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

Abstract

TaCx films were deposited by atomic layer deposition (ALD) using tris (neopentyl) tantalum dichloride, (Ta[CH2C (CH3)(3)](3)Cl-2) and H-2 plasma as the precursor and reactant, respectively, at substrate temperatures ranging from 200 degrees C to 400 degrees C. The ALD-TaCx films with the formation of nanocrystalline structures and a rock-salt phase were confirmed by X-ray and electron diffraction. The ALD temperature window was found to be 225 degrees C-300 degrees C with a growth rate of similar to 0.11 nm per cycle. The resistivity of the ALD-TaCx 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 mu Omega cm was obtained at 300 degrees C, which was within the ALD temperature window, by optimizing the H-2 plasma pulse time. The step coverage of the film deposited at 300 degrees C was approximately 100% over the trench structure (top opening width of 25 nm) with an aspect ratio of similar to 4.5. The performance of the ALD-TaCx films deposited under the optimized conditions was evaluated as a diffusion barrier for the Cu interconnects. The structure of Cu (100 nm)/ALD-TaCx (5 nm)/ Si was stable without the formation of copper silicide after annealing at 600 degrees C for 30 min.