We investigated capacitively coupled Ar/C 2 H 2 RF plasmas with a 1D fluid model that couples a 13.56 MHz discharge module, a long timescale chemical module and a flow transport module. A new solution procedure was developed in order to accurately describe the coupling between the short timescale discharge dynamics and the long characteristic time processes that play a major role in the molecular growth of reactive species. The plasma was simulated for different inlet gas configurations and flowrates. We showed that for a showerhead configuration one may distinguish two situations. For short residence time the plasma was strongly electronegative in the very center of the discharge gap and dominated by large hydrocarbon positive and negative ions. In this situation the acetylene conversion, although moderate, lead to a significant molecular growth. For long residence time, although C 2 H 2 underwent a total conversion, the products of the primary C 2 H 2 dissociation process were consumed by surface deposition which reduced drastically the molecular growth in the short gap discharge considered here. Whatever the conditions, we confirmed the key-role of Ar* in the acetylene conversion, ionization kinetics as well as the subsequent molecular growth for neutral and charged species. We also showed that remote feed gas and showerhead configurations predicted similar results at low flowrate. At larger flowrate the two configurations presented some discrepancy. Especially H 2 density was much larger for the remote feed gas configuration, which affected the overall plasma behavior. Our results highlight that realistic gas-flow models are essential for an accurate description of acetylene conversion in Ar/C 2 H 2 plasma.

A numerical model was used to investigate the effect of acetylene concentration in the feed gas on molecular growth and solid particle nucleation in argon-acetylene CCRF discharges. Results showed that for large acetylene conversion yields and small acetylene concentrations in the discharge, the ionization kinetic is driven by Penning process and the molecular growth is governed by neutral polyynes. The cluster size distribution predicted shows that nucleation is unlikely in this situation. On the opposite, for limited conversion yields and significant acetylene concentrations in the discharge, the ionization kinetic is driven by electron-impact process; the molecular growth is governed by positive ions and leads to significant concentrations of neutral polyynes and enhanced nucleation rate.