In a method for manufacturing a semiconductor device, insulation resistance of the porous film is stabilized, and leakage current between adjacent interconnects provides an improved reliability in signal propagation therethrough. The method includes: sequentially forming over a semiconductor substrate a porous film and a patterned resist film; forming a concave exposed surface of the substrate; forming a non-porous film covering the interior wall of the concave portion and the porous film; selectively removing the non-porous film from the bottom of the concave portion and the non-porous film by anisotropic etch; forming a barrier metal film covering the porous film and the interior wall; and forming a metallic film on the barrier metal film to fill the concave portion. The anisotropic etch process uses an etching gas with mixing ratio MR, 45≦MR≦100, where MR=((gaseous “nitrogen” containing compound)+(inert gas))/(gaseous “fluorine” containing compound).