Morphological study of {311} crystal planes anisotropically etched in (100) silicon: role of etchants and etching parameters

Abstract

Investigation was focused on the formation of {311} planes by wet anisotropic etching of (100) silicon and, in particular, on the characterization by means of surface roughness, etch rates and related convex and concave corner dynamic behaviour during maskless etching. KOH and TMAH water solutions were tested for their influence on previously mentioned parameters as well as the effect of isopropyl alcohol (IPA). It was found that convex corner undercutting is significantly reduced if {311} bounding planes are utilized instead of {111} bounding planes. For shallow structures a self-compensation can be obtained with KOH and when certain conditions are met, also with TMAH. The rounding of the concave corner that arises through prolonged etching is reported, which is particularly emphasized in KOH and less in TMAH etchant. Addition of IPA in maskless mode is experimentally investigated, showing minor influence on etching conditions and on reducing the undercut of convex corners. Etch rates and dimensional control of some microstructures are discussed and presented comparatively for different etching systems in a temperature range of 50-100 °C. By evaluation of surface quality with a surface profiler and SEM, it was found that the smoothest surface was achieved by etching in TMAH. The role of solution temperature in surface roughness was found to be of minor importance, as well as the stirring of the solution. It was determined that the IPA additive increases roughness when used with KOH, while with TMAH, the influence on roughness of the {311} planes is insignificant.

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).…”

Radiative properties of materials with surface scattering or volume scattering: A review

“…8(b) demonstrate the ability to predict two prominent side peaks, associated with the side peaks in the SDF of Si-2 at |ζ x |&|ζ y |&0.36. Moreover, a small side peak associated with |ζ x |&|ζ y |&1.15 appears at θ i = 45° [ 32]. The noticeable difference between modeling and measurement in Figs.…”

“…Dependence of the refractive index on wavelength is implicitly considered in the microfacet reflectivity. Furthermore, depolarization, i.e., polarization state of the scattered wave is different from that of the incident, can be considered in the calculation of the microfacet reflectivity as well [32]. For a 2D rough surface, even though the incident light is purely s or p polarized, both polarization components generally coexist in the local coordinates.…”

“…Lee et al [32] developed a Monte Carlo ray-tracing algorithm that incorporates measured surface topography into the simulation of rough surfaces. The surface topographic data are in the form of a 2D array storing heights and locations, similar to surface realizations.…”

“…By examining the crystalline structure of silicon, the side peaks can be associated with the {311} planes, since angles between any of the four {311} planes and the (100) plane are 25.2° [32]. On the contrary, the SDF of Si-1 does not show side peaks.…”