Photoresists are the materials of choice for micro/nanopatterning and device fabrication but are rarely used as a self-assembly material. We report for the first time a novel interplay of self-assembly and photolithography for fabrication of hierarchical and ordered micro/nano structures. We create self-organized structures by the intensified dewetting of unstable thin (∼10 nm to 1 μm) photoresist films by annealing them in an optimal solvent and nonsolvent liquid mixture that allows spontaneous dewetting to form micro/nano smooth dome-like structures. The density, size (∼100 nm to millimeters), and curvature/contact angle of the dome/droplet structures are controlled by the film thickness, composition of the dewetting liquid, and time of annealing. Ordered dewetted structures are obtained simply by creating spatial variation of viscosity by ultraviolet exposure or by photopatterning before dewetting. Further, the structures thus fabricated are readily photopatterned again on the finer length scales after dewetting. We illustrate the approach by fabricating several three-dimensional structures of varying complexity with secondary and tertiary features.
We
report fabrication of ordered polymeric nanodomains and control
of their morphology and size by self-organized intensified dewetting
of ultrathin polymer films which are selectively exposed to small
doses of electron beam (e-beam). Both positive and negative e-beam
tone polymers are used to produce variety of highly regular patterns
over large area (∼mm2) in significantly lesser time
as compared to e-beam lithography. Dewetting of selectively exposed
thin films under a mixture of water and organic solvents enables the
instability to grow much faster and in very confined domains. Patterns
ranging from straight and cross channels, array of circular and square
holes, aligned nanowires and square grid to the array of spherical
droplets can be fabricated by selection of e-beam exposure patterns
and the dewetting conditions. Fabrication of structures with sharp
corners and edges becomes possible because of ultralow interfacial
tension of polymer in the liquid mixture. Further, the length scale
of pattern can be tuned over a wide range which in some case extends
from about tenth of the natural wavelength of instability in dewetting
(λ
m
) to 2λ
m
. This is a significant improvement over the dewetting on physico-chemically
patterned substrate where alignment of polymer structures is lost
when substrate patterns are smaller than half of λ
m
. The dewetting mechanism of e-beam exposed films
is proposed as the change in the effective viscosity of e-beam exposed
region that leads to the faster growth of instabilities in the low
viscous regions and results in the formation of regularly aligned
structures. Nonlinear simulations are carried out which show very
good agreement with the experimentally obtained patterns.
Directed self-organization of a glassy material is demonstrated to generate ultra smooth, optically useful micro structures such as lens arrays and gratings. Liquid thin films of chalcogenide re-organize within the confinement provided by the mould.
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