Ion energy distributions in rf sheaths; review, analysis and simulation

TLDR

The review focuses on the collisionless regime of rf sheaths, which is of great interest for high‑density discharges with thin sheaths compared to conventional reactive ion etching systems. The authors review and analyze ion energy distributions arriving at the target of an rf discharge, assessing prior work and identifying factors that shape the IEDs. They discuss collisional effects and perform particle‑in‑cell simulations of a collisionless current‑driven rf sheath to examine how ion modulations influence the IEDs. The simulations reveal that ion modulations in an rf sheath significantly alter the IEDs when the ion transit time is shorter than the rf period (ion/rf < 1).

Abstract

We present a review and analysis of ion energy distributions (IED) arriving at the target of a radio frequency (rf) discharge. We mainly discuss the collisionless regime, which is of great interest to experimentalists and modellers studying high-density discharges in which the sheath is much thinner than in conventional reactive ion etching systems. We assess what has been done so far and determine what factors influence the shape of the IEDs. We also briefly discuss collisional effects on the IEDs. Having determined the important parameters, we perform some particle-in-cell simulations of a collisionless current-driven rf sheath which show that ion modulations in an rf sheath significantly affect the IEDs when ion/rf<1, where ion is the ion transit time and rf is the rf period.