The present invention reduces the effective dielectric constant of the interlayer insulating film while inhibiting the decrease of the reliability of the semiconductor device, which otherwise is caused by a moisture absorption. A copper interconnect comprising a Cu film 209 is formed in multilayer films comprising a L-Ox.TM. film 203 and a SiO.sub.2 film 204. Since the L-Ox.TM. film 203 comprises ladder-shaped siloxane hydride structure, the film thickness and the film characteristics are stable, and thus changes in the film quality is scarcely occurred during the manufacturing process.