The present disclosure provides a method for forming a semiconductor device. The method includes forming first conductive layer structures in a first dielectric layer on a substrate; forming a patterned photoresist layer having portions that are each disposed over a respective one of the first conductive layer structures; forming an energy removable film (ERF) on the sidewalls of each of the portions; forming a second dielectric layer over the ERFs, the portions of the patterned photoresist layer, and the first dielectric layer; removing the portions to leave behind a plurality of openings; filling a conductive material in the openings, the conductive material defining second conductive layer structures; forming a ceiling layer over the second conductive layer structures, the ERFs, and the second dielectric layer; and applying energy to the ERFs to partially remove the ERFs on the sidewalls of the portions thereby forming air gaps.