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 $p{\text{N}}_2(0-1)$ and subsequently annealed (T _a  =  450–950 °C). The structure, density, composition and electrical resistivity of the prepared films were systematically investigated. A $p{\text{N}}_2-T_a$ phase map was constructed from the results of structural analysis. With increasing of $p{\text{N}}_2$ from 0 to 0.2, a single-phase or two-phase mixture films of tetragonal Ta, Ta₂N ($T_a⩾450$ °C), ϵ-TaN ($T_a⩾850$ °C), θ-TaN ($T_a⩾850$ °C) and fcc δ-TaN are sequentially observed. For $p{\text{N}}_2=0.25$–0.45, the as grown and annealed films exhibit δ-TaN structure. Amorphous films grown in the $p{\text{N}}_2=0.45$–0.75 range crystallize as cubic Ta₂N₃ upon annealing at $T_a⩾650$ °C or as δ-TaN at $T_a⩾850$ °C. A cubic Ta₂N₃ is grown at highest $p{\text{N}}_2$ ($⩾$0.85), which decomposes to δ-TaN at $T_a⩾850$ °C. The N     / Ta atomic ratio in the film linearly increases for $p{\text{N}}_2=0$–0.5, ranging from 0 to 2.1, while the mass density monotonically decreases with $p{\text{N}}_2$. Upon annealing, a part of N atoms out-diffuses from the films deposited at $p{\text{N}}_2⩾0.3$. The electrical resistivity strongly depends on both $p{\text{N}}_2$ and T _a. However, in the as grown and annealed δ-TaN films the resistivity was of the order of 100–1000 $\mu \Omega$cm. 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. (paper)