Effect of Oxygen on the Electrical and Structural Properties of Triode-Sputtered Tantalum Films

The structural and electrical properties of oxygen-doped tantalum films, sputtered in a triode system, have been investigated. X-ray diffraction traces from films with a low oxygen content indicate the presence of bcc Ta with a strained lattice. The intensity of the (110) bcc Ta diffraction peak decreases with increasing oxygen content and is interpreted as a decrease in the amount of bcc Ta phase present. Over this same range the appearance and rise in intensity of the β-Ta (200) peak indicates the formation of β-Ta. As the oxygen content is further increased, the structural data indicate a reorientation of the tetragonal β-Ta (200) to the (202) planes with respect to the film surface, an effect which has been previously observed in diode-sputtered tantalum; further increase in oxygen content produces a stretching of the β-Ta lattice by as much as 10% of the value reported by Read and Altman. The room-temperature resistivity increases with increasing oxygen content until a ``plateau'' region is reached at ∼ 210 μΩ cm corresponding to 12 at. % oxygen, and together with the x-ray data the electrical measurements indicate a change of phase from bcc to β-Ta. Above approximately 40 at. % oxygen the resistivity increases rapidly suggesting the formation of tantalum oxide.