Développement et caractérisation de sources de neutres réactifs pour l’étude des interactions plasmas-surfaces
The goal of this Master thesis goal is to develop and characterize different sources of reactive neutrals aimed at fundamental studies of plasma-surface interactions. This project is part of a broader study on the physics driving plasma-wall interactions during plasma etching of advanced materials. Following our literature review of the various approaches used to generate radical beams, we have selected two types of sources. The first one, a thermal cracker, was characterized by line-of-sight mass spectrometry using C2F6 as the mother. We have shown that more than 90% of the C2F6 was dissociated at 1000ºC, producing CF4 that dissociates into CF2 at temperatures close to 900ºC. These results were in good agreement with the predictions of a model based on chemical equilibrium calculations, which also predicted the formation of F radicals at 1500 ºC. The second source, a surface-wave plasma, was characterised by optical emission spectroscopy and microwave interferometry. For a high-frequency (>1GHz) argon plasmas, we have shown a three temperature electron energy distribution function with Te-low>Te-high<Te-tail. We have concluded that the formation of suprathermal electrons was linked to the generation of plasma instabilities at the resonance point near the chamber walls, and to Landau damping of these instabilities. The same phenomenon was observed in Cl2 plasma, but this effect vanished at high pressures because of collisional damping. We have shown that this type of source could produce near 100% dissociation of Cl2, depending on operating conditions.
Plasma surface interactions reactive neutral sources plasma diagnostics surface wave thermal cracker