Experimental study on properties of radio frequency He/CF4/O2 discharges at atmospheric pressure

Abstract

Electrical and optical measurements of atmospheric pressure radio frequency (RF) (13.56 MHz) He/CF4/O2 discharges are carried out by changing the mixture ratio of CF4 and O2 at the volume fraction of He higher than 99%. These discharges are produced between two planar electrodes of 40 mm ∅ at a gap length of 1.0 mm or 1.44 mm in the dissipated power range from 30 to 150 W. The relationship between the applied voltage and the current in the He/CF4/O2 discharges does not strongly depend on the mixture ratio of CF4 and O2. The atomic fluorine density estimated by actinometry markedly increases with the increase in the O2 addition and then reaches a maximum when the ratio of the O2 fraction to the sum of CF4 and O2 fractions is around 0.2. The density of fluorine atoms produced in those discharges is on the order of 1014 cm−3. In addition, the density of fluorine atoms in the afterglow downstream of the reactor is also estimated using the ozone titration and is compared with the density in the plasma, which is estimated by actinometry.