Aspect-ratio enhancement of directed self-assembly patterns using extremely long chain polymer brush

Abstract

Self-assembled block copolymer (BCP) thin films have been extensively studied for applications involving the generation of functional nanostructures. Moreover, directed self-assembly (DSA) based on BCPs with excellent pattern resolution, cost-effectiveness, and scalability is a practical method for complementing optical lithography. Si-containing BCPs such as poly(styrene-block-dimethylsiloxane) (PS-b-PDMS) can provide sub-20 nm resolution with long range ordering and high etch resistance. However, the difficulty in achieving perpendicularly oriented micro-domains due to the large difference of surface energy between the two blocks limits aspect-ratio (AR) for the subsequent pattern transfer process. We introduce a way to enhance the AR of the self-assembled patterns obtained from cylinder-forming PS-b-PDMS BCPs by preparing thick PS brush layers underneath, successfully achieving ARs of 1.4-3.5. Moreover, nano-scale Si topographic patterns with AR of 4.1 obtained using the HAR patterns as an etch mask are also demonstrated. This study suggests a facile self-assembly methodology to obtain practical nano-patterns