Anisotropic chemical etching of silicon through anodic oxide films formed on silicon coated with microspheres

Periodic inverted pyramid arrays in silicon were fabricated using a nonlithographic technique combining the localized anodization of the substrate and the subsequent anisotropic chemical etching in an alkali solution. A silicon oxide layer with a honeycomb pattern, which was produced by the anodization of a silicon substrate coated with self-assembled microspheres, served as a passivation layer for alkaline etching. After the removal of microspheres, the unoxidized silicon region was etched selectively by chemical etching in tetramethyl ammonium hydroxide, resulting in the formation of ordered inverted pyramid arrays in silicon. The interval between inverted pyramid holes could be controlled by changing the diameter of the spheres used as an initial mask for silicon anodization.