Simulations of dual rf-biased sheaths and ion energy distributions arriving at a dual rf-biased electrode

Abstract

Spatio-temporal characteristics of collisionless dual rf-biased sheaths and ion energy distributions (IEDs) impinging on a dual rf-biased electrode are studied with a self-consistent one-dimensional hydrodynamic model. The model includes all the time-dependent terms in the ion fluid equations to ensure that it can describe the sheath dynamics over a wide range of frequencies. In addition, an equivalent circuit model is used to self-consistently determine the relationship between the instantaneous sheath thickness and the instantaneous voltage on the dual rf-biased electrode. The numerical results show that, due to dual radiofrequencies being applied to an electrode, the sheath structures and parameters of dual rf-biased sheaths are different from those in the case of single frequency-biased plasma. Multiple peaks appear in the IEDs arriving at the dual rf-biased electrode rather than a bimodal shape as the IEDs are incident onto a single frequency-biased electrode. It is also shown that some parameters such as the bias frequency and power of the lower-frequency source as well as the phase difference between the lower-frequency wave and the higher-frequency wave are crucial for determining the dual rf sheath structure and the shape of IEDs.