A semiconductor device having a nonconductive cap layer comprising a first metal element. The nonconductive cap layer comprises a first metal nitride, a first metal oxide, or a first metal oxynitride over conductive lines and an insulating material between the conductive lines. An interface region may be formed over the top surface of the conductive lines, the interface region including the metal element of the cap layer. The cap layer prevents the conductive material in the conductive lines from migrating or diffusing into adjacent subsequently formed insulating material layers. The cap layer may also function as an etch stop layer.