Relationship between nanoscale roughness and ion-damaged layer in argon plasma exposed polystyrene films

Abstract

The uncontrolled development of nanoscale roughness during plasma exposure of polymer surfaces is a major issue in the field of semiconductor processing. In this paper, we investigated the question of a possible relationship between the formation of nanoscale roughening and the simultaneous introduction of a nanometer-thick, densified surface layer that is formed on polymers due to plasma damage. Polystyrene films were exposed to an Ar discharge in an inductively coupled plasma reactor with controllable substrate bias and the properties of the modified surface layer were changed by varying the maximum Ar + ion energy. The modified layer thickness, chemical, and mechanical properties were obtained using real-time in situ ellipsometry, x-ray photoelectron spectroscopy, and modeled using molecular dynamics simulation. The surface roughness after plasma exposure was measured using atomic force microscopy, yielding the equilibrium dominant wavelength and amplitude A of surface roughness. The comparison of measured surface roughness wavelength and amplitude data with values of and A predicted from elastic buckling theory utilizing the measured properties of the densified surface layer showed excellent agreement both above and below the glass transition temperature of polystyrene. This agreement strongly supports a buckling mechanism of surface roughness formation.

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

“…Results of initial roughness formation and evolution are consistent with our speculation that aggregation is likely to be the origin of the surface roughening during plasma etching. The theory was previously supported by a correlation between the thickness of the modified layer and the lateral dimension of the roughness [28].…”

“…The data may also be examined in the context of surface buckling, an alternative theory that predicts surface roughness with uniform size and shape [17,28], in which the highly-stressed carbon-rich modified surface layer buckles, producing wrinkles. The predicted surface roughness magnitude is affected by the wavelength of the wrinkles, the lateral dimension of the surface roughness features.…”

“…But rather than cross-linking induced aggregation as proposed in previous studies, a buckling theory [17,28] is proposed by Bruce et al to explain the mechanism behind this observation. In the proposed model, a stressed modified surface layer could buckle and form wrinkles and thus surface roughness during plasma etching.…”

Nanotexturing and Wettability Ageing of Polypropylene Surfaces Modified by Oxygen Capacitively Coupled Radio Frequency Plasma

“…The aspect ratio of the nanofibrils and the separated distance between the nanofibrils further increased at longer oxygen CCP treated time. The nanoscale surface roughness with the corrugation wavelength about 30e70 nm on the polymers by plasma etching had been ascribed to the elastic buckling caused by the ion-induced formation of the highly compressed, modified surface layer [15,16] . The sputtering from the reactor wall also could be favorable to the formation of the nanodots [27] .…”

“…It is suspected that the column formation on PMMA and PEEK materials could be a result of alumina sputtering from the reactor wall and micromasking of the polymer surface. Bruce et al [15] reported the nanoscale roughening of polystyrene (PS) films using an Ar discharge in an inductively coupled plasma reactor with controllable substrate bias. It is suggested that the buckling caused by the ion-induced formation of a highly compressed, modified surface layer was the origin of the nanoscale roughness.…”