  We explore the effect of ionization fraction on the epitaxial growth of Cu
film on Cu (111) substrate at room temperature. We compare thermal evaporation,
dc magnetron sputtering (dcMS) and high power impulse magnetron sputtering
(HiPIMS). Three deposition conditions i.e. fully neutral, 50% ionized and 100%
ionized flux were considered as thermal evaporation, dcMS and HiPIMS,
respectively, for ~20000 adatoms. It is shown that higher ionization fraction
of the deposition flux leads to smoother surfaces by two major mechanisms i.e.
decreasing clustering in the vapor phase and bi-collision of high energy ions
at the film surface. The bi-collision event consists of local amorphization
which fills the gaps between islands followed by crystallization due to
secondary collisions. We found bi-collision events to be very important to
prevent island growth to become dominant and increase the surface roughness.
Regardless of the deposition method, epitaxial Cu thin films suffer from
stacking fault areas (twin boundaries) in agreement with recent experimental
results. In addition, HiPIMS deposition presents considerable interface mixing
while it is negligible in thermal evaporation and dcMS deposition, those
present less adhesion accordingly.
