Time evolution of the resist deformation process in the thermal nanoimprint lithography (NIL) has been investigated by both experiment and simulation study. For the numerical simulation, the authors newly developed a simulator using generalized Maxwell model as the viscoelastic constitutive model in conventional finite element method, which handles the complete NIL operations including resist pressing, cooling, and demolding processes. The dependency on the linewidth of the filling rate was investigated by both experiments and simulation and they sufficiently agreed with each other. It is confirmed that narrow pattern (high aspect ratio pattern) was difficult to be filled in a short period under the same imprinting pressure. (c) 2007 American Vacuum Society.