Fabrication of Three-Dimensional Bilayered Nanostructures via Block Copolymers*

The self-assembly of block copolymers (BCPs) has been received wide attention because of their great potentials in various advanced lithographic applications. For specific applications, one of the most significant is controlling the orientation of the microdomains. In this study, we synthesized ketene-based cross-linkable cylinder forming BCPs, PMMA-b-P(S-r-ketene), in which 3.0 mol% of cross-linkable functional groups were incorporated. Then we manufactured 3-D bilayered BCP films consisting of underlying cross-linked cylinder and top lamellar layers. Interestingly, it was found that the top lamellar layer exhibited perpendicular orientations, regardless of size of domain spacing of underlying cylinder layer and thickness of top lamellar layer. In monolayer lamellar BCP films, neutral layer makes perpendicular orientation near the 1L0. But in 3-D bilayerd BCP films, thickness of perpendicular orientation, by comparison, became significantly broader. This may be due to the entropically driven nematic interactions between these two layers, and the total free energy of this system was theoretically considered. In the work, the orientation of top lamellar films as functions of film thickness and domain spacing of underlying cylinder layers was systematically investigated.