The Mechanism of Ruthenium Oxide Catalyzed Electroless Etching of Silicon in Oxidizing HF Solution

While metal-assisted chemical etching (MACE) or metal-catalyzed electroless etching of silicon in oxidizing HF solutions typically employs noble metals as catalysts, this work investigates oxide-catalyzed chemical etching (OACE) using RuO₂ to induce localized silicon etching in aqueous H₂O₂-HF solutions. RuO₂ particles confine the reaction to localized sites. The formation of Ru₂O₃ during etching suggests that RuO₂ injects holes into silicon and is simultaneously reduced to Ru₂O₃. The oxidized silicon is locally dissolved in aqueous HF solution, and the pores are generated. A cyclic redox mechanism is proposed: RuO₂ is reduced to Ru₂O₃ by extracting electrons from silicon valence band, while Ru₂O₃ is rapidly reoxidized by H₂O₂, sustaining the etching process until H₂O₂ is exhausted. This work challenges the conventional assumption that the catalyst remains unchanged during MACE and offers novel insights into oxide-catalyzed silicon etching mechanisms.