Reaction mechanisms of ruthenium (Ru) etching by energetic oxygen and chlorine ions

The dimensions of semiconductor devices continue to diminish with the aim of reducing power consumption and achieving faster clock speeds. The performance of semiconductor devices can be bottlenecked by wiring materials, leading to the imminent choice between further miniaturizing existing copper (Cu) wiring or applying new wiring materials. Because copper wiring requires the deposition of barrier metal prior to the electrochemical deposition of Cu, ruthenium (Ru), which can be deposited by a plasma-based dry process, is considered superior to Cu for the new wiring material. It was shown that Ru was efficiently etched with a plasma generated with a mixture of oxygen (O₂) and chlorine (Cl₂) gases.[1] However, how the presence of O⁺ and Cl⁺ ions efficiently etches Ru was not well understood. This study aims to understand the chemical effects of O⁺ and Cl⁺ ions on Ru etching reactions, using mass-selected ion beam experiments,[2] where Ru surfaces were irradiated with O⁺ and Cl⁺ ions at ion energies ranging from 1,000 to 4,000 eV. With O⁺ ion injections, oxidized layers of several nanometers were formed on the Ru surfaces, exhibiting an etching suppression effect at low ion energies. With Cl⁺ ion injections, an etching enhancement effect was observed at high ion energies. Possible etching mechanisms of Ru by O⁺ or Cl⁺ ion irradiation will be discussed.