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Rapid shear alignment of sub-10 nm cylinder-forming block copolymer films based on thermal expansion mismatch
| Content Provider | Semantic Scholar |
|---|---|
| Author | Nicaise, Samuel M. Gadelrab, Karim R. Tavakkoli, Kg Amir Ross, Caroline A. Alfredoalexander-Katz Berggren, And Karl K. |
| Copyright Year | 2018 |
| Abstract | Directed self-assembly of block copolymers (BCPs) provided by shear-stress can produce aligned sub10 nm structures over large areas for applications in integrated circuits, next-generation data storage, and plasmonic structures. In this work, we present a fast, versatile BCP shear-alignment process based on coefficient of thermal expansionmismatch of the BCPfilm, a rigid top coat and a substrate. Monolayer and bilayer cylindricalmicrodomains of poly(styrene-b-dimethylsiloxane) aligned preferentially in-plane and orthogonal to naturally-forming or engineered cracks in the top coatfilm, allowing for orientation control over 1 cm substrates. Annealing temperatures, up to 275 °C, provided low-defect alignment up to 2mmaway from cracks for rapid (<1min) annealing times. Finite-element simulations of the stress as a function of annealing time, annealing temperature, and distance from cracks showed that shear stress during the cooling phase of the thermal annealingwas critical for the observedmicrodomain alignment. Directed self-assembly of block copolymer (BCP)microdomains in thinfilms has been used to enhance the correlation length of the periodic patterns for awide variety of applications, including integrated electronics [1–3], data storage [4], photonicmaterials [5], and bio-functionalized surfaces [6]. The limited correlation length of BCPmicrodomain arrays has been overcome through engineeringmethods to produce both longrange order and local control over patterns. These alignmentmethods have been based on templates (chemoepitaxy or graphoepitaxy [7, 8]), onfields (magnetic or electric [9]) or zone/gradient annealing, such as scanned solvent annealing [10], and on shear alignment. Previous shear alignment approaches sought to investigate the rheology of BCPfilms, and found that the shearing of the polymer during annealing aligned the assembledmicrodomains [11–15].More recent work has shown highly ordered, well-aligned line patterns over square-centimeter areas, as well asmillimeter-area orientation control [16–20] and have used shear-aligned BCP patterns as templates for further directed self-assembly [21]. Differentmechanical, light-based, and vapor-phasemethods have been developed to shear the surface of a BCP thinfilmwith a top coat.Many of themechanical approaches produce shear by in-plane displacement of a weighted PDMSpad or rotation of silicone oil [11–13, 22–27]. Shear can also be produced by swelling a top PDMSpadwith solvent vapor [19, 20, 28, 29] or by scanning a laser to locally heat substrates or PDMS top coats [18, 30]—in both cases, the expansion/contraction of the PDMSor substrate translates a shear stress to the adjacent BCPfilm.Other reports have observed shear-induced alignment during: viscous flowof BCPfilms [31, 32], specifically during nanoimprint lithography [33]; dewetting of a top coat poly(vinyl alcohol) pad [34, 35]; or scanned zone heating [16, 17, 36]. Chaikin et al have investigated shear alignment extensively via rheologicalmeasurements for both sphere and cylinder forming BCPs [11–13, 22, 24–27, 37, 38]. Yager et al have developed rapid alignment of cylinder domainswith scanned-laser heating [17, 18, 30, 39]. Shear alignment has been effective for a variety ofBCP chemistries,molecularweights, andnumbers of microdomain layerswithin thefilm thickness. The variety ofBCPs include differentmorphologies (body-centered RECEIVED |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://iopscience.iop.org/article/10.1088/2399-1984/aaa068/pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
