New interlayer insulating thin films with low dielectric constant were proposed for multilevel interconnection of ultralarge scale integration circuits. Hexamethyldisiloxane (HMDSO) monomer was used as an organic source and fluorinated Si based organic thin films were prepared by plasma enhanced chemical vapor deposition employing radio frequency inductively coupled plasma (ICP) with CF4. Moreover, Si based organic thin films containing benzene rings (phenyl groups) were deposited from a HMDSO/toluene (C6H5CH3) source mixture employing an O-2 ICP. From Fourier transform infrared spectroscopy, films had methyl-siloxane structure containing Si-O-Si and Si-CH3 bonds mainly. The dielectric constants of the films deposited from HMDSO/CF4 and HMDSO/toluene/O-2 at a substrate temperature of 200 degrees C were 2.9 and 2.8, respectively.