ION ENERGY-DISTRIBUTIONS IN OXYGEN AND ARGON IN A PULSED MODE RF DISCHARGE

The positive and negative ion energy distributions were measured at th e grounded electrode of a square wave modulated RF discharge in O-2 an d Ar at between 1.5 and 5 Pa gas pressure. The resulting ion energy di stributions were strongly affected by the modulation frequency accordi ng to the existence of different discharge periods during the modulati on cycle. These discharge periods were directly represented in the ene rgy distribution of the positive ions which is determined by the plasm a sheath voltage in front of the grounded electrode. Negative ions gen erated in the plasma sheath at the RF electrode were accelerated towar ds the bulk plasma and detected with a high energy at the opposite gro unded electrode. Additionally, during the afterglow with decaying shea th potential, low energy negative ions reached the electrodes. The int ensity ratio between the two groups of negative ions allowed conclusio ns on the negative ion generation process. (C) 1997 Elsevier Science L td.