The diffusion mechanism for elements of groups III and V in silicon

Model of the base-diffusivity push effect in a silicon transistor structure

“…We have produced also a two-dimensional calculation of the simultaneous diffusion of donor and acceptor impurities and we shall simulate the compensation of the push effect by means of the emitter diffusion together with a group IV impurity. This compensation was observed experimentally for germanium [29,301, and, in our opinion, it is due to the attraction of vacancies to the diffusion zone by these impurity atoms with a relatively large covalent radius. These results will be published elsewhere.…”

“…According to our model (see [20]), atoms of groups I11 and V diffuse into silicon by two interacting fluxes: through substitutional positions (E-centre mechanism, which is a special kind of vacancy mechanism with strong attraction between vacancies and impurity atoms (see [26]) and through interstices. Interstitial impurity atoms diffuse faster than substitutional ones and, captured by vacancies, they shape almost the whole impurity profile, excepting a flat region near the surface ('plateau').…”

“…As noted in [20,21], the equations of the two-flux model contain some parameters for which even approximate experimental data are not known. These are interstitial diffusivity and transition rates.…”

“…So far, we put the dependence Ds(q) to be the same for both impurities (excepting a pre-factor, i.e. intrinsic diffusivity, which is taken differently), and we use the same data which were used in [20,21] for phosphorus diffusion simulation.…”

“…This model allows a qualitative explanation of most of the main features of diffusion with a high surface concentration 112, 18,191. More recently we published the results of a numerical simulation of 'anomalous' diffusion profiles [20,21] and some effects of the radiation-enhanced diffusion [26]. The model does not involve the 'interstitial with substitution' mechanism [13 to 151.…”