Collisional effect on the time evolution of ion energy distributions outside the sheath during the afterglow of pulsed inductively coupled plasmas

Abstract

The time evolution of ion energy distributions (IEDs) during the afterglow is measured in various inert gas plasmas generated by an inductively coupled plasma source. The afterglow regimes are prepared by periodically pulsing the plasmas, with a period of 1000 mu s. The time-resolved retarding field energy analyzer method and Langmuir probe method are used to measure the detailed time evolution of IEDs at 5 mu s intervals to investigate precisely what happens in the vicinity of the rf-off moment. The measured results show that double-peaked IEDs appear at the early afterglow. By analyzing the force equation of the ions in a time-varying plasma potential environment, we found that this double-peaked structure originates from the delayed arrival of ions under our discharge conditions. This effect is expected to disappear under high-pressure conditions where ions lose their energy due to the momentum loss caused by collisions between background particles, and the time evolution of IEDs during the afterglow changes its form to a typically expected pattern, a single-peaked structure. The findings in this report can be utilized to understand pulsed plasma characteristics in the semiconductor fabrication area where pulsed plasmas are now widely used in the dry etching process.