Time-resolved evolution of plasma parameters in a plasma immersion ion implantation source

Abstract

The origin and nature of perturbations induced by a high-voltage pulse on plasma parameters and their relationship to operating conditions (power and pressure) in an argon inductively coupled radio-frequency plasma device is explored. The plasma parameters are measured with two radiofrequency compensated Langmuir probes positioned either vertically above the pulsing target or horizontally along the diameter of the chamber, in the same axial plane as the target and same distance from the RF antenna. Fluctuations are observed in electron density ne, temperature Te and plasma potential V pl following negative polarity high voltage pulses, and propagate deep in the plasma and well after the end of the pulse. Time-resolved data results indicate that the perturbations are significantly dampened at higher power, as well as when closer to the plasma RF coil. The perturbation amplitudes depart significantly from steady state values when the pulse amplitude exceeds 2.0 kV, and increase with increasing pulse amplitude. Perturbation amplitudes are also higher for target materials having larger secondary electron yield. Our experimental results suggest that the underlying mechanism of this perturbation could be plasma heating driven by damping of a beam-plasma instability as a result of a beam of secondary electrons emitted by the target streaming into the plasma.