Influence of pulsed substrate biasing on strain and mechanical properties of low-temperature-grown TiZrNbTaNx films by high-power impulse magnetron sputtering

In this work, we investigate the effect of pulsed substrate biasing on the microstrain, residual stress, and mechanical properties of multi-principal element TiZrNbTa nitride thin films deposited on silicon. The pulsed bias is synchronized with ionized sputtered species and gas ions during reactive high-power impulse magnetron sputtering. This was achieved by exploiting differences in their time-of-flight arising from mass contrasts allowing two distinct bias conditions. Synchronization with gas ions results in films with higher compressive stress (3.1–5.4 GPa) and an indentation hardness of 25 ± 1 GPa. In contrast, films grown under heavy metal-ion bombardment even with dominant Ar + flux overlap exhibit lower compressive stress (2.5–3.4 GPa) and slightly higher hardness (29 ± 1 GPa) independent of ion energies in the range of ~25–300 eV. These films show minimal variations in metal composition, accompanied by grain coarsening, reduced microstrain, and decreased Ar incorporation below ~100 eV. At higher ion energies (~200–300 eV), atomic peening by Ar + ions dominates, promoting strained growth. Overall, hardness is primarily governed by metal sublattice composition, with only a weak dependence on strain and grain size effects. These results demonstrate that synchronized pulsed biasing enables precise control of film properties without external heating.