Electron power absorption dynamics in a low pressure radio frequency driven capacitively coupled discharge in oxygen

TL;DR

This study investigates electron power absorption and electric field dynamics in low-pressure oxygen capacitively coupled discharges using particle-in-cell simulations, revealing pressure-dependent mechanisms and contributions.

Contribution

It provides a detailed analysis of electric field components and electron power absorption mechanisms at different pressures, highlighting the role of sheath expansion and electronegativity.

Findings

At 10 and 100 mTorr, ohmic contributions remain similar.

Ambipolar and temperature gradient effects vary with pressure.

Power absorption mechanisms depend on electronegativity and pressure.

Abstract

We use the one-dimensional object-oriented particle-in-cell Monte Carlo collision code oopd1 to explore the properties and the origins of both the electric field and electron power absorption within the plasma bulk for a capacitively coupled oxygen discharge operated at 10 and 100 mTorr for 45 mm of gap distance. The properties of the electric field at three different time slices as well as time averaged have been explored considering the moments of the Boltzmann equation. The electron power absorption is distinctly different at these operating pressures. The most relevant contributions to the electric field at different time steps come from the pressure terms, the ambipolar and the electron temperature gradient terms, along with the ohmic term. The same applies for the electron power absorption. At both 10 and 100 mTorr the relative ohmic contribution to the electron power absorption remains roughly the same, while the ambipolar term contributes to power absorption and the temperature gradient term to electron cooling at 100 mTorr, and the opposite applies at 10 mTorr. At 100 mTorr the discharge is weekly electronegative, and electron power absorption is mainly due to sheath expansion while at 10 mTorr it is strongly electronegative, and the electron power absorption occurs mainly within the electronegative core and drift-ambipolar mode dominates. The agreement between the calculated values and the simulations is good for both the electric field and the electron power absorption within the plasma bulk and in the collapsed sheath region for all the cases considered.