US Patent 7473635 Method for manufacturing semiconductor device

A four-layer structured hard mask composed of a SiC film, a first SiO2 film, a SiC film, and a second SiO2 film is formed on a porous silica film as an interlayer insulating film. Then, the second SiO2 film is etched with a resist mask. Subsequently, the SiC film is etched with the second SiO2 film. Thereafter, the first SiO2 film is etched with the SiC film. Subsequently, the SiC film is etched with the SiC film. Then, by etching the porous silica film with the SiC film, a wiring trench is formed. At this time, a selection ratio between the SiC film and the porous silica film is large, so that deformation of the SiC film rarely occurs, which prevents leakage caused by the deformation.