Reducing the oxygen contamination in conductive (Ti,Zr)N coatings via RF-bias assisted reactive sputtering

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, especially hardness and electrical properties. 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 compositional gradients are complemented by orthogonal deposition temperature gradients to cover broad regions of the synthesis phase diagram. 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 in large regions of the synthesis phase diagram. 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 as well as hardness. We demonstrate that the reduction in oxygen contamination is rather intrinsic to the process as well as due to changes in the microstructure, which also lead to varying oxidation resistance in ambient conditions. 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. • A practical approach to improve the phase-purity of sputter deposited transition metal nitrides is presented. • Applying a low-energy RF substrate potential during sputtering dramatically reduces the bulk‑oxygen contamination in TiN and ZrN as demonstrated by UHV-transfer XPS investigations. • A combinatorial screening in the (Ti,Zr)N alloy phase space demonstrates the feasibility of the approach for a wide range of compositions. • The functional properties of TiN, ZrN as well as their alloys, especially the conductivity and hardness are markedly improved upon application of the RF substrate bias.