Annealing effect on the microstructure and morphology of the nanostructured Ta-Si-N thin films

Ta-Si-N thin films were potentially applied as diffusion barriers for Cu interconnections. However, the thermal stability of Ta-Si-N is related to the composition and annealing methods. In this paper, we have investigated the effect of high- vacuum furnace annealing and vacuum rapid thermal annealing (RTA) on the microstructure and morphology of different nanostructured Ta-Si-N thin films fabricated by reactive cosputtering at varied Ta and Si powers and nitrogen flow ratio (FN₂%= FN₂/( FN₂+FAr) x 100%). As Si is added to the Ta-N compound to form Ta-Si-N, the microstructure becomes nanocrystalline grains embedded in an amorphous matrix i.e. amorphous-like microstructure, which is also affected by the nitrogen flow ratio. Amorphous-like Ta-Si-N films obtained at small 3-6 FN₂% had smoother morphology and lower resistivity compared to the polycrystalline film at high 20 FN₂%. The thermal stability of Ta-Si-N films increases with the Si/Ta ratio and magnitude of vacuum. Higher vacuum furnace annealing at 5 times 10^-5 Torr may make both amorphous-like and polycrystalline Ta-Si-N films enduring higher temperature up to 900degC for a longer time of 1 h while the higher pressure RTA at 2 times 10^-2 Torr make Ta-Si-N films transform of phase and morphology at 750-900degC just in 1 min. The increase of Si/Ta ratio may also increases the stability of Ta-Si-N films.