Keeping up with Moore's law becomes increasingly difficult as top-down photolithography approaches the diffraction limit. Bottom-up self-assembly of block copolymers (BCPs) in thin films serves as a promising solution to achieve patterns with sub-10 nm feature size, high lateral ordering, and good etching contrast. We developed a series of high-χ low-N block copolymers using solid-state conversion from phase-mixed poly(solketal methacrylate)-b-polystyrene to strongly microphase-separated poly(glycerol monomethacrylate)-b-polystyrene, where χ was massively increased. Before conversion, the BCPs are soluble in toluene, enabling spin-coating of thin films with uniform thickness. The solid-state conversion was achieved with either trifluoroacetic acid vapor or exposing polymer films embedded with photoacid generators to UV light followed by post-exposure baking or solvent vapor annealing.
Lamellae oriented parallel to the substrate was favored due to the imbalanced interfacial interactions between the two blocks and the substrate. Perpendicular lamellae were achieved by neutralizing the interfacial interactions between the two blocks by modifying the substrate with poly(solketal methacrylate)-random-polystyrene, which undergoes solid-state conversion simultaneously with the BCPs. We used grazing-incidence small-angle neutron scattering (GISANS) to examine the morphology of BCPs with deuterated polystyrene blocks. The polymer-air and polymer-substrate interfaces were selectively probed with the incidence angle below the critical angle. A mixture of parallel and perpendicularly oriented lamellae was observed near the top surface. Orientation deeper in the film was more random.

Solid-state conversion of PSM-<i>b</i>-PS into PGM-<i>b</i>-PS and the self-assembled morphologies in thin films

Solid-state conversion of PSM-b-PS into PGM-b-PS and the self-assembled morphologies in thin films

William Heller

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