Prof. Jin Kon Kim Develops Self-neutralized Vertically Oriented Lamellar and Cylindrical Nanodomains
Prof. Jin Kon Kim (Dept. of Chemical Engineering) and his research team at POSTECH have developed a vertically oriented lamellar and cylindrical nanodomains without the usual pre- or post- treatments such as surface neutralization or solvent annealing. This novel approach was introduced on the front cover of Advanced Functional Materials (issue 34, volume 25 published on Sept. 9, 2015).
Directed self-assembly (DSA) of block copolymers has received attention for its low cost and simplicity for the miniaturization of integrated circuits. However, parallel orientation is usually obtained in a thin film rather than vertical orientation. This is the challenge that Prof. Kim and his team of scientists sought to resolve in their research.
"Although vertical orientation of lamellar and cylindrical nanodomains of block copolymers on a substrate is desirable, parallel orientation is usually obtained in a thin film because of different affinity between two block segments in a block copolymer toward the substrate and/or air," explained Prof. Kim who is also the Director of the National Creativity Research Initiative Program for Smart Block Copolymers. "In order to induce vertical orientation, researchers have developed diverse treatments to neutralize the preferential affinity."
Prof. Kim and his team have developed a simpler and more cost-effective DSA process that does not require neutralization methods that are time-consuming and costly. The self-neutralization process was developed by controlling the molecular architecture of a block copolymer. By employing 18 arm star-shaped poly(methylmethacrylate)-block-polystyrene copolymers with two different polystyrene volume fractions (fPS of 0.60 and 0.78 corresponding to lamellar and PMMA cylindrical nanodomains), the researchers were able to develop vertically oriented lamellae and hexagonally packed cylinders on the substrate by spin-coating without using any pre- or post-treatment.
"We used star-shaped block copolymer containing PS and etchable PMMA block, but sub 10 nm domain spacing is impossible due to the low χ,” said Prof. Kim. "It would greatly contribute toward the commercialization of DSA for next-generation integrated circuit and data storage media if star-shaped block copolymer containing high χ blocks such as polystyrene-block-poly(dimethyl siloxane) that could provide sub 10 nm spacing could be aligned vertically by controlling molecular architecture – but this is also a future work."