Block copolymers (BCPs) have the potential to play a key role in templating materials for nanoscale synthesis. BCP lithography likely will be one of the first examples of BCP-based nanomanufacturing implemented in a production setting. One of the challenges in implementing BCP lithography is that the lamella need to be oriented perpendicular to the substrate. For many systems, this requires control over interfacial energies for both components at the substrate and interface. Top coats can be designed to provide a neutral interface for both blocks on the BCP surface. The preferentiality of the top coat as a function of composition has been determined qualitatively by examining the orientation of a BCP after annealing with a top coat. Measurements of the interfacial width between the top coat and homopolymers allows the interface energy to be quantitatively determined. Resonant soft X-ray reflectivity measurements on top coat/homopolymer pairs were used to extract the Flory-Huggins parameter (χ) and interface energy (γ) as a function of top coat composition. The difference between χ and γ for each top coat/homopolymer pair was minimized at compositions that resulted in the top coat promoting perpendicular orientation. As the composition moved away from the neutral point the difference between χ and γ for each pair grew larger.
Bibliographical noteFunding Information:
The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02- 05CH11231. We thank Eric Gullikson for assistance at BL. 6.3.2. and Paul Kienzle for the work developing the Refl1D software. The authors thank Nissan Chemical Industries, Lam Research, the ASTC, and the National Science Foundation (Grants EECS-1120823 and EEC-1160494) for financial support. M.J.M. thanks National Science Foundation Graduate Research Fellowship (Grant No. DGE-1110007) for financial support. C.J.E. thanks the Welch Foundation (Grant #F-1709) for partial financial support. C.G.W. thanks the Rashid Engineering Regents Chair and the Welch Foundation (Grant #F-1830) for partial financial support. Any opinion, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation or the sponsors.
© 2016 American Chemical Society.
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