Etching of porous silicon in basic solution

Abstract

This study reveals that a silicon sample with a porous layer immersed in strong basic solution is etched in several steps according to the surface area of the various materials to be dissolved (nano/macroporous or bulk silicon). As a result it demonstrates the possibility to produce various silicon surface morphologies. These morphologies range from macropore structure to inverted pyramids with crystalline facets. The technique used was the immersion of porous silicon in basic solution and the parameters varied were the immersion time and the concentration of the solution. This is a simple and interesting method to produce a desired morphology of silicon. Furthermore, this work shows the limit of the porosity determination by the weight measurement method.

Morphological Development from Uniform Microporous Structure to Macropore-Like Structure

“…They considered that the framework in the skeleton structure must correspond to the pore walls of macroporous structure. Moreover when high current density was applied, such structure was not observed (9). This result also corresponds to the observation by Vyatkin et al: the pore wall thickness changes with increasing current density (10).…”

“…The skeleton structure should be an important key to think of this surface dissolution. In this study, when a skeleton structure is observed, a uniform microporous structure is confirmed above the skeleton structure as Hamm et al reported (9). Wehrspohn et al and Ponomarev et al also observed such a uniform microporous layer even on the macroporous layer in their works (13,14).…”

“…% HF solution. Hamm et al reported that the appearance of framework depended on applied current density (9). However, no framework is observed no matter how much applied current density is changed in the MeOH solution.…”

“…There seems to be two possible paths to develop to macropore from the skeleton structure: one is the direct change due to dilute HF concentration, the other is the development via a uniform microporous structure with increasing current density. Hamm et al reported that the skeleton structure disappeared when current density increased in concentrated HF solution (9). They must have observed the morphological change from a skeleton structure to such a uniform structure.…”

Porous Silicon-based Electrochemical Biosensors

“…Tinsley-Bown and co-workers (Tinsley-Bown et al 2000) described a method based on immersing the porous layers in an ethanol-rich alkali (KOH) solution, whose effect on the pores' diameter may be controlled by the immersion time. Hamm and coworkers (Hamm et al 2003) used a similar method by immersing the PSi samples in a NaOH etching (0.1 and 1 M) solution. To avoid problems due the hydrophobic nature of the PSi walls, an ethanol drop is put on the samples' surface before the immersion in the NaOH solution.…”