The present invention describes a damascene process using a copper fill process to fill a trench (12). The copper fill (20) is started with a deposited seed layer which includes (5) copper and titanium. Some titanium migrates to the surface during the copper fill process. The structure is annealed in a nitrogen atmosphere which creates a self-aligned TiN barrier (24) at the surface of the copper fill (20). Air gaps (26) may be created in the same annealing process. The process may be used to form a multilayer structure.