Effect of substrate bias on microstructure and properties of Ni–TiN nanocomposite thin films deposited by reactive magnetron co-sputtering

• Ni–TiN films were grown by cosputtering Ni + Ti targets in Ar + N2 at different biases.
• Substrate bias influences film growth rate, TiN content, roughness, and grain size.
• Hardness and Young's modulus rise with TiN content following rule of mixtures.
• Scratch resistance of the films scales with resistance to plastic deformation.
• Resistivity scales with amount of TiN and decreases in grain size.

The effect of substrate bias variation on structure and properties of the Ni–TiN nanocomposite thin films deposited on Si (100) substrates by magnetron sputtering has been investigated. Deposition has been carried out by reactive co-sputtering of high purity Ti and Ni targets as RF and DC sources, respectively in an atmosphere with Ar:N2 = 1:2. The microstructures of the as-deposited films have been examined using grazing incidence X-ray diffraction and transmission electron microscopy. It has been observed that with an increase in negative substrate bias from 0 to − 80 V, the TiN volume fraction increases from 36 to 50%, whereas the average grain sizes of both Ni (≈ 10–17 nm) and TiN (≈ 6–9 nm) decrease. Moreover, the biaxial compressive residual stress as estimated by sin2ψ technique scales with negative substrate bias. The surface roughness determined using atomic force microscopy appears to be the least in the nanocomposite film deposited with substrate bias of − 60 V. Furthermore, X-ray photoelectron spectroscopy studies have confirmed the formation of oxygen-free stoichiometric TiN in this film. Hardness (≈ 12.6–16.9 GPa), elastic modulus (≈ 208–233 GPa) and scratch-resistance determined by nanoindenter, as well as electrical resistivity (≈ 26–47 μΩ·cm) measured using dc four-probe method, are found to scale with TiN content. An increase in hardness and electrical resistivity with an increase in negative substrate bias is also attributed to a decrease in Ni grain size and an increase in point defect density.