A method for fabricating an inter-metal dielectric layer. Several conducting wires are formed on a substrate, and openings lie between the adjacent conducting wires. A first dielectric layer fills the openings, and the surface of the first dielectric layer is lower than that of the conducting wires. A spacer is formed on a sidewall of each of the conducting wires. The first dielectric layer is removed to expose the bottom of the spacer. A second dielectric layer is formed to cover the conducting wires.