In thermal imprint lithography, most of the imprint failures occur during demolding, a process to separate the mold insert from the substrate after conformal molding. The success of demolding is determined by the stress generated in the resist with respect to the yield stress of the resist. In this paper we simulated the demolding process in thermal imprint lithography using the finite element method to study the stress distribution and deformation in poly(methyl methacrylate) (PMMA) resist during demolding. During demolding, the stress concentrates both at the transition corner zone between the residual layer and the replicated pattern, and close to the contact region with the moving stamp. As demolding proceeds, the highest local stress for both locations shows two maximums, indicating that a structural failure may occur not only when demolding starts, but also immediately before demolding ends. The structural failure at the second maximum becomes dominant as the angular offset from the ideal normal demolding to the substrate surface increases or for the structures located far away from the symmetric centerline. In addition, we will discuss the influence of other process and geometry parameters, including demolding rate and stamp aspect ratio.

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