PRESSURE AND ELECTRODE DISTANCE EFFECTS ON ION ENERGY-DISTRIBUTIONS IN RF DISCHARGES

We measured quasi-simultaneously the energy distributions of positive ions at the powered RF and grounded electrode of a parallel plate 13.5 6 MHz discharge using an energy selective mass spectrometer. The resul ting ion energy distributions show the discharge potential conditions expected from a capacitive sheath model. Effects of the discharge pres sure on the collision probability in the sheath, on the tendency of th e sheath thickness, and on the effective discharge geometry are clearl y demonstrated. The main ionization region is located in front of the powered electrode sheath, and the probability of ions reaching the opp osite grounded electrode is characteristically influenced by discharge pressure and electrode distance.