Comparative investigations of ion energy distributions in pulse-modulated and continuous wave Ar inductively coupled plasma

Using a retarding field energy analyzer, time-averaged ion energy distributions (IEDs) are systematically investigated in both continuous wave (CW) and pulse-modulated Ar radio frequency (RF) inductively coupled plasmas (ICPs) under grounded, CW RF, and pulse-modulated RF bias conditions. Sheath dynamics are further analyzed by incorporating Langmuir probe measurements of electron density and electron temperature. Under grounded bias conditions, CW discharges exhibit single-peaked IEDs, whereas pulse-modulated discharges show bimodal structures due to temporal variations in plasma potential. With the application of a CW RF bias, the sheath is jointly governed by the bulk plasma and RF bias, resulting in bimodal IEDs at low source power and a transition to single-peaked distributions at higher power. For pulse-modulated RF bias schemes, the sheath evolves continuously throughout the pulse cycle. In synchronous pulse-modulated ICPs, a pronounced bimodal IED is observed, originating from two distinct mechanisms: quasi-dc sheath acceleration during the initial active-glow stage and RF phase-modulated acceleration during the steady-state stage. The ion transit time relative to the RF period is identified as the key parameter governing ion energy modulation. By adjusting the pulse duty cycle, the relative contributions of these mechanisms can be effectively tuned, enabling precise control of ion energy and energy spread.