Discharge characteristics of a low-pressure geometrically asymmetric cylindrical capacitively coupled plasma with an axisymmetric magnetic field

TL;DR

This study explores how applying an axisymmetric magnetic field influences discharge parameters in a low-pressure asymmetric cylindrical plasma, revealing transitions in plasma behavior and offering new control methods for plasma processing.

Contribution

It demonstrates how magnetic fields can induce symmetry and control plasma characteristics independently in a cylindrical CCP system, enhancing plasma density and reducing electron temperature.

Findings

Discharge asymmetry transitions with magnetic field variation.

Plasma density peaks within a specific magnetic field range.

EEDF changes from bi-Maxwellian to Maxwellian with increasing magnetic field.

Abstract

We investigate the discharge characteristics of a low-pressure geometrically asymmetric cylindrical capacitively coupled plasma discharge with an axisymmetric magnetic field generating an EXB drift in the azimuthal direction. Vital discharge parameters, including electron density, electron temperature, DC self-bias, and Electron Energy distribution function (EEDF), are studied experimentally for varying magnetic field strength (B). A transition in the discharge asymmetry is observed along with a range of magnetic fields where the discharge is highly efficient with lower electron temperature. Outside this range of magnetic field, the plasma density drops, followed by an increase in the electron temperature. The observed behavior is attributed to the transition from geometrical asymmetry to magnetic field-associated symmetry due to reduced radial losses and plasma confinement in the peripheral region. In this region, the DC self-bias increases almost linearly from a large negative value to nearly zero, i.e., the discharge becomes symmetric. The EEDF undergoes a transition from bi-Maxwellian for unmagnetized to Maxwellian at intermediate B and finally becomes a weakly bi-Maxwellian at higher values of B. The above transitions present a novel way to independently control the ion energy and ion flux in a cylindrical CCP system using an axisymmetric magnetic field with an enhanced plasma density and lower electron temperature operation that is beneficial for plasma processing applications.