On the Ohmic-dominant heating mode of capacitively-coupled plasma inverted by boundary electron emission

TL;DR

This paper uses PIC-MCC simulations to identify a novel Ohmic-dominant heating mode in capacitively coupled plasma caused by boundary electron emission, characterized by sheath inversion and unique transport properties.

Contribution

It introduces a new heating mode in CCP driven by boundary electron emission leading to sheath inversion and modifies the understanding of plasma-sheath interactions.

Findings

Sheath inversion caused by boundary electron emission leads to Ohmic heating dominance.

Transition between classic and Ohmic modes depends on boundary emission flux, voltage, and pressure.

Key diagnostic indicators for this heating mode are proposed for experimental validation.

Abstract

Electron emission from the boundary is ubiquitous in capacitively coupled plasma (CCP) and precipitates nonnegligible influences on the discharge properties. Here we present the PIC-MCC simulation of an Ohmic-dominant heating mode of capacitively coupled plasma where the stochastic heating vanishes and only Ohmic heating sustains the discharge, due to sheath inversion by boundary electron emission. The inverted CCP features negative sheath potential without Bohm presheath, hence excluding plasma heating due to sheath edge oscillation. The particle and energy transport of the proposed heating mode is analyzed. The influences of boundary electron emission flux, source voltage, and neutral pressure on the transition between classic and Ohmic-dominant CCP heating modes are shown with designated simulation scans. A modified inverse sheath-plasma coupling due to excessive ionization is discovered. In the end, key indicators of the proposed heating mode in plasma diagnostics are provided for future experimental verifications.