Geometry modulation of microlens array using spin coating and evaporation processes of photoresist mixture

Abstract

Recently, cost effectiveness and environmental consideration have become essential issues in the fabrication techniques. In this study, microlens array has been fabricated with simple processes. On a silicon substrate, which has circular micro holes, photoresist mixture has been coated using the spin coating process. The process has been conducted for various spin speeds to change the centrifugal force, which influences the removed volume of the mixture in the micro holes. After that, concave menisci have been obtained in the holes because of the surface tension of the remaining mixture. Then, the heating process has been conducted to evaporate the solvent in the mixture and to solidify the photoresist so that deeper menisci could be obtained, which can be used as a mold for microlens array. The mixtures, which consist of photoresist and solvent, have been prepared in advance with different concentration. The fabrication method in this study is based on the volume shrinkage of the photoresist mixture, which is caused from the spin coating and evaporation processes. Therefore, it has been investigated that the geometry of the microlens can be modulated by the concentration of the mixture, as well as the process conditions of the spin coating and heating.