Control of Morphologies and Length Scales in Intensified Dewetting of Electron Beam Modified Polymer Thin Films under a Liquid Solvent Mixture

Abstract

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 (λm) to 2λm. 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 λm. 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.