A dual inlaid copper interconnect structure uses a plasma enhanced nitride (PEN) bottom capping layer and a silicon rich silicon oxynitride intermediate etch stop layer. The interfaces (16a, 16b, 20a, and 20b) between these layers (16 and 20) and their adjacent dielectric layers (18 and 22) are positioned in the stack (13) independent of the desired aspect ratio of trench openings of the copper interconnect in order to improve optical properties of the dielectric stack (13). Etch processing is then used to position the layers (16) and (20) at locations within the inlaid structure depth that result in one or more of reduced DC leakage current, improved optical performance, higher frequency of operation, reduced cross talk, increased flexibility of design, or like improvements.