Effective pitch reduction of self-assembled lamellae by the use of (PS-b-PMMA)n multiblock copolymers

The current directed self-assembly (DSA) process utilizes a diblock copolymer composed of polystyrene (PS) and polymethylmethacrylate (PMMA) as standard materials. However, domain spacing of the self-assembled PS-b-PMMA is limited to similar to 20-30 nm due to weak segregation strength. In this study, we explore a potential to overcome this size limitation through a multiblock approach that has previously been demonstrated with (PS-b-PI)n. Specifically, we simulate the self-assembled morphology of the linear multiblock copolymer, (PS-b-PMMA)n, using the so-called theoretically informed coarse-grained model developed for symmetric PS-b-PMMA. The simulation results demonstrate that the lamella pitch of (PS-b-PMMA)n can be reduced by similar to 20%-25% compared to that of diblock copolymer. This reduction is attributed to loop and bridge conformations of the multiblock copolymer chains. These findings indicate that (PS-b-PMMA)n could be advantageous for DSA, not only by enabling the size reduction, but also by potentially enhancing the guiding effects through physically cross-linked, self-assembled domains via bridged chains.