Deposition method and semiconductor device

The present invention relates to a deposition method in which an insulating film that coats wirings mainly made of copper film and has low dielectric constant. Its constitution in the deposition method, where deposition gas is transformed into plasma and reaction is caused to form the insulating film having low dielectric constant, is that the deposition gas has a first silicon containing compound having cyclic siloxane bond and at least one of methyl group and methoxy group, and a second silicon containing organic compound having straight-chain siloxane bond and at least one of methyl group and methoxy group, as primary constituent gas.