A device includes an interposer including a substrate having a top surface and a bottom surface. A plurality of through-substrate vias (TSVs) penetrates through the substrate. The plurality of TSVs includes a first TSV having a first length and a first horizontal dimension, and a second TSV having a second length different from the first length, and a second horizontal dimension different from the first horizontal dimension. An interconnect structure is formed overlying the top surface of the substrate and electrically coupled to the plurality of TSVs.