期刊
ACS APPLIED MATERIALS & INTERFACES
卷 14, 期 23, 页码 27466-27475出版社
AMER CHEMICAL SOC
DOI: 10.1021/acsami.2c05911
关键词
block copolymers; self-assembly; optical metasurfaces; structural color; thermal reflow; solvent vapor annealing; lithography
资金
- U.S. Department of Energy Office of Science User Facility, at Brookhaven National Laboratory [DE-SC0012704]
A general strategy is reported to overcome the limitation of fixed feature size in nanopatterning, using copolymer thin film as a hierarchical resist. Feature sizes can be tuned by thermal reflow or exposure-controlled chemical alteration. This approach enables the fabrication of complex optical metasurfaces using scalable self-assembly methods.
Nanopatterning for the fabrication of optical metasurfaces entails a need for high-resolution approaches like electron beam lithography that cannot be readily scaled beyond prototyping demonstrations. Block copolymer thin film self-assembly offers an attractive alternative for producing periodic nanopatterns across large areas, yet the pattern feature sizes are fixed by the polymer molecular weight and composition. Here, a general strategy is reported which overcomes the limitation of the fixed feature size by treating the copolymer thin film as a hierarchical resist, in which the nanoscale pattern motif is defined by self-assembly. Feature sizes can then be tuned by thermal reflow controlled locally by irradiative cross-linking or chemical alteration using lithographic ultraviolet light or electron beam exposure. Using blends of polystyrene-block-poly(methylmethacrylate) (PS-b-PMMA) with PS and PMMA homopolymers, we demonstrate both self-assembled PS grating and hexagonal hole patterns; exposure-controlled reflow is then used to reduce the hole diameter by as much as 50% or increase the PS grating linewidth by more than 180%. Transferring these nanopatterns, or their inverse obtained by a lift-off approach, into silicon yields structural colors that may be prescriptively controlled based on the nanoscale feature size. Furthermore, patterned exposure enables area-selective feature size control, yielding uniform structural color patterns across centimeter square areas. Electron beam lithography is also used to show that the lithographic resolution of this selective-area control can be extended to the nanoscale dimensions of the self-assembled features. The exposure-controlled retlow approach demonstrated here takes a pivotal step toward fabricating complex, hierarchical optical metasurfaces using scalable self-assembly methods.
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