Hierarchical nanopores formed by block copolymer lithography on the surfaces of different materials pre-patterned by nanosphere lithography

Abstract

Bottom-up patterning techniques allow for the creation of surfaces with ordered arrays of nanoscale features on large areas. Two bottom-up techniques suitable for the formation of regular nanopatterns on different length scales are nanosphere lithography (NSL) and block copolymer (BCP) lithography. In this paper it is shown that NSL and BCP lithography can be combined to easily design hierarchically nanopatterned surfaces of different materials. Nanosphere lithography is used for the pre-patterning of surfaces with antidots, i.e. hexagonally arranged cylindrical holes in thin films of Au, Pt and TiO2 on SiO2, providing a periodic chemical and topographical contrast on the surface suitable for templating in subsequent BCP lithography. PS-b-PMMA BCP is used in the second self-assembly step to form hexagonally arranged nanopores with sub-20 nm diameter within the antidots upon microphase separation. To achieve this the microphase separation of BCP on planar surfaces is studied, too, and it is demonstrated for the first time that vertical BCP nanopores can be formed on TiO2, Au and Pt films without using any neutralization layers. To explain this the influence of surface energy, polarity and roughness on the microphase separation is investigated and discussed along with the wetting state of BCP on NSL-pre-patterned surfaces. The presented novel route for the creation of advanced hierarchical nanopatterns is easily applicable on large-area surfaces of different materials. This flexibility makes it suitable for a broad range of applications, from the morphological design of biocompatible surfaces for life science to complex pre-patterns for nanoparticle placement in semiconductor technology.

Nanoscale Block Copolymer Self‐Assembly and Microscale Polymer Film Dewetting: Progress in Understanding the Role of Interfacial Energies in the Formation of Hierarchical Nanostructures

“…a) Sketch showing perpendicular (left) or parallel (right) orientation of PMMA cylinders in a PS matrix. Reproduced with permission . Copyright 2018, The Royal Society of Chemistry.…”

“…a–f) SEM images of microphase‐separated PS‐ b ‐PMMA (after PMMA removal) on SiO 2 surface functionalized with RCP, SiO 2 without RCP, electron beam evaporated gold, TiO 2 with RCP, TiO 2 without RCP, and electron beam evaporated platinum. (a–f) Reproduced with permission . Copyright 2018, The Royal Society of Chemistry.…”

“…a–c) SEM images of nanohole‐patterned thin films of Au, Pt, and TiO 2 serving as templates for the (directed) self‐assembly of PS‐ b ‐PMMA BCPs. Reproduced with permission . Copyright 2018, The Royal Society of Chemistry.…”

“…Thus, the minimum energy orientation is film thickness dependent (Figure 4b,e). [14,19,67,68,[77][78][79][80] Figure 4c,d gives examples of the changing polymer domain orientation with increasing polymer film thickness. The scanning electron microscopy (SEM) image in Figure 4c shows a film thickness gradient of a cylinderforming PS-b-PMMA block copolymer on a nonfunctionalized silica surface after thermal annealing in vacuum.…”

“…[11] One crucial issue in advancing BCP lithography to its next technological level, i.e., rendering the technique applicable for versatile device integration, is the fundamental understanding of the self-assembly process enabling control of the pattern formation and its guiding into desired surface architectures. In particular, interactions between the polymer and solid surfaces determine the morphology of nanostructures: polymer wetting behavior, [12][13][14] nanopattern orientation, [15][16][17][18][19] nanopattern uniformity through a thin film, [20][21][22] and defect density [22][23][24][25] in BCP thin films are fundamentally investigated by research groups contributing with insights from chemistry, physics, and material science.…”