In order to identify suitable diffusion barrier materials for Cu, the diffusion of Cu into Si through these barrier metals was investigated. The behavior of Cu in Cu/M/Si multi-layers was measured, after annealing, by using X-ray diffraction analysis, secondary ion mass spectroscopy, Rutherford back-scattering spectroscopy, and resistometry. It was found that only Cu/Ta/Si and Cu/W/Si multi-layers retained their multilayer structures after annealing (600C, 1h, H2), without resistivity increases. Multi-layers of the other metals did not retain their structures under the same annealing conditions. The differences in barrier properties were attributed to differing forms of the metal-Cu binary phase diagrams, and to their self-diffusion coefficients.

Diffusion Barrier Effects of Transition Metals for Cu/M/Si Multilayers (M = Cr, Ti, Nb, Mo, Ta, W). H.Ono, T.Nakano, T.Ohta: Applied Physics Letters, 1994, 64[12], 1511-3

Table 76

Diffusivity of Be in Cu Crystals