Highly ordered hexagonally arranged nanostructures on silicon through a self-assembledsilicon-integrated porous anodic alumina masking layer

Abstract

A combined process of electrochemical formation of self-assembled porous anodic aluminathin films on a Si substrate and Si etching through the pores was used to fabricate ideallyordered nanostructures on the silicon surface with a long-range, two-dimensionalarrangement in a hexagonal close-packed lattice. Pore arrangement in the alumina film wasachieved without any pre-patterning of the film surface before anodization. Perfect patterntransfer was achieved by an initial dry etching step, followed by wet or electrochemicaletching of Si at the pore bottoms. Anisotropic wet etching using tetramethyl ammoniumhydroxide (TMAH) solution resulted in pits in the form of inverted pyramids, whileelectrochemical etching using a hydrofluoric acid (HF) solution resulted in concave nanopitsin the form of semi-spheres. Nanopatterns with lateral size in the range 12–200 nm, depth inthe range 50–300 nm and periodicity in the range 30–200 nm were achieved either onlarge Si areas or on pre-selected confined areas on the Si substrate. The poresize and periodicity were tuned by changing the electrolyte for porous anodicalumina formation and the alumina pore widening time. This parallel large-areananopatterning technique shows significant potential for use in Si technology anddevices.