Electron-induced X-ray Emission Spectroscopy Research Articles

Effects of high in-situ source/drain boron doping in p-FinFETs on physical and device performance characteristics

In this study, the effects of high in-situ boron (B) doping in embedded source/drain (S/D) silicon germanium (SiGe) stressor of p-channel Fin Field Effect Transistors (FinFETs) in a 14 nm technology node were investigated. The device results were correlated to physical characteristics of B doped S/D regions which were probed using Transmission Electron Microscopy (TEM), Electron Energy Loss Spectroscopy (EELS) and Low Energy Electron Induced X-ray Emission Spectroscopy (LEXES) on representative device structures. B doping was established to be around low-E20 atoms/cm3 range as measured by LEXES. Reduction in on-state resistance (RON) and an increase in drive current (ION) was observed with higher B doping in SiGe but physical constraints, especially B segregation offered manufacturable challenges. These observed results are expected to critically help in SiGe stressor based S/D junction optimization of advanced FinFET Complementary Metal-Oxide-Semiconductor (CMOS) devices.

Magnesium degradation influenced by buffering salts in concentrations typical of in vitro and in vivo models

Magnesium and its alloys have considerable potential for orthopedic applications. During the degradation process the interface between material and tissue is continuously changing. Moreover, too fast or uncontrolled degradation is detrimental for the outcome in vivo. Therefore in vitro setups utilizing physiological conditions are promising for the material/degradation analysis prior to animal experiments. The aim of this study is to elucidate the influence of inorganic salts contributing to the blood buffering capacity on degradation. Extruded pure magnesium samples were immersed under cell culture conditions for 3 and 10days. Hank's balanced salt solution without calcium and magnesium (HBSS) plus 10% of fetal bovine serum (FBS) was used as the basic immersion medium. Additionally, different inorganic salts were added with respect to concentration in Dulbecco's modified Eagle's medium (DMEM, in vitro model) and human plasma (in vivo model) to form 12 different immersion media. Influences on the surrounding environment were observed by measuring pH and osmolality. The degradation interface was analyzed by electron-induced X-ray emission (EIXE) spectroscopy, including chemical-element mappings and electron microprobe analysis, as well as Fourier transform infrared reflection micro-spectroscopy (FTIR).

Chemical surface alteration of biodegradable magnesium exposed to corrosion media

The understanding of corrosion processes of metal implants in the human body is a key problem in modern biomaterial science. Because of the complicated and adjustable in vivo environment, in vitro experiments require the analysis of various physiological corrosion media to elucidate the underlying mechanism of “biological” metal surface modification. In this paper magnesium samples were incubated under cell culture conditions (i.e. including CO 2) in electrolyte solutions and cell growth media, with and without proteins. Chemical mapping by high-resolution electron-induced X-ray emission spectroscopy and infrared reflection microspectroscopy revealed a complex structure of the formed corrosion layer. The presence of CO 2 in concentrations close to that in blood is significant for the chemistry of the oxidised layer. The presence of proteins leads to a less dense but thicker passivation layer which is still ion and water permeable, as osmolality and weight measurements indicate.

Shallow As dose measurements of patterned wafers with secondary ion mass spectrometry and low energy electron induced x-ray emission spectroscopy

Secondary ion mass spectrometry (SIMS) and low energy electron induced x-ray emission spectroscopy (LEXES) are both well established technologies. SIMS tools are the ultimate reference for depth profiling and direct measurement of dopants with highest sensitivity and dynamic range. The LEXES-based shallow probe is a versatile, sensitive, in-line metrology tool for thin layer elemental composition and dopant dosimetry in semiconductor production. In this contribution, the ability of LEXES and SIMS techniques to differentiate nominal dose differences among three different 300mm patterned wafers are compared. In each die, several test pads were available for dose measurements. Five neighboring dies were measured by LEXES and afterward by SIMS. The repeatability measurements of both techniques (<0.5%) is suitable to determine dose nonuniformity from die to die and to discriminate nominal dose between wafers as small as 3%.

Spectroscopic study of interfaces in Al/Ni periodic multilayers

Using electron-induced X-ray emission spectroscopy (XES), we have studied two Al/Ni periodic multilayers that differ only by their annealing temperature: as-deposited and annealed at 115 °C. Our aim is to show that XES can provide further details about the chemistry at the metal-metal interface, in addition to what is obtained by X-ray diffraction. The distribution of valence states exhibiting Al 3p and Ni 3d character is determined from the analysis of the Al and Ni emission bands respectively. The multilayer emission bands are compared to those of reference materials: pure Al and Ni metals as well as Al 3 Ni, Al 3 Ni 2 and AlNi intermetallics. We provide evidence that, for temperatures up to 115 °C, Al 3 Ni is the major component of the multilayer.

Spectroscopic study of interfaces in Al/Ni periodic multilayers

Using electron-induced X-ray emission spectroscopy (XES), we have studied two Al/Ni periodic multilayers that differ only by their annealing temperature: as-deposited and annealed at 115C. Our aim is to show that XES can provide further details about the chemistry at the metal-metal interface, in addition to what is obtained by X-ray diffraction. The distribution of valence states exhibiting Al 3p and Ni 3d character is determined from the analysis of the Al Kbeta and Ni Lalpha emission bands respectively. The multilayer emission bands are compared to those of reference materials: pure Al and Ni metals as well as Al3Ni, Al3Ni2 and AlNi intermetallics. We provide evidence that, for temperatures up to 115C, Al3Ni is the major component of the multilayer.

Study of surface oxidation of iron foils by grazing incidence electron-induced X-ray emission spectroscopy

Surface oxidation of metallic iron was studied by grazing incidence electron-induced X-ray emission spectroscopy. We have shown the feasibility of the quantitative chemical-state analysis in the nanometer depth range on the basis of the results by Monte Carlo simulations in the grazing incidence setup. It is also found that the self-absorption effect is not negligible in the nanometer depth range.

4f−3demission spectra of the rare earths: An interpretation of the lines observed on both sides of the resonances

A general model using a multiconfiguration Dirac-Fock program with Breit interaction and QED corrections is established to calculate the $4f$ core-level transitions in the rare earths. This model is tested by comparing the calculated spectra to the experimental spectra of all the elements of the rare-earth series obtained by electron-induced x-ray emission spectroscopy. Agreement between the ab initio energies calculated in the free-ion model and the energies measured for the solid rare-earth spectra is of the order of $1\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, i.e., better than 0.2%. Each observed structure is interpreted. Variation of the intensity ratios of the various emissions along the lanthanide series is explained. These results prove the validity of our theoretical model to describe the $4f\text{\ensuremath{-}}3d$ transitions in the solids. This general model can be used to interpret the $4f$ core-level transitions observed from other spectroscopies.

Diffusion processes in NiTi/Si, NiTi/SiO 2 and NiTi/Si 3N 4 systems under annealing

We present a nanometric scale analysis of the NiTi/Si, NiTi/SiO 2 and NiTi/Si 3N 4 systems before and after annealing at 500 °C during 30 min, by secondary ion mass spectrometry and electron-induced X-ray emission spectroscopy. Before annealing, a few nanometers thick transition layer forms at the interface of each system. Under annealing, a NiSi 2 layer forms in the NiTi/Si system over several tens of nanometers, whereas a TiO x diffusion barrier builds up at the NiTi/SiO 2 interface. A few nanometers thick mix layer composed of TiSi 2, TiN and NiSi 2 forms at the NiTi/Si 3N 4 interface. This interface presents an intermediate reactivity under annealing between that of NiTi/Si and NiTi/SiO 2.

Study of thermal oxidation of LaSi x/Si(1 0 0) by grazing incidence electron-induced X-ray emission spectroscopy

A new X-ray emission spectroscopy (XES) apparatus for analyzing nondestructively the chemical states of the inner regions of layered materials was constructed. Using electron excitation at grazing incidence, it also enables the analyzing depth to be confined to the surfaces of the materials. The apparatus was employed to the study of oxidation of a La silicide layer formed on a Si substrate. By comparing the Si Kβ emissions with results by XPS analysis, it was concluded that the Si Kβ emission band of the oxidized sample at the excitation energy of 3.0 keV represents the Si 3p density of states (DOS) of a LaSiO mixed oxide. The variations of the spectra at increasing electron beam energies were compared with probing depths calculated by an empirical model. This result indicates that we can analyze the chemical states of a mixed oxide layer of one to two tens angstroms in thickness, and nondestructively probe into the depth of about several tens angstroms.

Depth profiling of P shallow implants in silicon by electron-induced X-ray emission spectroscopy

Electron-induced X-ray emission spectroscopy (EXES) combined with a semi-empirical electron scattering model, which describes the ionizations inside a material under electron irradiation, is used to determine the depth profile of shallow and ultra-shallow dopants in silicon. Two approaches are presented, depending on whether the shape of the profile is known or not. To test the method, X-ray intensities of implanted phosphorus atoms at various energies and doses in silicon are measured at a wide range of incident electron energies. From the experimental data combined with the model, the resulting profile parameters are determined. Comparison of secondary ion mass spectrometry and EXES associated with the electron scattering model shows that the proposed method is suitable for determining the shallow implant profiles with a depth resolution of one nanometer.

From diffusion processes to adherence properties in NiTi microactuators

Diffusion processes taking place at the NiTi/Si, NiTi/SiO 2 and NiTi/Si 3N 4 interfaces under annealing are studied in order to understand the adherence properties of these systems after annealing. Secondary ion mass spectrometry (SIMS), X-ray photoelectron spectroscopy (XPS) assisted by argon etching and electron-induced X-ray emission spectroscopy (EXES) are combined in order to analyse at a nanometric scale the interfaces before and after annealing. Considerable differences between diffusion processes in NiTi/Si and NiTi/SiO 2 are observed and can explain the difference between adherence properties of these systems after annealing. Among the three studied systems, NiTi/Si 3N 4 is shown to be the most suited for low voltage microactuation applications.

Spectroscopic studies of TM/Si and TM/SiO2 interfaces

We present a study on the interfacial behavior of TM/Si and TM/SiO2 systems (TM: Mo, NiTi) by electron-induced X-ray emission spectroscopy (EXES), X-ray photoelectron spectroscopy assisted by argon bombardment and secondary ion mass spectrometry (SIMS). A few nanometers thick amorphous interlayer forms without annealing at the interface of each system. We give an estimation of the composition of the interlayers, and of the spatial disposition of the compounds formed along the interfacial zone. We find a good agreement and complementarity between the analysis methods. Studied TM/SiO2 systems are shown to be more reactive than TM/Si systems. Moreover, the deposition rate of the metal could influence the reactivity between the metal and the substrate.

Physico-chemistry and morphology of silicon surface during the first stage of alumina deposition

The influence of temperature and polarization of the substrate during the in situ treatment under argon plasma of silicon is studied. This treatment is performed before microwave plasma enhanced chemical vapour deposition of alumina. The transitory period preceding the introduction of the aluminium precursor is simulated by a 1.5min oxygen plasma exposure of the substrate. The surface of the samples is analysed by electron-induced X-ray emission spectroscopy (EXES) to probe the physico-chemical environment around the silicon atoms, and by atomic force microscopy (AFM) to study the surface morphology. A thin superficial silica layer is evidenced, whose thickness is ranging from 0.8 to 1.8nm, depending mostly on the temperature and subsequently on the polarization. Upon treatment the morphology of the surface is changed and the roughness is increased. Furthermore, AFM observations of substrates exposed to the aluminum precursor during 2s are showing a columnar growth of the alumina film.

Physico-chemical environment of Al impurity atoms in amorphous silica

The physico-chemical environment around the aluminum impurity atoms in commercial Herasil silica is studied by electron-induced X-ray emission spectroscopy. Despite the low concentration of aluminum and the charging effect occurring upon electron irradiation , we have been able to characterize the environment of the Al atoms. We show that the Al atoms are in an octahedral environment , i. e. surrounded by 6 oxygen atoms. The presence of Al clusters , whose metallic character would make them candidates to be ultraviolet absorption centers , is ruled out.

Thickness determination of very thin SiO2 films on Si by electron-induced x-ray emission spectroscopy

Electron-induced x-ray emission spectroscopy (EXES) associate with a semi-empirical electron scattering model is used to determine thicknesses between 2 and 21 nm of SiO2 films on Si. The small charging effect occurring upon electron irradiation is taken into account by introducing a retarding potential in the model. The results are in very close agreement with those obtained by spectroscopic ellipsometry and x-ray reflectometry. It is demonstrated that the EXES with its model is a well-suited method for the quantitative analysis of thin insulating films with an uncertainty lower than 5%.

LEXES and SIMS as complementary techniques for full quantitative characterization of nanometer structures

A new technique, the Low energy Electron induced X-ray Emission Spectroscopy (LEXES) is used to determine dose of shallow dopants and film thicknesses; it is element selective and can resolve depth in the nanometer range. CAMECA has developed a specific instrumentation—called ‘Shallow Probe’—which adapts the LEXES to the requirements of the semiconductor industry in terms of sensitivity and reproducibility of dose and thickness measurements. The presented work reports performance of the shallow probe applied to a wide variety of dopants implanted into silicon wafers, nitrogen quantification in oxynitride barriers, as well as characterization of Si 1− x Ge x structures.

Chemical Interactions by Low-Energy Electron-Induced X-Ray Emission Spectroscopy, LEXES

The possibilities presented by low-energy electron-induced X-ray emission spectroscopy to study chemical interactions in solids are discussed. Examples of change observed for the emissions between core levels as a function of the chemical environment of the emitting atoms are given. By comparing the partial densities of the valence states associated to each type of atoms in the compound, it is shown that the strength of the metal-ligand interactions can be obtained. Information on the charge densities around each type of atoms can be deduced. Application to the study of the interactions at the atomic scale to solid–solid interfaces is presented.

Adhesion properties of aluminium-metallized/ammonia plasma-treated polypropylene: Spectroscopic analysis (XPS, EXES) of the aluminium/polypropylene interface

The purpose of this work was to investigate the influence of a low-pressure, low-frequency ammonia plasma treatment on the wettability of polypropylene (PP) thin films and its consequences on the adhesion properties of such treated films to thermally evaporated aluminium coatings. The wettability was determined by contact angle measurements while the adherence was evaluated by a U-Peel test especially suited to thin flexible substrates with thin metallic layers. Furthermore, an image processing system was used to measure the percentage of the peeled-off metal. Measurements carried out on NH3 plasma-treated PP films revealed a sharp increase in the wettability and in the adhesion properties for treatment times as short as 1s. Electron-induced X-ray emission spectroscopy and X-ray photoelectron spectroscopy showed the formation of new chemical bonds at Al/NH3 plasma-treated PP film interfaces. The new types of bonds have been characterized by well-defined chemical states (C–NHx, CO–NH, Al–N–C) in the N 1s (and C 1s) spectra. The interfacial complexes Al–N–C and Al–N–CO are formed by the NH3 plasma treatment which creates at the PP surface active sites (N(C–NHx) and N(CO–NH)) which react with the evaporated aluminium atoms. These interfacial bonds play an important role in the enhancement of the metal/polymer adhesion.

Study of the NiTi/SiO2 interface: analysis of the electronic distributions

We present a study of the interface between a NiTi film deposited by magnetron d.c. sputtering and a SiO2 film obtained by thermal oxidation. Electron-induced X-ray emission spectroscopy (EXES) is used to characterize the physicochemical environment around the Si atoms at the NiTi/SiO2 interface, and to obtain information about the interfacial reactivity. From analysis of the Si 3p valence states, the composition and the thickness of the interfacial zone before and after annealing are deduced. The composition of the passivation layer, located at the surface of the metallic film, is determined by EXES and X-ray Photoelectron Spectroscopy. Copyright © 2002 John Wiley & Sons, Ltd.