Control of ion energy distributions using a pulsed plasma with synchronous bias on a boundary electrode

Abstract

Ion energy distributions (IEDs) on a grounded substrate in a Faraday-shielded argon inductively coupled plasma were measured with a retarding field energy analyzer. A Langmuir probe was also used to measure space- and time-resolved plasma parameters. IEDs and plasma parameters were studied with continuous or pulsed positive dc bias voltage on a ‘boundary electrode’ in contact with the plasma. For continuous wave plasmas without applied bias, the IED exhibited a single broad peak at the plasma potential. Applying a continuous positive dc bias on the boundary electrode shifted the peak of the IED to higher energy. Application of a synchronous dc bias on the boundary electrode during the afterglow of a pulsed plasma resulted in a double-peaked IED. The mean energies of the two peaks, as well as the peak separation, were controlled by adjusting the applied dc bias and the discharge pressure. The full width at half maximum (FWHM) of the peak corresponding to the synchronous dc bias diminished with decreasing electron temperature. The FWHM was controlled by varying the time window in the afterglow during which dc bias was applied.