On the electrical properties of sputter deposited thin films: The role of energy and impurity flux

The energy available for an adatom diffusing on the substrate surface is an important parameter with regard to the morphological and structural properties of a thin film. A change of the available energy during film growth can be achieved by a modification of the process parameters. However, quite often the implied variation causes also an alteration of the impurity-to-metal impingement flux ratio on the substrate. In this work, the influence of the energy per arriving atom and the impurity-to-metal impingement flux ratio with respect to the resistive properties of chromel thin films deposited by direct-current magnetron sputtering is discussed. It is shown that an evaluation of the impurity-to-metal ratio is essential in order to properly disentangle energy effects from impurity effects. A correlation between the film resistivity and the variation in deposition conditions was found, and initially assigned to the variation in the energy per arriving atom. However, when impurity effects were excluded, the correlation between the available energy per atom and the resistivity could no longer be confirmed. At high levels of contamination, the effect of the energy variation under influence of target-to-substrate distance is fully absorbed by the effect of an increased impurity-to-metal impingement flux ratio. The increased impurity incorporation during growth of the film acts as a grain refiner and increases the film resistivity mainly due to a dominant contribution of grain-boundary scattering.