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.
Highlights
Periodic micro- and nanostructured free-standing dielectric membranes exhibit properties useful in a range of applications
06F402-2 Grepstad et al.: Nanostructuring of free-standing, dielectric membranes using e-beam lithography
06F402-3 Grepstad et al.: Nanostructuring of free-standing, dielectric membranes using e-beam lithography
Summary
Periodic micro- and nanostructured free-standing dielectric membranes exhibit properties useful in a range of applications. Using an e-beam for patterning resists on dielectric materials has the potential drawback that dielectric materials generally are insulating This can cause charge build up, which may deflect the electron beam, resulting in patterning defects and drift in periodic patterns, limiting the minimum feature size.. This can cause charge build up, which may deflect the electron beam, resulting in patterning defects and drift in periodic patterns, limiting the minimum feature size.14 This is especially the case when performing e-beam directly on thin, free-standing dielectric membranes. We present an improved process for direct patterning of free-standing dielectric membranes with e-beam, which reduces charging effects ( improving the pattern definition) and offers the possibility of high aspect ratios of the membrane structures The transferred pattern definition degrades with increasing aspect ratio since the PMMA pattern tends to taper due to the etch characteristic of the PMMA. Here we present an improved process for direct patterning of free-standing dielectric membranes with e-beam, which reduces charging effects ( improving the pattern definition) and offers the possibility of high aspect ratios of the membrane structures
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