Thin films of Au deposited on Si[(100), n type] wafers using a solid Au source and CF4+O-2 microwave plasma were studied. Solid Au heated at 200 degrees C in a vacuum crystal reactor was vaporized in a CF4+O-2 microwave (2.45 GHz power 200 W) plasma flow, and the Au film was deposited on a Si wafer heated to 270 degrees C in a low-pressure (10 mTorr) O-2 atmosphere. The density of Au in this film was about 91.7% as analyzed by x-ray photoelectron spectroscopy, and the film resistivity was 2.8 mu Omega cm, which is almost the same as that of the initial bulk Au (2.4 mu Omega cm). The deposition mechanism was deduced. The heated solid Au reacts with O-2 and (CF2)(n) from the CF4+O-2 microwave plasma, and then the Au is converted into AuO(CF2)(n). This Au compound carries Au atoms to the vacuum chamber. In the O-2 atmosphere, vaporized AuO(CF2)(n) is oxidized and changed into oxides such as AuO and COFx. AuO is deposited on the Si wafer heated to 270 degrees C, and then reduced into Au and O-2 by heating. This process results in a high purity deposited gold film.