. . . "If a SiOC low dielectric constant film, which is to be used widely on next-generation devices, is adopted as the insulation films 205, 203 shown in FIG. 7( 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." . .