Quantitative evaluation of the densities of active species of N2 in the afterglow of Ar-embedded N2 RF plasma

The N2 and Ar-20%N2 RF plasmas and afterglows have been generated in a quartz tube under a flowing condition maintained at 6–8 Torr and a flow rate of 0.5–0.6 slm. The detailed emission characteristics of active species have been analyzed by emission spectroscopy. Under such conditions, the plasma rotational temperature increases from 400 to 800 K with increasing RF powers from 50 to 130 W, while the characteristic vibrational temperature remains at about 104 K. The densities of active species (N, N2(A), N2(X, v > 13) and N2+) in the afterglow are measured to be in the order of ∼1015, ∼1011, ∼1014 and ∼1010 cm−3, respectively. In addition, the following characteristics of the afterglows are noted: First, the same densities of the active species can be obtained at lower RF powers (20–50 W) for Ar-20%N2 than for pure N2 which requires higher RF powers (50–100 W). Second, the ionization degree of N2+/N2 in the plasma increases readily to a saturation value at a lower RF power of 50 W for Ar-20%N2, whereas in the afterglow, the absolute density of N2+ is further reduced below 109 cm−3. •More N2+ ions are produced in the RF plasma at lower RF power when Ar is mixed with N2.•Higher densities of active species of N2 in the Ar-20%N2 afterglow are achieved at lower RF power.•The density of N2+ in the afterglow of the Ar-20%N2 mixture can be reduced below 109 cm−3.