Method of forming composite barrier layers with controlled copper interface surface roughness

摘要

A composite alpha-Ta/graded tantalum nitride/TaN barrier layer is formed in Cu interconnects with a controlled surface roughness for improved adhesion, electromigration resistance and reliability. Embodiments include lining a damascene opening, such as a dual damascene opening in a low-k interlayer dielectric, with an initial layer of TaN, forming a graded tantalum nitride layer on the initial TaN layer and then forming an alpha-Ta layer on the graded TaN layer, the composite barrier layer having an average surface roughness (Ra) of about 25 Å to about 50 Å. Embodiments further include controlling the surface roughness of the composite barrier layer by varying the N₂ flow rate and/or ratio of the thickness of the combined alpha-Ta and graded tantalum nitride layers to the thickness of the initial TaN layer.