Computational characterization of electron-beam-sustained plasma

Abstract

Electron-beam-sustained plasmas are of vital importance for separately controlling ion flux and ion energy. In this paper, we use an implicit particle-in-cell Monte Carlo method to study plasma kinetics in an electron-beam-sustained plasma under operating conditions relevant to the use of such plasmas for polymer processing. The results indicate that the electron and ion densities are uniformly distributed because of the uniform ionization rate and heating rate. The electron-energy distribution function is Druyvesteyn-like with an ultrahigh concentration of low-energy electrons and a high-energy tail. Low-energy electrons are beneficial for protecting the substrate in material processing and a high-energy tail is useful for the precise control of plasma-gas chemistry. For ion-energy distribution functions at the electrode surface, the low-energy (<5 eV) ion occupation rate increases with decreasing beam current or beam energy. The proportion of low-energy ions bombarding the electrode exceeds 99%, which indicates the superiority of electron-beam-generated plasma compared with a voltage- or current-driven discharge to obtain independent control of ion flux and ion energy. The results obtained herein are important for nondestructive etching in plasma processing because of the unique plasma characteristics provided by electron-beam injection.