Extraction and neutralization of positive and negative ions from a pulsed electronegative inductively coupled plasma

Almost electron-free (ion-ion) plasmas can be transiently formed during the afterglow phase of pulsed plasmas in electronegative gases. In ion-ion plasmas, both positive and negative ions can be extracted which makes them advantageous for a number of applications. In this paper, we investigate the extraction and acceleration of positive and negative ion beams from a pulsed inductively coupled plasma in SF6. The plasma is bounded by two electrodes biased synchronously with the discharge modulation. It is shown that when a DC bias voltage is applied during the afterglow phase, positive/negative ions are accelerated in a positive/negative space charge sheath formed in front of one of the electrodes. The energy of extracted ions closely follows the amplitude of the applied bias voltage (25-150 V) and the peak beam current density reaches 2 A m (2). With a view to using the described system as a source of energetic neutral beams for low damage material processing, simultaneous extraction and surface neutralization of positive and negative ions using an extraction electrode with high aspect ratio apertures is investigated.