Computer simulations of plasma-surface chemistry

Molecular dynamics (MD) simulations were conducted to develop a better mechanistic understanding of some of the important surface reactions involved in plasma-assisted etching and deposition processes. In particular, the MD simulations were performed to study the surface interactions of the energetic ions and reactive neutral species generated in the plasma.;First, I present the results of MD simulations of atomic Si and molecular SiFx (x = 1 to 3) species impacting fluorinated silicon surfaces. The species and surfaces were chosen to model the interactions of etch products with the surfaces of etched features. Sputtered species impact feature surfaces with energies on the order of a few eV. Etch products that are ionized in the plasma are accelerated back towards the substrate surface and impact the surfaces with energies on the order of tens to hundreds of eV. To model both of these cases, the incident energy was varied from 0.1 to 100 eV. I describe the events that occur during the picosecond(s) following the impacts of these reactive atomic and molecular species. These events include the sticking or reflection of the incident species, direct reactions with surface species, and the sputtering of surface material. The effects of the incident species, the incident energy and angle, and the surface coverage of fluorine are discussed.;I then describe the results of MD simulations of Ar+ , Cl+ , and Cl+2 ions impacting chlorinated silicon surfaces with energies from 20 to 100 eV. These simulations were conducted to examine the scattering of ions from the surfaces of etched features (e.g., the sidewalls of an etched trench). The reflection probabilities were obtained as functions of the incident ion species, energy, angle, chlorine surface coverage, and surface roughness. For incident angles ≥75° from the surface normal, the reflection probabilities were >90% in most cases. For these large angle impacts, I describe the energy and angle distributions of the reflected atoms and molecules. Correlation was observed between the average energy and angles of the reflected particles. The correlation observed in the MD data was compared with the predictions of two simple models based on the binary collision approximation. The binary collision models were found to provide an adequate description of this correlation.;The final set of MD simulations was performed to study the dynamics of weakly-bound or physisorbed Cl atoms on a chlorinated Si(100) surface. In particular, the MD simulations were conducted to study the rates of trapping, desorption, diffusion, and reaction of the physisorbed Cl atoms. The rate parameters obtained from the MD simulations were then used in models for the recombination of Cl atoms on a silicon surface. The models were developed to test the possible role of physisorbed Cl atoms in the surface recombination reactions. Various mechanisms involving physisorbed Cl atoms were assumed for the recombination reactions. The predictions of the models were compared with the available experimental data, and the relative importance of the various proposed mechanisms were examined. The model predictions for a recombination mechanism involving the diffusion and reaction of a physisorbed Cl atom with an activated or reactive chemisorbed Cl atom were found to be consistent with the experimental data.