A new microlens array fabrication method using UV proximity printing

Abstract

This paper presents a new microlens array fabrication method that controls the printing gap in the UV lithography process. This method can precisely control the microlens array geometric profile array in the fabrication process without thermal reflow. The proximity printing bends the UV light away from the aperture edges and produces a certain exposure in the photoresist outside the aperture edges due to the diffraction effects. This causes the photoresist bottom in two adjacent patterns to link together after development. The fabricated microlens diameter has the same size as the pitch distance between the two apertures. For example, a 120 µm aperture pitch distance will generate a 120 µm diameter microlens. The proximity gap between the mask and photoresist should be two times the aperture pitch distance or greater to generate an accurate microlens array. The experimental results showed that photoresist microlens arrays could be formed automatically without using the thermal reflow process when the printing gap ranged from 240 µm to 840 µm. A hemispherical microlens array with a 120 µm diameter and various geometric profiles can be fabricated using this method.