Microdomain orientation dependence on thickness in thin films of cylinder-forming PS-b-PMMA

Abstract

The self-assembly of block-copolymer thin films in periodic nanostructures hasreceived considerable attention during the last decade due to their potentialapplications in nanofabrication and nanolithography. We followed the morphologiesdeveloped in thin films of a cylinder-forming diblock copolymer polystyrene-b-poly(methylmethacrylate)((PS-b-PMMA),PS 46.1 kg mol − 1, PMMA21.0 kg mol − 1, lattice spacingL0 = 36 nm), as a function ofthe film thickness (t), analyzing the effect of thickness commensurability on domain orientation in respect tothe substrate. The study was circumscribed to the unexplored range of thickness belowL0. Two thickness windows with perpendicular orientation ofthe PMMA domains were identified: a well-known window att ∼ L0 and a newwindow at t ∼ L0/2. A half-parallel cylinder morphology was observed for with a progressive change in morphology when thickness increases fromL0/2 toL0. Thisexperimental evidence provides new insights on the mechanism of block copolymers self-organizationand indicates the possibility to tune the thickness of the nanostructured polymeric film belowL0, allowing the fabrication of ultrathin soft masks for advanced lithographic processes.