Hexamethyldisiloxane (HMDSO) has been used as a precursor for the deposition of silicon dioxide films at low substrate temperature (25-400 degrees C) by plasma enhanced chemical vapour deposition processing. Effects of the partial pressure of oxygen in the discharge on the deposition rate and the composition of the films are investigated. The deposition rate is found to decrease with increasing oxygen concentration in the HMDSO/O-2 mixture. The chemical composition of the formed films was characterized by X-ray photoelectron spectroscopy and infrared spectroscopy. Over 40% of the oxygen in the gas phase the carbon content of films deposited from HMDSO/O-2 mixtures is less than 5%.