INFLUENCE OF THE APPLIED-FIELD FREQUENCY ON THE CHARACTERISTICS OF ARAND SF6 DIFFUSION PLASMAS SUSTAINED AT ELECTRON-CYCLOTRON-RESONANCE ABOVE MULTIPOLAR MAGNETIC-FIELD STRUCTURES

In argon plasmas excited at electron cyclotron resonance above multipo lar magnetic field structures, ion density increases linearly with mic rowave input power but saturates as it gets near the critical density, This behaviour is observed at the three microwave frequencies investi gated, namely 960 MHz, 2.45 GHz, and 5.85 GHz, as well as for differen t magnetic field configurations. The saturation density is independent of the atomic or molecular nature of the gas, as shown with Ar and SF 6. Expectedly, the ion density saturation value varies as the square o f the excitation frequency, while the microwave input power required t o reach saturation is proportional to the critical density, For a give n multipolar magnetic field confinement, the electron temperature is s hown to decrease with increasing excitation frequency, This result ste ms from the confinement of the fast electrons, which generate the plas ma, The evolution of the F-atom concentration in SF6 discharges, as me asured by actinometry, is observed to saturate with microwave input po wer at values depending on gas pressures at both the 2.45 GHz and 5.85 GHz excitation frequencies. Ion density and F-atom concentration satu rate at distinct microwave input powers.