Silicon Etching Using Copper-Metal-Assisted Chemical Etching: Unveiling the Role of Cu2O in Microscale Structure Fabrication

Abstract

Achieving precise and cost-effective etching in the field of silicon three-dimensional (3D) structure fabrication remains a significant challenge. Here, we present the successful fabrication of microscale anisotropic Si structures with an etching anisotropy of 0.73 using Cu-metal-assisted chemical etching (Cu-MACE) and propose a mechanism to elucidate the chemical behavior of Cu within the MACE solution. Our study reveals the formation of cuprous oxide (Cu2O) within Cu thin films in the presence of hydrogen peroxide (H2O2), which plays a key role in Si etching. We propose that the holes generated through the reduction of Cu2O back to Cu are transferred to Si, promoting its etching through a galvanic reaction with Cu2O. This Cu-Cu2O cyclic redox process in the Si-Cu2O galvanic cell under the right conditions enables continuous etching of Si and significantly improves the chemical stability of Cu-MACE. Building on this cyclic process mechanism, we demonstrate the catalytic potential of Cu2O for oxide-assisted chemical etching (OACE) by directly using Cu2O in both thin-film and particle forms, rather than starting from Cu. This study opens possibilities for the precise control of Cu-MACE, extends the existing MACE mechanism, and contributes to our understanding of transition metal oxide behavior in OACE. © 2024 American Chemical Society.