On the basis of a network defect model, it was proposed that B diffused via a peroxy linkage defect whose concentration in the oxide depended upon the processing conditions. It was shown that, as the gate oxide fell below 8nm in thickness, additional chemical processes acted so as to increase the B diffusivity and decrease its activation energy, as a function of the distance from the Si/SiO2 interface. In the case of 1.5nm-thick oxide, the B diffusivity at 900C was expected to increase by a factor of 24 with respect to the value for 10nm-thick oxide. The role of nitridation, in creating a barrier to B diffusion, was modelled by assuming that the N atoms competed with B for the occupation of diffusion defect sites. The model predicted that nitridation would be ineffective in preventing B penetration when BF2 implantation was used.

R.B.Fair: Journal of the Electrochemical Society, 1997, 144[2], 708-12