In some embodiments, a trench (not shown) may be formed in the dielectric layer 154, a barrier layer (not shown) may be formed to line a bottom and sidewalls of the trench, and a conductive layer (not shown) may be formed on the barrier layer and to fill the trench. The conductive layer can include materials similar to those used to form the metal layers Mn; therefore, descriptions of such details are omitted for brevity. It should be understood that to mitigate metal diffusion, which may adversely affect electrical isolation of the surrounding IMD layers, the barrier layer may be required. Therefore, when the conductive layer includes Cu, the barrier layer can include conductive materials that form a Cu diffusion barrier. In some embodiments, a planarization may be performed to remove a superfluous conductive layer and a superfluous barrier layer. Accordingly, a via, such as a top via TEVA, can be obtained. The top via TEVA is coupled to the second conductive layer 144, as shown in FIG. 11.