M. Beregovsky

Kinetics of nickel silicide growth in silicon nanowires: From linear to square root growth

The common practice for nickel silicide formation in silicon nanowires (SiNWs) relies on axial growth of silicide along the wire that is initiated from nickel reservoirs at the source and drain contacts. In the present work the silicide intrusions were studied for various parameters including wire diameter (25–50 nm), annealing time (15–120 s), annealing temperature (300–440∘C), and the quality of the initial Ni/Si interface. The silicide formation was investigated by high-resolution scanning electron microscopy, high-resolution transmission electron microscopy (TEM), and atomic force microscopy. The main part of the intrusion formed at 420∘C consists of monosilicide NiSi, as was confirmed by energy dispersive spectroscopy STEM, selected area diffraction TEM, and electrical resistance measurements of fully silicided SiNWs. The kinetics of nickel silicide axial growth in the SiNWs was analyzed in the framework of a diffusion model through constrictions. The model calculates the time dependence of the intru...

Evolution of nickel silicide intrusions in silicon nanowires during thermal cycling

Thermally activated axial intrusion of nickel silicides into a silicon nanowire (NW) from pre-patterned Ni reservoirs is used in formation of nickel silicide/silicon contacts in SiNW field effect transistors. This intrusion consists usually of different nickel silicides which grow simultaneously during thermal annealing. Repeated annealing is often accompanied by local thickening and tapering of the NW, up to full disintegration of the silicide segment adjacent to Si. In the present work this process was investigated for SiNWs of various diameters in between 30 and 60 nm with pre-patterned Ni electrodes after a series of rapid thermal cycles including heating, holding at different temperatures of 400-440 °C for 5-15 s and cooling to room temperature. Kinetics of the nickel silicides axial growth was analyzed in the framework of diffusion model. This model is taking into account simultaneous formation of different nickel silicide phases and balance between transition of Ni atoms from the Ni reservoir to th...

From Contact to Diffusion Controlled Growth of Nickel Silicides in Silicon Nanowires

Semiconducting nanowires (NW) are implemented as the active channel of field effect transistor (FET) with linear and Schottky barrier source and drain contacts. Thermally activated axial intrusion of nickel silicides into the silicon NW from pre-patterned Ni reservoirs is used in the formation of nickel silicide/silicon contacts in SiNW FETs. In the present work, the kinetics of nickel silicide axial growth in SiNWs was analyzed in the framework of the model taking into account the balance between transition of Ni atoms from the Ni reservoir to the NW surface, diffusion transport of these Ni atoms from the contact area to the interfaces between different silicides and nickel silicide/Si interface, and corresponding reactions of Ni atoms with Si and the nickel silicides formed. Simultaneous growth of mono-and nickel rich silicide was described for different kinetic and geometrical parameters of the system. Critical parameters for transition from the linear to the parabolic dependences were introduced. The model was applied to the experimental results on nickel silicide growth in SiNWs of 25÷50 nm in diameters in a temperature range of 300÷440C°. The silicide intrusions were obtained by annealing of SiNWs with pre-patterned Ni electrodes in a rapid thermal annealing machine under nitrogen atmosphere for different temperatures and times up to 120 s. In most cases the intrusions consisted of two nickel silicides, Ni-rich and mono-silicide NiSi, as was confirmed by TEM and measuring the electrical resistance of the SiNW after full silicidation. The total intrusion length, L, and particular silicide lengths, showed various time dependences, from a linear (with low growth rates (1÷4nm/s)) to a square root, diffusion-type dependence (with higher rates (10÷15 nm/s)). This behavior is well described by the model developed.

Formation and Evolution of Nickel Silicide in Silicon Nanowires

Thermally activated axial intrusion of nickel silicides in silicon nanowires (SiNWs) is utilized to form nickel silicide/silicon contacts in SiNW field effect transistors. The growth of different nickel silicides is often accompanied by local thickening and tapering of the NW, up to its full disintegration. In this paper, this process was investigated in SiNWs of 30-60 nm in diameters with prepatterned Ni electrodes after annealing cycles at different temperatures of 300 °C-440 °C and times up to 120 s. From the temperature dependence of the intrusion lengths, activation energy of 1.45 eV for the surface diffusion of nickel was extracted. In several cases, periodic thickening of the nickel-rich part is accompanied by tapering of the monosilicide part up to its full dissolution. The kinetics of the nickel silicides growth was described by phenomenological model. For a certain set of parameters, tapering and dissolution of the monosilicide part of the intrusion were predicted, similar to the experimental results.

Effect of impurities on initial stages of phase formation for the system of Ti deposited on (001) Si–Ge layers

Effect of impurities (oxygen, carbon) on initial stages of phase formation for the system of Ti overlayer deposited in a 2×10−7 Torr vacuum on Si0.82Ge0.18 layers epitaxially grown on (001) Si has been studied by Auger electron spectroscopy, X-ray powder diffractometry, conventional and high resolution transmission electron microscopy and energy dispersive spectroscopy. The change in impurity contents at the Ti/SiGe interface was realized by changing the thickness of the Ti overlayer. Two sets of Ti/SiGe/Si samples with 10 and 60 nm thick Ti were investigated. It was shown that for the samples with 60 nm thick Ti the content of the oxygen and carbon at the Ti/SiGe interface was one order of magnitude lower than that in the samples with 10 nm thick Ti overlayer. The first crystalline phase formed as a result of annealing at a vacuum better than 2×10−7 Torr was Ti5(Si,Ge)3 for samples with a high level of the impurities and C49-Ti(Si,Ge)2 for samples with a low level of the impurities. An amorphous phase was revealed for both sets of specimens during the initial stages of phase formation. The results obtained were interpreted within the framework of a recently developed model of phase formation.

Electrical properties of the Ti(SiGe)2/Si0.89Ge0.11/Si(001) contact system

The electrical properties of a thin (350 A) layer deposited on a molecular beam epitaxial grown Si0.89Ge0.11/Si(001) heterostructure and subsequently annealed at Ta=550–800 °C were studied in a wide (80–325 K) temperature range. Annealing at 800 °C produces a single reaction product, the C54 phase of Ti(SiGe)2, while lower temperature anneals result in the coexistence of a few intermetallic compounds. It was found that while for annealing temperatures lower than 800 °C, the Fermi level is pinned with respect to the conduction band, annealing at 800 °C results in Fermi level partial pinning with respect to the valence band. The current flow in this case is controlled mainly by thermionic emission in the presence of interface states. Two kinds of traps were observed by deep level transient spectroscopy in the barrier region after the 800 °C annealing. Acceptor-like traps with an activation energy of ≈0.46–0.5 eV, a capture cross-section σa=1.3×10−12 cm2, and a density Dt≈3×1013 eV−1cm−2, which most likely o...

Quantitative Analysis of Ti-Si-Ge/Si-Ge/Si Structures by EDS and AES

Abstract. A method for quantitative analysis of Ti-Si-Ge/Si-Ge/Si structures with submicron thick layers by energy dispersive spectroscopy (EDS) in transmission electron microscopy (TEM) and Auger electron spectroscopy (AES) was developed. Quantitation of the results of both AES and EDS techniques was performed on the basis of a single reference specimen for the Ti-Si-Ge system comprising a uniform layer of the Ti(Si0.85Ge0.15)2 phase on a silicon substrate. The reference sample was prepared by the same procedure as the samples used in the study, and was thoroughly characterized by X-ray diffractometry, transmission electron microscopy and energy dispersive spectroscopy in scanning electron microscopy. Using this reference sample the elemental sensitivity factors relative to Si were found for both techniques, which enable us to obtain the elemental depth distributions for the studied samples. Good agreement between the results obtained by EDS/TEM, AES and supplementary techniques was found.