Positive and Negative Ions in RF Plasmas of SF 6/N 2 and SF 6/Ar Mixtures in a Planar Diode

Ionic species in 13.56 MHz discharge of SF6/N2 and SF6/Ar mixtures were measured by means of direct sampling using a quadrupole mass spectrometer. Dominant negative ions in the SF6/N2 discharge are F-, SF5 - and SF6 -, while the positive ions are SF3 +, SF5 + and N2 +. In the SF6/Ar discharge the major ions are the same as in the SF6/N2 discharge except that N2 + is replaced by Ar+. The signal intensity ratios of these ionic species depend on the ratio of N2 or Ar to SF6 in the discharge. In particular, the ratio of Ar to SF6 in the SF6/Ar discharge increases, the signal intensity ratio of SF3 + to SF5 + shows a concave variation, and the total intensity of negative ions decreases rapidly in the SF6/Ar discharge. These results in the SF6/Ar discharge are different from the variations in the SF6/N2 discharge, and seem to be based on the effects of the metastable atom Ar* on both production of SF3 + and extinction of negative ions.