Fabrication of a 100% fill-factor silicon microlens array

Abstract

A simple method has been developed for the fabrication of a silicon microlens array with a 100% fill factor and a smooth configuration. The microlens array is fabricated by using the processes of photoresist (SU8-2005) spin coating, thermal reflow, thermal treatment and reactive ion etching (RIE). First, a photoresist microlens array on a single-polished silicon substrate is fabricated by both thermal reflow and thermal treatment technologies. A typical microlens has a square bottom with size of 25 μm, and the distance between every two adjacent microlenses is 5 μm. Secondly, the photoresist microlens array is transferred to the silicon substrate by RIE to fabricate the silicon microlens array. Experimental results reveal that the silicon microlens array could be formed by adjusting the quantities of the reactive ion gases of SF6 and O2 to proper values. In this paper, the quantities of SF6 and O2 are 60 sccm and 50 sccm, respectively, the corresponding etch ratio of the photoresist and the silicon substrate is 1 to1.44. The bottom size and height of a typical silicon microlens are 30.1 μm and 3 μm, respectively. The focal lengths of the microlenses ranged from 15.4 to 16.6 μm.