Short-time diffusion of aluminium in silicon and co-diffusion with phosphorus and boron

Diffusion of aluminium in silicon and its interaction with boron and phosphorus has been investigated under rapid thermal process conditions. The resulting profiles were characterized by SIMS-analysis and attendant numerical simulations have been carried out. For Al-predeposition and drive-in steps without Al-source the derived diffusion coefficients are compared with data from literature. In subsequent diffusion processes of aluminium and boron or phosphorus respectively, a strong impact on the diffusion behaviour of aluminium was observed. Supersaturation of self-interstitials caused by high surface concentrations of boron or phosphorus leads to an accelerated Al-diffusion. Hence it is concluded, that Al diffuses to a considerably extent by using self-interstitials as diffusion-vehicles. An impact of the electric field caused by extrinsic B- or P-profiles on the diffusion of aluminium is observed indicating Al to migrate as a negatively charged ion. Ion-pairing as a dominant effect for trapping of aluminium is ascertained during Al-predeposition into P-doped wafers. Less distinctive trapping is observed in case of subsequent diffusions of Al after B. The dependence of aluminium-surface concentration on background doping indicates the Fermi-level effect.