Confinement-induced flow resistance in polystyrene thin films: A semi-empirical framework for nanoimprint lithography

초록

This study investigates the deformation behavior of spin-coated polystyrene (PS) thin films under nanoscale confinement during thermal nanoimprint lithography (T-NIL). As film thickness approaches the radius of gyration (R-g), polymer flow is significantly suppressed, and deformation resistance increases even under moderate imprinting pressures. To quantify this behavior, a semi-empirical model is developed that incorporates three physically meaningful parameters: bulk-limit deformability, critical cavity size linked to coil dimensions and entanglement thresholds, and confinement-induced resistance scaling. Experimental results reveal a sharp rise in the confinement-induced resistance scaling parameter below similar to 7 R-g, indicating strong confinement effects associated with reduced segmental mobility and disrupted entanglement networks. Complementing this framework, an apparent viscosity model is constructed based on modified Poiseuille flow. The apparent viscosity exhibits an inverse power-law dependence on film thickness, closely mirroring the classical scaling law of viscosity with molecular weight (eta similar to M-2.4) in entangled polymer melts. Together, these models provide predictive insight into deformation resistance in confined polymer systems and offer quantitative guidelines for NIL process optimization. Beyond NIL, the findings contribute to a broader understanding of rheological behavior in polymer thin films under geometric confinement.

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