  Ternary transition metal nitride coatings are promising for many applications
as they can offer improved hardness and oxidation resistance compared to binary
counterparts. A common challenge in the deposition of functional nitride thin
films is oxygen contamination. Even low amounts of oxygen contamination can
adversely affect the functional properties of the thin films. Here, we present
a practical approach for the growth of virtually oxygen-free (Ti, Zr)N thin
films. To cover the complete compositional range of (Ti,Zr)N coatings we employ
combinatorial reactive co-sputtering. The depositions are carried out with or
without applying a low-power radio-frequency (RF) bias voltage to the substrate
holder to study the possibility of decelerating energetic oxygen ions and
effectively reducing oxygen contamination in the growing film. High-throughput
structural analysis and functional property mapping are used to elucidate the
synthesis-property relationships. The structural analysis indicates solid
solution formation over the entire compositional range, as evidenced by
Vegardian lattice scaling, regardless of the applied RF substrate bias.
Irrespective of the composition of the films, the application of RF substrate
bias leads to a dramatic reduction of oxygen contamination, as demonstrated by
X-ray photoelectron spectroscopy (XPS) depth-profile mapping. This is reflected
in a significant improvement in the films' conductivity and hardness. We
demonstrate that the reduction in oxygen contamination is intrinsic to the
process and not due to changes in the microstructure. The approach presented
here is applicable to both conductive and insulating substrates and provides a
practical route to synthesize nitride thin films with improved purity that can
be applied in standard sputter chambers and on many different material systems.
