High-Aspect-Ratio Perpendicular Orientation of PS-b-PDMS Thin Films under Solvent Annealing

A perpendicular orientation of high-aspect-ratio polystyrene-block-polydimethylsiloxane (PS-b-PDMS) cylindrical and lamellar PDMS microdomains was achieved by solvent annealing and then slowly drying thick PS-b-PDMS films. Perpendicularly oriented microdomains occurred throughout the film thickness, except at the air interface, where a layer of in-plane microdomains formed due to the surface energy difference between PS and PDMS. In contrast, thermal annealing produced in-plane orientation throughout the film thickness. The solvent-annealed perpendicular orientation was observed for cylindrical morphology PS-b-PDMS of 16 and 45 kg/mol, where PDMS is the minority block, and lamellar PS-b-PDMS of 43 kg/mol. To obtain fully perpendicular microdomain patterns, a nonselective high-powered 450 W CF₄/O₂ reactive ion etching process was performed to remove the top layer of the films. Substrate patterning using electron beam lithography produced local registration of 17 nm period hexagonal cylinder patterns.