Decoupling inert and reactive gas supply to optimize ion beam sputter deposition apparatus for a more efficient material deposition

For all technologies, the energy-payback time (EPBT) serves as a critical metric. As an example, we study ion beam sputter deposition (IBSD), a sputter deposition approach where plasma, target, and substrate are decoupled. We compare three different configurations for reactive gas injection in order to demonstrate how the corresponding thin-film deposition processes can be improved, i.e., via the ion source, close to the target, or close to the substrate. The latter two decouple the introduction of inert and reactive gases, thus enabling substantial additional control in the deposition process. We investigate nickel oxide (NiOx) thin films as a versatile model system which is of interest for a wide range of applications. In the growth process, we vary growth times between 5 and 205 min and examine O2/Ar flow ratios between 0.13 and 5.82 for the different gas inlet configurations. Based on detailed structural and compositional analyses of the deposited thin films, we show that the deposition mode significantly influences crystal quality, growth rate, and surface roughness. Notably, the configuration where the reactive gas is injected close to the Ni target leads to significant improvement of the crystalline quality of the deposited NiOx layers for thicknesses of 30-200 nm. Furthermore, reactive gas injection close to the substrate yields films of comparable quality for thicknesses of 800 nm and above, but at almost twice the growth rate. These findings present a promising avenue for optimizing EPBT of IBSD by yielding better films in shorter process times and at less energy consumption. Yet, for low O2/Ar ratios the formation of a secondary phase of NiAl2O4 spinel is observed.