Double layer formation in the expanding region of an inductively coupled electronegative plasma

TL;DR

This study investigates the formation and stability of double-layers in inductively coupled argon/sulfur hexafluoride plasmas, revealing their dependence on electronegativity and their role as internal boundaries between different plasma regions.

Contribution

It provides new insights into the conditions for double-layer formation and their characteristics in electronegative plasmas, highlighting their stability range and formation boundary.

Findings

Double-layers form in specific electronegativity ranges (8-13%)

DLs are unstable at higher electronegativity levels

DLs act as internal boundaries with a potential amplitude of about 1.5 kT_e/e

Abstract

Double-layers (DLs) were observed in the expanding region of an inductively coupled plasma with $\text{Ar}/\text{SF}\_6$ gas mixtures. No DL was observed in pure argon or $\text{SF}\_6$ fractions below few percent. They exist over a wide range of power and pressure although they are only stable for a small window of electronegativity (typically between 8\% and 13\% of $\text{SF}\_6$ at 1mTorr), becoming unstable at higher electronegativity. They seem to be formed at the boundary between the source tube and the diffusion chamber and act as an internal boundary (the amplitude being roughly 1.5$\frac{kT\_e}{e}$)between a high electron density, high electron temperature, low electronegativity plasma upstream (in the source), and a low electron density, low electron temperature, high electronegativity plasma downstream.