A semiconductor device fabrication method includes the steps of forming a conductive plug in an insulating layer on a semiconductor substrate so as to be connected to an element on the substrate; forming a titanium aluminum nitride (TiAlN) oxygen barrier film over the conductive plug; forming a titanium (Ti) film over the oxygen barrier film; applying a thermal process to the titanium film in nitrogen atmosphere to allow the titanium film to turn into a titanium nitride (TiN) film; and forming a lower electrode film of a capacitor over the titanium nitride film.