Generation of energetic electrons by surface waves in VHF CCPs

TL;DR

This paper investigates how surface waves in high-frequency capacitively coupled plasmas influence electron energization and plasma uniformity, using advanced simulations to reveal complex kinetic interactions at low pressures.

Contribution

It presents a detailed kinetic analysis of surface wave effects on electron dynamics in CCPs, highlighting the importance of non-local phenomena at high frequencies.

Findings

Surface waves significantly affect electron energization profiles.

Higher driving frequencies alter surface wave excitation.

Non-local kinetic effects are crucial at low pressures.

Abstract

Capacitively coupled plasmas (CCP) comprise one of the main tool in active use in the plasma processing industry. However, increasing the driving frequency and electrode size is limited by the emergence of plasma radial nonuniformity detrimental for applications. The nonuniformity is caused by interactions of surface waves natural to the plasma-filled reactor with electrons of the plasma, leading to the complex electron energization and ionization dynamics. Using a self-consistent fully electromagnetic energy- and charge-conserving implicit particle-in-cell code ECCOPIC2M, we demonstrate that the electron energization and ionization profiles result from an involved interplay between different phenomena, demanding a kinetic and non-local description for the low pressures considered. Changes in the surface wave excitation with the driving frequency are discussed.