputtering are reported over the range x from 0.64 to 1.11. They indicate that the valence band comprises a shoulder immediately below the Fermi level E F and a peak at some 6 eV below it for all compositions x, due to the Hf 5d and 2p bands respectively. At compositions of HfN 0.80 and above, the following effects were found in the core levels as x was increased: the intensity of the Hf 4f 5 2 appeared to increase, relative to the Hf 4f 7 2 , due to the development of the N 2s below it. The binding energy of all hafnium levels increases whereas the N 1s remains invariant. The decrease in the relative binding energy is presumed to be due to increasing ionicity of the bonding. The data also appear to indicate that the additional lattice defects present in the films over and above those resulting from the substoichiometry do not affect the spectra. Below HfN 0.75 the core level data indicate a marked increase in ionicity which could be associated with a change in the behavior of the lattice parameters. This change is thought to be caused by the ordering of vacancies on the nitrogen sublattice.