Ordered Hexagonal Arrays of Holes with 40 nm Period by Shear Alignment of Diblock Copolymer Bilayers

An ordered hexagonal array of holes was fabricated by shear-aligning a molten bilayer film of a sphere-forming diblock copolymer in a nitrogen atmosphere. The block copolymer consisted of a polystyrene (PS) matrix and polyisoprene (PI) spheres, and was spin-coated onto a Si substrate prior to shearing. The top layer of microdomains in the bilayer was removed via a nonselective fluorine-based reactive ion etch (RIE). The PI spheres in the remaining bottom layer were then degraded with ozone to produce a PS mask with an ordered array of voids. The voids were transferred into the Si substrate by RIE, producing a dense array of holes approximately 20 nm wide and spaced 40 nm apart. This bilayer shearing procedure allows for the production of hole arrays with excellent long-range orientational order and few grain boundaries, which are unachievable by shearing a single-layer film. In addition, Au was evaporated onto the array, yielding a film of Au with regular perforations having a 40 nm period.