BORON-DIFFUSION THROUGH THIN GATE OXIDES - INFLUENCE OF NITRIDATION AND EFFECT ON THE SI/SIO2 INTERFACE ELECTRICAL CHARACTERISTICS

The diffusion of boron in N2 ambient is studied by using p+ polysilicon metal-oxide-silicon structures annealed during times long enough to allow boron diffusion through the gate oxide, up to the underlying substrate. Assuming equilibrium segregation at the interfaces, the boron diffusivity in the oxide is calculated by numerically fitting the resulting profile in the substrate. It is found that B diffuses in SiO2 with an activation energy of about 3 eV. We also quantify the influence of the nitridation of the oxide, and confirm its efficiency as a diffusion barrier. However, this study reveals a strong inconsistency between the extracted diffusivity values of B in SiO2 and the amount of B atoms being able to reach the Si/SiO2 interface to account for the observed interface state density.