Noninvasive Monitoring of Ion Energy Drift in an Inductively Coupled Plasma Reactor
Mark A. Sobolewski
A non-invasive method for monitoring ion current and ion kinetic energy has been used to monitor drift in an inductively coupled, rf-biased plasmareactor. The technique detects a slow decrease in ion current over time caused by the deposition of a conductive layer on the dielectric window ofthe inductive source. Accompanying this drift in ion current are changes in ion energy that, depending on conditions, may be large or small,increasing or decreasing. The changes in ion energy are explained by three different kinds of mechanisms: bias voltage effects, sheath impedanceeffects, and ion transit time effects. These mechanisms, and the monitoring technique itself, are not limited to the particular experimentalconditions of this study; rather, they apply to a wide range of plasmas and reactors. Drifts in ion energy similar to those reported here haveundoubtedly occurred in many plasma reactors but have gone unnoticed for lack of any method to detect them.