Investigation of the dual-frequency bias effect on inductively coupled Cl₂ plasmas by hybrid simulation

In the etching process, a bias source is usually applied to the bottom electrode in inductively coupled plasmas (ICPs) to achieve independent control of the ion flux and ion energy. In this work, a hybrid model, which consists of a global model combined bi-directionally with a fluid sheath model, is employed to investigate the dual-frequency (DF) bias effect on the inductively coupled Cl-2 plasmas under different pressures. The results indicate that the DC self-bias voltage developed on the biased electrode is approximately a linear function of the phase shift between the fundamental frequency and its second harmonic, and the value only varies slightly with pressure. Therefore, the ion energy on the bottom electrode can be modulated efficiently by the bias voltage waveform, i.e. the fluctuation of the ion energy with phase shift is about 40% for all pressures investigated. Besides, the ion energy and angular distribution functions (IEADFs) in DF biased inductive discharges is complicated, i.e. the IEADFs exhibits a four-peak structure under certain phase shift values. Although the species densities and ion fluxes also evolve with phase shift, the fluctuations are less obvious, especially for Cl-2 (+) ions at low pressure. In conclusion, the independent control of the ion energy and ion flux are realized in DF biased ICPs, and the results obtained in this work are of significant importance for improving the etching process.