Thru-thickness Vertically Ordered Lamellar Block Copolymer Films with Dynamic Thermal Annealing*

Template-free directed self-assembly of ultrathin lamellar block copolymer (l-BCP) films into vertically oriented nanodomains holds much technological relevance for fabrication of next-generation devices from nanoelectronics to nanomembranes. We report the formation of thru-thickness vertically oriented lamellae in polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) thin films on quartz substrate, without any PMMA-block wetting layer formation, quartz surface modification or system modifications. A molecular relaxation induced vertical l-BCP ordering occurs under a transient macroscopic vertical strain field, imposed by sharp thermal gradient (▽T) cold zone annealing (CZA-S). The parametric window for vertical ordering is quantified via a coupling constant, C (= v.▽T), whose range is established in terms of ▽T above a threshold value, and an optimal dynamic sample sweep rate (v ~ d/τ), where τ = l-BCP’s longest molecular relaxation time and d = T_g,heat-T_g,cool distance. This study also reports a thorough understanding of the dynamic molecular mechanisms involved in the nanostructure formation and morphology evolution of vertically oriented l-BCP along the CZA-S ▽T tracked in real-time by in-situ GISAXS.