in conventional plasma generation techniques a plasma is generated and maintained either by capacitive coupled inductively coupled or microwave coupled energy by far the most common approach uses capacitive coupling of radio frequency rf power through parallel plate electrodes a magnetic field may be used to enhance the density of the plasma fig1 depicts a vacuum reactor chamber 10 a lower electrode 12 referred to as the cathode and an upper electrode 14 referred to as the anode which typically also functions to introduce process gases into the chamber through openings in the electrode as indicated by the arrows 16 power is applied to the lower electrode 12 as indicated by an rf generator 18 one terminal of which is connected to the lower electrode and the other terminal of which is grounded the upper electrode is typically connected to the walls of the chamber 10 which is grounded as indicated at 20 since the upper electrode in this embodiment is electrically continuous with the chamber walls as is typical the upper electrode is also grounded when process gases are introduced as indicated at 16 and a suitable rf power is applied across the electrodes 12 and 14 a plasma of ions electrons and other particles is generated and sustained in the chamber 10 moreover as is well known the lower electrode 12 becomes negatively self biased with respect to the plasma this dc bias level is used to accelerate ions in the plasma into a semiconductor wafer 22 secured to the surface of the lower electrode 12 by a suitable clamp or.