Modelling boron diffusion in heavily implanted low-pressure chemical vapor deposited silicon thin films during thermal post-implantation annealing

Abstract

We have investigated and modelled boron (B) diffusion in heavily implanted silicon (Si) thin films deposited from disilane (Si 2H 6) by low pressure chemical vapor deposition (LPCVD) at low temperatures. A comprehensive one-dimensional two-stream diffusion model adapted to the particular structure of deposited Si films and to the effects of high B concentrations has been developed. This model includes B clustering in grains as well as in grain boundaries. In addition, the effects of Si-films crystallization, during thermal post-implantation annealing, on B diffusion as well as on B clusters formation and dissolution were considered. The effects of clustering, growth of grains, dopant-enhanced grains growth and the driving force for grains growth were coupled with the dopant diffusion coefficients and the process temperature based on thermodynamic concepts. To investigate complex B diffusion in heavily implanted Si films deposited by LPCVD, we have used experimental profiles obtained by secondary ion mass spectroscopy (SIMS) for B implantation with doses of 1 × 10 15 at./cm 2, 4 × 10 15 at./cm 2 and 5 × 10 15 at./cm 2 at an energy of 15 keV. Thermal post-implantation anneals were carried out at relatively low-temperatures (700 °C and 850 °C) for various short-times of 1 min to 15 min. The good adjustment of the simulated profiles with the experimental SIMS profiles allowed the validation of this model. It was found that the simulation well reproduces the experimental SIMS profiles when the growth of grains and immobile B clusters are considered.