Lamellar orientation of block copolymer using polarity switch of Nitrophenyl self-assembled monolayer (SAM) induced by electron beam.

Directed self-assembly (DSA) was investigated on self-assembled monolayers (SAMs) of 6-(4-nitrophenoxy) hexane-1-thiol (NPHT), which were chemically modified by electron beam (EB) irradiation. By irradiating a responsive interfacial surface, the orientation and selective patterning of block copolymer domains could be achieved. We demonstrated that spatially-selective lamellar orientation of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) could be induced via modification of an underlying SAM; for instance the conversion of an NO2 group to an NH2 group, induced by EB. The lamellar orientation of PS-b-PMMA was controlled by the change in the polarity of different regions of the SAM using EB lithography. The reductive treatment of SAM substrates plays a crucial role in the orientation of block copolymer. This method might greatly simplify block copolymer DSA processes as compared to the conventional multi-step chemo-epitaxy DSA process. By examining the lamellae orientation by EB, we found that the vertical orientation persists only for appropriate an irradiation dose and annealing temperature.