A method of forming a semiconductor device, comprising: providing a Si-containing layer; forming a barrier layer over said Si-containing layer, said barrier layer comprising a compound including a metallic element; forming a metallic nucleation_seed layer over said barrier layer, said nucleation_seed layer including said metallic element; and forming a metallic interconnect layer over said nucleation_seed layer, wherein said barrier layer and said nucleation_seed layer are formed without exposing said semiconductor device to the ambient atmosphere.