Effect of structured electrodes on heating and plasma uniformity in capacitive discharges

Abstract

The effect of various structured (non-planar) electrode topologies, e.g. rectangular, rounded and triangular trenches, on the electron heating dynamics and ion density profile in capacitively coupled radio frequency plasmas is investigated experimentally and by an analytical model. The measurements are carried out in neon. 2D Phase resolved optical emission spectroscopy is utilized to study the dynamics of energetic electrons inside and outside these structures at the kinetic level. In the presence of structured electrodes, non-planar RF sheaths form and affect the electron heating dynamics. We observe a local agglomeration of energetic electrons above the structures. These electrons originate from sheath expansion heating. Inside the structures, opposite vertical sheaths cause a temporal confinement of electrons. Non-planar sheaths at the trench orifice cause convergent fluxes of energetic electrons. Also, the ionization and, as a consequence, the plasma density are modified by these effects. This is characterized by radially resolved Langmuir probe measurements and described by a diffusion model with localized sources. Subsequently, the control of the radial plasma density profile is demonstrated. Via customized electrode topologies, high plasma uniformity at specific pressures and heights above the electrode is achieved with the additional benefit of strong enhancement of the plasma density.