Spatial arrangement of block copolymer nanopatterns using a photoactive homopolymer substrate

Abstract

Spatial control of the orientation of block copolymers (BCPs) in thin films offers enormous opportunities for practical nanolithography applications. In this study, we demonstrate the use of a substrate comprised of poly(4-acetoxystyrene) to spatially control interfacial interactions and block copolymer orientation over different length scales. Upon UV irradiation poly(4-acetoxystyrene) undergoes a photo-Fries rearrangement yielding phenolic groups available for further functionalization. The wetting behaviour of PS-b-PMMA deposited on the poly(4-acetoxystyrene) films could be precisely controlled through controlling the UV irradiation dose. After exposure, and a mild post-exposure treatment, the substrate switches from asymmetric, to neutral and then to symmetric wetting. Upon exposure through photomasks, a range of high fidelity micro-patterns consisting of perpendicularly oriented lamellar microdomains were generated. Furthermore, the resolution of chemically patterned poly(4-acetoxystyrene) substrate could be further narrowed to submicrometer scale using electron beam lithography. When the BCP was annealed on an e-beam modified poly(4-acetoxystyrene) surface, the interface between domains of parallel and perpendicular orientation of the BCPs was well defined, especially when compared with the substrates patterned using the photomask.