# The role of ionization fraction on the surface roughness, density and interface mixing of the films deposited by thermal evaporation, dc magnetron sputtering and HiPIMS: An atomistic simulation

## TL;DR

This study uses atomistic simulations to investigate how ionization fraction affects surface roughness, interface mixing, and film quality during Cu film deposition by different methods, revealing key mechanisms behind surface smoothness and interface properties.

## Contribution

It introduces a comparative atomistic simulation analysis of Cu film growth under varying ionization conditions across multiple deposition techniques.

## Key findings

- Higher ionization leads to smoother surfaces.
- Bi-collision events prevent island growth and reduce roughness.
- HiPIMS causes significant interface mixing and lower adhesion.

## Abstract

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.