Interlayer-mediated catalyst engineering for ultra-high aspect ratio silicon nanostructures

TL;DR

This paper introduces an interlayer technique to improve catalyst stability and pattern transfer in vapor-phase metal assisted chemical etching, enabling reliable fabrication of ultra-high aspect ratio silicon nanostructures.

Contribution

The study presents a novel interlayer approach using Cr and Al₂O₃ to enhance catalyst stability and etching fidelity in MacEtch, facilitating the production of dense, high aspect ratio silicon nanostructures.

Findings

Improved catalyst stability and reproducibility in MacEtch.

Successful fabrication of nanostructures with aspect ratios over 250:1.

Demonstrated patterning of X-ray optics using the interlayer method.

Abstract

Reliable and precise etching of silicon nanostructures with ultra-high aspect ratios is required in many fields. Metal assisted chemical etching (MacEtch) in vapor is a plasma-free etching method that attracts considerable attention owing to the ability to create smooth, high aspect ratio nanostructures. MacEtch understanding and applications are limited by low fidelity and inconsistent pattern transfer from the catalyst layer to the silicon substrate. The locally constrained electrochemical interactions at the catalyst site make MacEtch particularly sensitive to catalyst contamination reducing the reaction rate and pinning the catalyst during etching. Removing contaminants is essential to improve pattern transfer for reliable processes on a larger area and higher aspect ratio. Physically separating the main source of carbon - the resist - from the catalyst with a sacrificial and functional interlayer solves this issue. The interlayer separates the resist and the catalyst and allows for thorough cleaning of the substrate before catalyst deposition. The resulting clean catalyst has improved stability, quality and reproducibility, enabling reliable fabrication of dense (50% patterned area) high aspect ratio (>250:1) nanostructures. Two different interlayer materials (Cr and Al$_{2}$O$_{3}$) and two patterning approaches are presented, showcasing etching of various high aspect ratio nanostructures, such as X-ray Optics.