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

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

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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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 which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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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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