Desorption model of volatile Ru species induced by partial chlorination on Ru(0001) under an O2/Cl2-based plasma process

Abstract

Ruthenium (Ru) is known to be effectively etched by O2-based plasma with a 10%–20% amount of Cl2, while it is less etched by pure O2-based or Cl2-rich plasma. In this work, reaction paths and energy profiles on a metallic Ru surface were calculated in density functional theory (DFT) simulations to reveal the chemical role of the small amount of Cl2 in the O2-based plasma for Ru etching. We prepared three Ru(0001) surfaces with (1 × 1) adatoms in which chemisorption sites were occupied by O and Cl adatoms. Subsequently, we assumed that convex Ru moieties, which are precursors to form volatile Ru species, were formed on the surface and that they were oxidized by the irradiation of O2-rich plasma. In each Ru(0001) surface, we calculated the production and activation energies of each elementary reaction path to desorb the volatile Ru products. Compared with the surface where all chemisorption sites were covered with O, both energies decreased in locations where some chemisorption sites were replaced by Cl. Our DFT-based research showed that a small amount of Cl2 in the O2/Cl2 plasma contributes to decreasing the production and activation energy to form volatile Ru products on the Ru surface, resulting in the etching rate being increased.