High aspect ratio arrays of Si nano-pillars using displacement Talbot lithography and gas-MacEtch

Abstract

Structuring Si in arrays of vertical high aspect ratio pillars, ranging from nanoscale to macroscale feature dimensions, is essential for producing functional interfaces for many applications. Arrays of silicon 3D nanostructures are needed to realize photonic and phononic crystals, waveguides, metalenses, X-ray wavefront sensors, detectors. In particular, arrays of Si nanopillars are used as bio-interfaces in neural activity recording, cell culture, microfluidics, sensing and on-chip manipulation. Here, we demonstrate a strategy for realizing arrays of protruding sharp Si nanopillars, using displacement Talbot lithography combined with metal-assisted chemical etching (MacEtch) in gas phase. Such combination enables reliable and low cost pathway for fabrication of ordered nanopillars arrays on large scale. With the double exposure of a linear grating mask in orthogonal orientations and the lift-off technique, we realized a catalyst pattern of holes in a Pt thin film with a period of 1 μm and hole diameter in the range of 100–250 nm. MacEtch in gas phase by using vapor HF and oxygen from air allows to etch arrays of protruding Si nanopillars 200 nm-thick and aspect ratio in the range of 200 (pillar height/width) with an etching rate up to 1 μm/min. Gas-MacEtch has the advantage of no capillary stiction, no ion beam damage of the Si substrate, nanometric resolution and high fidelity of pattern transfer. In combination with controlled uniformity of feature size on large area, spatial frequency doubling and high resolution of Talbot lithography, the proposed method is an easy-to-scale-up processing that can support the fabrication of Si pillars arrays for many valuable applications both at micro and nano-scale.