"If a SiOC low dielectric constant film, which is to be used widely on next-generation devices, is adopted as the insulation films (10, 12) shown in FIG. 1(a), the carbon-containing side chains in the SiOC film, such as chains of methyl groups which are alkyl groups, are etched by high-frequency plasma with NH3 gas and consequently CH3, C2H5 and other alkyl groups in the SiOC film are lost." . . . . .