Optimization of control parameters in micro hot embossing

The key control parameters in hot embossing (such as the imprint pressure, the imprint temperature, the holding time and the demolding temperature) can significantly impact on the pattern quality. The finite element method was used to analyze the embossing, cooling and demolding step to acquire the optimized process parameters. The simulation results show that the polymer flow has a reference to the imprint pressure, the imprint temperature and the holding time. While the adhesion force between the polymer and the mold can significantly influence the replication accuracy. Because of polymer flow, non-uniform pressure distribution can be observed and this results in the pattern height difference. The hydraulic pressure system was designed to acquire uniform pressure. Thermal stress caused by the difference of the thermal expansion coefficients between the mold and the polymer can induce stress concentration at the corner. If the demolding direction is not vertical to horizon, another stress concentration will appear. Excessive stress results in defects and causes fracture at the base part of the pattern during the demolding step. To eliminate the defects, cooling to a relative high temperature was introduced to reduce the stress concentration and an auto-demolding device was used to insure no additional stress was imported at the demolding step. The following experiment showed the successful fabrication of fine patterns with the optimized parameters.