The diffusion of B, in samples under an N2 atmosphere, was studied by using p+ poly-Si/metal-oxide/Si structures which were annealed for times that were long enough to permit B diffusion through the gate oxide and up to the underlying substrate. Assuming the presence of equilibrium segregation at the interfaces, B diffusivity in the oxide was calculated by numerically fitting the resulting profile which existed in the substrate. It was found that B diffused in SiO2, with an activation energy of about 3eV. The effect of nitridation of the oxide was also quantified, and its efficiency as a diffusion barrier was confirmed. However, the present study revealed a marked inconsistency between the deduced diffusivity of B in SiO2 and the numbers of B atoms which had to reach the Si/SiO2 interface in order to account for the observed interface state density.

D.Mathiot, A.Straboni, E.Andre, P.Debenest: Journal of Applied Physics, 1993, 73[12], 8215-20