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Phase map, composition and resistivity of reactively magnetron sputtered and annealed Ta– N films

Thin films of tantalum nitride (Ta–N) have been prepared by reactive magnetron deposition under various nitrogen partial pressures pN2=0-1 and subsequently annealed (Ta = 450–950 °C). The structure, density, composition and electrical resistivity of the prepared films were systematically investigated. A pN2-Ta phase map was constructed from the results of structural analysis. With increasing of pN2 from 0 to 0.2, a single-phase or two-phase mixture films of tetragonal Ta, Ta2N (Ta > 450 °C), eps-TaN (Ta > 850 °C), theta-TaN (Ta > 850 °C) and fcc delta-TaN are sequentially observed. For pN2 = 0.25–0.45, the as grown and annealed films exhibit delt-TaN structure. Amorphous films grown in the pN2 = 0.45–0.75 range crystallize as cubic Ta2N3 upon annealing at Ta > 650 °C or as delt-TaN at Ta > 850 °C. A cubic Ta2N3 is grown at highest pN2 (>0.85), which decomposes to delt-TaN at Ta > 850 °C. The N /Ta atomic ratio in the film linearly increases for pN2 = 0–0.5, ranging from 0 to 2.1, while the mass density monotonously decreases with pN2. Upon annealing, a part of N atoms outdiffuses from the films deposited at pN2 > 0.3. The electrical resistivity strongly depends on both pN2 and Ta. However, in the as grown and annealed delt-TaN films the resistivity was of the order of 100–1000 µOhmcm. In these films, a correlation between the resistivity and the average number of defects (Ta vacancies and N atom excess) is observed. Finally, the influence of thermally introduced oxygen on the films resistivity has been revealed.

tantalum nitride ; magnetron sputtering ; thermal annealing ; phase composition ; resistivity

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