Fast Simulation of Pattern Formation and Process Dependencies in Roller Nanoimprint Lithography
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Fast Simulation of Pattern Formation and Process Dependencies in Roller Nanoimprint Lithography Hayden K. Taylor School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798. ABSTRACT We contribute a fast numerical approach to simulating the roller-imprinting of complex patterns. The technique predicts the extent to which imprinted patterns are fully formed, as well as variation of the imprinted material’s residual layer thickness (RLT). The approach can be used for roll-to-roll and roll-to-plate configurations, and for rollers with or without elastomeric coatings. If patterns vary in pitch, shape or areal density across the roller, RLT and the completeness of pattern transfer can vary with position as well as with processing parameters, and our technique is able to model these effects. The technique has been successfully validated against published experimental data from two different roller-NIL processes: one involving an ultraviolet-curing resist film on a glass plate, and another involving a flexible thermoplastic web softened at its surface. INTRODUCTION Nanoimprint lithography (NIL) often exhibits strong, systematic pattern dependencies, whereby spatial variation of the size, shape and areal density of geometries leads to parasitic elastic deflections of the stamp during imprinting [1]. These stamp deflections result in variation of RLT or incomplete cavity filling. Meanwhile, the load, loading duration, and temperature or illumination history of the imprinted resist are key parameters that determine pattern fidelity and yield. Both the pattern and the process must be optimized to ensure acceptable yield and throughput. Process development for NIL is often done experimentally, which is laborious and wasteful of materials. Modeling and numerical simulation can accelerate the development of suitable designs and processes. There have been several attempts to develop simulation techniques for NIL [1], ranging from molecular dynamics, through finite-element approaches to coarse-grain models. We have previously developed and experimentally validated a computationally simple algorithm for the chip- and wafer-scale imprinting of thermoplastic polymers [2], [3]. This algorithm has been applied to the microembossing of polymeric sheets for microfluidics [4], [5], and to investigating the influence of wafer/stamp surface roughness and bending compliance upon RLT [6], [7]. The method has been extended to include capillary forces between the stamp and resist, which become relevant in ultraviolet-curing NIL (UV-NIL) where the resist viscosity is orders of magnitude lower than in thermoplastic NIL [8]. For roller-based imprinting, modeling is less advanced. Some use has been made of analytical squeeze-flow models [9], which predict average RLTs but take no account of material flow at the scale of nanofeatures. Here we describe a new simulation technique that builds on our earlier chip- and wafer-scale work. The new technique integrates material deformations from the fe
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