AVS 52nd International Symposium
    Plasma Science and Technology Tuesday Sessions
       Session PS-TuM

Invited Paper PS-TuM5
The Spontaneous Etching of Silicon by F Atoms, Cl Atoms and XeF@sub 2@ : A Unified Model Supported by Experiment and Simulation

Tuesday, November 1, 2005, 9:40 am, Room 304

Session: Plasma Surface Interactions I
Presenter: H. Winters, Unversity of California at Berkeley
Authors: H. Winters, Unversity of California at Berkeley
D. Humbird, University of California, Berkeley
D.B. Graves, University of California, Berkeley
Correspondent: Click to Email
Insights gained from a recent molecular dynamics simulation (denoted HG) are used to refine a model that quantitatively predicts spontaneous etch rates of silicon and explains various experimental observations@footnote 1@ This model is based on the electronic structure of Si and the electron affinity of the incident gas, and assumes that the rate-limiting reaction step is associated with negatively-charged particles in the halogenated Si surface layer. The density of such charge centers in the layer is a function of its thickness and can be calculated using a formalism similar to one previously published.@footnote 2@ HG predicts a ~5 @Ao@-thick SiF@sub x@ layer on undoped silicon exposed to F atoms; XPS data agree with this prediction, and indicate that the layer is about twice as thick for XeF@sub 2 @exposure. Layer thickness is observed via XPS and temperature programmed desorption to be independent of incident halogen flux and temperature over significant ranges of these parameters, also consistent with the HG simulations. Closed-form expressions for the reaction probability of Si (111) as a function of various parameters will be presented. These expressions correlate well with experiments, including reaction probability measurements as a function of temperature (200K--1000 K), dopant concentration (~10@super 15 @ - 10@super 20@ dopants/cm@super 3@), and incident species (F, Cl, and XeF@sub 2@). The model rationalizes the observation that the doping effect in Cl is large relative to F, even though the opposite trend is observed for the spontaneous etch rate. Finally, the HG result that etch products desorb with significant kinetic energy allows modulated beam mass spectrometry data to be quantitatively calibrated, making measured etch reaction probabilities absolute. @FootnoteText@@footnote 1@ D. Humbird and D. Graves, J. Appl. Phys. 96 791 (2004) @footnotes 2@ H.F. Winters and D. Haarer, Phys. Rev. B 36 6613 (1987) See also erratum @footnote 3@ H.F. Winters and D. Haarer, Phys. Rev. B 36 6613 (1987)