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.
Highlights
Nanoscale structures have many applications, including integrated circuit manufacturing and biological applications
In order to find the lower limit of biomimetic cellular response to surface topography, self-assembly regulated domain nanostructures of diblock copolymer have been exploited as a way to create templates for nanoscale patterning beyond the limit of conventional optical lithography [7,8,9,10,11]
To characterize roughness initiation during plasma etching, PS blanket film samples etched with bias voltage of −10 V and etch time from 0 second to 266 seconds were measured with atomic force microscopy (AFM)
Summary
Nanoscale structures have many applications, including integrated circuit manufacturing and biological applications. Biomimetic nanostructures with surface topography are used to study how living cells or micro-organisms respond to their environments [1,2,3,4,5,6]. In order to find the lower limit of biomimetic cellular response to surface topography, self-assembly regulated domain nanostructures of diblock copolymer have been exploited as a way to create templates for nanoscale patterning beyond the limit of conventional optical lithography [7,8,9,10,11]. Diblock copolymer structures contain two chemically distinct polymer blocks. The chemical distinction between the two polymer domains allows selective removal of one component of the structure by either wet etching or plasma etching
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