Fusion Bonding with Ultra-Thin Dielectric Layers for Photonic Interposer Applications

Evanescent-wave coupling is a promising way to vertically couple light between device and interposer. A key challenge involved in this coupling is the thin gap requirement to keep the coupling loss low. This paper explores the various process challenges and requirements for fusion bonding between interfaces with ultra-thin dielectric layers. In particular, we show the importance of controlling for the wafer-level bonding oxide thickness and considering surface planarity across multiple length-scales to achieve successful fusion bonding down to oxide gaps of <300nm.