GEC Student Excellence Award Finalist Presentation - Uniformity control by customized electrode designs in capacitive RF plasmas

Plasma uniformity control in capacitive RF discharges by tailored electrode topologies and materials is investigated in argon at low pressure by 2D Particle-In-Cell/Monte Carlo collision simulations. Embedding ring-shaped trenches into an electrode is found to increase the plasma density locally by enhancing the electron interaction with the sheath at the trench position. By analyzing the trajectories of selected electrons as well as the time evolution of their energy and velocity inside and above such trenches, the electrons are found to gain high energies by bouncing between the sheaths at the trench sidewalls, leading to high ionization rates at the trench orifice. Radial variations of the electrode material characterized by different secondary electron emission/electron reflection coefficients are also found to provide control of the radial profile of the ionization rate due to the significant contribution of the emitted/reflected electrons to the ionization. Both methods of customizing the electrode design are able to remarkably improve the plasma uniformity above the wafer placed on the powered electrode by tailoring only the design of the grounded counter electrode.