Lithography based on self-assembling block copolymers exploits the phase separation of block copolymer domains into nanoscopic structures that can be used as lithographic masks—templates for patterning and synthesizing inorganic materials and printing biomaterials. But before we proceed further, it is necessary to provide a brief background on block copolymers, how they are made, the condition under which they phase separate and self-assemble, and why they do this.
Block copolymers (BCPs) comprise two or more chemically distinct
polymer chains (called blocks) that are covalently bonded at one end to form a larger, more complex macromolecule. If the constituent polymers are immiscible, upon heating, phase separation can be induced (without resulting in total separation because of the covalent bonding connectivity between the copolymer chains). The separated phases are on a scale that is directly related to the size of the copolymer chains, resulting in morphologies typified by a pattern of chemically distinct domains of periodicity L0 in the 5- to 100-nm range. The size, shape, and arrangement of these morphologies are all tunable through synthetic chemistry of the constituent molecules, thereby enabling a diverse and expanding range of practical applications in, for example, drug delivery, lithographic masks, photonic and electronic materials, and advanced plastics, to mention but a few. Buoyed by new developments, block copolymers, thoroughly studied for more than 50 years, are yet again garnering renewed research interest, principally because of their potential applications in nanotechnology, of which lithography is an enabler.
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