Ion energy distributions in a pulsed dual frequency inductively coupled discharge of Ar/CF₄ and effect of duty ratio

Controlling time averaged ion energy distribution (IED) is becoming increasingly important in many plasma material processing applications for plasma etching and deposition. The present study reports the evolution of ion energy distributions with radio frequency (RF) powers in a pulsed dual frequency inductively discharge and also investigates the effect of duty ratio. The discharge has been sustained using two radio frequency, low (P_2MHz=2MHz) and high (P_13.56MHz=13.56MHz) at a pressure of 10 mTorr in argon (90%) and CF₄ (10%) environment. The low frequency RF powers have been varied from 100 to 600W, whereas the high frequency powers from 200 to 1200 W. Typically, IEDs show bimodal structure and energy width (energy separation between the high and low energy peaks) increases with increasing P_13.56MHz; however, it shows opposite trends with P_2MHz. It has been observed that IEDs bimodal structure tends to mono-modal structure and energy peaks shift towards low energy side as duty ratio increases, keeping pulse power owing to mode transition (capacitive to inductive) constant.