Copper diffusion characteristics in single-crystal and polycrystalline TaN

We have investigated the diffusivity of copper in single-crystal (NaCl-structured) and polycrystalline TaN thin films grown by pulsed-laser deposition. Polycrystalline TaN films were grown directly on Si(100), while single-crystal films were grown with TiN buffer layers. Both poly- and single-crystal films with Cu overlayers were annealed at 500, 600, 650, and 700 °C in vacuum to study the copper diffusion characteristics. The diffusion of copper into TaN was studied using scanning transmission electron microscopy (STEM) Z contrast, where the contrast is proportional to Z2 (atomic number), and TEM. The diffusion distances (2Dτ) are found to be about 5 nm at 650 °C for 30 min annealing. The diffusivity of Cu into single-crystal TaN follows the relation D=(160±9.5)exp[−(3.27±0.1)eV/kB T] cm2 s−1 in the temperature range of 600–700 °C. We observe that Cu diffusion in polycrystalline TaN thin films is nonuniform with enhanced diffusivities along the grain boundary.