Mechanism and dynamics of the reaction of XeF2 with fluorinated Si(100): Possible role of gas phase dissociation of a surface reaction product in plasmaless etching

Abstract

Xenon difluoride is observed to react with Si-Si sigma-dimer and sigma-lattice bonds of Si(100)2 x 1 at 150 K by single and two atom abstraction at F coverages above 1 ML. As in the limit of zero F coverage, a measurable fraction of the scattered, gas phase product of single atom abstraction, XeF, is sufficiently internally excited to dissociate into F and Xe atoms before detection. Using the XeF internal energy and orientation distributions determined in the limit of zero coverage, the laws of conservation of momentum, energy, and mass are applied to the measured F velocity and angular distributions at higher coverage to simulate the Xe atom velocity and angular distributions and their intensities at higher coverage. The simulation predicts the observed Xe atom velocity and angular distributions at high coverage reasonably well, largely because the exothermicity channeled to XeF remains approximately constant as the coverage increases. This constancy is an opportune consequence of the trade-off between the attractiveness of the potential energy surface as the coverage is increased and the dynamics of the XeF product along the potential surface. The energy, momentum, and mass conservation analysis is also used to distinguish between Xe atoms that arise from XeF gas phase dissociation and Xe atoms that are produced by two atom abstraction. This distinction enables the calculation of percentages of the single and two atom abstraction pathways, as well as the percentages of the two pathways available to the Xe atom produced by two atom abstraction, inelastic scattering, and desorption. Finally, the simulation reveals that between 9% and 12% of F atoms produced by gas phase dissociation of XeF are scattered back toward the surface. These F atoms likely react readily with Si to form the higher fluorides that ultimately lead to etching. Gas phase dissociation of the scattered product of a surface reaction is a novel mechanism to explain the unique reactivity of XeF(2) to etch Si in the absence of a plasma.

Formation of Nanoporous Features, Flat Surfaces, or Crystallographically Oriented Etched Profiles by the Si Chemical Dry Etching Using the Reaction of F2 + NO → F + FNO at an Elevated Temperature

“…When the Si 9 H 12 reacted with F 2 , F was abstracted and reacted with two dangling bonds at the Si surface. F abstraction from the reaction between the F 2 and Si surface with the dangling bonds was empirically observed in previous studies. − When the FNO approached to the Si 9 H x surface, F reacted with the dangling bond, and NO was placed in the middle of the Si–Si σ-dimer bonds. During the cleavage of the Si–Si σ-dimer bonds, new dangling bonds were formed at the Si surface .…”

Photochemical Fluorination of TiO2(110) Produces an Atomically Thin Passivating Layer

“…XeF 2 is a relatively stable molecule with a total bond strength of 2.75 eV; however, the removal of one F atom produces XeF, a very unstable molecule with a bond strength of only 0.13 eV . When XeF 2 reacts with a clean Si(100) surface, the first step of the reaction is the abstraction of a F atom to produce a fluorinated surface site and a scattered XeF molecule. , The XeF molecule is rovibrationally excited by a combination of the scattering process and the reaction exothermicity. As a result of this excitation, 60–90% of the scattered XeF dissociates within a few Å of the surface, producing a highly reactive F radical .…”

Tuning Charge Transfer in Ion–Surface Collisions at Hyperthermal Energies

“…Fluorination of the surface is accomplished during the N + ion‐scattering experiment by introducing XeF 2 gas directly onto the Au foil with a doser pipe situated approximately 2 cm from the surface. XeF 2 adsorbs dissociatively onto metal surfaces, thus providing a convenient way to change the F‐atom surface coverage by controlling the XeF 2 background gas pressure. Though not measured, fluorine coverage is kept sub‐monolayer by limiting the background pressure below the point where the scattered signal saturates.…”