The relationship between the microstructure of WSi0.6N films and copper diffusion was considered. While WSi0.6N was amorphous below 850C, W microcrystals occurred in amorphous WSiN at 850C. Their average grain size increased from 3 to 8nm and their numerical densities increased from 200 to 7400/μm2 at 850 to 880C. From X-ray photo-electron spectroscopic measurements, it was thought that the W of Si-W bonds in WSiN films was transformed into metallic W. The amount of Cu that diffused through the WSiN layer into Si was calculated by integrating the depth profiles of Cu measured using secondary ion mass spectroscopy. The activation energy of the diffused Cu was constant at 2.8eV at 700 to 900C. Consequently, the barrier property was suggested to be due to the absence of continuous grain boundaries throughout the film. That is, W microcrystal formation did not change the Cu diffusion mechanism up to 900C, and Cu diffusion was controlled by migration  in an amorphous matrix.

Correlation of W-Si-N Film Microstructure with Barrier Performance against Cu Diffusion. Y.Shimooka, T.Iijima, S.Nakamura, K.Suguro: Japanese Journal of Applied Physics – 1, 1997, 36[3B], 1589-92