Tunable ion flux density and its impact on AlN thin films deposited in a confocal DC magnetron sputtering system

An in-situ coil implemented in a confocal magnetron sputtering system is used to modify the ion flux impacting the substrate, thereby tuning the ion-to-neutral ratio. Plasma characterization performed at the substrate is used to map the spatial dependence of the ion flux density and the total energy flux density across the substrate holder. In addition, spatially-resolved temperature measurements are performed for different plasma conditions. Aluminum nitride (AlN) thin films were deposited by reactive sputtering in the fully poisoned mode on Si (100) and borosilicate glass substrates using the open field configuration. Texture, growth morphology, and residual stress of the films were determined and correlated with the plasma conditions and substrate temperatures obtained by applying the coil's magnetic field. All AlN films were stoichiometric and showed a hexagonal structure with (001) texture. The film stress was found to change from 0.9 GPa (tensile) to 4 GPa (compressive) with increasing ion flux density. Electron microscopy revealed an evolution from an open grain boundary to a dense film morphology compatible with the observed residual stress dependence of the films on the ion flux. No change in residual stress and film morphology was observed within the 100 °C-500 °C temperature range used here.