Assembly and characterization of a magnetron sputtering facing target for hydroxyapatite Thin Film Growth

Abstract

Due to its high biocompatibility, hydroxyapatite (HAp) is widely used as a coating for surgical, orthopaedic and dental implants in order to enhance implant biocompatibility and osseointegration. However, due to the structural complexity of HAp (Hydroxyapatite), Conventional coating techniques do not provide good uniformity, substrate adhesion, and control over stoichiometry, resulting in poor structural  quality. One of the techniques to obtain coatings with high crystallinity and uniformity is magnetron facing target sputtering (MFTS), also known as right angle magnetron sputtering (RAMS). In this article we describe the required conditions for the implementation of such a system. The arrangement of the targets, the distribution of the field lines, the determination of the working zone, the ionisation states of the elements due to the plasma and the oxygen/argon ratio in the chamber were studied to optimise the formation of HAp thin films. The field lines were computationally simulated to determine the working zone, which was found to be in a range of heights from 32 to 36 mm above the axial axis of the magnetrons. A power of 120 W in an atmosphere of Ar and O₂ with a ratio of 5 to 1 was used to generate the plasma. The plasma characterisation shows the ionisation states of the elements corresponding to the HAp, suggesting the complete decomposition of the HAp structure. Finally, using a high purity HAp target, a HAp film was grown. The film, after heat treatment, was characterised by X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The diffraction patterns indicate the formation of single-phase HAp, and the compositional analysis by EDS yielded a Ca/P ratio of 1.57 ± 0.071, which is close to the stoichiometric composition. this results confirm that it is feasible to produce HAp films of good structural quality using a facing target magneton sputering equipment.