Interface-regulated metal-assisted chemical etching for stable fabrication of high-aspect-ratio silicon trenches

Abstract Fabricating high-aspect-ratio silicon trenches via metal-assisted chemical etching (MaCE) is often hindered by unstable sidewall evolution and restricted reactant transport. To address these challenges, we propose an interface-regulated electrochemical strategy by introducing concentrated sulfuric acid ( H 2 SO 4 ) into the etching system. This approach simultaneously modulates interfacial reaction kinetics and the electric double-layer (EDL) structure. Results show that moderate H 2 SO 4 addition effectively suppresses trench deformation and branching. It expands the viable Au catalyst thickness window to 5 – 7 nm , enabling the fabrication of highly vertical silicon trenches with aspect ratios up to 75 : 1 . Mechanistic studies via XPS and EIS reveal that increased ionic strength and specific SO 4 2 − adsorption lead to pronounced EDL compression and homogenized interfacial charge transfer. This synergistic interface-regulation mechanism stabilizes the etching front and prevents directional deviation. Overall, this work establishes a generalizable electrochemical approach for stable, ultra-deep MaCE of silicon.