WO, thin film was deposited on a Si substrate by low pressure chemical vapor deposition using the Hf(N(C2H5)(2))(4) (tetrakis-diethylamido-hafnium)/O-2 gas system. Hf(N(C2H5)(2))(4) is liquid at room temperature and has a moderate vapor pressure for the chemical vapour deposition process. The precursor was translated to the deposition chamber by a bubbling system, and the WO, films were deposited as functions of the deposition temperature and O-2 gas flow rate. Typical deposition temperature was 300-450 degreesC. Although the source gas has N in the molecule, the amount of residual N was small. The residual C amount was reduced by increasing the injected O-2 gas flow rate. On the other hand, the amount of the residual N was almost constant independent of O-2 gas flow rate, and was decreased by increasing the deposition temperature.