Paper PS+SS-TuA2
The Reaction of Fluorine Atoms with Silicon: Controversies 38 Years in the Making

Tuesday, October 31, 2017, 2:40 pm, Room Ballroom B

Chemical etching of silicon by fluorine atoms in the absence of ion bombardment is reviewed. Controversies on the identity of etching products and reaction probabilities are discussed. Attempts are made to explain the apparent presence of SiF₂ as a primary product in many studies, dating back to 1980, but not in others, including those of Harold Winters from as early as 1979. Reported estimates of reaction probabilities (here defined as the probability of removing a Si atom from the substrate per incident F atom) vary by a factor of 2000. When these values, with some corrections and normalizations applied, are plotted as a function of F atom flux, most of them fall on a “universal curve” that reveals a large (~30-fold) decrease in the reaction probability with increasing F flux, from 0.03 at a F flux 10¹²cm^-2s^-1 to 0.001 at a flux of 10²⁰ cm^-2s^-1. These values were extracted from beam experiments with F atoms generated from cracking of F₂, including those by Harold Winters, from isotropic etching in plasma experiments (both in-plasma and downstream) with F₂, CF₄/10%O₂, and NF₃ feed gases, as well as from molecular dynamics simulations. Reaction coefficients derived from chemical etching rates in SF₆ plasmas do not follow this trend, however, suggesting a large enhancement in the F reaction probability (~20 to 100-fold at F fluxes of 10¹⁸-10¹⁹cm^-2s^-1), due to the presence of sulfur.