Correlation of W-Si-N Film Microstructure with Barrier Performance against Cu Diffusion.

The relationship between the microstructure of WSi0.6N films and the barrier property against Copper (Cu) diffusion is discussed in this paper. While WSi0.6N is amorphous below 850° C, W microcrystals in amorphous WSiN occur at 850° C. Their average grain sizes increase from 3 nm to 8 nm and their numerical densities also increase from 200/µ m2 to 7400/µ m2 at temperatures ranging from 850° C to 880° C. From the X-ray photoelectron spectroscopy (XPS) measurements, it is thought that the W of Si–W bonds in WSiN films is 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 (SIMS). The activation energy of the diffused Cu was constant at 2.8 eV in the temperature range of 700–900° C. Consequently, the excellent barrier property is thought to be due to the absence of continuous grain boundaries throughout the film where Cu atoms can easily migrate. That is, the W microcrystal formation does not change the Cu diffusion mechanism up to 900° C, and the Cu diffusion is controlled by diffusion of it in an amorphous matrix.