Impact of alcohol additives concentration on etch rate and surface morphology of (100) and (110) Si substrates etched in KOH solutions

Krzysztof P Rola,Irena Zubel

doi:10.1007/s00542-012-1675-x

Krzysztof P Rola, Irena Zubel

Open Access

https://doi.org/10.1007/s00542-012-1675-x

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Abstract

The influence of alcohol concentration on etch rate and surface morphology of (100) and (110) Si planes was investigated in this paper. The etching processes were carried out in KOH solutions with different concentrations of isopropanol and butanols. The etch rate minima versus alcohol concentration were observed for all the alcohols used in the experiments. Furthermore, close to the concentrations of etch rate minima, the smooth (110) planes were obtained. However, the (100) surfaces were covered with hillocks at these concentrations. Based on the surface tension measurements and literature reports, the explanation of appearance of the etch rate minimum was suggested. In the proposed model, the adsorption maximum corresponds to the complete formation of an alcohol monolayer on Si surface and, consequently, to the etch rate minimum. At higher concentrations of alcohol, the monolayer disappears and the etch rate increases.

Highlights

Micromachining of monocrystalline silicon by anisotropic wet chemical etching is a well-known technique for fabrication of three-dimensional MEMS and MOEMS structures (Hoffmann and Voges 2002; Pal and Sato 2009, 2010)
The influence of alcohol concentration on etch rate and surface morphology of (100) and (110) Si planes was investigated in this paper
To understand the surface related phenomena occurring in the KOH aqueous solutions containing alcohol additives at different concentrations, it seems to be necessary to analyze what generally happens in the water-based solutions as alcohol concentration changes

Summary

Introduction

Micromachining of monocrystalline silicon by anisotropic wet chemical etching is a well-known technique for fabrication of three-dimensional MEMS and MOEMS (optical MEMS) structures (Hoffmann and Voges 2002; Pal and Sato 2009, 2010). The KOH solution saturated with isopropyl alcohol ( called isopropanol or IPA) was often used, because it provides high etch rate ratio R(100)/R(110), smooth (100) surface and reduction of convex corner undercut (Backlund and Rosengren 1992; Zubel 2001; Zubel and Kramkowska 2004). Smooth {110} planes can be obtained in TMAH-based solution (Resnik et al 2005; Yagyu et al 2010; Xu et al 2011), it is quite expensive and usually provides lower etch rates than KOH. There is still a need for searching for the composition of the KOH-based solution in which smooth {110} planes are achievable

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