Characterisation of high voltage pulser performance in radiofrequency plasmas

Abstract

The performance of a high voltage pulser in plasma immersion ion implantation is strongly influenced by the plasma load into which it operates. There are a number of plasma parameters, such as ion density, potential distribution and ionisation rate, that affect the formation of the cathodic sheath around the workpiece. In turn, these place limitations on the range of voltage, ion current density and duty cycle that is possible to achieve with the pulser. In this paper, we present results of studies into the performance of a 50 kV, 8 A pulser in the ANSTO PI 3 facility (∼ 0.4 m 3). The plasma is a low pressure radiofrequency discharge formed by 300 W of r.f. power at 13.56 MHz applied 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 × 10 −3 mbar. The plasma parameters can be altered by varying the r.f. power, the plasma potential, the gas mixture and the filling pressure. Optical emission spectroscopy has shown a large increase in emission from atomic species that are sputtered from the surface of the workpiece during the high voltage pulse. This emission decays very rapidly when the high voltage pulse is terminated.