K. Hoummada

First stages of the formation of Ni silicide by atom probe tomography

Atom probe tomography assisted by femtosecond laser pulses has been performed on a Ni(Pt) film on (100)Si. Two phases with different compositions were found to form during deposition at room temperature: a NiSi layer with a relatively constant thickness of approximately 2nm and a particle of Ni2Si. The shape of the Ni2Si particle is in accordance with nucleation followed by lateral growth formation. This confirms the growth model deduced from calorimetric measurement of silicides and intermetallics and from atom probe tomography studies of the Al∕Co system. A nonuniform redistribution of Pt was also observed.

Three dimensional distributions of arsenic and platinum within NiSi contact and gate of an n-type transistor

Atom probe tomography was used to study the redistribution of platinum and arsenic atoms after Ni(Pt) silicidation of As-doped polycrystalline Si. These measurements were performed on a field-effect transistor and compared with those obtained in unpatterned region submitted to the same process. These results suggest that Pt and As redistribution during silicide formation is only marginally influenced by the confinement in microelectronic devices. On the contrary, there is a clear difference with the redistribution reported in the literature for the blanket wafers. Selective etching used to remove the non-reacted Ni(Pt) film after the first rapid heat treatment may induce this difference.

Lattice and grain-boundary diffusion of As in Ni2Si

The diffusion coefficient of As in 260 nm thick polycrystalline Ni2Si layers has been measured both in grains and in grain boundaries (GBs). As was implanted in Ni2Si layers prepared via the reaction between a Si layer and a Ni layer deposited by magnetron sputtering on a (100) Si substrate covered with a SiO2 film. The As concentration profiles in the samples were measured using secondary ion mass spectroscopy before and after annealing (400–700 °C). The diffusion coefficients in the grains and the GBs have been determined using two-dimensional finite element simulations based on the Fisher model geometry. For short time annealing (1 h) and temperatures lower than 600 °C, lattice diffusion has not been observed. However, GB diffusion was evidenced for temperatures as low as 400 °C. For higher thermal budgets, As diffuses simultaneously in the volume of the grains and in the GBs. Lattice diffusion is characterized by a pre-exponential factor D0v∼1.5×10−1 cm2 s−1 and an activation energy Qv∼2.72±0.10 eV. I...

Three-dimensional distribution of Al in high-k metal gate: Impact on transistor voltage threshold

The three-dimensional spatial distribution of Al in the high-k metal gates of metal-oxide-semiconductor field-effect-transistors is measured by atom probe tomography. Chemical distribution is correlated with the transistor voltage threshold (VTH) shift generated by the introduction of a metallic Al layer in the metal gate. After a 1050 °C annealing, it is shown that a 2-A thick Al layer completely diffuses into oxide layers, while a positive VTH shift is measured. On the contrary, for thicker Al layers, Al precipitation in the metal gate stack is observed and the VTH shift becomes negative.

Atomic-scale redistribution of Pt during reactive diffusion in Ni (5% Pt)–Si contacts

The NiSi silicide that forms by reactive diffusion between Ni and Si active regions of nanotransistors is used nowadays as contacts in nanoelectronics because of its low resistivity. Pt is added to the Ni film in order to stabilise the NiSi phase against the formation of the high-resistivity NiSi(2) phase and agglomeration. In situ X-ray diffraction (XRD) experiments performed on material aged at 350 degrees C (under vacuum) showed the complete consumption of the Ni (5 at% Pt) phase, the regression of Ni(2)Si phase as well as the growth of the NiSi phase after 48 min. Pt distribution for this heat treatment has been analysed by laser-assisted tomographic atom probe (LATAP). An enrichment of platinum in the middle of the NiSi phase suggests that Pt is almost immobile during the growth of NiSi at the two interfaces: Ni(2)Si/NiSi and NiSi/Si. In the peak, platinum was found to substitute for Ni in the NiSi phase. Very small amounts of Pt were also found in the Ni(2)Si phase close to the surface and at the NiSi/Si interface.

Ge atom distribution in buried dome islands

Laser-assisted atom probe tomography microscopy is used to provide direct and quantitative compositional measurements of tri-dimensional Ge distribution in Ge dome islands buried by Si. Sub-nanometer spatial resolution 3D imaging shows that islands keep their facets after deposition of the Si cap, and that the island/substrate/Si cap interfaces are abrupt. The core of the domes contains 55% of Ge, while the island shell exhibits a constant composition of 15% of Ge. The {113} facets of the islands present a Ge enrichment up to 35%. The wetting layer composition is not homogeneous, varying from 9.5% to 30% of Ge.

Superconducting properties of laser annealed implanted Si:B epilayers

We report on the superconducting properties of heavily doped silicon epilayers obtained by the implantation of B atoms in silicon wafers and subsequent laser annealing (pulsed laser induced epitaxy). A critical temperature ?250?mK has been obtained for samples with a boron concentration (cB) ranging from 2 to 10 at.%, which were checked by atom probe tomography to be free of any significant boron clustering. The standard dopant implantation technique is therefore an alternative (with respect to gas immersion laser doping) process to induce superconductivity in boron-doped silicon. Superconductivity was not observed with any of the other implanted dopants (P, As, Al) with similar concentrations down to 50?mK.

Diffusion Measurements in Nanostructures

Due to experimental issues, atomic transport kinetics in nanostructures is still rarely quantitatively investigated despite its significant importance for the design of nanostructure fabrication processes and the prediction of nanoobject structure and physical property ageing. Atomic diffusion in nanostructures is expected to be mainly mediated via atomic transport in interfaces. However, in order to fully understand atomic transport in nanostructures, it is necessary to develop experimental methods allowing for the measurement of diffusion coefficients in nanovolumes, in interfaces, and in interface intersections. To date, this type of measurement has been essentially performed in nanocrystalline materials, giving access to diffusion measurements in nanocrystals corresponding to the nanograins, in grain boundaries corresponding to the interfaces between disoriented crystals of same nature, and in triple junctions corresponding to the grain boundary intersections. This chapter presents the current methods and techniques reported in the literature that have been used for such a type of measurement. Some of the original observations concerning atomic transport in nanocrystalline materials are also presented and discussed.

Laser Atom Probe Tomography: some applications

Laser atom probe tomography was used to investigate the inter-diffusive reactions at the silicon-nickel interface. The early stages of formation of a NiSi silicide was studied. The addition of Pt was shown to increase the temperature of formation of the high resistivity NiSi2 phase by approximately 150 degC