Coupled numerical analysis to investigate the heating mechanism of ultrasonic imprint lithography

Ultrasonic imprint lithography (UIL) is a micropattern replication technology on thermoplastic polymers using ultrasonic vibration energy. The UIL process involves three steps: (i) microscale vibration from an ultrasonic horn causes repetitive deformation of a polymer surface, (ii) the polymer surface is locally softened by repetitive deformation and friction, and (iii) micro/nanoscale patterns engraved on the horn or the mold are replicated on the softened substrate. To replicate micro/nano patterns with high accuracy, the effects of various processing conditions should be investigated, and so far, these have been studied experimentally. In this study, coupled numerical analysis was performed using finite element simulation to investigate the heating mechanism of the UIL process, by joining transient structural analysis and heat transfer analysis. The effect of imprinting conditions on the heating capability was investigated using the proposed coupled simulation. The differences between direct and indirect imprinting are also discussed in terms of heating mechanism, and compared with experiments.