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Properties of TaAl films reactivity sputtered in an argon-nitrogen atmosphere

Thin Solid Films
Publication Date
DOI: 10.1016/0040-6090(75)90115-7
  • Engineering


Abstract The effect of nitrogen doping on the electrical and structural properties of Ta-Al films has been investigated. The Ta-Al-N films were prepared by sputtering from composite Ta-Al cathodes in an argon-nitrogen atmosphere. Two series of such films were prepared. Series 1 films consisted of 63 % Ta-37 % Al, and series 2 films consisted of 55 % Ta - 45 % Al when sputtered in argon only. The nitrogen partial pressure was varied from 5.0 x 10 -6 to 1.0 x 10 -3 torr. Electron microprobe analysis indicated that the Al:(Al + Ta) ratio varied with nitrogen partial pressure only in series 2 films. X-ray diffraction analysis suggested the existence of an f.c.c. phase in the series 1 films and of an h.c.p. phase in series 2 films. The phase changes in the film were reflected in the resistivity and absolute thermoelectric power. The resistivity increased sharply while the t.c.r. decreased slowly (becoming more and more negative) with increasing nitrogen content until the films transformed to the f.c.c. or h.c.p. phase. The t.c.r. then dropped precipitously. After these transformations the resistance was markedly non-linear in its variation with temperature, suggesting the dominance of a thermally activated conduction process. In order to evaluate Ta-Al-N films for possible use as a resistor material, a study of their anodizability was undertaken. A 1:1 solution of aqueous saturated oxalic acid-ethylene glycol was a satisfactory electrolyte. It was found that the scintillation voltage fell off with increasing nitrogen content in the Ta-Al-N films. During the anodization process gas evolution occurred at the oxide-electrolyte interface for all nitrogen doping levels. It became severe at high doping levels and seriously limited the ability to form protective anodic films. Power-aging studies of Ta-Al-N resistors indicated that their stability deteriorated with increasing nitrogen content. This, together with the anodization results, suggests that further development of the Ta-Al-N system using conventional anodic resistor processing is not merited. Alternative processing techniques do seem feasible.

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