CHARACTERIZATION OF HIGH-VOLTAGE PULSER PERFORMANCE IN RADIOFREQUENCYPLASMAS

The performance of a high voltage pulser in plasma immersion ion impla ntation is strongly influenced by the plasma load into which it operat es. There are a number of plasma parameters, such as ion density, pote ntial distribution and ionisation rate, that affect the formation of t he cathodic sheath around the workpiece. In turn, these place limitati ons on the range of voltage, ion current density and duty cycle that i s possible to achieve with the pulser. In this paper, we present resul ts of studies into the performance of a 50 kV, 8 A pulser in the ANSTO PI3 facility (similar to 0.4 m(3)). The plasma is a low pressure radi ofrequency discharge formed by 300 W of r.f. power at 13.56 MH2 applie d to a single-loop antenna immersed in a plasma with an ion density of approximately 10(9) cm(-3) and filling pressure of 0.5-5 x 10(-3) mba r. The plasma parameters can be altered by varying the r.f. power, the plasma potential, the gas mixture and the filling pressure. Optical e mission spectroscopy has shown a large increase in emission from atomi c species that are sputtered from the surface of the workpiece during the high voltage pulse. This emission decays very rapidly when the hig h voltage: pulse is terminated. (C) 1997 Elsevier Science S.A.