Kun-Hua Tu

Universal pattern transfer methods for metal nanostructures by block copolymer lithography

A universal block copolymer pattern transfer method was demonstrated to produce Co nanostructures consisting of arrays of lines or dots from a polystyrene-block-polydimethylsiloxane (PS-b-PDMS) diblock copolymer. Three processes were used: liftoff, a damascene process, and ion beam etching using a hard mask of tungsten, including a sacrificial poly(methyl methacrylate) layer under the PS-b-PDMS for the etch and liftoff processes. The ion beam etch process produced the most uniform magnetic arrays. A structural and magnetic comparison in terms of uniformity, edge roughness and switching field distribution has been reported.

Morphology, directed self-assembly and pattern transfer from a high molecular weight polystyrene-block-poly(dimethylsiloxane) block copolymer film

The self-assembly of block copolymers with large feature sizes is inherently challenging as the large kinetic barrier arising from chain entanglement of high molecular weight (MW) polymers limits the extent over which long-range ordered microdomains can be achieved. Here, we illustrate the evolution of thin film morphology from a diblock copolymer of polystyrene-block-poly(dimethylsiloxane) exhibiting total number average MW of 123 kg mol-1, and demonstrate the formation of layers of well-ordered cylindrical microdomains under appropriate conditions of binary solvent mix ratio, commensurate film thickness, and solvent vapor annealing time. Directed self-assembly of the block copolymer within lithographically patterned trenches occurs with alignment of cylinders parallel to the sidewalls. Fabrication of ordered cobalt nanowire arrays by pattern transfer was also implemented, and their magnetic properties and domain wall behavior were characterized.