Effect of radio frequency bias on the ion extraction from high-density electropositive plasmas

Modern industry heavily relies on inductively coupled plasmas for the generation of energetic ions. In electric propulsion, these ions generate thrust. In the semiconductor industry, they are used to etch high aspect ratio features. In materials science, they are crucial in the deposition and modification of thin films, which are essential for developing advanced materials with unique properties. There are a lot of studies of ion distribution functions at the biased electrodes for the low- and moderate ion energies, which are of interest for electric propulsion and film deposition. However, there are limited numbers of studies examining the regimes relevant to semiconductor applications, such as high aspect ratio etching. These regimes use high-density plasmas and high-power RF biasing. The accessibility of these regimes is difficult due to requirements on hardware. Their self-consistent computational studies are also difficult due to the high computational cost. This paper uses a one-dimensional collisionless sheath model coupled with a basic circuit equation to analyze how radio frequency bias affects the peak energies of ions extracted from the inductively coupled plasma. It is observed that, to extract high-energy ions from this plasma, the electron and ion conduction currents from the plasma must be such that they cannot compensate for the radio frequency current. Then, the capacitive high-voltage sheath builds up in front of the biased electrode, enabling ion acceleration to kiloelectron volt energies. It is found that at low radio frequencies, the ion energy at the biased electrode increases linearly with radio frequency power.