Fabrication of AZ4562 refractive microlenses array for light enhancement on optical microsystems

Abstract — This paper presents the fabrication of an array of high aspect ratio photoresist based refractive microlenses (ML) using photolithography and thermal reflow. First, and in order to evaluate and predict the MLs optical properties and physical dimensions, finite element analysis was done. These simulations helped to design the super high resolu-tion chrome on soda lime glass photomask as well as the parameters for the lithographic processes. Then, an array of high aspect ratio structures (length 4.9 mm, width 30 µm and 5 µm spacing between adja-cent structures) with 5 µm thickness were fabricated. The thermal reflow technique (using a hotplate) was applied and an array of MLs measuring 5 and 32 µm at the vertex and radius, respectively, was achieved. When the photoresist (PR) is heated up above its glass transition temperature, it melts and the surface tension effect causes the fabricated microstructure to obtain the spherical lens profile. The hotplate ther-mal reflow is simple and easy to control, thus permit-ting the fabrication of smooth and homogeneous surfaces essential for good quality refractive mi-crolenses