Composite interposer and method for producing a composite interposer

A composite interposer for providing power and signal connections between an integrated circuit chip or chips and a substrate. The interposer includes a signal core formed from a conductive power/ground plane positioned between two dielectric layers. A method for fabricating a composite interposer comprising disposing a silicon layer on a substrate, and selectively etching the silicon layer down to the substrate to develop silicon openings with a silicon profile, and to expose part of the substrate. Vias are formed through the exposed part of the substrate. The method additionally includes filling the vias and the silicon openings with a filler material (e.g., a high-aspect-ratio-capable photodefinable epoxy polymer) to form filled silicon openings and filled vias, forming first openings through the filled silicon openings and through the filled vias, forming second opening through filler material to expose semiconductor devices on the silicon layer, and interconnecting electrically, through the first openings and through the second openings, the exposed semiconductor devices with pads disposed against a bottom of the substrate.