AVS 49th International Symposium
    Surface Science Wednesday Sessions
       Session SS1-WeA

Paper SS1-WeA8
A New Mechanism for Ion-Stimulated Surface Processes at Low Energies

Wednesday, November 6, 2002, 4:20 pm, Room C-108

Session: Gas-Surface Dynamics
Presenter: E.G. Seebauer, University of Illinois
Authors: Z. Wang, University of Illinois
E.G. Seebauer, University of Illinois
Correspondent: Click to Email
Ion surface interactions at low energies (<100 eV) characterize an increasingly diverse array of material processing steps in ion beam assisted deposition (IBAD), plasma enhanced deposition, reactive ion etching (RIE), and other applications. Overall process behavior in these applications often reflects a delicate balance among several competing kinetic effects. The governing kinetic phenomena are often tacitly considered to lie at one of two poles: physical effects where momentum matching dominates, and chemical effects involving thermal activation of atomic bonds according to Arrhenius expressions. Here we report molecular dynamics simulations of low-energy noble gas atoms impacting Si and Ge surfaces, and describe a new phenomenon that lies at neither pole. The simulations, backed by experiments on surface diffusion, exhibit a surprising new form of tradeoff between the ion energy threshold for point defect formation and substrate temperature. Because of the vast difference in scales between ion energies and thermal energies, the tradeoff resembles an elephant being balanced by a mouse on a seesaw. The effect originates from instantaneous nonuniformities in net surface potential induced by thermal vibrations, which dramatically affect the locality of momentum transfer to the surface and greatly amplify the effect of temperature. This amplification may offer a new means for selecting specific elementary rate processes during plasma processing or ion beam assisted deposition by judicious tuning of temperature and ion energy.