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

Abstract. 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 underlayers pinning stripe compared to the periodicity of the BCP is defined as the density multiplication. Molecular dynamics simulations are used to explore the effect that density multiplication and pinning stripe position (PSP) have 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 PSPs, the free energy of defective films is significantly higher than that of defect-free films, suggesting that the presence of defects in experiments 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.