a method for fabricating a self - aligned diffusion - barrier cap on a cu - containing conductive element in an integrated - circuit device comprises :— providing a substrate having a cu - containing conductive element embedded laterally into a dielectric layer and having an exposed surface ;— depositing a metal layer on the exposed surface of conductive element ;— inducing diffusion of metal from the metal layer into a top section of the conductive element ;— removing the remaining metal layer ;— letting diffused metal in the top section of the conductive element and particles of a second constituent react with each other so as to build a compound covering the conductive element . the metal of the metal layer and the second constituent are chosen so that the compound forms a diffusion barrier against cu diffusion . a reduction the dielectric constant of the dielectric material in an interconnect stack of an integrated - circuit device is achieved .