TaC_x Thin Films Prepared by Atomic Layer Deposition as Diffusion Barriers for Cu Metallization

摘要

TaC_x films were deposited by atomic layer deposition (ALD) using tris (neopentyl) tantalum dichloride, (Ta[CH_2C (CH_3)_3]_3C1_2) and H_2 plasma as the precursor and reactant, respectively, at substrate temperatures ranging from 200℃ to 400℃. The ALD-TaC_x films with the formation of nanocrys-talline structures and a rock-salt phase were confirmed by X-ray and electron diffraction. The ALD temperature window was found to be 225℃-300℃ with a growth rate of ～0.11 nm per cycle. The resistivity of the ALD-TaC_x films was dependent on the microstructural features, such as the grain size and crystallinity, as well as their composition (C/Ta ratio), and the presence of impurities in the films, which could be controlled by varying the deposition parameters, such as the deposition temperature and reactant pulse conditions. With increasing deposition temperature and reactant pulse time, Ta-rich films with a low Cl impurity concentration and larger grain size were obtained. The film with a resistivity less than 400 μΩ cm was obtained at 300℃, which was within the ALD temperature window, by optimizing the H_2 plasma pulse time. The step coverage of the film deposited at 300℃ was approximately 100% over the trench structure (top opening width of 25 nm) with an aspect ratio of ～4.5. The performance of the ALD-TaC_x films deposited under the optimized conditions was evaluated as a diffusion barrier for the Cu interconnects. The structure of Cu (100 nm)/ALD-TaC_x (5 nm)/ Si was stable without the formation of copper silicide after annealing at 600℃ for 30 min.