US Patent 7187084 Damascene method employing composite etch stop layer

A damascene structure is provided comprising a substrate, a lower intermetal dielectric layer over the substrate, an exposed conductive structure within the lower intermetal dielectric layer, a composite etch stop layer over the lower intermetal dielectric layer and the exposed conductive structure; the composite etch stop layer comprising a first lower sub-layer and a second upper sub-layer, an upper intermetal dielectric layer over the composite etch stop layer, a trench interconnection opening forming within the upper intermetal dielectric layer and the composite etch stop layer, the trench interconnection opening exposing the conductive structure, a barrier metal layer at least lining the trench interconnection opening. and a conductor plug within the trench interconnection opening, contacting the conductive structure. The upper surface of the barrier metal layer is coplanar with the upper surface of the conductor plug.