Study of the Anisotropic Wet Etching of Nanoscale Structures in Alkaline Solutions

Abstract

A qualitative and semi quantitative analysis of anisotropic etching of silicon nanostructures in alkaline solutions was done. Dedicated nanostructures were fabricated on 300mm wafers and their geometric change during wet etching was analyzed, stepwise, by top down SEM or TEM. We challenge the previously described wagon wheel technique towards nanodimensions and describe the pros and cons of the technique using relevant experimental conditions. The formation of specific geometric patterns are explained by the face-specificity of the etch rates. Clear differences in anisotropy were revealed between pillars etched in KOH or in TMAH, and for wagon wheels etched in TMAH or in NH4OH. Finally etch rates were extracted for the different types of crystal planes and compared.

Scaled-Down c-Si and c-SiGe Wagon-Wheels for the Visualization of the Anisotropy and Selectivity of Wet-Chemical Etchants

“…Therefore, low (RT) temperatures were chosen in order to have an acceptable time window for the observation of etching phenomena and to avoid the complete dissolution of structures. The same order of velocities, R (110) > R (100) , is observed in this study, done at RT and 5 wt.% TMAH, but the calculated values of the R (110) / R (100) ratio are well above 2 (see also reference [27]). Thus, this confirms the trend that this anisotropic ratio increases with decreasing TMAH temperature.…”

Wet Etching of Silicon in Planar Nanochannels

“…One of the most fundamental wet etching reactions frequently employed in the semiconductor industry and scientific research is Si etching using alkaline solutions. This process has widespread applications, including bulk etching of crystal-silicon for microelectromechanical systems (MEMSs), , etching of poly silicon or amorphous silicon in nanoconfinements for the fabrication of 3-D memory and logic devices, ,− and surface texturing for solar cells. , While the reaction mechanisms, etching anisotropy, and reactant concentration dependencies of Si bulk etching have been extensively examined, − and Si wet etching in nanoscale has been employed to create nanostructures (e.g., nanopillars, nanowires, nanotips, and nanogaps), ,,− the confinement dependence of Si wet etching in nanoconfinement using alkaline solutions has not been reported. It is not clear if the etching reaction would be diffusion/reaction-limited, and the nanoconfinement would change the reaction.…”