Molecular Tailoring of Poly(styrene‑<i>b</i>‑methyl methacrylate) Block Copolymer Toward Perpendicularly Oriented Nanodomains with Sub-10 nm Features

We demonstrate a novel approach for fabricating vertically orientated, sub-10 nm, block copolymer (BCP) nanodomains on a substrate via molecular tailoring of poly­(styrene-<i>b</i>-methyl methacrylate) (PS-<i>b</i>-PMMA) BCP, one of the most widely used BCPs for nanopatterning. The idea is to incorporate a short middle block of self-attracting poly­(methacrylic acid) (PMAA) between the PS and PMMA blocks, where the PMAA middle block promotes phase separation between PS and PMMA, while maintaining the domain orientation perpendicular to the substrate. The designed PS-<i>b</i>-PMAA-<i>b</i>-PMMA triblock copolymers, which were synthesized via well-controlled anionic polymerization, exhibited order–disorder transition temperatures higher than that of pristine PS-<i>b</i>-PMMA BCPs, indicating the promotion of phase separation by the middle PMAA block. For PS-<i>b</i>-PMAA-<i>b</i>-PMMA BCPs with total molecular weights of 21 and 18 kg/mol, the domain spacing corresponds to 19.3 and 16.7 nm, respectively, allowing us to fabricate sub-10 nm nanodomain structures. More importantly, it was demonstrated that the PMAA middle block, which has a higher surface energy than PS and PMMA, does not significantly alter lateral concentration fluctuations, which are responsible for phase-separation in the lateral direction. This enabled the vertical orientation of microdomains with sub-10 nm feature size on a PS-<i>r</i>-PMMA neutral surface without an additional neutral top layer. We anticipate that this approach provides an important platform for next-generation lithography and nanopatterning applications that require sub-10 nm features over large areas with simple process and reduced cost