Self-organization of random copolymers to nanopatterns by localized e-beam dosing

Strategic electron beam (e-beam) irradiation on the surface of an ultrathin (<100 nm) film of polystyrene-poly(methyl methacrylate) (PS-PMMA) random copolymer followed by solvent annealing stimulates a special variety of dewetting, leading to large-area hierarchical nanoscale patterns. For this purpose, initially, a negative (positive) tone of resist PS (PMMA) under weak e-beam exposure is exploited to produce an array of sites composed of cross-linked PS (chain-scissioned PMMA). Subsequently, annealing with the help of a developer solvent engenders dewetted patterns in the exposed zones where PMMA blocks are confined by the blocks of cross-linked PS. The e-beam dosage was systematically varied from 180 mu C cm(-2) to 10 000 mu C cm(-2) to explore the tone reversal behavior of PMMA on the dewetted patterns. Remarkably, at relatively higher e-beam dosing, both PMMA and PS blocks act as negative tones in the exposed zone. In contrast, the chain scission of PMMA in the periphery of the exposed regions due to scattered secondary electrons caused confined dewetting upon solvent annealing. Such occurrences eventually lead to pattern miniaturization an order of magnitude greater than with conventional thermal or solvent vapor annealed dewetting. Selective removal of PMMA blocks of RCP using a suitable solvent provided an additional 50% reduction in the size of the dewetted features.

Automated summary

Strategically using electron beam irradiation and solvent annealing on an ultrathin film of polystyrene-poly(methyl methacrylate) can lead to the formation of large-area hierarchical nanoscale patterns. The variation of e-beam dosage and the tone reversal behavior of the resist significantly affect the dewetted patterns, while selective removal of PMMA blocks using suitable solvent can further reduce the size of the features.