Self-assembly of Block Copolymers in Thin Films with Photo-Induced Solid-State Conversion*

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-X 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 X 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. Lamellae oriented perpendicular to the substrate was 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.