The chemical dynamics of XeF₂ and Xe(F₂) reactions with Si(100)

The chemistry of fluorine, F2, and xenon difluoride, XeF2, with clean Si are nearly indistinguishable. Both species react via the atom abstraction mechanism, whereby a surface dangling bond abstracts a F atom from the incident molecule, scattering the complementary F atom or XeF fragment into the gas phase. However, once all dangling bonds are fluorinated and a coverage of 1 ML F is attained, the chemistry of these two species diverges. Further exposure to F2 results in no increase in F coverage, indicating reactions of F2 with the Si-Si -bonds do not occur. In contrast, further exposure to XeF2 results in additional reaction, cleaving the Si-Si bonds and increasing the coverage beyond 1 ML F. Eventually, sufficient fluorination occurs to effect the desorption of the etch product SiF4. The experiments described in this thesis have been designed to probe the origin of the observed difference in reactivity of F2 and XeF2 with a fluorinated Si surface. Two possible explanations are presented that likely account for the difference in reactivity of F2 and XeF2 with fluorinated Si. The first is the reaction of atomic fluorine, which is produced by the gas phase dissociation of XeF following an abstraction event, with the Si. The second is vibrational excitation of the Si lattice, induced by the initial collisions of XeF2, thereby enabling reaction of the F atoms with the Si-Si bonds. The first chapter describes experiments investigating the chemical dynamics of the reaction of a beam of XeF2 with Si(100). The scattered intensities and the time-of-flight distributions of the reaction products XeF2, XeF, and Xe are measured as a function of coverage and scattering angle, as is the intensity of scattered F atoms.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Chemistry.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2004

Author dc:creator

• Hefty, Robert Charles, 1976-

Advisor dc:contributor.advisor

• Sylvia T. Ceyer.

• Chemistry.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/30113

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/30113