Selective directed self-assembly of coexisting morphologies using block copolymer blends.

A Stein,C T Black,K G Yager,G Wright,G S Doerk

doi:10.1038/ncomms12366

Abstract

Directed self-assembly (DSA) of block copolymers is an emergent technique for nano-lithography, but is limited in the range of structures possible in a single fabrication step. Here we expand on traditional DSA chemical patterning. A blend of lamellar- and cylinder-forming block copolymers assembles on specially designed surface chemical line gratings, leading to the simultaneous formation of coexisting ordered morphologies in separate areas of the substrate. The competing energetics of polymer chain distortions and chemical mismatch with the substrate grating bias the system towards either line/space or dot array patterns, depending on the pitch and linewidth of the prepattern. This is in contrast to the typical DSA, wherein assembly of a single-component block copolymer on chemical templates generates patterns of either lines/spaces (lamellar) or hexagonal dot arrays (cylinders). In our approach, the chemical template encodes desired local spatial arrangements of coexisting design motifs, self-assembled from a single, sophisticated resist.

Highlights

Directed self assembly (DSA) is a nanofabrication technique in which self-assembling block copolymer thin films (BCP) are ordered using larger-scale, pre-defined guides patterned by standard lithography (Figure 1a)[1,2,3]
Directed self assembly is limited in the range of structures that can be fabricated in a single layer because each BCP material defines only a single equilibrium morphology
We recently demonstrated that in thin films, blends of BCP cylinders and lamellae can either form a single-phase or two-phase morphologies[16]

Summary

Introduction

Directed self assembly (DSA) is a nanofabrication technique in which self-assembling block copolymer thin films (BCP) are ordered using larger-scale, pre-defined guides patterned by standard lithography (Figure 1a)[1,2,3]. Previous work has shown that BCP patterning using two morphologies can be achieved through irradiation induced BCP cross-linking and subsequent morphology alteration in non-cross-linked areas through solvent annealing[11,12]. These approaches to create mixed morphology patterns require multiple steps, potentially limiting the registration accuracy of the two morphologies. Non-bulk morphological phases based on surface reconstruction of very thin cylinder-forming BCP films may provide a route to achieving mixed morphological patterning in a single-layer[13], but utilizing this in DSA requires impeccable control over BCP film thickness across nanometer scale distances

Methods

Results

Conclusion