Issues in Nanoimprint Processes: the Imprint Pressure

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Abstract
A technical thermoplastic polystyrene with broad molecular weight distribution was characterised with respect to its thermo mechanical behaviour. In comparison to two other polystyrenes with narrow molecular weight distribution its temperature behaviour was investigated and could be generalised making use of well-known basic common principles of polymer rheology. The role of the temperature and the molecular weight choice with respect to an imprint process was contrasted to the role of the imprint pressure, which is a free parameter without impact on polymer characteristics. Pressure determines the initial shear rate in the process. Correspondingly simulations of the course of an imprint were performed, where shear thinning was assumed and the viscosity changed throughout the process according to the measured polymer behaviour. Two different filling situations were investigated, bottom up filling of the stamp cavities and lateral filling of the stamp cavities. In both cases the simulations show a quick decrease of the polymer height within the first seconds of the imprint. Shear rate effects suggest being effective to end up with very short processing times during thermal imprint under appropriate pressure with medium molecular weight thermoplastics. This is an interesting approach towards high throughput nanoimprint processes.

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