An integrated circuit structure includes a semiconductor substrate having a front side and a backside, and a conductive via penetrating the semiconductor substrate. The conductive via includes a back end extending to the backside of the semiconductor substrate. A redistribution line (RDL) is on the backside of the semiconductor substrate and electrically connected to the back end of the conductive via. A passivation layer is over the RDL, with an opening in the passivation layer, wherein a portion of the RDL is exposed through the opening. A copper pillar has a portion in the opening and electrically connected to the RDL.