Effect of Self-assembled Wetting Layer in Block Copolymer Thin Film

Abstract

The role of the interface becomes more important in block copolymer (BCP) thin film self-assembly compared than in the bulk. The self-assembled BCP structures in the bulk are mainly governed by their segregation strength and relative block ratio, whereas in case of thin films it is additionally influenced by interface condition. Therefore, much efforts have been made to understand interfacial behaviors of BCPs and to control the self-assembled structure in the thin films. A common method is to modify substrate-BCP interactions such that the neutral polymers can be grafted onto the substrate to direct the self-assembly of BCPs. However, a simple physical coating of BCP instead of grafting cannot be employed as a wetting layer because subsequent layers can be easily intermixed upon thermal annealing. Here, we introduce an ultrathin BCP film as a wetting layer to control the interface interactions, which is stable for additional spin-coating and following thermal annealing. The ultrathin BCP wetting layer is produced using Langmuir-Blodgett (LB) technique while the interfacial self-assembled BCP structures are systemically controlled with surface pressure at LB. We show that the use of ultrathin BCP films can effectively control and direct the BCP self-assembly in the upper layer.