Spatiotemporal optical emission spectroscopy of rf discharges in SF ₆

Space- and time-resolved emission spectroscopy was applied to obtain information on the kinetics of radio-frequency (rf) discharges for 100 kHz, 800 kHz, and 13.56 MHz in SF₆. Emission lines of fluorine and SF _x radical were used, but particularly useful were the second positive (2+) and the first negative (1-) bands of nitrogen. The two nitrogen bands gave an opportunity to separate, respectively, the behavior of middle-energy (11-20 eV) and higher-energy (above 20 eV) electrons. Development of double layers was studied from the excess emission close to the anode due to an increased electric field. Also observed were the emission from the bulk and emission due to the electrons accelerated in the instantaneous cathode sheath. The development of these features was followed as a function of the pressure, frequency, and power.