Synthesis of hafnium nitride films by 0.5–5 keV nitrogen implantation of metallic Hf: an X-ray photoelectron spectroscopy and factor analysis study

Hafnium nitride thin films have been grown by “in situ” nitrogen implantation of metallic hafnium at room temperature over the energy range of 0.5–5 keV. X-ray photoelectron spectroscopy (XPS) and factor analysis (FA) have been used to characterise the chemical composition of the films. By means of FA of the Hf 4f and N 1s XPS core level peaks, comprising principal component analysis (PCA) and iterative target transformation factor analysis (ITTFA), the number and spectral shape of the different Hf–N phases formed during nitrogen implantation, as well as their concentrations, have been obtained without any prior assumptions. FA results show that the composition of the hafnium nitride films depends on both the ion fluence and ion energy, the formation of the superstoichiometric Hf3N4 phase being limited by the ion beam energy. For ion beam energies, Ep⩾2 keV, the hafnium nitride films formed are a mixture of metallic hafnium, a substoichiometric hafnium nitride that could be associated with the trigonal ε-Hf3N2 and/or ξ-Hf4N3 phases, and the stoichiometric HfN phase. In addition, for Ep<2 keV, the superstoichiometric Hf3N4 phase is also present in the films for higher ion doses. Comparison of the experimental nitrogen concentration obtained by FA with that obtained from TRIDYN simulations suggests that in addition to nitrogen implantation and atomic mixing, other mechanisms like ion beam enhanced diffusion or the chemical reactivity of the Hf substrate towards nitrogen should be also taken into account.