Electrical asymmetry reversal induced by fundamental excitation frequency in capacitively coupled plasmas driven by tailored voltage waveforms

In low-pressure capacitively coupled plasmas (CCPs), discharge asymmetry—induced either geometrically, electrically, or magnetically—plays a crucial role in generating self-bias on the powered electrode that shapes the ion energy distribution function (IEDF) required for dry etching. The electrical asymmetry effect (EAE), in particular, provides a powerful mechanism to decouple ion energy and ion flux by exciting the plasma with two or more consecutive harmonics at fixed but tunable phase shifts. In this work, we present a comprehensive experimental and numerical investigation of EAE in a capacitively coupled argon discharge driven by tailored voltage waveforms (TVWs) over a broad range of fundamental excitation frequencies (40 kHz to 2.72 MHz) at 2 Pa. The IEDF on the powered electrode is measured with a retarding field energy analyzer, while phase-resolved optical emission spectroscopy provides spatiotemporal profiles of electron-impact excitation rates. For both peak- and valley-waveforms, we observe a clear reversal of electrical asymmetry as the fundamental excitation decreases from 2.72 MHz to 40 kHz. The experimental observations are compared with those obtained by the equivalent circuit model and particle-in-cell simulations with Monte Carlo collisions, showing a good agreement.