Heat conduction and polymer flow in spot/scanning laser-assisted imprinting

Abstract

Laser-assisted thermal imprinting (LATI) is a promising high-throughput direct replication method for micro- or nanostructured films. In LATI, only the surface of the mold is heated by laser irradiation and the surface of the polymer is heated by heat transfer; subsequently, the polymer surface lowers its viscosity and fills into the micro- or nanostructures of the mold. After the laser irradiation, the imprinted polymer surface is cooled by heat conduction to the inside of the film and mold immediately after the micro- or nanostructures are replicated. Therefore, not only a short cycle time but also low energy consumption in the imprinting process can be realized. However, the mechanism of heat conduction and polymer flow in the microstructured mold in LATI has not been clarified. In this study, we performed model experiments and simulations of heat conduction to determine the approximate time schedule of heat conduction in the polymer and the flow of the polymer. In the model experiments, we found that the replication speed of scanning irradiation was much higher than that of spot irradiation in spite of the same power density. It was found that the partial contact was decreased in scanning irradiation and the polymer flow easily occurred. This is because the surface profiles were different depending on the filling method. In spot irradiation, the surface exhibited a concave shape owing to the surface tension between the polymer and mold surface; meanwhile, in scanning irradiation, the surface exhibited a convex shape owing to pushing pressure.

Keywords

• laser assistance
• nanoimprinting
• heat conduction
• pressure distribution
• polymer flow