Free Energy of Defects in Ordered Assemblies of Block Copolymer Domains

We investigate commonly occurring defects in block copolymer thin films assembled on chemically nanopatterned substrates and predict their probability of occurrence by computing their free energies. A theoretically informed 3D coarse grain model is used to describe the system. These defects become increasingly unstable as the strength of interactions between the copolymer and the patterned substrate increases and when partial defects occur close to the top surface of the film. The results presented here reveal an extraordinarily large thermodynamic driving force for the elimination of defects. When the characteristics of the substrate are commensurate with the morphology of the block copolymer, the probability of creating a defect is extremely small and well below the specifications of the semiconductor industry for fabrication of features having characteristic dimensions on the scale of tens of nanometers. We also investigate how the occurrence of defect changes when imperfections arise in the underlying patterns and find that, while defects continue to be remarkably unstable, stretched patterns are more permissive than compressed patterns.