Study on bubble defects in roll-to-roll UV imprinting process for micropyramid arrays II: Numerical study

Roll-to-roll ( R2R) ultraviolet ( UV) imprinting process is a very competitive technique for the large-area fabrication of micropyramid structures on polymer substrates. However, bubble defect is a serious problem that significantly deteriorates the performance of the optical films. The elimination of bubble defects in microstructures is pivotal to the successful application of optical films in various fields. Based on previous experimental results, a numerical model for the R2R UV imprinting of micropyramid structure was established to analyze the generation mechanism of the bubble defect in the micropyramid structure. The flow behavior of the resist in the microcavities was observed and discussed. The relationship between processing parameters and bubble defects in the R2R UV imprinting process was investigated, and the possible reasons for the difference in the filling of the micropyramid structures and the generation of bubble defect were presented and discussed. Also, the material inlet direction in accordance with the pyramid structure placement was considered and its influence on the filling process of the technique was analyzed. It was found that inlet direction has a significant impact on the filling condition of the pyramid structure. It could cause the difference between full and partial filling, and the difference of the shape and the location of bubble defects if they exist. These findings provide insights into the flow behavior of the resist material on microscale and shed light on what is causing the differences in the final filling condition of the micropyramid structures, which can be of good theoretical guidance to the industrial application of the technique. (C) 2016 American Vacuum Society.