Grains-growth and clustering effects on boron diffusion in polysilicon during thermal post-implantation annealing.

Abstract

We propose a double diffusion model adapted to the granular structure of polysilicon and to the effects of high concentrations. This model takes account of the temporal and thermal changes of the morphological structure of polysilicon, by the grains growing in size, during the thermal post-implantation treatment. In addition, it combines the effects of the trapping and the segregation of dopant to the grain boundaries, with the complex phenomena related to the effects of the strong concentrations, such as the exceeds of the solubility solid limit, the ion implantation damages and the formation of inactive and immobile clusters. This is permit to simulate and study the complex kinetics of redistribution and activation of dopant, on the other hand, to understand more exactly the influence of the grains size increase during the thermal annealing on the dopant diffusion. Indeed, the increase of the grains size by the crystallization of the films, play a significant role for the determination of the diffusion profiles with a good precision. In particular, for the transient enhanced diffusion of the dopant (TED). The adjustment of the profiles simulated with the experimental SIMS profiles for short times of treatments ranging between 1 and 15 minutes at the temperature of 850/spl deg/C, allowed the validation of this model. We have concluded that the dominant mechanism of dopant transfer to the grain boundaries is the grains growth. During this growth, the grain boundaries collect dopant by the trapping and segregation mechanism.