INFLUENCE OF AR METASTABLE ON THE DISCHARGE STRUCTURE IN AR AND NA MIXTURE IN RF DISCHARGES AT 13.56-MHZ

The influence of Ar metastable atoms on the discharge structure in rf glow discharges is investigated in Ar and N-2 mixed gas experimentally and theoretically. The purpose of adding a small amount of N-2 is to control the metastable density. Time- and space-resolved optical emission spectroscopy is applied to investigate the behavior of high-energy electrons. The density profile of Ar metastables in Ar and Na mixture is estimated from the optical emission intensity of the second positive band of N-2, which results from the energy transfer from Ar metastables to N-2 molecules. The decreases of current and optical emission intensity, as well as the Ar metastable density with increase of N-2 ratio, are observed. It is concluded that ionization through metastables is one of the important processes in increasing the plasma density, especially at higher pressures.