Influence of Ar pressure on r.f. magnetron-sputtered Ca5(PO4)3OH layers

Currently. medical and dental implants are often provided with thin calcium phosphate ceramic coatings (preferably Ca₅(PO₄)₃OH (HA)) to improve their biological behaviour. Previous studies have demonstrated that ratio-frequency (r.f.) magnetron sputtering is a suitable technique for depositing such thin Ca-PO layers. Although X-ray diffraction showed that the deposited film had an HA structure, the Ca/P ratio of the layers was higher than the theoretical value of 1.67 for HA. In the present study the influence of the argon pressure and input power on the structure and chemical composition of the sputtered layers, especially the Ca/P ratio, is investigated. Rutherford backscattering spectrometry (RBS), stylus profilometer (alpha-step), X-ray diffraction spectrometry (XRD)), and IR spectrometry (FTIR) were used to characterise the coatings. Although the Ca/P ratio became lower when sputtered at lower input power, it was still higher than the value of 1.67 for HA. The density measured for the films sputtered at 200 and 400 W did not show a simple relation with the argon pressure. For all the films after annealing XRD and FTIR showed an HA-like structure and HA bonds. However, the OH bond appeared to be dependent on the partial pressure of water vapour during sputtering.