Morphological and crystallographic evolution of patterned silicon substrate etched in TMAH solutions

Wet etching of Si substrate enables fabrication of sophisticated Si microstructures for a number of applications. However, the detailed anisotropic etching behavior of Si in the alkaline TMAH solutions is still not well understood. In this study, insights into the wet etching behavior of (100) patterned silicon substrate (PSiS) with circular aperture SiO₂ mask in TMAH solutions of varying concentrations (1–25 wt%) are obtained through systematically studying the morphological and crystallographic evolutions of PSiS. Etching in 1 wt% TMAH revealed the widest spectrum of morphological evolutions including the rounded apertures, inverted octahedral frustums, octahedral pyramids, and pyramids. In contrast, etching in 5–25 wt% TMAH revealed features of inverted octahedral frustums, pyramidal frustums, and pyramids. A series of crystallographic planes formed due to anisotropic crystallographic etching were indexed as—C₁ {3¯40}, C₂ {1¯10}, C₃ {1¯11¯}, C₄ {2¯11¯}, and C₅ {1 14 0}, and the etching rates of which were determined to explain the morphological evolution and anisotropic etching mechanism. This work contributes to the controllable fabrication of sophisticated Si microstructures for Si-based optoelectronic devices with potentially enhanced performance.