Top Coats: Control of Orientation, Alignment and Morphologies of Sub-10 nm Block Copolymer Microdomains

Achieving sub-10 nm high-aspect-ratio patterns from diblock copolymer self-assembly requires both a high interaction parameter (χ, determined by the incompatibility between the two blocks) and a perpendicular orientation of microdomains. However, these two conditions are extremely difficult to achieve simultaneously because the blocks in a high-χ copolymer typically have very different surface energies, favoring in-plane microdomain orientations. We introduce top coat for the control of orientation, alignment and morphology of a high-χ block copolymer, poly(styrene-block-dimethylsiloxane) (PS-b-PDMS). Using partially hydrolyzed PVA top coats with a solvent annealing, perpendicular orientation of PS-b-PDMS can be obtained despite the large surface energy differences between PS and PDMS. Extremely straight and laterally aligned cylindrical microdomain of BCP films were prepared by simply covering the BCP films with a top coat and dewetting the latter via thermal annealing to generate shear flow in the BCP underlayer. We also observed the gyriod-cylinder phase transition using interfacial-energy-tailored top-coat. At the optimized top-coat composition, gyroid nanostructures with sub-10 nm strut width were achieved down to ∼125 nm.