AVS 51st International Symposium
    Plasma Science and Technology Monday Sessions
       Session PS1-MoA

Paper PS1-MoA7
Spontaneous Etching of Silicon with F Atoms and XeF@sub 2@: A Unified Model

Monday, November 15, 2004, 4:00 pm, Room 213A

Session: Plasma Surface Interactions in Etching
Presenter: H.F. Winters, UC Berkeley
Authors: H.F. Winters, UC Berkeley
D. Humbird, UC Berkeley
D.B. Graves, UC Berkeley
Correspondent: Click to Email
A recently proposed molecular dynamics simulation of spontaneous etching of undoped silicon with F has been successful in describing a variety of experimental observations.@super 1@ Insights gained from this simulation (denoted HG) have been used to refine a model which explains other spontaneous etch observations, including etching by XeF@sub 2@ and various effects of doping on spontaneous etching, among others. The model is based on the assumption that the reaction is proportional to the negative ion concentration on the silicon surface (e.g. at SiF@sub 3@@super -@ centers)@super 2@ using the umbrella-type reaction mechanism observed in the simulation. HG predicts a 5 Å SiF@sub x@ layer on silicon exposed to F atoms and it will be demonstrated that XPS data are consistent with this prediction. It will also be shown that XPS data indicate a layer twice as thick (~10 Å) for XeF@sub 2@. Experimental data showing that the layer thickness is relatively independent of incident flux and temperature over significant ranges of these parameters as predicted by HG will be presented. Assuming these layer thicknesses are correct allows us to calculate the negative ion concentration on the silicon surface being etched.@super 2@ These results are correlated with various experiments including reaction probability measurements over the temperature range 200--1000 K and doping experiments with concentrations from ~10@super 15@ to 10@super 20@ dopants/cm@super3@. It will be shown that one model can be used to describe the experimental results for the spontaneous etching of Si(111) by both F and XeF@sub 2@. A plausible explanation will be presented as to why the doping effect in chlorine is large relative to fluorine even though the opposite trend is observed for spontaneous etch rate. Many other experimental results (etch rate proportional to reactant density, insensitivity of product distribution to doping level, etch product composition, and the doping and reaction probability differences between F and XeF@sub 2@) are consistent with this model. Finally, the HG conclusion that etch products are desorbed with significant kinetic energy allows data from modulated beam mass spectrometry calibrated for 300K products to be interpreted properly, leading to determination of the reaction probability from T(surface) = 200 K - 1000 K. The data will be presented and compared with theory. @FootnoteText@@Footnote 1@ David Humbird and David B. Graves, J. Appl. Phys, in press, (2004) @Footnote 2@ H. F. Winters and D. Haarer, Phys.Rev. B, 36. 6613 (1987); 37 ,10379 (1988)