Neutral species in inductively coupled SF6/SiCl4 plasmas
Résumé
Inductively coupled SF6/SiCl4 plasmas interacting with a bulk silicon substrate and a SiO2-coated substrate have been investigated. Mass spectrometry and optical emission spectroscopy diagnostics were used to characterize the neutral population in the diffusion chamber. SiF4 molecules were detected as the dominant species, and their formation has been attributed to the high reactivity of F radicals with SiClx species. In a complementary experiment, a silicon chloride layer was deposited on the reactor walls during a SiCl4 plasma step and subsequently etched by a SF6 plasma. Time-resolved measurements of the neutral densities during the SF6 plasma step showed the importance of heterogeneous reactions between impinging F radicals and SiClx species deposited on the reactor walls. In SF6/SiCl4 plasmas, these reactions lead to a depletion in F radicals, which results in a decrease in the silicon substrate etch rate. Furthermore, this impacts on the concentration of SFx species and on the creation of new species, such as ClF, SF5Cl and S2Cl2.