Impact of alcohol additives concentration on etch rate and surface morphology of (100) and (110) Si substrates etched in
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TECHNICAL PAPER
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
Received: 6 July 2012 / Accepted: 21 September 2012 / Published online: 6 October 2012 Ó The Author(s) 2012. This article is published with open access at Springerlink.com
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.
1 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). In the field of MOEMS, manufacturing of micromirrors formed by {hkl} sidewall planes is particularly interesting (Sadlery et al. 1997; Resnik et al. 2000; Strandman et al. 1995), due to the exact geometries of the
K. P. Rola (&) I. Zubel Faculty of Microsystem Electronics and Photonics, Wrocław University of Technology, Janiszewskiego 11/17, 50-372 Wrocław, Poland e-mail: [email protected]
etched microstructures and the simplicity of the wet etching technology. The {110} planes are especially attractive, because they can serve as micromirrors inclined at 45° towards the (100) substrate and thus reflect a light beam at an angle of 90° (Strandman et al. 1995; Resnik et al. 2005; Yagyu et al. 2010; Xu et al. 2011). However, to be useful as micromirrors, the {110} planes ought to be very smooth. Moreover, if a light beam is emitted from an optical fiber aligned in a groove fabricated in (100) substrate, the quality of the (100) surface is also important. The large hillocks covering the (100) surface after anisotropic etching could make the appropriate alignment of optical fiber on (100) surface difficult. Many studies have been done on surface morphologies and etch rates of (100) and (110) Si planes so far (Bressers et al. 1996; Sato et al. 1999; Zubel et al. 2001; Zubel and Kramkowska 2001; van Veenendaal et al. 2001; Gosalvez and Nieminen 2003; Cho Wen-June et al. 2004; Cheng et al. 2006). The etching processes were usually carried out in TMAH or KOH aqueous solutions, optionally wit
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