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Polymers 2010, 2(4), 649-663; doi:10.3390/polym2040649
Article

Surface Roughening of Polystyrene and Poly(methyl methacrylate) in Ar/O2 Plasma Etching

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1,*
1 Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA 2 Department of Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA 3 Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA
* Author to whom correspondence should be addressed.
Received: 2 September 2010 / Revised: 31 October 2010 / Accepted: 26 November 2010 / Published: 2 December 2010
(This article belongs to the Special Issue Nano-Structures of Block Copolymers)
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Abstract

Selectively plasma-etched polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer masks present a promising alternative for subsequent nanoscale patterning of underlying films. Because mask roughness can be detrimental to pattern transfer, this study examines roughness formation, with a focus on the role of cross-linking, during plasma etching of PS and PMMA. Variables include ion bombardment energy, polymer molecular weight and etch gas mixture. Roughness data support a proposed model in which surface roughness is attributed to polymer aggregation associated with cross-linking induced by energetic ion bombardment. In this model, RMS roughness peaks when cross-linking rates are comparable to chain scissioning rates, and drop to negligible levels for either very low or very high rates of cross-linking. Aggregation is minimal for very low rates of cross-linking, while very high rates produce a continuous cross-linked surface layer with low roughness. Molecular weight shows a negligible effect on roughness, while the introduction of H and F atoms suppresses roughness, apparently by terminating dangling bonds. For PS etched in Ar/O2 plasmas, roughness decreases with increasing ion energy are tentatively attributed to the formation of a continuous cross-linked layer, while roughness increases with ion energy for PMMA are attributed to increases in cross-linking from negligible to moderate levels.
Keywords: diblock copolymer; plasma etching; surface roughness; cross-linking; polymer aggregation diblock copolymer; plasma etching; surface roughness; cross-linking; polymer aggregation
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).
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Ting, Y.-H.; Liu, C.-C.; Park, S.-M.; Jiang, H.; Nealey, P.F.; Wendt, A.E. Surface Roughening of Polystyrene and Poly(methyl methacrylate) in Ar/O2 Plasma Etching. Polymers 2010, 2, 649-663.

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