Ordered Meso-Pattern Formation over a Topographically Patterned Substrate by a Combination of Thermal and Spin Dewetting

Abstract We report the formation of ordered mesoscale features when a dilute polymer solution (polystyrene, PS) is spin-coated over soft-lithographically fabricated, topographically patterned substrates, with square-box, hexagonal, and circular patterns. At lower concentrations, the dispensed solution fails to form a continuous film over the topographically patterned substrates, resulting in isolated features arranged along the contours of the substrate patterns due to spin dewetting. We show that the morphology of the spin-dewetted features is governed by the effective initial film thickness (hE), which increases with the concentration of the dispensed polymer solution, and by the orientation of the topographically patterned regions with respect to the direction of the advancing meniscus during spin coating over square-box and hexagonally patterned substrates. With a progressive increase in hE, the polymer progressively fills the recessed regions of the patterned substrate and eventually forms a continuous film over the topographically patterned substrates. We also show that subsequent thermal annealing of these depositions/films leads to multilength-scale ordered patterns along the recessed and raised portions of the topographically patterned surfaces. Our experiments reveal the critical role of the geometry of the substrate patterns, particularly how they intercept the advancing meniscus during spin dewetting and the eventual ordering of the dewetted features.