Computational simulations of spatio-temporal plasma dynamics in a very high frequency capacitively coupled reactor

The standing wave effect in Very High Frequency Capacitively Coupled Plasma (VHF CCP) reactors is a major cause of plasma non-uniformity. The nonlinearly excited higher harmonics exacerbate this non-uniformity. In this work we analyze the physical mechanisms of plasma-electromagnetic wave coupling in detail for a single RF cycle of the input electric field. We consider a simplified CCP reactor geometry operated at 100 mTorr and computationally simulate three cases where the bulk electron density increases from order 10(15) m(-3) to 10(17) m(-3). We see the appearance of higher harmonics in the B-dot signal with increasing bulk electron density in accordance with recent experimental measurements. By looking at the spatio-temporal variations of different quantities at a periodic steady state, we observe significant changes in the dynamics of current flow, electromagnetic power deposition and ionization rates within the reactor. In particular, as the electron density increases, we see that the current profile in the bulk plasma exhibits a re-circulation pattern that is correlated with the appearance of structural features in the B-dot signal seen in the measurements.