Atom abstraction and gas phase dissociation in the interaction of XeF2 with Si(100)

Abstract

Xenon difluoride reacts with Si(100)2x1 by single atom abstraction whereby a dangling bond abstracts a F atom from XeF(2), scattering the complementary XeF product molecule into the gas phase, as observed in a molecular beam surface scattering experiment. Partitioning of the available reaction energy produces sufficient rovibrational excitation in XeF for dissociation of most of the XeF to occur. The resulting F and Xe atoms are shown to arise from the dissociation of gas phase XeF by demonstrating that the angle-resolved velocity distributions of F, Xe, and XeF conserve momentum, energy, and mass. Dissociation occurs within 2 A of the surface and within a vibrational period of the excited XeF molecule. Approximately an equal amount of the incident XeF(2) is observed to react by two atom abstraction, resulting in adsorption of a second F atom and scattering of a gas phase Xe atom. Two atom abstraction occurs for those XeF product molecules whose bond axes at the transition state are oriented within +/-60 degrees of the normal and with the F end pointed toward the surface.

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

“…The flight-time distribution for each scattered product is measured by a cross-correlation TOF method described previously. 39,48 For measurements at m / e = 167, 148, and 19, the electron energy of the electron impact ionizer is set to 75 eV. For m / e = 129, it is set to 26.5 eV in order to minimize contributions from dissociative ionization of XeF 2 and XeF.…”

“…The mechanism for reaction in the limit of zero F coverage was previously established to occur by atom abstraction, [35][36][37] with the possibility of both single and double F atom abstraction. 38,39 The reaction was found to proceed only at the dangling bonds of Si dimers. 40 The present work explores the effect of F coverage on the F atom single and double abstraction mechanism and specifically explores whether the abstraction mechanism remains operable at sites other than the dangling bond sites.…”

“…41 At 1 ML F coverage, the exothermicity for single atom abstraction plummets to about 15 kcal/mol for reaction at the -dimer and -lattice bonds, using a value of 54 kcal/ mol for the Si-Si bond energy in crystalline Si. 45 The total energy available to the single atom abstraction products is defined as the sum of the exothermicity of the first atom abstraction event and the incident energy of the XeF 2 reactant, which is 2 kcal/mol as discussed previously 39 and below. Therefore, the total energy available to the products of a single atom abstraction at zero coverage, intermediate coverages and coverages over 1 ML are 69, 71, and 17 kcal/mol, respectively, in this experiment.…”

“…The model result was found to accurately predict the observed Xe atom velocity and angular distributions. 38,39 Clearly, the potential energy surface that dictates the abstraction reaction in the limit of zero coverage is modified at higher coverage by the change in reaction exothermicity and by lateral interactions with the surrounding F atoms. In turn, the probability of XeF dissociation is governed by the amount of exothermicity channeled to XeF internal energy above its dissociation limit and by the XeF orientation in the transition state of the abstraction reaction.…”

Selective patterning of Si-based biosensor surfaces using isotropic silicon etchants

“…XeF 2 etching is known to add several fluorosilyl layers, approximately 10–20 Å thick in entirety, to the surface [35]. This etching mechanism begins with XeF 2 attacking the dangling bonds of the Si dimers by means of atom abstraction [36–37]. After saturating the dangling bonds, at about a monolayer of coverage, fluorine begins to attack the Si-Si σ-dimer and σ-lattice bonds [38].…”