The importance of HiPIMS ionization flux fraction on the film microstructure and surface roughness: A molecular dynamic simulation

We demonstrate the effect of ionization flux 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) with fully neutral, 50 % ionized and 100 % ionized flux, respectively. It is shown that higher ionization flux fraction of the deposition flux leads to smoother surfaces by two ma-jor 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 experi-mental results. In addition, HiPIMS deposition presents considerable interface mixing while it is negligible in thermal evaporation and dcMS deposition, those present less adhesion accordingly.