Ionic liquid mediated directed self-assembly of diblock/triblock copolymer thin films for advanced lithography

Block copolymers (BCP) self-assemble into a variety of microstructures and controlling the orientation of these structures relative to the substrate surface allows for their use in lithographic techniques. Control over the orientation is non-trivial and requires chemical treatment of the substrate or external fields that can interact and orient these BCP microstructure domains. With this research we highlight a facile thin film casting methodology that produces and orients diblock copolymer microstructure perpendicular to the substrate in the casting process itself. The films are cast from a solvent mixture with a block selective Ionic Liquid (IL) that plasticizes the BCP, enhances repulsive interactions between blocks, and screens preferential interactions between the BCP and the substrate. With a well-developed and fully perpendicular microstructure these films can find applications in sub-20nm lithography processes and as ultrafiltration membranes after selectively etching out the assembled domains.