Fabrication techniques of high aspect ratio vertical lightpipes using a dielectric photomask

Abstract

We report the development of new fabrication techniques for creating high aspect ratio optical lightpipes in SiO₂ layers of 10μm thickness and above. A dielectric photo mask was used for deep reactive ion etching. Our experiments show that CF₄-based reaction gases were best for deep etching with high selectivity and etch rate. Trenches with diameters or width of 1.5μm were demonstrated, with an aspect ratio of 7.2:1 and a sidewall angle of 87.4 degrees. We also present the lift-off process of the etch masks and the via-filling procedures for the lightpipes. These structures are useful for image sensors, vertical interconnect and waveguiding applications.