Surface Roughness-Mediated Ordering in Block Copolymer Films toward Spatially Controlled Patterns

Abstract

We studied structure development in block copolymer films with a regular surface roughness induced by the deposition on corrugated supports. Upon thermal annealing, the residual surface roughness in thin films of cylinder-forming polystyrene-b-polybutadiene (PS-b-PB) diblock copolymer was found to be independent both on the averaged starting film thickness h 0 and on the initial thickness gradient induced by spin-coating. Surface patterns in PS-b-PB films on linear and squared wave gratings appear in a form of spatially registered cylinder and nonbulk lamella phases with the morphological sequences coupled to the topography of the substrate. The observed complex phase behavior is independent of the h 0 in up to three layers thick films. At the same time, the initial surface roughness was shown to be essential for the flow-field-induced sequenced ordering of the microdomains. We identify a number of specific features of complex confinement on corrugated substrates as compared to flat space, such as extreme deviations from the bulk cylinder morphology to nonbulk lamella structures in thick films, as well as the violation of the surface-tension-driven segregation of the soft PB component to the free surface. Differences in the flow behavior of PS-b-PB films and of PS homopolymer films under strong confinement, reported earlier, confirm the decoupling of the dynamics of the chains at the free surface from the underlying layers and suggest novel insights into the distribution of the surface fields through the film.

Curvature as a Guiding Field for Patterns in Thin Block Copolymer Films

“…2), it can be observed that the thin film dewets at the region with the highest curvature, where H max R g ∼ 0.03, while the stable region with the strongest guiding field corresponds to H max R g 0.007. These results are in good agreement with recent experiments on curved substrates by Park and Tsarkova [51], who also found dewetting for H > 0 and thin film thickening for H < 0 in agreement with Fig. 4e,f (green curves).…”

Controlled Spacing between Nanopatterned Regions in Block Copolymer Films Obtained by Utilizing Substrate Topography for Local Film Thickness Differentiation

“…Hence, the formation of different morphologies on the plateaus and in the trenches suggests that the thicknesses of the BCP film above each region are different. 61,62 Partially exposing the substrate by scratching the film with a syringe needle enabled film profiling by SFM and determining the local film thicknesses above the plateaus and above the trenches for each sample (Figure 1e each sample, which differ in the lateral dimensions of the trenches and plateaus but feature the same trench depth and nominal (cast) film thickness. For each sample, the nominal film thickness, denoted as h nominal , was measured in topographically smooth areas on the same substrate.…”

“…The combination of thickness confinement and strong substrate selectivity leads to extreme sensitivity of the morphology to the local film thickness. Hence, the formation of different morphologies on the plateaus and in the trenches suggests that the thicknesses of the BCP film above each region are different. , Partially exposing the substrate by scratching the film with a syringe needle enabled film profiling by SFM and determining the local film thicknesses above the plateaus and above the trenches for each sample (Figure e–g). Local film thickness values were averaged for at least four patterns on each sample, which differ in the lateral dimensions of the trenches and plateaus but feature the same trench depth and nominal (cast) film thickness.…”

Aligned Morphologies in Near-Edge Regions of Block Copolymer Thin Films

“…Printing methods have been applied to creating isolated patterns of BCP film material . The dewetting of block copolymer filmswhich naturally forms film discontinuities at the edges of dropletshas been studied extensively. − Many publications also report results where the BCP morphology undergoes a morphological or orientational transition in the vicinity of film edges, − the height-steps associated with islands and holes, ,,− or due to other thickness variations. ,− The rich set of results on block copolymer ordering in response to substrate topography (graphoepitaxy) established how film edges can drive ordering ,,− as well as uncovered effects where film thickness variation controls orientation. In particular, annealing of BCP films covering topographic templates can lead to alignment due to the flow of material. ,,, It is generally easiest to generate a film discontinuity in submonolayer BCP films; that is, inducing a film edge by dewetting a film thickness insufficient to form a continuous monolayer of the BCP morphology. , As a result, there is comparatively less investigation into how thicker films (multiple morphological layers) on flat substrates respond to film discontinuities.…”