Abstract: A low-permittivity interlayer insulating film of the present invention is formed by a plasma CVD method and includes at least carbon and silicon, wherein a ratio of the carbon to the silicon is 2.5 or more, and relative permittivity is 3.8 or less. Also, a film formation method of a low-permittivity interlayer insulating film of the present invention includes forming a film of an insulating film material that includes at least carbon and silicon by a plasma CVD method, wherein a hydrocarbon is not used as the insulating film material, and a ratio of the carbon to the silicon is 2.5 or more, and relative permittivity is 3.8 or less in the formed low-permittivity interlayer insulating film.

Abstract: An insulating film material for plasma CVD of the present invention is constituted of a silicon compound including two hydrocarbon groups bonded to each other to form a ring structure together with a silicon atom, or at least one branched hydrocarbon group, wherein within the branched hydrocarbon group, ?-carbon that is a carbon atom bonded to the silicon atom constitutes a methylene group, and ?-carbon that is a carbon atom bonded to the methylene group or ?-carbon that is a carbon atom bonded to the ?-carbon is a branching point.