Stress, microstructure and temperature stability of reactive sputter deposited Ta(N) thin films

Interest in tantalum nitride thin films for use as diffusion barriers in Cu-based microelectronic interconnects merits the study of tantalum nitride thin film properties as a function of deposition conditions and elevated temperature exposure. In this investigation, the influence of nitrogen content and post deposition annealing on the stress, microstructure and resistivity of Ta(N) films was analyzed. Ta(N) thin films were deposited by reactive de magnetron sputtering of a Ta target in Ar/N-2 gas mixtures. With an increasing N-2 to Ar flow ratio, the as-deposited crystal structure of the films changed from beta -Ta to bcc Ta with N in solid solution to TaN0.1 to Ta2N and finally to TaN. The as-deposited Ta(N) stress, grain size and resistivity of the Alms were found to be strongly dependent on the phase(s) present. Films with less than 20 at. % nitrogen concentration displayed large compressive stress increases during 650 degreesC anneals in flowing N-2. Phase transformations to Ta2N occurred after 650 degreesC anneals in films with nitrogen concentrations from similar to 15 to 25 at. %. Microstructural characterization using transmission electron microscopy and x-ray diffraction, and chemical analysis by x-ray photoelectron spectroscopy and Auger electron spectroscopy of the Ta(N) films were used to identify the as-deposited and transformed phases.