Synthesis and Characterization of Mo Films Deposited by RF Sputtering at Various Oxygen Ratios

We report here the results of deposition and physicochemical characterization of molybdenum thin films deposited by RF magnetron sputtering. The physical and the chemical properties of these films were examined with X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. The obtained film at 0% oxygen ratio showed a crystalline cubic Mo(110) phase. After the oxygen ratio had been increased to more than 5% in the sputtering gas, the molybdenum films were formed as an amorphous phase. The thickness of the Mo thin film was drastically decreased from 1000 to ca. 70 nm after introducing oxygen in the sputtering gas, which was confirmed by spectroscopic ellipsometer (SE) and scanning electron microscopy (SEM). The calculated band gap of the film deduced from the SE data increased from 3.17 to 3.63 eV by adding oxygen to the sputtering gas. The roughness of the Mo film was examined with atomic force microscopy (AFM), and it was dramatically decreased by introducing oxygen during sputtering. XPS results revealed that the ratio of metallic Mo species in the film decreased, as the ratio of oxygen increased in the sputtering gas but the contents of the Mo(VI) species increased. In addition, Mo species with low oxidation states (IV and V) were fully oxidized to Mo(VI) at low oxygen content in the sputtering gas.