EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The large-scale fabrication of nanoporous materials has generated significant research interest on account of the wide range of possible applications, including nanophotonics, optoelectronics, biomedical systems, and environmental sciences. Block copolymer (BCP) self-assembly is one such potential fabrication strategy, owing to its low cost and large-area production of periodic ordered domains. Nonetheless, a number of roadblocks remain – in particular obtaining reliable and controlled self-assembly of suitable templates for nanoporous structures. In this regard, the present report studied the microphase separation of an “inverse” cylindrical P2VP-b-PS BCP system (where P2VP is the majority block (fP2VP = ~0.7)), with the intention of producing perpendicular cylindrical arrays consisting of PS cylinders and a P2VP matrix. Self-assembly was achieved using solvent vapour annealing (SVA) in a non-selective solvent, which was optimised via fine-tuning of parameters including film thickness, annealing temperature, and time. The resulting films were characterised using reflectometry, AFM, SEM, TEM and GISAXS, showing long-range lateral order and highly ordered, vertically aligned cylinder structures. The cylinder diameter and cylinder-cylinder separation had average values of 34 nm and 60 nm, respectively. The BCP films were subsequently infiltrated with metal ions and exposed to UV/ozone treatment, hence removing the polymeric material, and leaving a metal oxide hard mask. These hard masks were then utilised for pattern transfer into the silicon substrate through the use of an ICP etcher. This resulted in the creation of pores with the same diameter as the original PS cylinder, showing that the mask was resistant to the process. Altogether, we expect our BCP lithography strategy will enable the controlled production of nanoporous membranes, with potential applicability in cooling, separation, filtration, and sensor systems.