Semiconductor device having a multilayer interconnection structure

1. 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 or under 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,

said second interconnection layer comprising a second conductor pattern embedded in a second interlayer insulation film and constituting a part of said interconnection pattern,

said second conductor pattern having an extension part extending in a layer identical to said second conductor pattern,

said second conductor pattern being electrically connected to said first conductor pattern at a first part of said extension part by a via-plug,

said extension part having a second part extending beyond said via-plug,

said extension part having a first width in said first part and a second width narrower than said first width in said second part,

each of said second conductor pattern, said extension part and said via-plug forming a damascene structure.

2. The semiconductor device as claimed in claim 1 , wherein said first interlayer insulation film is embedded with a third conductor pattern different from said first conductor pattern, said extension part contacting with said third conductor pattern via a second via-plug at said second part away from or closer to said main part of said second conductor pattern with regard to said first part, said extension part having a first width at said first part and a second width narrower than said first width in said second part.

3. The semiconductor device as claimed in claim 1 , wherein said second interconnection layer is provided over said first interconnection layer, and wherein said main part of said second conductor pattern, said extension part, said first via-plug and said second via-plug form a dual damascene structure together with said second interlayer insulation film.

4. 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.