Growth of grains effect on boron diffusion in heavily doped LPCVD polysilicon thin films

Abstract

In this study, we propose a two stream diffusion model adapted to the granular structure of polysilicon and to the effects of high-concentrations. This model takes into account temporal and thermal changes of the morphological structure of polysilicon by the grains growth during post-implantation annealing. The dopant trapping and segregation effects were combined with those of complex phenomena related to the strong concentrations such as clustering and exceeds of the solubility solid limit. This will permit to understand more exactly the significant role of the grains growth effect for the precise determination of the diffusion profiles. The adjustment of simulated profiles with the experimental SIMS profiles for short annealing times ranging between 1 and 15 minutes at the temperature of 850°C allowed the validation of this model. Grains growth and boron clustering are the major effects for the precise simulation of the diffusion profiles. The dominant mechanism of boron transfer to the grain boundaries is grains growth during which the grain boundaries collect boron by the trapping and segregation mechanism.

Keywords: boron, diffusion, model, grains, grain boundaries, polysilicon.

Technologies Avancees Vol. 18 2006: pp. 5-11