Paper PS-TuP20
A Novel Interatomic Potential Model for MD Simulation of Si Etching by Cl⁺/Br⁺ Containing Plasmas

Tuesday, October 21, 2008, 6:30 pm, Room Hall D

Plasma-surface interaction is an important research subject both academically and industrially. Particularly, the understanding of interaction between chemically reactive plasmas and semiconductors is inevitable for further improvement in the fabrication of semiconductor devices. At present, HBr plasmas are utilized for state-of-the-art fine Si etching processes. However, fundamental experimental data were not sufficient except for some plasma experiments.¹ In addition, potential models for Si/F and Si/Cl systems were only available for Si etching simulations. Here we present an novel interatomic potential models to realize classical molecular dynamics (MD) simulation of Si etching by HBr plasmas. Our simulation target is Si etching by HBr or Cl₂ plasmas. First, the scheme to construct potential function was renewed, where all parameters could be systematically determined based on ab-initio data obtained from quantum chemical calculation. As a potential form, we selected the well-known Stillinger-Weber (SW) model, where the total potential is expressed by the sum of two- and three-body functions. SW model could reproduce ab-initio data with high accuracy when systems include only two or three atoms. Secondly, a new discipline to construct potential model is also proposed. We clarified how the potential functions affect etching characteristics in MD simulations.² Until now, SW potential models for etching simulation were determined on the basis of potential energies calculated for small clusters while the energies for ion penetration and stay in interstitial sites have not been considered. However, the latter crucially affects the results of etching simulation, especially the morphology of the reaction layer. Then, the accurate estimation of potential energies for ion penetration in interstitial sites is essential for qualitative improvement of etching simulations. After careful examination, it was founded this energy was overestimated when the original SW model was used. Based on this fact, we proposed an improved SW model, where a new term is added to three-body potentials. In this conference, we present a detail derivation of the new model and the comparison between results by old and new SW models.

¹e.g., S. A. Vitale et al., J. Vac. Sci. Technol. A 19, 2197 (2001).; C. C. Cheng et al., J. Vac. Sci. Technol. A 13, 1970 (1995).
²A. Iwakawa et al., to be published in Jpn. J. Appl. Phys.