AVS 51st International Symposium
    Plasma Science and Technology Monday Sessions
       Session PS2-MoM

Paper PS2-MoM9
Atomic-scale Simulations of Spontaneous and Ion-assisted Etching of Silicon

Monday, November 15, 2004, 11:00 am, Room 213B

Session: Silicon Etching
Presenter: D. Humbird, University of California, Berkeley
Authors: D. Humbird, University of California, Berkeley
D.B. Graves, University of California, Berkeley
Correspondent: Click to Email
Molecular dynamics (MD) simulations model the phenomenon of thermal halogen atoms etching silicon spontaneously, and capture the atomic-scale mechanisms of Ar@super +@ ions and neutral halogen atoms working together. Using improved interatomic potential energy functions for Si-F and Si-Cl, MD predicts steady halogen uptake and spontaneous etching as F and Cl atoms impact Si. At 300 K, the simulations agree semi-quantitatively with experimental measurements of total surface coverage, halosilyl group coverage, reaction probability, and etch product distribution. Etch products that remain weakly bound to the surface are detected in significant quantities. At higher temperature, agreement between simulation and experiment is qualitative; the simulation matches trends in reaction probability and etch product redistribution. Below 450 K, etch products form and promptly desorb. At higher temperatures, internal decomposition of the halogenated silicon layer dominates. The forthcoming phenomenological model of Winters et al. is based in part on some of the observations of our simulations@footnote 1@. Significant etching enhancements are realized when simultaneous energetic Ar@super +@ ions impact the halogenated Si surface. Si etch yields are in good agreement with experiments. The atomic-scale mechanisms of ion-enhanced etching are classified as enhanced spontaneous etching, chemically enhanced physical sputtering, and chemical sputtering. The primary effects of ions are to increase the local surface coverage of etchant species and to create products by inducing chemical reactions within the halogenated surface layer. Ion-assisted effects are most pronounced at low neutral/ion ratio and decline as this ratio increases. Explicit ion enhancements are greater for Cl than for F. @FootnoteText@ @footnote 1@HF Winters, D Humbird, and DB Graves, in preparation (2004).