Mechanisms of Directed Self-assembly in Cylindrical Hole Confinements

The directed self-assembly of block copolymers in cylindrical holes is a promising technology for lithographic patterning, particularly in the context of vertical interconnect accesses. While the hole-shrink process for single cylinders has been extensively explored, the proliferation of morphological defects remains a significant technological barrier. We use a coarse-grained model to explore morphologies that form within cylindrical confinements for combinations of template surface energies. We identify metastable defect morphologies, in addition to the desired cylindrical morphology, in majority-wetting sidewall templates. We use our coarse-grained model and the string method to identify transition pathways between defective morphologies and the cylindrical morphology to elucidate the mechanism of defect annihilation within the confinements; the transition pathway from a disordered state is also identified. This work demonstrates that the minimum free energy path for the formation of a cylinder goes through defective morphologies, and that designing confinements can eliminate these undesirable transition states.