Comparison of Power Absorption Ability of Ar and O2, N2 Plasma of RF Inductive Discharge

The measurements of the RF power absorption efficiency have been performed in the pressure range of argon in the range of 1 × 10–3–0.7 Torr, oxygen pressures in the range of 8 × 10–4–0.05 Torr, nitrogen pressure 3 × 10–3–4 × 10–2 Torr at the operating frequency of 4 MHz. In argon the efficiency of RF generator power coupling to plasma in the considered pressure range weakly increases with increasing argon pressure. In oxygen and nitrogen plasma at powers below 500 W the RF power coupling efficiency depends non-monotonically on pressure. The admixture of even small amount of oxygen to argon discharge leads to the decrease of RF power coupling efficiency at high Ar pressure and RF generator power below 400 W. A decrease in the fraction of RF generator power absorbed by the plasma under pressure growth leads to a decrease in the plasma density and discharge disruption. Thus, the area of existence of the discharge appears to be limited on the high-pressure side. The higher is the RF generator power, the wider is the range of pressures at which the RF inductive discharge can exist. The numerical simulation showed that the observed experimental facts were due to the peculiarities of the dependence of equivalent plasma resistance on electron density and frequency of electron collisions with heavy particles.