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Resist filling behavior is crucial to the quality of final imprinted patterns in microimprint lithography (MIL). This article investigates the velocity field of the resist in microimprint lithography through numerical simulations and visualization experiments. To achieve the microscale velocity field of resist, a numerical model based on the computational fluid dynamics was built to predict the resist filling behavior, and the surface tension and contact angle were considered in this model. Meanwhile, a 3-D defocusing digital particle image velocimetry (DDPIV) was established. The spatial coordinates of the fluorescent tracer particles were derived from their DDPIV images. Time-resolved 3-D particle field inside the resist was obtained with the spatial coordinates. Particle tracking velocimetry was utilized to derive the velocity field from the particles' spatial position in the imprinting process. The investigation of the velocity field, including the horizontal and vertical velocity history, was carried out to directly describe the filling mode of the resist and hence determining the resist filling mechanism. The results of the visualization experiments and the numerical simulations were compared to obtain an in-depth understanding of the resist flow in MIL.

In microimprint lithography, the resist deformation directly influences the quality of the final imprinted patterns. The resist velocity field was investigated through numerical simulations and visualization experiments. A numerical model based on the computational fluid dynamics was built to predict the resist filling behavior. Meanwhile, a 3D defocusing digital particle image velocimetry (DDPIV) system was developed to achieve the microscale velocity field of resist. The spatial coordinates of the fluorescent tracer particles were derived from their defocused images, and then the three-dimensional particle field and velocity field inside the resist were obtained according to the particles' spatial coordinates and time interval recording the particle images. The investigation of the velocity field, including the horizontal and vertical velocity history, was performed to help describe the filling mode and flow behavior of the resist. The experimental results agreed well with the simulation prediction, which justified the use of the micro DDPIV system to investigate the resist filling behavior and verified the numerical model. The combined effect of the mold's local asymmetric geometries and resist's initial thickness on its own deformation was further analyzed by numerical simulation.

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A coarse-grained molecular dynamics model was established to investigate the deformation characteristics of the polymer in nanoimprint lithography (NIL). The proposed simulation model consists of a Si mold with a line pattern, an amorphous PMMA thin film, and a Si substrate with the periodic boundary condition in the horizontal direction. The effect of the degree of polymerization and the imprinting temperature on the polymer deformation behavior were investigated from the aspects of the density change of the polymer and the pressing force required to fill the mold cavity. Simulation results show that the closer the polymer molecules are getting to the mold surface, the more obvious the effect of extension due to the interfacial friction and adhesion between the polymer molecules and the mold surface is. The pressing force increases with increasing degree of polymerization and/or decreasing imprinting temperature.