Collective die-to-wafer assembly process for optically interconnected System-on-wafer

A collective die-to-wafer (CoD2W) assembly process is demonstrated enabling low-loss die-to-wafer evanescent optical coupling, paving the way to future wafer-level optically interconnected multi-XPU compute systems. As a proof-of-concept demonstrator, PIC chiplets and an optical interconnect wafer were co-designed and fabricated, each having embedded SiN waveguides (WG) and evanescent couplers (EVC). Frontside and backside alignment structures were included to enable accurate alignment of the PIC dies to the interconnect wafer. Before assembly, the PIC dies were thinned to 100 μm and subsequently transferred from a temporary carrier to the target interconnect wafer. After the full process, we realized an assembly yield of up to 96% of mostly void-free dies with die-to-target wafer alignment of 2.4 μm (m+3s), resulting in die-to-wafer optical coupling losses below 0.5 dB at 1310 nm for 76% of the dies.