Influence of Ar Metastable on the Discharge Structure in Ar and N ₂ 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 N₂ mixed gas experimentally and theoretically. The purpose of adding a small amount of N₂ 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 N₂ mixture is estimated from the optical emission intensity of the second positive band of N₂, which results from the energy transfer from Ar metastables to N₂ molecules. The decreases of current and optical emission intensity, as well as the Ar metastable density with increase of N₂ 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.