Sheath Model for Dual-Frequency Capacitively Coupled Plasmas

Abstract

Lieberman's radio-frequency (RF) sheath theory is extended to dual-frequency capacitively coupled plasmas. The extended RF sheath theory describes the nonlinear motion of the sheath, for example, the very high frequency (VHF) component of plasma potential varies during the low frequency (LF) cycle and shrinks at the phase such that the lower electrode potential becomes closer to the plasma potential. The theory also describes the plasma potential having a variety of frequency components due to the interaction between VHF and LF. Then the plasma potential and the sheath thickness described in the extended RF sheath theory are incorporated into the Particle-in-Cell, Monte-Carlo-Collision (PIC-MCC) sheath model. The plasma potential, the sheath thickness, and the energy distribution functions of electrons and ions impinging on the biased electrode obtained using the PIC-MCC sheath model correlate well with the results from the one-dimensional PIC-MCC plasma model.