Mechanics of Catalyst Motion during Metal Assisted Chemical Etching of Silicon

Abstract

Metal assisted chemical etching (MACE) of Si has been used to fabricate both simple and complex Si nanostructures, through the relatively straightforward process of noble metal deposition and patterning followed by immersion in a suitable etching solution. Under appropriate conditions, etching is catalyzed by the metal and occurs only at the metal–silicon interface. MACE therefore requires that a force be present that keeps the metal and silicon in close proximity during etching. The geometrical characteristics of the etched nanostructures therefore depend not only on the solution chemistry, but also on the mechanical properties and constraints of the noble metal catalysts. Here we report experimental studies of etching with nanoscale Au catalyst strips that are mechanically constrained at both ends. The mechanical constraint of these strips leads to termination of etching when a mechanical force balance is achieved. Through experimental characterization of the etching end-state and through modeling, we determine the force between the catalyst and the silicon during etching, and determine how this force depends on the chemistry of the solution