Role of energetic ions in the growth of fcc and {\omega} crystalline phases in Ti films deposited by HiPIMS

TL;DR

This study explores how energetic ions influence the formation of different crystalline phases, including fcc and ω phases, in Ti films deposited by HiPIMS, revealing phase evolution dependent on ion energy and film thickness.

Contribution

It demonstrates the impact of ion energy and deposition conditions on phase formation in Ti films, highlighting the emergence of fcc and ω phases under specific HiPIMS parameters.

Findings

Ti α-phase observed in DCMS films with tensile stress.

HiPIMS films show residual stress variation with thickness.

High energy ion conditions induce ω-phase formation at certain thicknesses.

Abstract

Titanium (Ti), due to its excellent properties, is widely exploited in thin film technology that usually leads to the production of {\alpha}-phase (hcp) Ti films. In this work, we investigate the phase evolution of Ti films deposited by varying type and energy of the film-forming species. To investigate different plasma species environments, films with different thicknesses are grown by using conventional Direct Current Magnetron Sputtering (DCMS) and High Power Impulse Magnetron Sputtering (HiPIMS). Furthermore, HiPIMS depositions with different substrate bias voltage US (0 V, -300 V and -500 V) are performed to investigate different ion energy ranges. Microstructure, morphology and residual stress of the deposited films, as well as the DCMS and HiPIMS plasma composition, are analysed with different characterization techniques. The DCMS samples exhibit the Ti {\alpha}-phase only and show a tensile residual stress decreasing with thickness. As far as HiPIMS samples are concerned, a compressive-tensile-compressive (CTC) behavior is observed for residual stresses as thickness increases. Specifically, films deposited in low energy ion conditions (US =0 V) show the presence of the Ti fcc phase up to a maximum thickness of about 370 nm. Differently, films deposited under high energy conditions (US = -300 V and -500 V) show the nucleation of the Ti {\omega}-phase for thicknesses greater than 260 and 330 nm, respectively. The formation of these unusual Ti phases is discussed considering the different deposition conditions.