Characteristics of 1-MHz Discharges in SF 6/Ar and CF 4/Ar Mixtures in a Parallel-Plate System

In SF6/Ar and CF4/Ar mixtures at a total pressure of 0.5 Torr, the discharge characteristics at 1-MHz have been investigated as a function of the mixing ratio. In the case of the SF6/Ar mixture, discharge parameters, such as discharge-sustaining voltage and discharge current, suddenly decrease by mixing only 5% SF6 with Ar, and the plasma exists uniformly only inside the gap between electrodes. By increasing the SF6 ratio, the electron temperature rises, and tends to saturate at large SF6 ratios. In the case of the CF4/Ar mixture, the plasma density near the discharge axis is lower than that around the edge of the electrode at small CF4 ratios. At a CF4 ratio of 20%, in particular, the plasma density in the interelectrode gap becomes very low, and the spatiotemporal emission profile across the gap around the edge of the electrode is different from that at the axis. At CF4 ratios greater than 60%, the discharge parameters suddenly change due to the electronegativity of CF4. These characteristics are synergistic.