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 RuO 2 to induce localized silicon etching in aqueous H 2 O 2 -HF solutions. RuO 2 particles confine the reaction to localized sites. The formation of Ru 2 O 3 during etching suggests that RuO 2 injects holes into silicon and is simultaneously reduced to Ru 2 O 3 . The oxidized silicon is locally dissolved in aqueous HF solution, and the pores are generated. A cyclic redox mechanism is proposed: RuO 2 is reduced to Ru 2 O 3 by extracting electrons from silicon valence band, while Ru 2 O 3 is rapidly reoxidized by H 2 O 2 , sustaining the etching process until H 2 O 2 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.