A study of highly c-axis oriented AlN films for diamond-based surface acoustic wave devices: Bulk structure and surface morphology

A systematic study on the optimisation of the sputtering deposition technique for AlN films on diamond substrates is presented. The dependence of the film quality has been analysed versus deposition temperature, for diamond substrates pre-treated with a reactive ion etching (RIE) process for a time duration between 0 and 4 min. These two parameters were found to be critical to obtain highly textured films with the c-axis perpendicular to the substrate surface and with a low surface roughness, as required by surface acoustic wave (SAW) applications. In particular, the RIE time was individuated to be crucial in defining the substrate-morphological quality, influencing, in turn, the films structure. The structural characterization of the films was performed by energy dispersive X-ray diffraction (EDXD) analysis and supported by further energy dispersive X-ray reflectometry (EDXR) morphological measurements. Indeed these non-conventional techniques, making use of a non-monochromatized X-ray radiation, are particularly suited when this kind of measurements are required.