Inelastic scattering dynamics of hyperthermal fluorine atoms on a fluorinated silicon surface

The interaction of energetic fluorine atoms with a fluorinated silicon surface has been studied by monitoring energy and angular distributions of scattered fluorine atoms. Two beams with average translational energies of 284 and 544 kJ/mol were directed onto the SiFx layer, known to exist during steady-state etching. While thermal scattering of unreacted fluorine atoms is observed, nonthermal scattering dominates and includes both single- and multiple-bounce collisions at the complex surface. Multiple-bounce collisions often lead to a near-thermal (cosine) distribution of exit angles but incomplete thermalization of translational energy. A hard-sphere kinematic model, based on single atom-surface collisions, can be used to predict the overall average energy transfer as a function of deflection angle, indicating that the complex scattering events at the surface can appear on average like single collisions.