Modeling and simulation of the deformation process of PTFE flexiblestamps for nanoimprint lithography on curved surfaces

In the presented work, simulations of the deformation process of flexible stamps used for nanoimprint lithographron curved surfaces are presented. The material used for the flexible stamps was polytetrafluoroethylene (PTFE) whose material behavior was found to be viscoelastic-viscoplastic. This behavior was described in a temperature dependent constitutive model consisting of a Zenerbody for the viscoelastic deformation and the Johnson-Cook model for the description of the viscoplastic deformation. The constitutive model was implemented in the general purpose finite element software ABAQUS through a user material subroutine. In order to take the large strains and deformations during the imprinting manufacturing process into account, non-linear geometry was applied in the simulations. The model was first verified through a series of experiments, where nanoimprint lithography on a curved tool insert for injection molding were performed with various process parameters such as temperature, imprinting pressure and flexible stamp thickness. Good agreement between simulations and experimental results was found. The optimum process parameters were then used in the final application, where nanoimprint of a nanostructure giving a color effect was performed numerically and experimentally. Both experiment and simulation showed a mismatch between the defined and measured nanostructures as a result of stretching of the flexible stamp. The model was shown to predict the stretch of the nanostructures with a maximum error of 0.5%, indicating that the model is able to capture the physics of this manufacturing process and can be used to give an insight into the nanoimprinting procedure on curved surfaces. (C) 2014 Elsevier B.V. All rights reserved.