Grain-Boundary-Induced Alignment of Block Copolymer Thin Films

Abstract

We present and discuss the capability of grain boundaries to induce order in block copolymer thin films between horizontally and vertically assembled block copolymer grains. The system we use as a proof of principle is a thermally annealed 23.4 nm full-pitch lamellar Polystyrene-block-polymethylmetacrylate (PS-b-PMMA) di-block copolymer. In this paper, grain-boundary-induced alignment is achieved by the mechanical removal of the neutral brush layer via atomic force microscopy (AFM). The concept is also confirmed by a mask-less e-beam direct writing process. An elongated grain of vertically aligned lamellae is trapped between two grains of horizontally aligned lamellae. This configuration leads to the formation of 90° twist grain boundaries. The features maintain their orientation on a characteristic length scale, which is described by the material’s correlation length ξ. As a result of an energy minimization process, the block copolymer domains in the vertically aligned grain orient perpendicularly to the grain boundary. The energy-minimizing feature is the grain boundary itself. The width of the manipulated area (e.g., the horizontally aligned grain) does not represent a critical process parameter.

Templating Functional Materials Using Self-Assembled Block Copolymer Thin-Film for Nanodevices

“…The surface free energy of a neutral surface, can be selectively altered in number of different ways, including oxygen plasma treatement, (Oria et al, 2013), photolithography, (Cheng et al, 2010), electron-beam lithography (EBL) (Evangelio et al, 2019); (Laura et al, 2015) and scanning-probe lithography. (Gottlieb et al, 2020) During graphoepitaxy, three-dimensional (3D) topographic features are patterned on the substrate, such as trenches or holes, and the constraint employed by them on the BCP films is exploited for DSA. It is possible to tailor the physical geometry and dimension of the patterned topographies, while also chemically modifying their surface characteristics (i.e., bottom and walls) to selectively govern their affinity towards each BCP domain, thus in effect orienting their self-assembly.…”

Directed Self-Assembly of Block Copolymers for the Fabrication of Functional Devices

“…Chemoepitaxy involves the creation of dense chemical patterns on a neutral substrate to generate preferential wetting sites for one of the blocks [ 57 ]. Multiple processes and techniques have been successfully used to selectively tune the surface free energy of a neutral surface, including photolithography [ 58 ], electron-beam lithography (EBL) and oxygen plasma functionalization [ 59 , 60 , 61 , 62 , 63 ], direct EBL exposure [ 64 ] and scanning-probe lithography [ 65 , 66 , 67 ].…”

Self-Aligned Assembly of a Poly(2-vinylpyridine)-b-Polystyrene-b-Poly(2-vinylpyridine) Triblock Copolymer on Graphene Nanoribbons

“…This neutral/preferential interface modulation phenomenon provides an alternative solution to realize BCP alignment and greatly alleviates the requirement of making a highresolution guide pattern for the conventional DSA process. 28 Here, we propose using graphene nanoribbons as the neutral stripes with the gap among them consisting of the P2VPpreferential silicon oxide (SiO 2 ) substrate to realize onedimensional self-aligned assembly of the triblock copolymer poly(2-vinylpyridine)-block-polystyrene-block-poly(2-vinylpyridine) (P2VP-b-PS-b-P2VP). The P2VP-b-PS-b-P2VP used in our experiment has a pitch size of 16 nm.…”

“…The neutral stripe had a width of 200 nm, which was several times larger than L 0 of PS- b -PMMA (36 nm). This neutral/preferential interface modulation phenomenon provides an alternative solution to realize BCP alignment and greatly alleviates the requirement of making a high-resolution guide pattern for the conventional DSA process …”