“Mesh-assisted” colloidal lithography and plasma etching: A route to large-area, uniform, ordered nano-pillar and nanopost fabrication on versatile substrates

Abstract

We propose a variation of colloidal (microparticle) lithography, which we term “mesh-assisted” colloidal lithography, to improve uniformity and quality of monolayer microparticle assembly over large areas: a square mesh with 200–1000μm open squares (total open-area larger than 75%) and of appropriate height is created/placed on a substrate surface, and acts as template facilitating uniform, monolayer assembly of polystyrene (PS) microparticles with spin-coating. We also study the pattern transfer, the pillar/post formation and their dimensional control on several substrates, namely polymers, silicon and silicon dioxide. Highly ordered nanopillar or nanopost arrays are produced on: (a) PMMA plates by one anisotropic etching step, (b) silicon, and (c) silicon dioxide. The silicon nanopillars and silicon dioxide nanoposts are fabricated by a two step plasma etching: an isotropic oxygen plasma step which shrinks the PS microspheres followed by an anisotropic step to transfer the pattern. The obtained pillars have nanotexture on top of the PS sphere due to plasma roughening, and thus present dual-scale topography, useful for applications such as superhydrophobic surfaces. Our method is thus a combination of photolithography, colloidal lithography, and plasma etching for low-cost, large area nanopost formation.