Spatially resolved atomic excitation temperatures in CH4/H2 and C3H8/H2 RF discharges by optical emission spectroscopy

Spatially resolved optical emission spectroscopy was used to determine the atomic excitation temperature of the capacitively coupled radio-frequency (RF) plasma system. Low pressure plasmas of methane or propane in hydrogen were excited at 13.56 MHz in a parallel plate system. Ar was added as an actinometer. Optical emission lines in the 300-850 nm spectral range were investigated at typical conditions of 100 W RF power, similar to 30 mTorr pressure, 20 mm electrode spacing and 50 sccm total flow rate. Two-dimensional intensity profiles of the important species were collected along the vertical and radial axes. The raw radial intensity was transformed into the actual local radiation intensity by Abel inversion. The atomic hydrogen and argon excitation temperature distributions between the power and grounded electrodes were derived from these data and distinct differences were found in methane-and propane-containing plasmas.