Directed Assembly of High Molecular Weight Block Copolymers: Highly Ordered Line Patterns of Perpendicularly Oriented Lamellae with Large Periods

Abstract

The directed assembly of block copolymer nanostructures with large periods exceeding 100 nm remains challenging because the translational ordering of long-chained block copolymer is hindered by its very low chain mobility. Using a solvent-vapor annealing process with a neutral solvent, which was sequentially combined with a thermal annealing process, we demonstrate the rapid evolution of a perpendicularly oriented lamellar morphology in high molecular weight block copolymer films on neutral substrate. The synergy with the topographically patterned substrate facilitated unidirectionally structural development of ultrahigh molecular weight block copolymer thin films-even for the structures with a large period of 200 nm-leading to perfectly guided, parallel, and highly ordered line-arrays of perpendicularly oriented lamellae in the trenched confinement. This breakthrough strategy, which is applicable to nanolithographic pattern transfer to target substrates, can be a simple and efficient route to satisfy the demand for block copolymer assemblies with larger feature sizes on hundreds of nanometers scale.

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“…To the best of our knowledge, the longest pitch of a nano-pattern formed with BCP was around 200 nm [8]. In contrast, we were able to obtain nano-patterns larger than 200nm by using a BCP whose molecular weight was over 1 million.…”

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“…This method has already been reported in previous studies regarding DSA defects. [ 32,35 ] For line/space patterns, typical examples of self-assembly defects are dots, junctions, dislocations, and terminal points. According to a power law, the defect density ( ρ ) of self-assembled BCP patterns as a function of the assembly time ( t ) can be expressed as t v ρ − , where v is the empirical kinetic exponent.…”

“…[ 30,34 ] Ryu et al found that two-step annealing consisting of solvent and thermal treatments is highly effective for the assembly of high-N BCPs. [ 35 ] Ross and co-workers also reported a signifi cant reduction of the assembly time of BCPs on densely guided narrow trench templates by rapidly increasing the substrate temperature following a conventional room-temperature solvent annealing process. [ 36 ] However, the rapid, one-step assembly of long-range ordering of high-χN BCPs on micrometer-scale wide templates, obtainable by low-cost photolithography, has yet to be demonstrated.…”

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“…Various reports on large BCP features are now evident and may present an ideal route to fabricating metamaterials and photo nic structures. [ 220 ] Reports have detailed the self-assembly of large periods using large molecular weight (>1 million g mol −1 ) BCPs [ 221 ] and brush-type BCPs. [ 222,223 ] A recent review [ 224 ] has also highlighted this emerging area of patterning large period features from such polymer materials.…”