PIC/MCC simulations of the effects of a radio-frequency bias on inductively coupled plasmas

Many plasma processing applications require precise RF bias control. In this study a 2D Particle-in-cell/Monte Carlo Collisions model of Inductively coupled plasmas (ICP) with complex electrode geometry and RF bias is validated against experimental measurements performed in a GEC reference cell. The results show that the RF bias nonlinearly reduces the plasma density while shifting the Electron energy probability distribution function (EEPF) to lower energies and transforming the Ion energy and angular distribution function (IEADF) from a single to a double peak structure with a narrow angular distribution. Furthermore, we confirm and explain three experimentally observed ICP-CCP coupling mechanisms^[1] that potentially limit independent control of ion flux and energy: Even at high ratios of the inductively (P_ICP) and capacitively (P_CCP) applied powers, P_ccp significantly affects the EEPF through sheath heating, demonstrating its nonnegligible influence on plasma density and ion flux; P_ICP modifies the voltage drop across the sheath at fixed P_CCP and, thus, the IEADF, since increasing P_ICP raises the plasma current, thereby reducing the sheath voltage. P_ICP alters the frequency and damping characteristics of plasma series resonance (PSR) oscillations of the RF current. The simulation results show good experimental agreement and advance understanding of ICP-CCP coupling.

[1] Schulze J et al. APL. 100, 024102 (2012).

Funded by NSFC (12275095, 11975174, 12011530142) and DFG (428942393).