Fabrication of versatile nanoporous templates with high aspect ratios by incorporation of Si-containing block copolymer into the lithographic bilayer system

We report a new approach to fabricate versatile nanoporous templates with high aspect ratios by incorporating silicon-containing block copolymers into the lithographic bilayer system. This approach used a top thin film of self-assembled asymmetric polystyrene-block-poly(4-(tert-butyldimethylsilyl)oxystyrene) (PS-b-PSSi) as a hard etch mask and an underlying thick film of a negative-tone photoresist (SU-8) for pattern transfer. The assembly of PS-b-PSSi was well-controlled by solvent annealing on the SU-8 and deep nanopores were formed in the underlying layer by oxygen reactive ion etching due to high etch contrast. As a result, highly dense and uniform nanoporous templates with high aspect ratios were obtained over a large area. These templates have versatilities to easily control the sizes of nanopores and to make on the diverse functional substrates. Moreover, the dry-etch process during removal of nanotemplates prevented collapse and aggregation of nanostructures. As a demonstration, we fabricated vertically ordered freestanding gold nanorod arrays by using these templates.