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

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Abstract
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.