Understanding Film Thickness‐Dependent Block Copolymer Self‐Assembly by Controlled Polymer Dewetting on Prepatterned Surfaces

Block copolymer (BCP) lithography is a versatile bottom-up approach for the creation of regular nanoscale patterns on large surface areas. The pattern morphology evolving during the microphase separation of a BCP is strongly dependent on the polymer film thickness. Thus, surface wetting as well as interfacial energies between polymer and substrate determine the polymer behavior, however, the complex interplay of those effects is not yet fully understood. In this work, a model describing the film thickness dependence of BCP self-assembly on prepatterned surfaces is proposed. Polymer dewetting on nanohole-patterned surfaces is controlled using different prepattern dimensions, polymer amounts, and microphase-separation temperatures. This is found to allow for a precise local film thickness modulation and thus allows to guide BCP self-assembly into arrays of tailored hierarchical nanoarchitectures. Analytical calculations of the total surface free energies of the microphase-separated polymer of different film thicknesses confined inside nanoholes confirm the model. The insights contribute to the understanding of fundamental processes in polymer dewetting and BCP self-assembly and allow for the controlled creation of advanced hierarchical nanostructures on large areas for applications in optics, plasmonics, and biomedical devices.