Carbohydrate-based block copolymer systems: directed self-assembly for nanolithography applications

Self-assembly of block copolymers (BCPs) provides an attractive nanolithography approach, which looks especially promising for fabrication of regular structures with characteristic sizes below 10 nm. Nevertheless, directed self-assembly (DSA) and pattern transfer for BCPs with such small features remain to be a challenge. Here we demonstrate DSA of the maltoheptaose-block-polystyrene (MH_1,2k-b-PS_4,5k) BCP system using graphoepitaxy. BCP thin films were self-organized by solvent vapor annealing in tetrahydrofuran (THF) and water into sub-10 nm scale cylinders of the maltoheptaose (MH) block oriented horizontally or perpendicularly to the surface in a polystyrene (PS) matrix. The guiding patterns for graphoepitaxy were made by the electron beam lithography (EBL) and lift-off process with the distance gradually varying between 0 and 200 nm. Atomic force microscopy (AFM) investigation of MH_1,2k-b-PS_4,5k BCP DSA patterns revealed good ordering of vertical and horizontal cylindrical MH arrays for DSA lines with 150-200 nm separation. Reactive ion etching (RIE) of MH_1,2k and PS_4,5k thin films in O₂ and CF₄ plasma showed up to 14 times higher etch rate of MH compared to PS. These results indicate that MH_1,2k-b-PS_4,5k is a promising BCP for nanolithographic applications below 10 nm.