A method is disclosed for manufacturing a semiconductor device with a copper interconnect structure. The method includes providing a substrate, forming a first interconnect dielectric layer on the substrate, and forming a second interconnect dielectric layer on a surface of the first interconnect dielectric layer. The method also includes forming a plurality of conduits extending through the first interconnect dielectric layer and the second interconnect dielectric layer, and depositing copper in the plurality of conduits to form a copper interconnect layer of the copper interconnect structure. Further, the first interconnect dielectric layer, between neighboring conduits, contains cavities such that dielectric constant of the first interconnect dielectric layer is reduced. The second interconnect dielectric layer seals the top of the cavities, the substrate is the bottom of the cavities, and a width of the top of the cavities is less than a width of the bottom of the cavities.