Ni(Pt)-silicide contacts on CMOS devices: Impact of substrate nature and Pt concentration on the phase formation

Ni silicides used as contacts in source/drain and gate of advanced CMOS devices were analyzed by atom probe tomography (APT) at atomic scale. These measurements were performed on 45 nm nMOS after standard self-aligned silicide (salicide) process using Ni(5 at.% Pt) alloy. After the first annealing (RTA1), δ-Ni2Si was the only phase formed on gate and source/drain while, after the second annealing (RTA2), two different Ni silicides have been formed: NiSi on the gate and δ-Ni2Si on the source and drain. This difference between source/drain and gate regions in nMOS devices has been related to the Si substrate nature (poly or mono-crystalline) and to the size of the contact. In fact, NiSi seems to have difficulties to nucleate in the narrow source/drain contact on mono-crystalline Si. The results have been compared to analysis performed on 28 nm nMOS where the Pt concentration is higher (10 at.% Pt). In this case, θ-Ni2Si is the first phase to form after RTA1 and NiSi is then formed at the same time on source (or drain) and gate after RTA2. The absence of the formation of NiSi from δ-Ni 2Si/Si(1 0 0) interface compared to θ-Ni2Si/Si(1 0 0) interface could be related to the difference of the interface energies. The redistributions of As and Pt in different silicides and interfaces were measured and discussed. In particular, it has been evidenced that Pt redistributions obtained on both 45 and 28 nm MOS transistors correspond to respective Pt distributions measured on blanket wafers. © 2013 Elsevier B.V. All rights reserved.

Direct epitaxial growth of θ-Ni2Si by reaction of a thin Ni(10 at.% Pt) film with Si(1 0 0) substrate

The reaction between an 11 nm Ni(10 at.% Pt) film on a Si substrate has been examined by in situ X-ray diffraction (XRD), atom probe tomography (APT) and transmission electron microscopy (TEM). In situ XRD experiments show the unusual formation of a phase without an XRD peak through consumption of the metal. According to APT, this phase has an Si concentration gradient in accordance with the θ-Ni2Si metastable phase. TEM analysis confirms the direct formation of θ-Ni2Si in epitaxy on Si(1 0 0) with two variants of the epitaxial relationship. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Influence of AlN buffer layer thickness on structural properties of GaN epilayer grown on Si (111) substrate with AlGaN interlayer

We present the growth of GaN epilayer on Si (111) substrate with a single AlGaN interlayer sandwiched between the GaN epilayer and AlN buffer layer by using the metalorganic chemical vapour deposition. The influence of the AlN buffer layer thickness on structural properties of the GaN epilayer has been investigated by scanning electron microscopy, atomic force microscopy, optical microscopy and high-resolution x-ray diffraction. It is found that an AlN buffer layer with the appropriate thickness plays an important role in increasing compressive strain and improving crystal quality during the growth of AlGaN interlayer, which can introduce a more compressive strain into the subsequent grown GaN layer, and reduce the crack density and threading dislocation density in GaN film.

Au@Si-n: Growth behavior, stability and electronic structure

The configurations, stability, and electronic structure of AuSin (n = 1-16) clusters have been investigated within the framework of the density functional theory at the B3PW91/LanL2DZ and PW91/DNP levels. The results show that the Au atom begins to occupy the interior site for cages as small as Si-11 and for Si-12 the Au atom completely falls into the interior site forming Au@Si-12 cage. A relatively large embedding energy and small HOMO-LUMO gap are also found for this Au@Si-12 structure indicating enhanced chemical activity and good electronic transfer properties. All these make Au@Si-12 attractive for cluster-assembled materials.

Effects of AlGaN/AlN Stacked Interlayers on GaN Growth on Si (111)

We report the growth of high quality and crack-free GaN film on Si (111) substrate using Al0.2Ga0.8N/AlN stacked interlayers. Compared with the previously used single AlN interlayer, the AlGaN/AlN stacked interlayers can more effectively reduce the tensile stress inside the GaN layer. The cross-sectional TEM image reveals the bending and annihilation of threading dislocations (TDs) in the overgrown GaN film which leads to a decrease of TD density.

Effect of indium-doped interlayer on the strain relief in GaN films grown on Si(111)

Crack-free GaN films have been achieved by inserting an Indoped low-temperature (LT) AlGaN interlayer grown on silicon by metalorganic chemical vapor deposition. The relationship between lattice constants c and a obtained by X-ray diffraction analysis shows that indium doping interlayer can reduce the stress in GaN layers. The stress in GaN decreases with increasing trimethylindium (TMIn) during interlayer growth. Moreover, for a smaller TMIn flow, the stress in GaN decreases dramatically when In acts as a surfactant to improve the crystallinity of the AlGaN interlayer, and for a larger TMIn flow, the stress will increase again. The decreased stress leads to smoother surfaces and fewer cracks for GaN layers by using an In-doped interlayer than by using an undoped interlayer. In doping has been found to enhance the lateral growth and reduce the growth rate of the c face. It can explain the strain relief and cracks reduction in GaN films. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Growth-Parameter Spaces and Optical Properties of Cubic Boron Nitride Films on Si(001)

Cubic boron nitride (c-BN) films were deposited on Si(001) substrates in an ion beam assisted deposition (IBAD) system under various conditions, and the growth parameter spaces and optical properties of c-BN films have been investigated systematically. The results indicate that suitable ion bombardment is necessary for the growth of c-BN films, and a well defined parameter space can be established by using the P/a-parameter. The refractive index of BN films keeps a constant of 1.8 for the c-BN content lower than 50%, while for c-BN films with higher cubic phase the refractive index increases with the c-BN content from 1.8 at chi(c) = 50% to 2.1 at chi(c) = 90%. Furthermore, the relationship between n and rho for BN films can be described by the Anderson-Schreiber equation, and the overlap field parameter gamma is determined to be 2.05.

The diphasic nc-Si/a-Si : H thin film with improved medium-range order

A series of silicon film samples were prepared by plasma enhanced chemical vapor deposition (PECVD) near the threshold from amorphous to nanocrystalline state by adjusting the plasma parameters and properly increasing the reactions between the hydrogen plasma and the growing surface. The microstucture of the films was studied by micro-Raman and Fourier transform infrared (FTIR) spectroscopy. The influences of the hydrogen dilution ratio of silane (R-H = [H-2]/[SiH4]) and the substrate temperature (T-s) on the microstructural and photoelectronic properties of silicon films were investigated in detail. With the increase of RH from 10 to 100, a notable improvement in the medium-range order (MRO) of the films was observed, and then the phase transition from amorphous to nanocrystalline phase occurred, which lead to the formation of diatomic hydrogen complex, H-2* and their congeries. With the increase of T-s from 150 to 275 degreesC, both the short-range order and the medium range order of the silicon films are obviously improved. The photoconductivity spectra and the light induced changes of the films show that the diphasic nc-Si/a-Si:H films with fine medium-range order present a broader light spectral response range in the longer wavelength and a lower degradation upon illumination than conventional a-Si:H films. (C) 2004 Elsevier B.V. All rights reserved.

Characterization of stress induced in SOS and Si/gamma-Al2O3/Si heteroepitaxial thin films by Raman spectroscopy

Raman spectroscopy technique has been performed to investigate the stress induced in as-grown silicon-on-sapphire (SOS), solid-phase-epitaxy (SPE) re-grown SOS, and Si/gamma-Al2O3/Si double-heteroepitaxial thin films. It was demonstrated that the residual stress in SOS film, arising from mismatch and difference of thermal expansion coefficient between silicon and sapphire, was reduced efficiently by SPE process, and that the stress in Si/gamma-Al2O3/Si thin film is much smaller than that of as-grown SOS and SPE upgraded SOS films. The stress decrease for double heteroepitaxial film Si/gamma-Al2O3/Si mainly arises from the smaller lattice mismatching of 2.4% between silicon top layer and the gamma-Al2O3/Si epitaxiial composite substrate, comparing with the large lattice mismatch of 13% for SOS films. It indicated that gamma-Al2O3/Si as a silicon-based epitaxial substrate benefits for reducing the residual stress for further growth of silicon layer, compared with on bulk sapphire substrate. (c) 2005 Elsevier B.V. All rights reserved.

Crack-free GaN/Si(111) epitaxial layers grown with InAlGaN alloy as compliant interlayer by metalorganic chemical vapor deposition

A new method is demonstrated to be effective in reducing mismatch-induced tensile stress and suppressing the formation of cracks by inserting InAlGaN interlayers during the growth of GaN upon Si (1 1 1) substrate. Compared with GaN film without quaternary interlayer, GaN layer grown on InAlGaN compliant layers shows a five times brighter integrated PL intensity and a (0 0 0 2) High-resolution X-ray diffraction (HRXRD) curve width of 18 arcmin. Its chi(min), derived from Rutherford backscattering spectrometry (RBS), is about 2.0%, which means that the crystalline quality of this layer is very good. Quaternary InAlGaN layers, which are used as buffer layers firstly, can play a compliant role to endure the large mismatch-induced stress and reduce cracks during the growth of GaN epitaxy. The mechanisms leading to crack density reduction are investigated and results show that the phase immiscibility and the weak In-N bond make interlayer to offer tenability in the lattice parameters and release the thermal stress. (c) 2005 Elsevier B.V. All rights reserved.

Reduction of dislocations in GaN epilayer grown on Si (111) substrates using a GaN intermedial layer

GaN intermedial layers grown under different pressures are inserted between GaN epilayers and AlN/Si(111) substrates. In situ optical reflectivity measurements show that a transition from the three-dimensional (3D) mode to the 2D one occurs during the GaN epilayer growth when a higher growth pressure is used during the preceding GaN intermedial layer growth, and an improvement of the crystalline quality of GaN epilayer will be made. Combining the in situ reflectivity and transmission electron microscopy (TEM) measurements, it is suggested that the lateral growth at the transition of growth mode is favourable for bending of dislocation lines, thus reducing the density of threading dislocations in the epilayer.

Investigation of Mn-doped Si films prepared by magnetron cosputtering

Mn-doped Si films were prepared on Si(001) substrates by magnetron cosputtering and post-annealing process. The structural, morphological and magnetic properties of the films have been investigated. X-ray diffraction results show that the as-prepared film is amorphous. By annealing at 800 degrees C, however, the film is crystallized. There is no secondary phase found except Si in the two films. Chemical mapping shows that no segregation of the Mn atoms appears in the annealed film. Atomic force microscopy images of the films indicate that the annealed film has a granular feature that covers uniformly the film surface while there is no such kind of characteristic in the as-prepared film. The field dependence of magnetization was measured using an alternating gradient magnetometer, and it has been indicated that the annealed film shows room-temperature ferromagnetism. (c) 2006 Elsevier B.V. All rights reserved.

Temperature dependence of the formation of nano-scale indium clusters in InAlGaN alloys on Si(111) substrates

The temperature dependence of the formation of nano-scale indium clusters in InAlGaN quaternary alloys, which are grown by metalorganic chemical vapour deposition on GaN/Si(111) epilayers, is investigated. Firm evidence is provided to support the existence of phase separation, or nano-scale In-rich clusters, by the combined results of high-resolution transmission electron microscopy (HRTEM), high-resolution x-ray diffraction (HRXRD) and micro-Raman spectra. The results of HRXRD and Raman spectra indicate that the degree of phase separation is strong and the number of In clusters in the InAlGaN layers on silicon substrate is higher at lower growth temperatures than that at higher growth temperatures, which limits the In and Al incorporated into the InAlGaN quaternary alloys. The detailed mechanism of luminescence in this system is studied by low temperature photoluminescence (LT-PL). We conclude that the ultraviolet (UV) emission observed in the quaternary InAlGaN alloys arises from the matrix of a random alloy, and the second emission peak in the blue-green region results from the nano-scale indium clusters.

Band gap renormalization and carrier localization effects in InGaN/GaN quantum-wells light emitting diodes with Si doped barriers

The optical properties of two kinds of InGaN/GaN quantum-wells light emitting diodes, one of which was doped with Si in barriers while the other was not, are comparatively investigated using time-integrated photoluminescence and time-resolved photoluminescence techniques. The results clearly demonstrate the coexistence of the band gap renormalization and phase-space filling effect in the structures with Si doped barriers. It is surprisingly found that photogenerated carriers in the intentionally undoped structures decay nonexponentially, whereas carriers in the Si doped ones exhibit a well exponential time evolution. A new model developed by O. Rubel, S. D. Baranovskii, K. Hantke, J. D. Heber, J. Koch, P. Thomas, J. M. Marshall, W. Stolz, and W. H. Ruhle [J. Optoelectron. Adv. Mater. 7, 115 (2005)] was used to simulate the decay curves of the photogenerated carriers in both structures, which enables us to determine the localization length of the photogenerated carriers in the structures. It is found that the Si doping in the barriers not only leads to remarkable many-body effects but also significantly affects the carrier recombination dynamics in InGaN/GaN layered heterostructures. (c) 2006 American Institute of Physics.

Growth and properties of magnetron cosputtering grown Mn(x)Ge(1-x)on Si(001)

We have grown MnxGe1-x films (x=0, 0.06, 0.1) on Si (001) substrates by magnetron cosputtering, and have explored the resulting structural, morphological, electrical and magnetic properties. X-ray diffraction results show there is no secondary phase except Ge in the Mn0.06Ge0.94 film while new phase appears in the Mn0.1Ge0.9 film. Nanocrystals are formed in the Mn0.06Ge0.94 film, determined by field-emission scanning electron microscopy. Hall measurement indicates that the Mn0.06Ge0.94 film is p-type semiconductor and hole carrier concentration is 6.07 X 10(19) cm(-3) while the MnxGe1-x films with x=0 has n-type carriers. The field dependence of magnetization was measured using alternating gradient magnetometer, and it has been indicated that the Mn0.06Ge0.94 film is ferromagnetic at room temperature. (c) 2005 Elsevier Ltd. All rights reserved.