Plasma density and ion energy control via driving frequency and applied voltage in a low pressure capacitively coupled plasma discharge

TL;DR

This study uses simulations to explore how varying RF voltage and driving frequency in low pressure CCPs can independently control plasma density and ion energy, revealing operational regimes and transition thresholds.

Contribution

It demonstrates that voltage and frequency can be tuned independently to control plasma parameters, providing new insights for plasma processing optimization.

Findings

Plasma density remains constant over a frequency range before increasing rapidly.

Threshold frequency for density increase depends on applied voltage.

Sheath width increases with frequency, affecting ion energy without changing density.

Abstract

The dynamical characteristics of a single frequency low pressure capacitively coupled plasma (CCP) device under varying applied RF voltages and driving frequencies are studied using particle-in-cell/Monte Carlo collision simulations. An operational regime is identified where for a given voltage the plasma density is found to remain constant over a range of driving frequencies and to then increase rapidly as a function of the driving frequency. The threshold frequency for this mode transition as well as the value of the constant density is found to increase with an increase in the applied voltage. Over the constant density range, for a given voltage, the sheath width is seen to increase as a function of the increasing driving frequency, thereby changing the ion energy without affecting the ion density. Our parametric study thus indicates that the twin knobs of the applied voltage and driving frequency offer a means of independently controlling the density and the ion energy in a low pressure CCP device that may be usefully exploited for plasma processing applications.