Profile Control in Block Copolymer Nanostructures using Bilayer Thin Films for Enhanced Pattern Transfer Processes

Although control over the domain orientation and long-range order of block copolymer nanostructures self-assembled in thin films has been achieved using various directed self-assembly techniques, more challenging but equally important for many lithographic applications is the ability to precisely control the shape of the interface between domains. Here, a novel layer-by- layer approach is reported for controlling the interface profile of block copolymer nanostructures and the application of an undercut sidewall profile for an enhanced metal lift-off process for pattern transfer is demonstrated. Bilayer films of lamellar-forming poly(styrene-block-methyl methacrylate) are assembled and thermally cross-linked on wafer substrates in a layer-by-layer process. The top layer, while being directed to self-assemble on the lamellae of the underlying layer, has a tunable composition and polystyrene domain width independent of that of the bottom layer. Undercut or negative sidewall profiles in the PS nanostructures are proven to provide better templates for the lift-off of Au nanowires by achieving complete and defect-free pattern transfer more than three times faster than comparable systems with vertical sidewall profiles. More broadly, the layer-by-layer approach presented here provides a pathway to achieving sophisticated interface profiles and user-defined 3D block copolymer nanostructures in thin films.