Master of Science in Mechanical Engineering (MSME)
The objective of present study was to analyze the mechanical behavior of polymer resist during the demolding process, such as stress distribution and evolution; distortion and tilt of microstructures in thermal imprint lithography, a new emerging technique in mass production of micro/nanoscale patterns. One of the most challenging technical issues for thermal imprint lithography is the structural damages during demolding process. Thermal stress, adhesion force and friction force all play important roles in determination of the success of demolding and it is crucial to understand the underlying physics in order to optimize the structure and process design. In present study, we first studied the stress and deformation behavior of polymer during demolding by commercial finite element method (FEM) software ANSYS 10.0. Based on plane stress assumption, a 2-D model was created to represent one segment of the periodic structure. A 10 element Maxwell model was employed to describe the viscoelasticity of polymer resist. The normal demolding process was simulated and local stress was found to be concentrated at two locations: the corner of transition zone between patterns and residual layer and the contact region between patterns and releasing stamp. Parametric study was conducted and the influence of demolding angle, demolding rate, demolding temperature, friction coefficient and stamp geometry were all identified. To verify the simulation results, we measured the force required to separate stamp from substrate (demolding force) at three different temperatures (25ÂºC, 70ÂºC and 100ÂºC) and the lowest value was shown at 70ÂºC, which implied the lowest mechanical resistance. Scanning electronic microscopy (SEM) images also confirmed that the imprinted patterns showed both better overall quality and sharper local profiles at 70ÂºC, which showed good agreement with simulation results.In addition, we extended the FEM simulation to the demolding process of UV imprint lithography and injection molding. In UV imprint lithography, the residual stress was shown much lower than the thermal imprint lithography; in injection molding, we predicted that local shear stress can be reduced up to 25% by building a 10 Î¼m, 45Âºdraft angle structure.
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Song, Zhichao, "Study of demolding process in thermal imprint lithography via numerical simulation and experimental approaches" (2007). LSU Master's Theses. 2965.