A device includes an interposer, which includes a substrate having a top surface. An interconnect structure is formed over the top surface of the substrate, wherein the interconnect structure includes at least one dielectric layer, and metal features in the at least one dielectric layer. A plurality of through-substrate vias (TSVs) is in the substrate and electrically coupled to the interconnect structure. A first die is over and bonded onto the interposer. A second die is bonded onto the interposer, wherein the second die is under the interconnect structure.