The role of Triton surfactant in anisotropic etching of {1 1 0} reflective planes on (1 0 0) silicon

Abstract

Etching characteristics and properties of {1 1 0} silicon crystal planes used as 45° optical mirrors for deflecting optical beams from/to optical fibers were investigated. Fiber aligning grooves and passive mirror-like planes were realized by wet micromachining of (1 0 0) silicon in KOH–IPA and TMAH–IPA systems. Implementation of Triton-x-100 surfactant as an additive to 25% TMAH in anisotropic etching of {1 1 0} silicon passive mirror planes is reported and discussed. It was found that Triton-x-100 contents in the range of 10–200 ppm to the 25% TMAH–water etchant significantly increase the anisotropy mostly by decreasing the {1 1 0} etch rate and retaining the {1 0 0} etch rate. It is also shown that {1 1 0} surface roughness is substantially improved compared to two other etching systems. Furthermore, efficient convex corner underetching reduction is demonstrated. The results of optical characterization of passive mirrors with 632 nm incident light show reduced scattering of reflected optical beam due to improved microroughness for mirrors made by TMAH–Triton. For the reflection of the optical beam with 1.33 µm and 1.54 µm wavelengths, sputtered layer of gold is used as reflective coating on silicon mirrors thus increasing the reflected optical beam intensity by an additional 8%.

Silicon 45° micromirrors fabricated by etching in alkaline solutions with organic additives

“…The {110} planes are patterned with stripes after etching in the KOH solution with isopropanol, whereas the striped pattern is considerably less pronounced in the TMAH/ Triton solution. These results are in a good agreement with those reported in the literature (Backlund and Rosengren 1992;Strandman et al 1995;Resnik et al 2005). The stripes almost do not appear on the {110} surface when 20 ppm of Triton is added to the KOH etchant.…”

“…The low concentration of (2 M) KOH solution was chosen because it proved to produce the best parameters of 45°micromirrors (Rola and Zubel 2011b), while the 25 % TMAH solution with Triton concentration close to 200 ppm was reported to provide the high etch rate ratio R(100)/R(110) and the smooth 45°mirror planes (Resnik et al 2005). The amounts of Triton for the KOH solutions were selected during the authors' preliminary experiments.…”

“…The tetramethylammonium hydroxide (TMAH) solution containing Triton X-100 nonionic surfactant was proposed for silicon etching by Resnik et al (2005). This etching mixture allowed one to obtain high etch rate ratio R(100)/ R(110) and relatively smooth {110} sidewalls.…”

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

“…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 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°t owards 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.…”

“…However, the {110} planes are patterned with stripes after etching in this solution (Backlund and Rosengren 1992;Zubel and Kramkowska 2004). Although 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. Therefore, there is still a need for searching for the composition of the KOH-based solution in which smooth {110} planes are achievable.…”