Polysiloxane thin films were proposed as low dielectric constant interlayer dielectrics for multilevel interconnection of ultralarge scale integration circuits. The films were prepared using oxygen-radical polymerization of siloxane oligomers. A variety of siloxane oligomers were thermally produced by the decomposition of polysiloxane bulk target using CO2 laser irradiation. Oxygen radicals generated by a remote microwave O-2 plasma were injected into the vacuum chamber during film deposition. The films deposited with the oxygen radical injection were transformed from polysiloxane to carbon-deficient silicon oxide with increase of substrate temperature as confirmed by x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analyses. At a CO2 laser power of 10 W, an O-2 pressure of 50 mTorr, a microwave power of 100 W, and a substrate temperature of 100 degrees C, the dielectric constant of the polysiloxane film was 2.0.