Optimization of long-range order in solvent-annealed polystyrene-$b$-polylactide block polymer thin films for nanolithography

We demonstrate long-range order in solvent-annealed polystyrene-$b$-polylactide block polymer thin films for nanolithographic applications. This is accomplished \textit{via} climate-controlled solvent vapor annealing, \textit{in situ} solvent concentration measurements, and small angle x-ray scattering. By connecting the properties of swollen and dried films, we identify ``best practices'' for solvent-annealing, including that exposing block polymer films to a neutral solvent concentration just below the identified (\textit{via }x-ray scattering) order-disorder transition, at low pressures, with fast solvent evaporation rates, will consistently yield large lateral correlation lengths (\textgreater 6.9 $\mu $m) of hexagonally-packed cylinders that span the entire thickness of the film with center-to-center spacing ranging from 43 -- 59 nm. The resultant films have sufficient fidelity for pattern transfer to an inorganic material, as evidenced by patterning of Ni metal nanodots using a damascene-type approach. We argue that our results can be qualitatively understood by analogy to thermal annealing of a single-component solid, where annealing just below the melting point leads to optimal recrystallization. Such reliability, combined with recently developed pattern-transfer techniques, places this cheap and rapid method of nanolithography in competition with conventional lithography schemes. Funded by NSF MRSEC and Creighton University Summer Research Award.