The authors investigate the implications of amorphizing ion implants on the crystalline integrity of sub-20nm wide fin field-effect transistors (FinFETs). Recrystallization of thin body silicon is not as straightforward as that of bulk silicon because the regrowth direction may be parallel to the silicon surface rather than terminating at it. In sub-20nm wide FinFETs surface proximity suppresses crystal regrowth and promotes the formation of twin boundary defects in the implanted regions. In the case of a 50nm amorphization depth, random nucleation and growth leads to polycrystalline silicon formation in the top ∼25nm of the fin, despite being only ∼25nm from the crystalline silicon seed.

Articles you may be interested inInfluence of boron-interstitials clusters on hole mobility degradation in high dose boron-implanted ultrashallow junctions Impact of the end of range damage from low energy Ge preamorphizing implants on the thermal stability of shallow boron profiles

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The formation of ultra-shallow junctions (USJs) for future integrated circuit technologies requires preamorphization and high dose boron doping to achieve high activation levels and abrupt profiles. To achieve the challenging targets set out in the semiconductor roadmap, it is crucial to reach a much better understanding of the basic physical processes taking place during USJ processing. In this paper we review current understanding of dopant-defect interactions during thermal processing of device structures – interactions which are at the heart of the dopant diffusion and activation anomalies seen in USJs. First, we recall the formation and thermal evolution of End of Range (EOR) defects upon annealing of preamorphized implants (PAI). It is shown that various types of extended defect can be formed: clusters, {113} defects and dislocation loops. During annealing, these defects exchange Si interstitial atoms and evolve following an Ostwald ripening mechanism. We review progress in developing models based on these concepts, which can accurately predict EOR defect evolution and interstitial transport between the defect layer and the surface. Based on this physically based defect modelling approach, combined with fully coupled multi-stream modelling of dopant diffusion, one can perform highly predictive simulations of boron diffusion and de/re-activation in Ge-PAI boron USJs. Agreement between simulations and experimental data is found over a wide range of experimental conditions, clearly indicating that the driving mechanism that degrades boron junction depth and activation is the dissolution of the interstitial defect band. Finally, we briefly outline some promising methods, such as co-implants and/or vacancy engineering, for further down-scaling of source-drain resistance and junction depth.

We demonstrate that boron diffuses at high concentrations during low-temperature thermal annealing in amorphous silicon pre-amorphized by germanium ion implantation. For a typical boron ultrashallow junction doping profile, concentrations as high as 2ϫ10 20 cm Ϫ3 appear to be highly mobile at 500 and 600°C in the amorphous silicon region before recrystallization. In crystalline silicon at the same temperatures the mobile boron concentration is at least two orders of magnitude lower. We also show that boron diffusivity in the amorphous region is similar with and without fluorine. The role of fluorine is not to enhance boron diffusivity, but to dramatically slow down the recrystallization rate, allowing the boron profile to be mobile up to the concentration of 2 ϫ10 20 cm Ϫ3 for a longer time.