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Analysis of Low Interface Resistance in NiSi/Si Junctions by APT

As the scale of transistors decreases significantly, parasitic resistance has become problematic to develop next-generation devices. Especially, the interface resistance between NiSi layer and Si-substrate was considered as one of largest problems. In this situation, doping some impurities in NiSi layer, which led to reducing the interface resistance, has been proposed. In order to reveal the mechanism of this doping method, distribution of dopants around a NiSi/Si-substrate interface were investigated by APT.

Impurity distribution in a NiSi layer

A network distribution of platinum atoms, which probably meant segregation at grain boundaries of a NiSi layer, was observed clearly. In addition, non-uniform distribution of arsenic atoms were also found there. In this case, arsenic atoms seemed to aggregate locally like precipitates.
(Specimen provided by Toshiba Memory Corporation)

Atom Map of the Entire Specimen (Side View) Pt (Yellow) and As (Violet) Atom Maps at the Silicide Interface (Top View)

APT image (SideView)

Distribution of platinum(yellow) and arsenic(purple) atoms
at a NiSi/Si-substrate interface (TopView)

Impurity distribution around a NiSi/Si-substrate interface

It was found by APT depth profiles that impurities as platinum and arsenic were segregated at surface of a NiSi layer. At the same time, they were also segregated at an interface between a NiSi layer and Si-substrate. However, due to interfacial roughness, width of impurity peaks in a depth profile became broader. In this case, proxigram application was effective to obtain a depth profile without influence of interfacial roughness. By applying the proxigram to the 3D NiSi image, it was found that arsenic atoms segregated within the range of ±1nm from a NiSi/Si-substrate interface.



Proxigram Concept

Schematic illustration of proxigram application


Depth Concentration Profile
Compositional profile of the NiSi sample along Z direction
Proxigram at the Silicide-Si Substrate Interface
Proxigram profile at a NiSi/Si-substrate interface

※T. Sonehara et al. IEEE Trans. Electron Devices, vol. 58, no. 11, pp.3778 - 3786, Nov. 2011

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[Last updated: April 18, 2019]

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