Energetic ions for the growth of amorphous and crystalline tungsten-nitrogen layers by HiPIMS

This study investigates the deposition of tungsten‑nitrogen (WNx) coatings using high-power impulse magnetron sputtering (HiPIMS), integrating experimental analysis and numerical simulations. We explore how varying N2/Ar flow ratios and energetic ion bombardment influence coating properties. Specifically, the characteristics of the ion flux impinging on the growing film were controlled by tuning the pulsed bias voltage applied to the substrate in terms of its amplitude and synchronization to the HiPIMS cathode pulse. The nitrogen content of WNx coatings increases with the N2/Ar flow ratio but decreases with the bias amplitude. Additionally, the bias synchronization to the main pulse influences film morphology and structure: a bias synchronous to the HiPIMS pulse onset favors β-W2N crystallization while delayed bias induces film amorphization. Ionization Region Modeling (IRM) simulations of relevant discharges were performed to predict the HiPIMS plasma composition and support the interpretation of experimental results. Findings suggest that precise control over substrate bias in reactive HiPIMS allows to tailor and achieve desired morphological and structural properties of WNx films.