Oxidation and Chlorination Reaction Characteristics: A Density Functional Theory Perspective toward the Fundamental Understanding of Etching of Ruthenium and Tantalum Surfaces.

Abstract

Given the profound industrial relevance of metal surface etching, we performed a detailed density functional theory investigation of the nature of intermolecular interactions between the O₂ (and Cl₂) etchant(s) and the ruthenium (Ru) (and tantalum (Ta)) surface(s). We assessed the formation energies of the MO _<i>x</i> and MCl _<i>x</i> families of molecular entities (where M denotes Ta or Ru and x spans from 1 to 6), in the gas phase, along with the landscapes of adsorption and desorption energies for O _<i>x</i> /MO _<i>x</i> and Cl _<i>x</i> /MCl _<i>x</i> on the metal surfaces, to offer valuable insights into the energy profiles required for the fundamental understanding of O₂- and Cl₂-plasma environments. Our findings unveil that molecular RuO₄ may stand out as a prime byproduct for etching the Ru surface when exposed to the O₂-plasma, while etching Ru by the Cl₂ plasma is much more energetically challenging. Conversely, TaCl₃, TaCl₄, and TaCl₅ may emerge as the predominant etching byproducts for the Ta surface in the Cl₂ plasma environment. The climbing image nudged elastic band calculations carried out for analyzing detailed etching reaction paths reveal that the desorption of RuO₄ from the Ru surface is a rate-limiting phenomenon, characterized by the formation of a metastable intermediate state [RuRuO₄], effectively reducing the energy needed for etching.