Silicon oxide etching processes in C2F6 and C4F8+80% Ar plasmas were investigated. Neutral and ion compositions in the plasma were measured using quadrupole mass spectrometry and etching yield was measured by a quartz-crystal microbalance. In C2F6 plasma, the concentration of atomic fluorine in the neutral flux was 5%-25%, whereas there was less than 0.5% of atomic fluorine in C4F8 + 80% Ar plasma. A surface plot representing the etching yield as a function of neutral and ion fluxes was constructed and used to qualitatively explain the etching characteristics of silicon oxide in fluorocarbon plasmas. In C2F6 chemistry, etching yield decreases slightly with increasing rf coil power. This is attributed to the decrease in both F/ion and CFx/ion, which is caused by an increase in ion flux, with a more significant effect due to a decrease in F/ion. In C4F8+80% Ar chemistry, however, etching yield increases with increasing rf coil power. This is attributed to the decrease in CFx, without the effect of F/ion due to the low atomic fluorine concentration. With increased operating pressure, etching yield decreases for both chemistries because as the pressure increases, ion current decreases, and CFx neutral concentration increases to have more deposition and less etching. (c) 2006 American Vacuum Society.