Electroless deposition of conformal ultra-thin (~10nm-thick) films of Co0.9W0.02P0.08 was demonstrated. Electroless Co0.9W0.02P0.08 was an effective barrier against Cu diffusion up to 450C; unlike physical vapor deposited Co, which was a poor barrier. The role of the microstructure in determining the barrier properties was considered. The microstructure of the as-deposited layers consisted of nanocrystallites of hexagonal close-packed Co and an amorphous CoWP component. The amorphous component crystallized, at about 290C, to hexagonal close-packed Co. The orthorhombic Co2P phase nucleated at 420C, while the majority phase remained hexagonal close-packed Co. As it was found that, at up to 450C, there was no phase formation between Cu and the Co0.9W0.02P0.08 film, it was concluded that the mechanism of barrier failure was grain-boundary diffusion. The dependence of Cu grain-boundary diffusivity upon the microstructure was qualitatively demonstrated by comparing electroless deposited Co0.9W0.02P0.08, Co0.9P0.1 and physical vapor deposited Co. Secondary ion mass spectrometry depth-profiling measurements were performed on the films, after subjecting them to annealing (400C) that resulted in type-C Cu grain-boundary diffusion. The Cu diffusivity in the Co0.9W0.02P0.08 film was lower than that in Co0.9P0.1, and substantially lower than that in physical vapor deposited Co. The difference in Cu diffusivity was explained by varying degrees of grain boundary passivation, due to the P and W which enriched the grain boundaries. This passivation effect was more marked in Co0.9W0.02P0.08 films.

The Role of Microstructure in Nanocrystalline Conformal Co0.9W0.02P0.08 Diffusion Barriers for Copper Metallization. A.Kohn, M.Eizenberg, Y.Shacham-Diamand: Applied Surface Science, 2003, 212-213, 367-72

Table 53

Diffusion of Cr in Cr2O3