Growth optimization of non-polar Al0.7Sc0.3N(1120)/Al2O3(1102) thin films using reactive magnetron sputter epitaxy

A-plane Al0.7Sc0.3N(1120) thin films are grown on r-plane Al2O3(1102) substrates using reactive pulsed-DC magnetron sputter epitaxy. This is the first report of successful synthesis of non-polar epitaxial AlScN films with a high scandium concentration (30%). The influence of different sputtering conditions, such as magnetron power, temperature, and process gas flow rates are investigated. The film characteristics is also compared on different substrate off-cuts. Controlling the diffusion of adatoms on surface of the substrate is found to have the highest influence on film quality. The X-ray diffraction measurements confirm in-plane oriented AlScN(1120) layers and the final optimized films show significant improvement in rocking curve full width at half maximum (ω-FWHM) of (1120) reflection. Corresponding atomic force microscopy (AFM) measurements show mean root square surface roughness (Rq < 0.4 nm) nearing atomically smooth levels. The optimized films also exhibit anisotropic growth characteristics. A growth model for a-plane AlScN has been proposed based on the growth parameters of the film.