Semiconductor device having a multilayer interconnection structure

A semiconductor device having a multilayer interconnection structure,

• said multilayer interconnection structure comprising at least a first interconnection layer and a second interconnection layer formed over said first interconnection layer;
• said first interconnection layer comprising a first conductor pattern embedded in a first interlayer insulation film and constituting a part of an interconnection pattern, and a second interconnection pattern different from the first interconnection pattern embedded in said first interlayer insulation film,
• said second interconnection layer comprising a third conductor pattern embedded in a second interlayer insulation film and constituting a part of said interconnection pattern,
• said third conductor pattern having an extension part in a part thereof so as to extend in a layer identical to said third conductor pattern,
• said third conductor pattern being electrically connected to said first conductor pattern at a first region of said extension part via a first via plug,
• said extension part making a contact with said second conductor pattern at a second region further away from, or closer to said third conductor pattern with regard to said first region via a second via-plug of a diameter smaller than said first via-plug,
• said extension part of said third conductor pattern, said first via-plug and said second via-plug forming, together with said second interlayer insulation film, a dual damascene structure, and
• said second via plug has an irregular cross-sectional shape distorted from true circle.