Controlling the microdomain orientation in block copolymer thin films via cross-linkable random copolymer neutral layer

Block copolymer (BCP) thin films are capable of producing periodic nanoscale features that are hardly accessible by conventional ‘top-down’ lithography. Such is the potential of BCP thin films that many research groups are intensively studying this field. Notwithstanding their advantages, BCP thin films suffer from an inherent tendency to produce microdomains parallel to the substrate due to selective wetting. To date, various approaches to induce perpendicular orientation have been reported using surface neutralization, solvent annealing, external fields and nano-fillers. Of these approaches, surface neutralization using random copolymers is the most widely used because of its straightforward and intuitive methodology. Surface neutralization alleviates the preferential interaction of one block with the substrate, and thus selective wetting, which enables the formation of microdomains perpendicular to the substrate. In this review, advances in surface neutralization are covered by introducing four efficient cross-linkable random copolymers incorporated with benzocyclobutene, glycidyl methacrylate, azide and ketene functional groups. Various cross-linkable poly(styrene- random -methyl methacrylate) (P(S- r -MMA)) that can neutralize substrates are reviewed. Four efficient cross-linkable random copolymers incorporated with benzocyclobutene (BCB), glycidyl methacrylate (GMA), azide and ketene functional groups can be used to prepare a thin, cross-linked neutral layer. On this cross-linked layer, polystyrene- block -poly(methyl methacrylate) (P(S- b -MMA)), thin films produce microdomains oriented perpendicular to the substrate, confirming the effective neutralization of the substrate to both PS and PMMA blocks.