We have developed a technique which enables us to reduce the self-bias voltage without introducing any substantial disturbance to the main plasma. This approach is based on decreasing the floating potential of the powered electrode by means of injecting an electron current from the electrode. Instead of employing a hot cathode, we have used an auxiliary glow discharge to supply the electron emission. The controllable range of the self-bias has been extended to almost 0 V. A theoretical explanation of the variation of the floating potential with the emission current has been carried out. Measurements of the floating voltage(Vf) are plotted against ln(1/Iau), where Iau is the auxiliary discharge current. A good linear relationship of Vf vs. ln(1/Iau) is obtained as expected from the theory, and its slope gives the electron temperature.
In order to appraise the degree of damage induced by the bombardment of ions accelerated by the sheath voltage, we have estimated the damage by measuring the dark current of a sample diode fabricated from the film. It has been observed experimentally that when the sheath voltage was depressed from -73 V to -36 V at a pressure of 0.11 Torr, the dark current of the sample diode was suppressed drastically from 1.3 ×10−10 A to 5.3×10−11 A