Reaction Chemistry in the Afterglow of an Oxygen−Helium, Atmospheric-Pressure Plasma

The reaction chemistry in the afterglow of a non-equilibrium, capacitive discharge, operated at 600 Torr total pressure with (0.5 to 5.0) 1017 cm-3 of oxygen in helium, has been examined by ultraviolet absorption spectroscopy, optical emission spectroscopy, and numerical modeling. The densities of the active species, O(3P), O2(1¢g), O2(1“g+), and O3, have been determined as a function of the operating conditions. At RF power densities between 6.1 and 30.5 W/cm3 and a neutral temperature of 100 ( 40 °C, the plasma generated (0.2 to 1.0) 1016 cm-3 of O(3P) and O2(1¢g), (0.2 to 2.0) 1015 cm-3 of O2(1“g+), and (0.1 to 4.0) 1015 cm-3 of O3. After the power was turned off, the singlet-sigma and singlet-delta states decayed within 0.1 and 30.0 ms, respectively. The concentration of oxygen atoms remained constant for about 0.5 ms, then fell rapidly due to recombination with O2 to form O3. It was found that the etching rate of polyimide correlated with the concentration of oxygen atoms in the afterglow, indicating that the O atoms were the active species involved in this process. I.