Measurements of electron energy distribution function in an asymmetric radio-frequency discharge plasma

Electron energy distribution functions in an asymmetric radio-frequency (rf) discharge helium plasma were measured using an electrostatic energy analyzer looking opposite ways toward both the powered electrode and the bulk plasma. The grid and collector in the analyzer were connected to a series of parallel inductance-capacitance (L-C) filters to minimize rf interference. Electrons with high energies (15–30 eV) flowing from the electrode toward the bulk plasma were observed near the electrode. The energy is caused by the acceleration mechanism due to the rf sheath expansion, which should be the rf discharge sustaining mechanism. The electrons with high energies decreased in number with the distance from the electrode and became Maxwellian far from it. Electrons directed toward the electrode from the plasma were almost Maxwellian, and this situation was almost independent of the distance from the electrode.