Ion energy distribution transitions from multimodal to quasi-single-peak in capacitive discharges driven by tailored voltage waveforms

The ion energy distribution (IED) bombarding the electrodes plays an important role in capacitively coupled argon discharges that are applied in plasma etching. In this work, we employed a fully kinetic particle-in-cell Monte Carlo collision model to investigate the ion energy distributions (IED) in low pressure (~10mTorr) capacitive argon discharge with one electrode driven by a high frequency voltage source (60 MHz) and the other electrode driven by a low-frequency composed tailored voltage waveform. It is found that the IEDs exhibid a transition from a multimodal to quasi-single-peak profile while increasing the amplitude of the low frequency tailored voltage waveform and keeping the high frequency voltage amplitude a constant. This is because the DC bias exhibits an apparent change from a positive to negative value when the tailored waveform amplitude increases. The secondary electron emission from the surface also significantly influences the ion/electron energy distribution and a detailed analysis of the dynamics of the oscillating sheath field will be discussed.