Doping of germanium by phosphorus implantation: Prediction of diffused profiles with simulation

Wafers made of germanium epitaxied on silicon were implanted at various doses and energies and were then annealed at temperatures ranging from 515 to 600 °C and process times ranging from 10 to 60 s. The corresponding SIMS profiles were used as targets for the optimization of the parameters of a diffusion model. Although diffusion in germanium is often believed to be mediated by vacancies, physical considerations on the damaging of the substrate led us to consider an interstitially mediated diffusion mechanism. The amorphization caused by the implantation was taken into account to set the initial distribution of point defects. Our predictions of the diffused phosphorus profiles were obtained using a pair-model with various charge states including solubility limit and outdiffusion. This modelling allowed us to accurately fit with the same set of parameters more than 15 experimental profiles, even the box-shaped ones that occur at higher thermal budget.