Comparison of Properties of Atmospheric-Pressure Radio Frequency He/SF6/O2 and He/CF4/O2 Discharges

Electrical and optical measurements of atmospheric-pressure radio frequency (13.56 MHz) He/SF 6 /O 2 and He/CF 4 /O 2 discharges are carried out by changing the mixture ratio of a fluoride compound gas to oxygen, where the fraction of He is fixed at 99.5%. Such discharges are produced between two planar electrodes of 40 mm$\phi$ at a gap length of 1.0 or 1.44 mm in the dissipated power range from 30 to 170 W. The phase difference between applied voltage and current in the He/SF 6 /O 2 discharges is approximately 20--30\mbox{ \circ }, whereas that in the He/CF 4 /O 2 discharges is approximately 50--60\mbox{ \circ }. The density of fluorine atoms in such discharges, which should be estimated by actinometry, depends on the mixture ratio of the fluorine compound gas to oxygen. The maximum density is observed when the ratios of the oxygen fraction to the sum of the oxygen and fluoride compound gas fractions are approximately 0.3--0.5 for the He/SF 6 /O 2 discharges and 0.2 for the He/CF 4 /O 2 discharges. The density of fluorine atoms in such discharges is on the order of $10^{14}$ cm -3 . In addition, the results obtained by ozone titration are compared with the density of fluorine atoms in the plasma, which is estimated by actinometry.