Charge Transport in Uniform Metal-Assisted Chemical Etching for 3D High-Aspect-Ratio Micro- and Nanofabrication on Silicon

Recently, metal-assisted chemical etching (MaCE) has been proposed as a promising method for micro- and nanostructures fabrication on silicon (Si) with high aspect ratio, high geometric uniformity and low cost. In MaCE, electron holes (h+) are injected into Si through catalytic reduction of H2O2 on metal catalyst thin film patterns. Si beneath the metal is etched through a redox reaction where h+ are involved. This work investigated a fundamental electrochemical process during MaCE: the transport of h+, and revealed its unique correlation with the 3D profile of the etching results. It is discovered that under the uniform etching condition, etching occurs both in the Si beneath the catalysts as well as on the sidewall of the etched space. On N-type Si, the sidewall etching is intrinsically depressed, and highly vertical HAR structures are formed; on P-type Si and undoped Si, the sidewall tapering becomes significant as the pattern number and density increase. The variation of the 3D profile can be explained by the CT during etching using a Schottky junction model, which show dependence on the intrinsic properties of the Si. CT involved in the two etching process can further be correlated by diffusion or drift of h+, which explains the influence of catalysts geometry. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY