2, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
The metastable beta phase of tantalum is of interest due to the recent discovery of a giant Hall spin effect in this material, which enable much higher magnetic information storage densities. Both this phase and the stable BCC alpha phase can be made by sputter deposition. However, despite fifty years of study, the mechanism of phase selection remains unknown. We prepared a series of films under varying Ar sputter pressures while holding all other parameters constant and minimizing the effect of impurities. Measurements of film stress as a function of sputter gas pressure allow us to unambiguously index diffraction peaks to determine phase and texture. We find only the beta phase in the form of a dominant (002) beta Ta fiber component that becomes broader as the pressure increases. Based on calculations of the energy of incident Ta atoms and Ar neutrals, we show that resputtering could account for the changes in texture distribution. By comparing these results with a detailed review of the literature, we are able to propose a reproducible phase selection mechanism that is consistent with the vast majority of published results.