Directed Self-Assembly of Block Copolymer Films

Directed Self-Assembly of Block Copolymer Films 

Directed self-assembly shows promise in advanced lithography and a variety of other applications that have less complex requirements. For example, directed self-assembly could be used for enhancing etch selectivity, placing dopants in ordered arrays, or generating high-density, close-packed electrodes in capacitor arrays [6]. Additionally, the assembled nanostructures could be used for fabricating densely packed porous templates [12-14] or membranes [15, 16] at the nanoscale. Other potential applications of assembled block copolymer thin films include the fabrication of MOSFETs (metal-oxide-semiconductor field-effect transistors) [17], quantum dots [18], high surface area devices [19, 20], photovoltaic devices [21], and bit patterned media [22-24]. 

Generating Micro- and Nanopatterr s on Polymeric Materials. Edited by A. del Campo and E. Arzt Copyri t 2011 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-32508-S 

Enei etics of the Basic Directed Assembly System 

For a thin film of block copolymer on a chemical pattern, the effect of the surfaces can be described as follows. In the absence of stronger driving forces, the energy of the free surface, Fsurf, will lead the block with the lowest surface energy to populate the surface layer. Fsurf per chain in the film can be expressed as Equation 10.2 [33,38]  

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I 10 Directed Self-Assembly of Block Copolymer Films... 

Mikihito Takertaka received both the master s degree in engineering in 1988 and the doctor s degree in engineering in 1993 with Prof Takeji Hashimoto from Kyoto Urriversity. In 1997, he was appointed as an assistant professor of the Department of Polymer Chemistry in Kyoto University. He was promoted to associate professor in 2011. His research scope includes the dynamics of phase transitions of polymer alloys and the directed self-assembling of block copolymer thin films. 

Recently, researchers paid more attention to the guided self-assembly of block copolymer thin films on a patterned surface. The patterned surface means the surface of a constrained situation is chemically or physically modified to form a pattern with specific property and size. A series of exquisite structures are found in the microphase separation of block copolymer under the patterned surface. In the theoretic work of Wu and Dzenis [43], they designed two kinds of patterned surface to direct the block copolymer self-assembly (Fig. 15.7). The self-assembled structures are found strongly influenced by the commensurability of polymer bulk period and pattern period. With mismatched patterns on two surfaces, both MC simulation [44] and SCFT researching [45] predicted the titled lamellae and perforated lamellae structures for symmetric diblock copolymers. Petrus et al. carried out a detailed investigation on the microphase separation of symmetric and asymmetric diblock copolymers confined between two planar surfaces using DPD simulation [46,47]. It is found that various nonbulk nanostructures can be fabricated by the nanopatterns on the surfaces. 

The crystallization of polymers within the domains formed by self-assembly of block copolymers has been already discussed. In thin films, the direction of the crystal growth and the probability to nucleate are influenced by boundaries like three-phase contact lines offered by wetting and dewetting processes.The effects of the particularities of thin films on crystallization within block copolymers have been extensively studied by the group of A representa-... 

Nealey and coworkers [75,76,146] took a similar approach and applied lithographically defined self-assembled monolayers as substrates to direct the orientation of block copolymer thin films. After EUV interferometic lithography on octadecyltrichlorosilane (OTS) or phenylethyltrichlorosilane (PETS) monolayers, PS-fr-PMMA block copolymers were deposited and annealed on the substrates. Due to the selective wetting of PS and PMMA on the unexposed and exposed regions, respectively, they were able to obtain large areas of perpendicular lamella when the commensurate condition was fulfilled. 

Mishra, V., Eredrickson, G.FI., Kramer, E.J. Effect of film thickness and domain spacing on defect densities in directed self-assembly of cylindrical morphology block copolymers. ACS Nano 6, 2629 (2012)... 

The inherent ability of block copolymers to self-assemble into various well-ordered supramolecular structures makes them attractive for numerous technological applications. For instance, thin films self-assembled from block copolymers have been used as building blocks in nanotechnology and materials science [89-91 ]. Block copolymers have been employed directly without further manipulation as nanomaterials [92], or used as self-organized templates for the creation of nanos-tructured materials [92, 93]. Block copolymer blends demonstrated their applicability as patterning templates for the fabrication of well-ordered arrays [94], as well as for nanoscale manufacturing of more complex patterns [95]. The use of amphiphilic block copolymers for templating applications has been reviewed by FOrster [96]. 

Summary Well-defined amphiphilic block copolymers containing a poly(dimethyl siloxane) (PDMS) and a poly(ethylene oxide) (PEO) block were synthesized by ringopening polymerization of hexamethylcyclotrisiloxane, followed by chain extension with a PEO block of a defined length. These amphiphilic molecules were used as structure-directing agents in a solvent evaporation-driven synthesis approach to self-assembled mesostructured silica films. In addition, a general theoretical approach for an understanding and ultimately a prediction of the phase behaviour of block copolymers is presented. 

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