Novel approach to sputtered tantalum film resistors with controlled pre-defined resistance

A controlled magnetron sputtering method to obtain precision thin-film tantalum resistors with preset resistance values, is presented. These tantalum film resistors consist of layers of pure tantalum atoms and tantalum oxides. The proposed sputtering method is based on a previous mathematical modeling developed by the authors. With this modeling, one can predict the final product performance as a function of its technological deposition parameters. Feasibility tests to obtain tantalum and tantalum oxide film resistors with a controlled range of resistances, were done on a dedicated sputtering set-up. As a reactive agent in the experimental tests, only residual gases were used. Using the proposed model, precision film resistors with repeatable properties, were achieved in direct relations to the sputtering process parameters. It was found that only two major independent parameters are influencing the resistivity of the tantalum films: (a) the argon pressure in the vacuum chamber; and (b) the sputtering high voltage given to the target. A threshold level of tantalum phase transition from metal to dielectric, was found. Around this threshold level all types of pre-defined resistance may be achieved. The resistance stability of the obtained films, following an annealing Vacuum Photothermal Processing (VPP) was studied as well. It was shown that the electrical properties of the obtained resistors following a VPP treatment were improved with a better resistance stability.