Nanostructuring of free-standing, dielectric membranes using electron-beam lithography

Abstract

Nanostructured dielectric membranes are used in several applications ranging from de Broglie matter-wave optical elements to photonic crystals. Precise pattern transfer and high aspect ratio structures are crucial for many applications. The authors present an improved method for direct patterning on free-standing, dielectric membranes using electron-beam (e-beam) lithography. The method is based on an advanced etchmask that both reduces charging and allows for tuning of the etch mask thickness to support high aspect ratios even for small structures. The authors etched structures as small as 50 nm radius holes in a 150 nm thick membrane and achieved aspect ratios of up to 1.3 for this structure size range. The etch mask thickness can be tuned to achieve the required aspect ratio. The etchmask is composed of a three layer stack consisting of poly(methyl methacrylate), SiO2 and an antireflective coating polymer. Scanning-electron micrographs of membranes produced with the fabrication method are presented.