To enhance adhesion when a silicon oxide film is formed on an organic insulation film containing fluorine by plasma processing the surface of the organic insulation film using a gas containing at least hydrogen and then depositing a silicon oxide film on the surface of the organic insulation film.

Fluorine is removed from the surface of an organic insulation film 103 by plasma processing through action of hydrogen in the plasma and an SiC layer 104 is formed on the surface of the organic insulation film 103. Subsequently, a silicon oxide film 105 is formed on the organic insulation film 103 subjected to plasma processing and the surface of the silicon oxide film 105 is planarized by chemical mechanical polishing. Consequently, a composite insulation film of the organic insulation film 103 containing fluorine (including the surface layer 104 thereof) and the silicon oxide film 105 excellent in adhesion is formed and a semiconductor device employing the composite insulation film as an interlayer insulation film can be obtained.