Effect of Isopropanol on Gold Assisted Chemical Etching of Silicon Microstructures

TL;DR

This paper presents an optimized Metal-Assisted Chemical Etching process using isopropanol to improve the uniformity, control, and quality of high-aspect-ratio silicon microstructures.

Contribution

It introduces the use of isopropanol as a surfactant in MacEtch to enhance etching uniformity and reduce nanoporosity in silicon microstructures.

Findings

Isopropanol reduces etching rate and nanoporosity.

Addition of KOH removes residual nanowires.

Optimal isopropanol concentration improves etching quality.

Abstract

Wet etching is an essential and complex step in semiconductor device processing. Metal-Assisted Chemical Etching (MacEtch) is fundamentally a wet but anisotropic etching method. In the MacEtch technique, there are still a number of unresolved challenges preventing the optimal fabrication of high-aspect-ratio semiconductor micro- and nanostructures, such as undesired etching, uncontrolled catalyst movement, non-uniformity and micro-porosity in the metal-free areas. Here, an optimized MacEtch process using with a nanostructured Au catalyst is proposed for fabrication of Si high aspect ratio microstructures. The addition of isopropanol as surfactant in the HF-H2O2 water solution improves the uniformity and the control of the H2 gas release. An additional KOH etching removes eventually the unwanted nanowires left by the MacEtch through the nanoporous catalyst film. We demonstrate the benefits of the isopropanol addition for reducing the etching rate and the nanoporosity of etched structures with a monothonical decrease as a function of the isopropanol concentration.