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Reactions of Photogenerated CF2 and CF3 on Silicon and Silicon Oxide Surfaces

Published online by Cambridge University Press:  25 February 2011

John Langan ,
J.A. Shorter ,
Xu Xin  and
J.I. Steinfeld
J.A. Shorter
Affiliation:
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
Xu Xin
Affiliation:
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
J.I. Steinfeld
Affiliation:
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
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Abstract

We have investigated the reactions of neutral fluorocarbon fragments, generated by laser photolysis of suitable precursors, with single-crystal silicon and thermally deposited silicon oxide surfaces. CF3 free radicals are generated by infrared multiple-photon dissociation of C2F6. While CF3 undergoes dissociative chemisorption on Si, it adsorbs very little on annealed SiO2 surfaces, and even on ion-damaged oxide surfaces, CF3 adsorbs but does not undergo transfer of fluorine from the fluorocarbon to surface silicon atoms. CF2, produced by excimer-laser photolysis of C2F4, is adsorbed on SiO2 surfaces. As with CF3, no transfer of fluorine from carbon to silicon is observed, even after argon-ion sputtering or ultraviolet irradiation of the surface. These measurements have been extended to NF3; this species chemisorbs and dissociates on a silicon surface, but even a monolayer of oxide is sufficient to block this process. A simple model based on the relative strengths of C-F, N-F, Si-F, Si-C, Si-O, and Si-N bonds appears to account for the observed behavior of CF3, CF2, and NF3 species on silicon and silicon oxide surfaces. In other cases, however, a barrier appears to be implicated in the chemisorption process.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 129: Symposium B – Laser and Particle-Beam Modification of Chemical Processes on Surfaces , 1988 , 311
Copyright
Copyright © Materials Research Society 1989

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References

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