Influence of Homopolymer Addition in Templated Assembly of Cylindrical Block Copolymers

Templated assembly of cylindrical block copolymers provides a promising strategy for patterning holes at the nanoscale. However, remaining challenges include the ability to achieve defect-free patterns and to generate architectures useful for device patterning. The aim of this work is to gain insight into the influence of homopolymer addition on the assembly of a cylindrical block copolymer in confined space. To do so, a concerted examination that relies on experiments and simulations is carried out for different block copolymer/homopolymer blends. It is shown that by adding a majority block homopolymer with low molecular weight (compared to the blocks that make up the block copolymer), the pattern quality is significantly improved and a larger defect-free window is obtained in terms of template dimensions for two-hole features in elliptical confinements. The redistribution of the homopolymer chains effectively enables the assembly of two cylinders, despite the geometrical mismatch between the elliptical shape of the confinement and the natural hexagonal ordering of the unguided block copolymer. Monte Carlo simulations show that the homopolymer segregates to the spaces in the template that are entropically unfavorable for the block copolymer. This work serves to highlight the importance of optimizing block copolymer formulation.