Bioinspired Multifunctional Nanopatterns Through Regenerative Secondary Mask Lithography

Bioinspired nanopatterning to impart superior functionality and performance has been actively pursued, with demonstrations spanning solar cells, energy storage, sensors, antibacterial, and special wetting surfaces [1-3]. To afford such functionalities however, it is crucial to control both the morphology and dimensions of nanofeatures while accommodating a continuous demand for higher resolution and aspect ratio. To this end, pattern transfer using block copolymers (BCPs) has attracted a great attention due to their morphological diversity and a high-degree order at 10-100 nm scales. Nonetheless, when exposed to the etching plasma, they suffer from rapid degradation which leads to low aspect-ratio structures with limited control over morphologies.<br/>Here, we introduce and exploit regenerative soft mask lithography [4] to obtain high-aspect ratio (&gt;7), densely-packed (pitch~50-300 nm), periodic nanopillar/cone arrays in glass; notoriously difficult to structure due to its high stability. The approach is scalable and simple, comprising just two-steps. Firstly, we generate a high-resolution etch-mask through BCP micelles. Secondly, we overcome its durability problem via our innovative cyclic etching. Here, micelles become embedded within a secondary organic mask, which is tuned and regenerated, permitting nanofeature profiling.<br/>Our process (with record etching selectivity to BCP &gt;1:32), can also be adapted to other popular etch-masks (e.g., photoresists) and silicon nanostructuring by utilising glass as a hard mask. The latter allows for a library of silicon nanostructures to be formed from a single BCP: thin/thick pillars; sharp, truncated, and re-entrant cones. During BCP-to-glass pattern transfer, not only the mask diameter can be decreased but also uniquely increased; constituting the first method to achieve such tunability without necessitating a different molecular weight BCP. Consequently, the hard mask modulation (height, diameter) advances the flexibility in attainable inter-pillar spacing, aspect ratios, and re-entrant profiles (=glass on silicon). Combined with adjusted silicon etch conditions, the morphology of nanopatterns can be highly customized. The process control and scalability enable uniform patterning of a 6’’-wafer, and we verify the structural homogeneity through its excellent antireflectivity (&lt;5%) and robust superhydrophobicity across the wafer with ultralow hysteresis (&lt;1^o).<br/>It is envisioned the implementation of this approach to glass and silicon nanostructuring to be far-reaching, facilitating fundamental studies and targeting applications spanning solar panels, antifogging/antibacterial surfaces, sensing, amongst many others.<br/>[1] T. Mouterde, G. Lehoucq, S. Xavier, A. Checco, C. T. Black, A. Rahman, T. Midavaine, C. Clanet and D. Quéré, <i>Nat. Mater.</i>, 2017, <b>16</b>, 658–663.<br/>[2] A. Rahman, A. Ashraf, H. Xin, X. Tong, P. Sutter, M. D. Eisaman and C. T. Black, <i>Nat. Commun.</i>, 2015, <b>6</b>, 5963.<br/>[3] M. Michalska, F. Gambacorta, R. Divan, I. S. Aranson, A. Sokolov, P. Noirot and P. D. Laible, <i>Nanoscale</i>, 2018, <b>10</b>, 6639–6650.<br/>[4] M. Michalska, S. K. Laney, T. Li, M. Portnoi, N. Mordan, E. Allan, M. K. Tiwari, I. P. Parkin and I. Papakonstantinou, <i>Adv. Mater.</i>, 2021, 2102175.