Behavior of F Atoms and CF2 Radicals in Fluorocarbon Plasmas for SiO2/Si Etching

Abstract

Densities of F atoms and CF2 radicals were measured in CF4, C2F6 and CHF3 plasmas by vacuum ultraviolet laser absorption and laser-induced fluorescence techniques, respectively, using an RF (400 kHz) plasma source. In the measurement of source gas dependence, the F atom density became highest in CF4 and lowest in CHF3, while the tendency was reversed for the CF2 radical density. Dilution of the source gases with O2 caused increases in the F atom density and decreases in the CF2 density, but dilution with H2 brought about significant decreases in the F atom density. The density of CF2 radicals was largely affected by the chamber wall conditions, with or without polymer deposition. The decay time constants of these species were also measured during the pulsed afterglow, and the results were qualitatively consistent with the behavior of the densities. However, some quantitative disagreements remain, suggesting that the loss rates of these species in active plasmas are different from the rates in the afterglow.