Combining Mn oxide/Ta encapsulation and a self-aligned CuSiN barrier enhanced reliability of both wiring and dielectrics, reducing wiring resistance by 10%, compared with that of a control sample. The CuSiN barrier effectively concentrated Mn, resulting in a composite barrier consisting of Mn oxide, Mn silicate, and MnSiN forming on top of the Cu wiring. Mn concentration is attributed to the large difference in the standard heat of formation between Mn silicide and Cu silicide. The composite barrier that formed on top of the Cu wiring played a critical role in enhancing the reliabilities by suppressing surface Cu self-diffusion, vacancy diffusion, and Cu ion drift under electrical and thermal stresses. Suppressing the surface self-diffusion, for example, increased electromigration lifetime by a factor of 51. This combination technique has an advantage over a previous self-formation of a Mn oxide barrier in terms of reliabilities since the previous technique cannot form such a composite barrier on top of the Cu wiring.