Self-Aligned Via Formation Using Spacers

A method includes forming a first mandrel and a second mandrel over a dielectric layer, and forming a first spacer and a second spacer on the first mandrel and the second mandrel, respectively. The first spacer and the second spacer are next to each other with a space in between. The dielectric layer is etched to form an opening in the dielectric layer, with the opening being overlapped by the space, and with the first spacer and the second spacer being used as a part of an etching mask in the etching. A conductive material is filled into the opening. A planarization process is performed on the conductive material.