An object of the present invention is to provide a semiconductor device which comprises a barrier film having a high etching selection ratio of the interlayer insulating film thereto, a good preventive function against the Cu diffusion, a low dielectric constant and excellent adhesiveness to the Cu interconnection and a manufacturing method thereof.The barrier film (for instance, a second barrier film 6) disposed between the interconnection or the via plug and its overlying interlayer insulating film is made to have a layered structure made of a plurality of films containing silicon and carbon (preferably, silicon, carbon and nitrogen), with different carbon contents, and, in particular, a low-carbon-concentration film 6a with a small carbon content is set to be a lower layer therein and a high-carbon-concentration film 6b with a large carbon content is set to be an upper layer therein, whereby the effectual prevention against the Cu diffusion, a high etching selection ratio and good adhesiveness to the Cu interconnection can be certainly provided by the presence of the low-carbon-concentration film 6a, while the overall dielectric constant can be well reduced by the presence of the high-carbon-concentration film 6b.