Characteristics of C3 radicals in high-density C4F8 plasmas studied by laser-induced fluorescence spectroscopy

Abstract

Spatial and temporal variations of C3 density in high-density octafluorocyclobutane (c-C4F8) plasmas were examined using laser-induced fluorescence spectroscopy. The C3 density varied slowly for a long time after the initiation of discharge, suggesting the importance of surface chemistry for the formation of C3. Hollow-shaped spatial distributions (the C3 density adjacent to the chamber wall was higher than that in the plasma column) were observed in the C3 density. This result indicates that C3 radicals are produced from fluorocarbon film on the chamber wall and are lost in the plasma column due to electron impact processes. The surface production of C3 was also observed in the afterglow for 1 ms after the termination of rf power. The decay time constant of the C3 density in the late (>1 ms) afterglow, where the surface production of C3 stopped, was almost independent of discharge parameters, suggesting that the loss of C3 due to gas-phase reactions is negligible.

A global model for C4F8plasmas coupling gas phase and wall surface reaction kinetics

“…The need to include a surface production mechanism for CF x radicals (x = 1-3) is reinforced by several experimental measurements which verify the production of CF x radicals at the walls of the reactor in C 4 F 8 [15,16,[29][30][31] as well as in CHF 3 [66,68], CF 4 [48,[68][69][70] and C 2 F 6 [71] plasmas. Note that C 2 [72] and C 3 [73] radicals were also found to be produced by the fc film on the reactor walls during C 4 F 8 discharges; however, these species are not included in the model due to the lack of the gas phase reactions which these radicals join.…”