Thermal stability of Ta–Si–N nanocomposite thin films at different nitrogen flow ratios

Ta–Si–N thin films were applied as diffusion barriers for Cu interconnections or hard coatings in mechanical application. The resistivity, hardness and thermal stability were the important issues in the interconnections and hard coatings, respectively. In this paper, we investigated the relationship between the microstructures, resistivity, nanohardness and thermal stability of the Ta–Si–N thin films at different nitrogen flow ratios of 0–30% (N2% = N2 / (Ar + N2) × 100%) by magnetron reactive co-sputtering. The Ta–Si–N films were annealed at 600, 750 and 900 °C at about 6 × 10−3 Pa for 1 h, respectively, to examine their thermal stability. The microstructures of Ta–Si–N films at low N2% of 2–10% still retained the amorphous-like phase with nanocrystalline grains in an amorphous matrix at annealing of 600–900 °C. The nanohardness of amorphous-like Ta–Si–N film at N2% of 3% was measured to be 15.2 GPa much higher than that of polycrystalline film of 10.1 GPa at N2% of 20%. The average nanohardness of both films is stable up to 900 °C and varied in the range of 0.43–0.83 GPa. The resistivity of the as-deposited Ta–Si–N films increase with increasing N2 flow rate. It is small around 220–540 μΩ cm for low N2% of 2–10% while it increases abruptly to about 7700–43,000 μΩ cm at high N2% of 20–30%. The best thermal stability of resistivity of Ta–Si–N film occurs at the N2% of 2% in the range of 220 to 250 μΩ cm from RT to 900 °C.