TITLE:

Reactivity of Fluorinated Si(100) with F₂

AUTHORS:

Pullman, D.P.; Dept. of Chem., SDSU, San Diego, CA, USA; Tsekouras, A.A.; Dept. of Chem., UoA, Athens, Greece; Li, Y.L.; Yang, J.J.; Tate, M.R.; Gosalvez, D.B.; Laughlin, K.B.; Schulberg, M.T.; Ceyer, S.T.; Dept. of Chem., MIT, Cambridge, MA, USA

PUBLICATION:

Journal of Physical Chemistry B, vol.105, no.2, p. 486-496, 18 January 2001 46 Refs.

ABSTRACT:

The dissociative chemisorption of F₂ on the Si(100)(2 x 1) surface saturated with 1 monolayer (ML) of fluorine is investigated as a function of the incident F₂ translational energy. At energies below 3.8 kcal/mol, no reaction with the Si-Si bonds occurs. Above this threshold, the probability of dissociative chemisorption rises linearly with the normal component of the incident translational energy up to a value of 3.6 x 10^-3 at 13 kcal/mol. The relatively small effect of translational energy implies a late barrier in the potential energy surface for the interaction of F₂ with the Si-Si bonds. These probabilities are measured by exposing the fluorine-saturated surface to supersonic F₂ beams of variable energy, followed by thermal desorption measurements to determine the resulting fluorine coverage. Information regarding the specific Si-Si site (Si-Si dimer or Si-Si lattice bonds) at which the translationally activated reaction occurs is obtained from He diffraction measurements. The intensity of the diffracted beams is monitored after exposing the fluorine-saturated surface to F₂ of variable energy. The intensities remain constant after exposure to low-energy (<3.8 kcal/mol) F₂, whereas they decline monotonically as a function of F₂ normal energy above the 3.8 kcal/mol threshold. Moreover, the similarity of the relative cross sections for diffusive scattering measured after exposure to translationally fast F₂ to those measured after Ar⁺ ion bombardment strongly suggests that the reaction does not occur preferentially at the Si-Si dimer bonds, which are the weakest Si-Si bonds in the system. Reaction at Si-Si lattice bonds also occurs, leading to surface disorder. Additional data show that for submonolayer coverages generated from low energy F₂, no reaction with Si-Si bonds occurs, while exposure to high-energy F₂ leads to reaction with Si-Si bonds.