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 degreesC 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 Z(2) (atomic number), and TEM. The diffusion distances (2rootDtau) are found to be about 5 nm at 650 degreesC 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/k(B) T] cm(2) s(-1) in the temperature range of 600-700 degreesC. We observe that Cu diffusion in polycrystalline TaN thin films is nonuniform with enhanced diffusivities along the grain boundary. (C) 2002 American Institute of Physics.