Tailoring microstructure and stress through energetic ion bombardment: A molecular dynamic simulation

Abstract

We studied high power impulse magnetron sputtering (HiPIMS) and different substrate bias for the epitaxial growth of Cu film on Cu (111) substrate by molecular dynamics simulation. We assumed a fully ionized deposition flux to represent the high ionization fraction in the HiPIMS process. Three different substrate biases, roughly low, moderate and high, were applied to the kinetic energy of the deposition flux with a flat energy distribution in each range. In low energy regime, the results were compared to the case of completely neutral flux, in analogy with thermal evaporation. In the low energy range, HiPIMS presents a slightly smoother surface and more interface mixing compared to that of thermal evaporation. However, in the moderate energy HiPIMS an atomically smooth surface was obtained with a slight increase in the interface mixing compared to low energy HiPIMS. In the high energy regime, HiPIMS presents severe interface mixing with a smooth surface with a limited growth due to resputtering from the surface. The results also indicate that in the film obtained by moderate energy HiPIMS fewer crystal defects appear. This behavior can be attributed to the repetition frequency of collision events demonstrated recently by Kateb et al. (2019). In particular high energy HiPIMS suffers from high repetition of collision events which does not allow recrystalization of the film. In the low energy HiPIMS, collision events are not enough to overcome island growth. At moderate energy, collision events repeat in a manner that provides enough time for recrystalization that results in a smooth surface, fewer defects and limited intermixing.