A study on the fabrication of microlens array based on the volume shrinkage of the photoresist solution during evaporation

This study investigates the fabrication process for microlens array using the solution of photoresist and solvent. A silicon substrate, where micro holes have been made in advance by deep reactive ion etch process, is coated with the solution of the photoresist and solvent. And the substrate is heated so that the solvent evaporates and the volume of the solution shrinks. Due to the surface tension of the liquid, the photoresist in the holes will have concave meniscus after the evaporation of the solvent, which can be used as a mold for the microlens arrays. The geometry of the microlens can be adjusted by changing the concentration of the solution, which is related to the volume shrinkage ratio during the evaporation. Experiments have shown that the microlenses with various heights can be fabricated out of the same substrate. This study is expected to provide a new fabrication method which enables great flexibility of designing microlens array for various optical applications.