Self-assembly of block copolymer films on chemically patterned surfaces

A strategy to control the orientation and ordering of the domains in block copolymer films over macroscopic dimensions that combines advanced lithographic techniques and guided self-assembly of block copolymers was developed and implemented. Organic imaging layers of self-assembled films of octadecyltrichlorosilane (OTS) were patterned with regions of different chemical functionality using advanced lithographic tools, e.g., proximity x-ray lithography and extreme ultraviolet interferometric lithography. Regions of the imaging layer that were exposed to radiation in the presence of oxygen underwent a chemical transformation that altered the surface chemistry of the imaging layer from initially methyl-terminated surfaces to aldehyde- and hydroxyl-terminated surfaces. The chemically patterned imaging layers guided the self-assembly of the lamellar domains of symmetric polystyrene-b-methyl methacrylate) (P(S-b-MMA)) films during annealing by controlled wetting of the different blocks of the copolymer on adjacent regions of the chemically patterned surface. The structure and extent of modification by exposure of the OTS films were tuned such that the PS block preferentially wet unexposed regions of the OTS (denoted symmetric wetting) and the PMMA block preferentially wet exposed regions of the OTS (denoted asymmetric wetting). When the period of the surface pattern, L _s, was much larger than the bulk lamellar period, L_o, the lamallae oriented parallel to the plane of the film. The underlying surface pattern was replicated in the polymer film by undulations in topography due to alternating symmetric and asymmetric wetting regions of the block copolymer films over adjacent unexposed and exposed regions of the OTS, respectively. The alternating wetting behavior of the polymer film resulted in thickness differences in the film with a maximum difference of 1/2L _o, corresponding to the difference between the quantized values of thickness for symmetric and asymmetric wetting. When L_s = L_o, the lamellae were oriented perpendicular to the plane of the film and registered with the surface pattern over macroscopic dimensions. Macroscopically ordered block copolymer films have potential for use in nanofabrication of magnetic storage media, quantum dot arrays, photonic crystals, or templates for nanolithography.