In this work we studied the relationship between condition of deposition (especially, nitrogen partial pressure) and material properties (chemical and phase compositions, microstructure, mechanical stress, surface morphology, resistivity, diffusion barrier performance), of W-Ti-N thin films.
Thin binary W-Ti and ternary W-Ti-N films were deposited by reactive magnetron sputtering from a W-Ti (30 at.%) target in Ar or Ar/N₂ discharges. A d.c. power density of 1.7 W/cm² was applied to the target and the partial pressure of N₂ was varied from 0 to 0.35 Pa at a total gas pressure of 0.5 Pa.
The investigation of W-Ti-N films by XRD, RBS, AFM, four-point probe and stress measurements showed that the structure, composition, resistivity, stress and barrier properties are strongly dependent on the nitrogen concentration in these films.
We found that nitrogen-free film was composed of a β-W matrix seeded with fine α-Ti precipitates. For W₆₅Ti₁₇N₁₈ films, the structure is a dense mixture of ultrafine crystallites of tungsten, TiN, W₂N and/or Ti₂N and amorphous phase. At high nitrogen concentrations N > 30 at.%, the structure is a mixed phase of W₂N and TiN. The resistivity of pure W₈₈Ti₁₂ film was 100 μΩcm and rose slowly up to 365 μΩcm for the ternary W₄₅Ti₁₀N₄₅ film. When the N₂ partial pressure reaches 0.35 Pa, the film resistivity is 850 μΩcm, which may be attributed to the reduction in crystalline size. The 100 nm thick amorphous W₆₅Ti₁₇N₁₈ film shows excellent barrier property preventing the interaction between Au and GaAs under annealing at 750^o C.
Research was partially supported by grant from NATO (ref. NUKR.RIG.981275), and one author (A.V. Kuchuk) was supported by stipendium of NASU for young scientists.