Probing polymer deformation profiles at varying depths in nanoimprint lithography.

We use immiscible polystyrene (PS)/polyacrylic acid (PAA) bilayer films as resist materials for nanoimprint lithography to probe the deformation profiles of the resist after the cavity filling process. By systematically varying the composition of the bilayers, we determined the deformation profiles of the bilayer resists at different depths after filling the 240 and 480 nm wide cavities. A single-peak deformation mode was observed for the bilayer films when the thickness of the top PS layer is less than the minimum thickness (H(c)) needed to completely fill the cavities. This is in good agreement with simulations based on pressure-driven viscous flow. However, for bilayers with a PS layer thickness close to H(c), a dual-peak deformation mode was observed near the entrance of the cavities, which is attributed to the stronger shear thinning of the polymer resist around these corners.