Finite element method simulation of the molding process for thermal nano-imprint lithography

We made a numerical study on the deformation of a viscoelastic polymethyl methacrylene (PMMA) resist when a rigid SiO2 stamp with a rectangular line pattern is imprinted into the PMMA resist for thermal nano-imprint lithography (NIL). The stress distribution in the polymer resist during the molding process is calculated by a finite element method (FEM). Our simulation results reveal that the asymmetric von Mises stress is distributed over the polymer around the external line, which seems to be due to the squeezing flow under the flat space. The stress seems to be concentrated at the sidewall close to the centerline of the whole structure. Our simulation also reveals that a micro gap is formed between the replicated structure and the outer wall of the mold.