Facile fabrication of wafer-scale, micro-spacing and high-aspect-ratio silicon microwire arrays

One dimensional micro-/nanostructures of semiconductors are attracting increasing attention due to their large specific surface area, their high aspect ratio and their unique physical/chemical properties. However, fabrication of large-area, micro-spacing and high-aspect-ratio silicon microwire arrays (SiMWAs) is still challenging relative to the usual SiMWAs with submicro-/nanoscale spacing or a small aspect ratio. In this work, we combined metal assisted chemical etching (MACE) and photolithography to successfully prepare wafer-scale (2.5 × 2.5 cm2) SiMWAs, with 4 μm spacing which are over 70 μm long with unconventional etching conditions. We find that the key factor for achieving the desired SiMWAs is to keep the metal catalyst uniformly and steadily migrating into the substrate during the MACE for as long as possible. The most effective route to realizing this delicate control is a combination of a bilayered metal catalyst and low etching temperature (instead of the conventional room or higher temperature). Furthermore, metal migrations into the substrate are systematically investigated and the corresponding processes are categorized as various models. This work promotes an understanding of the MACE mechanisms and supplies guidelines for etching Si with a large lateral dimension.