Dual patterning process by the combination of photolithography and self-assembly of block copolymer

Abstract

Self-assembly of the block copolymer is one of the most promising ways for the formation of nanometer-sized structures varied from spheres, to hexagonally close-packed cylinders, and to lamellar structures. Whereas the long range ordering and precise placement of the domains are needed for the practical applications, it is much harder to achieve since there are no driving forces for the domains of close-packed columns to align macroscopically. To achieve the further alignment, several techniques such as strong electric, magnetic fields, chemically patterned substrate, or balanced surface chemistry have been applied. Also, the positional ordering of the domains can be achieved through the use of nanoimprint lithography or topographically patterned substrate. Through the combination of top-down and bottom-up approaches, all advantages on both sides can be realized. In this study, we were investigating the use of photolithography as one of the top-down approaches. By photolithographic technique, positional ordering of patterns could be achieved, and those patterns would be served as topographic boundary within which the block copolymer could be self-assembled into thermodynamically most-stable structure. We synthesized polystyrene-b-poly(tert-butyl acrylate) (PS-b-PtBA), which would be transformed into polystyrene-b-poly(acrylic acid) (PS-b-PAA) by the deprotection of tert-butyl acrylate linkages by photogenerated acid. The patterns were made by this kind of solubility change in a positive-type patterning process. And the self-assembly test confirmed that the target block copolymer could be self-assembled into cylindrical or spherical structure. Eventually, we thought that the dual patterns could be expected through the combination of these two processes with much smaller sizes and more controllable alignment. But the expected results was not detected clearly maybe due to the high content of photo-acid generator, its incompatibility with the PtBA block, and detec...