Brushless and controlled microphase separation of lamellar polystyrene-b-polyethylene oxide thin films for block copolymer nanolithography

Creating perpendicular alignment in lamellar block copolymer (BCP) systems has considerable industrial and commercial significance, most importantly for generating nanowire structures in electronic devices. In general, these lamellar systems require careful interface engineering to obtain vertical orientation of the blocks. To avoid the strong preferential adsorption of one block to either the substrate or the polymer/air interface, the surface must be "neutralized" by chemical brushes or external forces, for example, solvent fields. Reported here is a stepwise thermo/solvent annealing process allowing the formation of perpendicular domains of polystyrene-b-polyethylene oxide lamellar structures while avoiding brush or other surface modifications. This BCP has a relatively small minimum feature size and can be used to generate substrate patterns for use in fabrication of nanowire electronic device structures.