Free energy of defects in chemoepitaxial block copolymer directed self-assembly: effect of pattern density and defect position

Block copolymers (BCPs) can phase separate to form periodic structures with small spacings, making BCPs an attractive option for furthering the ability of optical lithography. Chemoepitaxy is a method of directed self-assembly (DSA) that uses preferential pinning stripes to guide the BCP. The periodicity of the underlayer’s pinning stripe compared to the periodicity of the BCP is defined as the density multiplication. In this study molecular dynamics simulations are used to explore the effect density multiplication and pinning stripe position has on the free energy difference between a defective and defect-free BCP film. For all defect orders the highest free energies were obtained when a pinning stripe was located directly under or adjacent to the terminating block. At high density multiplications, the defects were found to approach the free energy of the same defect on an unpatterned underlayer. For all density multiplications and pinning stripe positions the free energy of defective films is significantly higher than that of defect-free films, suggesting the presence of defects in experiment is likely due to kinetic entrapment of defects. Free energy initially increases with increasing defect size, but was found to level off and even decrease for the largest defects in this work.