AN ADVANCED MODEL FOR DOPANT DIFFUSION IN HEAVILY IMPLANTED POLYCRYSTALLINE SILICON THIN FILMS

S ABADLI, F MANSOUR

Résumé


This work is dedicated to the study of the transient enhanced diffusion (TED) of boron in polycrystalline-silicon thin films. This phenomenon is a major problem for the development of P+ polysilicon gate metal-oxide-semiconductor (MOS) devices; for future polysilicon technologies. The highly doped, P+, gate is made by ion implantation followed by thermal post-implantation annealing. In these conditions, the boron atoms diffuse in a transient and enhanced way which can be some thousand times to some hundred times faster than in equilibrium. At the same time, the solubility limt excess due to the very strong doping level and ion-implantation damages, lead to various complex phenomena
sush as dopant trapping, segregation, and clustering. Taken all these phenomena into account, we propose a theoretical one-dimensional two-stream diffusion model adapted to the granular structure of polycrystalline-silicon and to the effects of the strong-concentrations. This model includes dopant clustering in grains as well as in grain boundaries. Moreover, growth of grains and energy barrier height are coupled with the dopant diffusion coefficients and the process temperature based on thermodynamic concepts. The adjustment of the simulated profiles with the experimental SIMS profiles, for short treatment times ranging between 1 and 30 minutes at different temperatures (700, 750 and 800°C), will allow the study of the boron transient enhanced diffusion; as well as the understanding of the grainsgrowth effect on boron diffusion during annealing


Mots-clés


modeling; boron; diffusion; grain-growth; grain-boundaries; polysilicon

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