Properties of plasma-enhanced atomic layer deposited TiCx films as a diffusion barrier for Cu metallization

TiCx films were grown on thermally grown SiO2 substrate by atomic layer deposition (ALD) using tetrakis-neopentyl-titanium [Ti(CH2C(CH3)3)4, TiNp4, Np = neopentyl, CH2C(CH3)3] and direct plasma of H2 as a reactant at the substrate temperature ranging from 200 to 400 °C. A narrow ALD temperature window from 275 to 300 °C was shown and a growth rate of 0.054 nm/cycle at the ALD temperature window was obtained. The ALD-TiCx films formed nanocrystalline structure with rock-salt phase that was confirmed by X-ray diffractometry and transmission electronic microscopy (TEM) analysis. Its resistivity was dependent on the microstructure features characterized by grain size and crystallinity as well as its density, which could be controlled by varying the deposition temperature. Resistivity of ~ 600 μΩ cm was obtained at the deposition temperature 300 °C where is in the ALD temperature window, by optimizing deposition condition. In this study, a performance of very thin ALD-TiCx (6 nm) as a diffusion barrier for Cu interconnects was evaluated. The results showed that the structure of Cu (80 nm)/ALD-TiCx (6 nm)/Si was stable after annealing at 600 °C for 30 min. Cross-sectional view TEM analysis combined with energy-dispersive spectroscopy revealed that ALD-TiCx diffusion barrier failed by the diffusion of Cu through the thin barrier layer into Si at 650 °C without interfacial reactions between the layers.