MOLECULAR-DYNAMICS SIMULATIONS OF REACTIONS OF HYPERTHERMAL FLUORINE-ATOMS WITH FLUOROSILYL ADSORBATES ON THE SI(100)-(2X1) SURFACE

Molecular dynamics simulations of the reactions between gaseous fluori ne atoms and (SiFx)(n) adsorbates on the Si(100)-(2 x 1) surface are p erformed using the SW potential with the WWC reparameterization. The o bjective of the simulations is to determine how the chemical compositi on and energy distribution of the etched gas-phase products depend on the identity of the reacting adsorbate. Reactions of normal incident f luorine atoms with SiF3, SiF2-SiF3, and SiF2-SiF2-SiF3 adsorbates are simulated at incident kinetic energies from 3.0 to 9.0 eV. SiF4 is the major product in nearly all cases. An S(N)2-like mechanism is respons ible for the formation of SiF4, Si2F6, and Si3F8. In addition, at 7.0 and 9.0 eV, the simulations have discovered a previously unknown mecha nism for the formation of SiF4, which involves an insertion between a silicon-silicon bond. The simulations predict that radical species are formed predominantly from fragmentation of the higher mass etched pro ducts with only a few being formed directly from the reaction between the incoming fluorine atom and the adsorbate. Comparisons are made to experimental data on silicon-fluorine etching with both thermal and hy perthermal fluorine atoms.