An integrated circuit structure includes a semiconductor substrate including a front side and a backside. A through-silicon via (TSV) penetrates the semiconductor substrate, and has a back end extending to the backside of the semiconductor substrate. A redistribution line (RDL) is over the backside of the semiconductor substrate and connected to the back end of the TSV. The integrated circuit structure further includes a passivation layer over the RDL; an opening in the passivation layer, wherein a portion of the RDL is exposed through the opening; and a nickel layer in the opening and contacting the RDL.