Preparation of Molybdenum Films and Tantalum Oxide Films by Laser CVD

Molybdenum and tantalum oxide films were prepared by laser CVD method from molybdenum hexacarbonyl(Mo(CO)₆)and tantalum pentamethoxide(Ta(OCH₃)₅), respectively,in expectation of possible application to the corrosion protective coating. Mo(CO)₆ decomposition by CO₂ laser in the presence of SF₆ as a sensitizer obeys roughly a first order kinetics with respect to Mo(CO)₆ concentration. The decomposition rate was seriously decreased by added gases. When the laser beam was parallel to the substrate,the Mo films deposited contained hexagonal molybdenum carbide, whereas the cubic carbide was included in the deposit by direct irradiation of the substrate. In KrF laser photo reaction, the rate of decomposition of Mo(CO)₆ could be also approximately represented by the first order reaction kinetics and coexistence of H₂, He, and N₂ was found to retard the reaction to some extent. A possible course of decomposition reaction was proposed,considering the deactivation of excited Mo(CO)₆^* by collisions with their surrounding molecules. In the case of CO addition,decomposition rate of Mo(CO)₆ was decreased to zero value possibly because of attachment of CO molecules to the coordinately unsaturated carbonyls. The deposits obtained by direct irradiation of the substrate of KrF laser was found to consist of an amorphous form or a fine crystalline of molybdenum and the cubic Mo₂C, however, the crystallinity of deposits was dependent on the fluence and the repetition rate of the laser. As for the preparation of tantalum oxide films from Ta(OCH₃)₅ by the irradiation of KrF laser,the deposits obtained at a higher fluence was ƒÀ-Ta₂0₅ and was quasi-amorphous oxide at a lower fluence. However, the oxygen content determined by XPS was less than that of stoichiometric Ta₂0₅. The stoichiometry of the deposit could be recovered by activated oxygen species produced by KrF laser irradiation and microwave discharge of oxygen.