Molecular dynamics simulation for focused ion beam processing: a comparison between computational domain and potential energy

Abstract

Molecular dynamics calculation was performed to simulate nano-Focused Ion Beam (FIB) processing on a Silicon surface. A combination of potential functions of impacting ion and target atoms was evaluated, and the influence of computational domain along the lateral directions was estimated. The target Silicon atoms on (100) surface of Si crystal were described by Tersoff potential. Ion-beam source was represented by Ga ions, where the optimal potential of the Ga ion was chosen by comparing Lennard-Jones, Tersoff, and ZBL (Ziegler, Biersack and Littmark) potentials. The initial velocity of ion was 3.327×105 m/sec at 40 keV. First, for the evaluation of combined potential functions of Si atoms and Ga ion, a small computation volume (2.58 nm × 2.58 nm × 51.99 nm) consisting of 19200 Si atoms was chosen with a single Ga ion impacting on Si (100) surface. On the combination of Tersoff potential for Si atom, and ZBL potential for Ga ion, the depth of the combination was found to be in good agreement with the depth of SRIM. Next, the influences of computational domain in lateral direction were evaluated by a larger region with a combination of potentials where the computational volume was (8.55 nm × 8.55 nm × 51.99 nm) constructed by 196608 Si atoms. Consequently, the energy transfer along lateral computational length was faster in larger region than in smaller region, and the entire initial energy of Ga ion was transmitted to the target material.