Dynamic-Monte Carlo simulations of diamond-like carbon film synthesis by ion-assisted deposition

The structure of a diamond-like carbon (DLC) film synthesized by ion-assisted deposition can be characterized by the hydrogen concentration and the relative fraction of sp2 bonded carbon and sp3 bonded carbon. Substrate bias, i.e. the energy of the impinging ion, plays a crucial role for the film structure and thereby the mechanical, electrical and optical properties of the film. Dynamic-Monte Carlo simulations with the binary collision approximation have been applied to the synthesis of DLC films by ion beam-assisted deposition. In the model, energetic CH3+ ions and CH3 radicals are incident on the surface alternately, and for the radicals on the surface, it is assumed that only the atoms receiving enough energy to overcome the surface barrier enter the solid. We assumed (a) a unity and only one monolayer sticking of CH3 radicals on the surface; (b) the incorporation of H and C atoms into the bulk by binary collisions with energetic CH3+ ions; (c) the release of H atoms by the dissociation of CH3 radicals on the surface; and (d) the complete dissociation of CH3+ ions into one C atom and three H atoms with identical velocities upon bombarding the surface. In addition to the above assumptions, (e) release of the displaced H atoms after the subsequent collision cascade is also assumed. The model takes into account full collision cascade induced by the impinged atoms and the changes of cross-sections of nuclear and electronic collisions induced by the accumulation of atoms and damage. Results are presented for the dependence of H concentration and of the deposition rate on the threshold displacement energy of H, the dissociation energy of CH3, the trapping rate of displaced H atoms, and the ion/neutral arrival ratio and the ion energy.