Formation of pillared arrays by anodization of silicon in the boundary transition region: an AFM and XRD study

Abstract

The anodization of Si «100» and «111» wafers in dilute HF solutions has been investigated, with particular reference to probing the surface chemistry and features between the porous and electropolishing regions (the ‘boundary transition’ region). Conditions have been found for inducing the formation of ordered arrays of columnar (or ‘pillar’) artefacts, shown to occur only in this region, and whose formation depends crucially on electrochemical parameters and anodization times. Detailed atomic force microscopy (AFM) observations confirm this suggestion, and demonstrate that the arrays consist of relatively ordered long grooves and trenches, though the pillars forming them vary greatly in size. AFM also shows that the best anodization time for maximum ordering of these arrays isca. 12 min, both low (4 min) and high (40 min) anodization times giving rise only to disordered surface structures (though still columnar even after 40 min). These arrays form pseudo-planes which attenuate the absorption of X-rays by (111) and (100) reflections, whereas the non-pillared ones do not. Relevance to current pore formation theories is discussed.