Spatial structure of radio-frequency capacitive discharge plasma with ring-shaped hollow electrode using Ar and O2 mixture gases

Abstract

The spatial structures of plasma parameters in a radio-frequency capacitive discharge plasma with a ring-shaped hollow electrode operated in argon were measured at various oxygen gas concentrations for plasma processing by moving a cylindrical Langmuir probe. Their distinctive profiles are obtained around the ring-shaped hollow trench. The electron temperature Te at the hollow trench of radial position r = 37.5 mm has a peak value at an O2 gas concentration of 0%, whereas at O2 gas concentrations of 5 and 10% Te decreases everywhere except for positions close to the hollow trench. The plasma potential Vs at an O2 gas concentration of 0% is higher than that at O2 gas concentrations of 5% and 10%. The electron density ne has a peak value at the hollow trench at all O2 gas concentrations and decreases with increasing O2 gas concentration. Their axial profiles indicate unique distributions around the hollow inlet at a radial position of r = 37.5 mm, while at a radial position of r = 0 the profiles are almost uniform. It is found that a double layer is formed from the axial profiles of the plasma potential at r = 37.5 mm for all oxygen gas concentrations.