A method is provided for fabricating a semiconductor structure. The method includes providing a substrate; and forming a to-be-etched layer made of porous low dielectric constant material on one surface of the semiconductor substrate. The method also includes forming a first hard mask layer made of nitrogen-doped silicon oxycarbide (SiOC(N)) on the to-be-etched layer; and etching the first hard mask layer to have patterns corresponding to positions of subsequently formed openings. Further, the method includes forming the plurality of openings without substantial undercut between the to-be-etched layer and the first hard mask layer in the to-be-etched layer using the first hard mask layer as an etching mask; and forming a conductive structure in each of the openings.