Numerical study of ion energy and angular distributions in dual-frequency capacitively coupled CF4 plasmas

Abstract

A one-dimensional hybrid model is presented in the paper to study the characteristics of ion energy and angular distributions on the rf-biased electrode in dual frequency capacitively coupled CF4 discharges. The hybrid model includes two parts: a fluid module and a Monte Carlo (MC) module. The fluid module determines the spatiotemporal evolutions of bulk plasma, and the MC module describes the ion-neutral collisions to predict the ion energy and angular distributions on rf-biased electrode. The discussion of this paper focuses on the influence of pressure, voltage, amplitude, and frequencies of the low frequency source on ion energy distributions (IEDs) and ion angular distributions (IADs) of CF3+ and F+ ions. For the CF3+ ions, the IEDs appear to have multiple-peak structures in the dual frequency capacitively coupled rf discharge, and the IADs have a significant peak at a small angle. With the increase of pressure, the maximum energy in IEDs decreases, and the IADs spread to a large angle region. With the decrease of the low frequency or increase of the LF voltage, more ions get a higher energy while they are going across the sheath region, the width and maximum ion energy of IEDs increase, and the peaks in IADs shift toward small angle regions. For the F+ ions, the IEDs are modulated strongly by the sheath field, and the peaks are more prominent than those of heavy ions. The width between different peaks is narrower than that of CF3+ ions, and the maximum energy is also higher.