Study of the influence of oxygen on the composition of thin films obtained by r.f. sputtering from a Ca5(PO4)3OH target

In this paper we present a study of the influence of the presence of oxygen during sputter deposition on the properties of the films obtained from a Ca₅(PO₄)₃OH (HA) target. The films were characterised using X-ray diffraction, Fourier transform infrared spectroscopy and profilometer measurements. The composition of the deposited films was obtained by Rutherford backscattering spectrometry measurements. We found that an increase of the oxygen pressure resulted in a strong reduction of the growth rate of the films. Also a better stoichiometry of the films with respect to HA was obtained by intentional introduction of oxygen in the sputtering gas. Furthermore, we have shown that the average Ca/P ratio increases to a higher value than the Ca/P ratio of the target, with increasing film thickness and with increasing external negative bias on the substrate.