A method includes forming silicon waveguide sections in a first oxide layer over a substrate, the first oxide layer disposed on the substrate, forming a routing structure over the first oxide layer, the routing structure including one or more insulating layers and one or more conductive features in the one or more insulating layers, recessing regions of the routing structure, forming nitride waveguide sections in the recessed regions of the routing structure, wherein the nitride waveguide sections extend over the silicon waveguide sections, forming a second oxide layer over the nitride waveguide sections, and attaching semiconductor dies to the routing structure, the dies electrically connected to the conductive features.