Parallel processes for patterning densely packed nanometre-scale structures are critical for many diverse areas of nanotechnology. Thin films of diblock copolymers can self-assemble into ordered periodic structures at the molecular scale (approximately 5 to 50 nm), and have been used as templates to fabricate quantum dots, nanowires, magnetic storage media, nanopores and silicon capacitors. Unfortunately, perfect periodic domain ordering can only be achieved over micrometre-scale areas at best and defects exist at the edges of grain boundaries. These limitations preclude the use of block-copolymer lithography for many advanced applications. Graphoepitaxy, in-plane electric fields, temperature gradients, and directional solidification have also been demonstrated to induce orientation or long-range order with varying degrees of success. Here we demonstrate the integration of thin films of block copolymer with advanced lithographic techniques to induce epitaxial self-assembly of domains. The resulting patterns are defect-free, are oriented and registered with the underlying substrate and can be created over arbitrarily large areas. These structures are determined by the size and quality of the lithographically defined surface pattern rather than by the inherent limitations of the self-assembly process. Our results illustrate how hybrid strategies to nanofabrication allow for molecular level control in existing manufacturing processes.
The cylindrical domain diameter (d), spacing (D), and uniformity in thin films of ternary blends of a cylinder-forming polystyrene-block-poly(methyl methacrylate) block copolymer and the corresponding homopolymers were investigated as a function of the molecular weight (M n ) and concentration (j H ) of the homopolymers. Thin films (20-65 nm) of the blends were deposited on silicon wafers that had been modified with random copolymer brushes such that the cylindrical domains of the annealed blends were oriented perpendicular to the substrate. The best uniformity of d, at a given j H , was achieved in the blends with lower homopolymer M n s. For blends made with homopolymers that had M n values of the same order of magnitude as those of the corresponding blocks of the copolymer, D increased with increasing j H as D= D 0 (1 -j H ) -β , where D 0 is the domain spacing of the block copolymer and β is a parameter that depends on the ratio of the homopolymer and block copolymer molecular weights. The cylindrical domains of the blends could be swollen up to 150% of the original diameter while maintaining hexagonal ordering. For most of the blends on the random copolymer brushes, uniform arrays of perpendicular cylinders were formed most frequently at a film thickness near D 0 . A ternary blend with homopolymers with very low M n s produced markedly different results: D decreased in size with increasing j H , measurable up to j H = 0.4, and produced uniform patterns in films with thicknesses ranging from 20 to 37 nm.
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