Hexagonal microlens array fabricated by proximity printing via UV lithography

This paper presents a new method to fabricate hexagonal microlens array in photoresist by controlling the printing gap in the UV lithography process. This method can precisely control the geometric profile of hexagonal microlens array in the fabrication process without thermal reflow. The proximity printing bends the UV light away from the aperture edges and produces certain exposure in the photoresist outside the aperture edges due to diffraction effects. It causes the photoresist bottom on two adjacent patterns to link each other after development. The fabricated hexagonal microlens diameter has the same size of the pitch distance between two apertures. For example, the aperture pitch distance 120 μm will generate microlens with diameter 120 μm. As found the proximity gap between the mask and photoresist should be twice or more than the aperture pitch distance, the microlens array in photoresist can be generated properly. The experimental results showed that microlens arrays in photoresist were automatically formed without using the thermal reflow process at the printing gap ranged from 240 im to 840 im. Hemispherical microlens array with diameter 120 μm and various geometric profiles can be fabricated in this method.