  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.

Materials Science