Low Energy Secondary Ion Mass Research Articles

Probing a chemical state during ultra low impact energy secondary ion mass spectrometry depth profiling

Ultra low impact energy SIMS allows probing a chemical state and provides qualitative information about strong covalent bonds.

An origin behind Rashba spin splitting within inverted doped sGe heterostructures

In this paper, we demonstrate why cubic Rashba spin splitting is observed within inverted doped strained germanium (sGe) hetrostructures. Magnetotransport measurements showed beating within the SdH oscillation, with fast Fourier analysis revealing cubic Rashba spin splitting to be present. A cubic Rashba coefficient of β=7.97×10−29 eVm3 and a spin-splitting energy of Δ=1.17 meV were determined. The source of the cubic Rashba spin splitting was identified from a combination of ultra low energy secondary ion mass spectrometry analysis and subsequent band structure modelling using Nextnano3. Ultra-low energy secondary ion mass spectrometry revealed an unintentional, highly B doped near surface region accounted for structure inversion asymmetry, whereas subsequent band structure modelling using Nextnano3 demonstrates how this asymmetric B doping generates structural inversion asymmetry within the sGe QW structure and cubic Rashba spin splitting realized.

An O2+ probe energy study for boron quantification in Si1−xGex (0 ≤ x ≤ 1) using secondary ion mass spectrometry

With SiGe device technology still developing, a concomitant effort to develop accurate dopant quantification over the entire Si1−xGex (0≤x≤1) range using ultra low energy secondary ion mass spectrometry is required. Here we present a comprehensive secondary ion mass spectrometry study of the B11+ yield behaviour from a range of Si1−xGex (0≤x≤1) reference samples implanted with the same B dose. Depth profiling conditions include near normal incidence O2+ over an energy range of 0.2−1.0 keV. Quantification of the B concentration for each profile was achieved by determining the individual profile sensitivity factor. Only for EP≤300 eVwas the variation in sensitivity factor with Ge well described by a linear dependence over the whole Si1−xGex (0≤x≤1) matrix.

Low energy SIMS characterization of passive oxide films formed on a low-nickel stainless steel in alkaline media

Low-energy secondary ion mass spectrometry (SIMS) was used to study the oxide films formed on a low-nickel austenitic stainless steel (SS), potential replacement to conventional AISI 304 SS in reinforced concrete structures (RCS) that are subjected to aggressive environments. The effect of carbonation and the presence of chloride ions were studied. The oxide films formed a chemically gradated bi-layer structure with an outer layer predominately constituted by iron oxides and an inner layer enriched in chromium oxides. Chloride ions were not found in the oxide film but did have an effect on film structure and thickness.

ChemInform Abstract: Low Energy Ion Scattering and Secondary Ion Mass Spectrometry

AbstractReview: 160 refs.

High-quality Ge/Si0.4Ge0.6 multiple quantum wells for photonic applications: growth by reduced pressure chemical vapour deposition and structural characteristics

Strain-symmetrized Ge/SiGe multiple quantum wells have been grown on a thin (2.1 µm) relaxed Si0.2Ge0.8/Ge/Si(1 0 0) virtual substrate (VS) by reduced pressure chemical vapour deposition. Such structures are of interest in optoelectronic applications for which the structural integrity of the quantum well layers, after processing, is critical. The layer composition, thickness and interface quality have been studied for wafers both as-grown and after annealing between 550 and 700 °C. Transmission electron microscopy indicated precise thickness control of ±0.1 nm and sharp abruptness between the Ge QWs and SiGe barrier layers. A smooth surface was observed, with an average rms roughness of 1.5 ± 0.1 nm determined by atomic force microscopy. High-resolution x-ray diffraction (HR-XRD) indicated that both the QWs and barriers were fully strained compared with the relaxed VS. The thermal stability of the epilayers was investigated both by ultra low energy secondary ion mass spectroscopy of post-growth annealed layers and by in situ annealing in a high temperature HR-XRD stage. No obvious interdiffusion and strain relaxation was observed provided the annealing temperature was below 600 °C, but significant atomic rearrangement was evident for greater thermal budgets, thereby setting an upper processing temperature for this type of structure.

Influence of Si precursor on Ge segregation during ultrathin Si reduced pressure chemical vapor deposition on Ge

This letter reports on the Ge segregation mechanism occurring during ultrathin (few monolayers) Si cap growth on Ge substrates by reduced pressure chemical vapor deposition. Thanks to extremely low energy secondary ion mass spectroscopy, we have highlighted that Ge segregation in Si-covered Ge does not depend on the growth temperature (in the 350–500 °C range) or on the carrier gas (H2,N2) used during Si growth. Solely the Si precursor used, i.e., the Si incorporation mechanism, impacts the Ge segregation rate. A multi-Ge segregation model is proposed, considering probabilities of sites exchanges in between all Si–Ge stacked atoms within the first nanometer of the layers.

Low energy secondary ion mass spectrometry with sub-keV O2+ beams at glancing incidence

The ever increasing interest in surface analysis techniques with excellent depth resolution, great detection sensitivity, and good throughput has been a driving force for development of dynamic secondary ion mass spectrometry using low energy primary beams. This work investigated sputtering erosion of Si and emission of secondary ions from Si bombarded by sub-keV O2+ beams at glancing incidence. It was demonstrated that surface roughening remained minimal for 250 and 500eV O2+ beams at an angle of incidence above 80° but developed rapidly at angles between 60° and 80°. The depth resolution for B and Ge appeared very different at the glancing incidence and changed dramatically in opposite ways as the angle of incidence decreased. The difference in the depth resolution was explained by the different diffusion/segregation behavior between B and Ge during O2+ bombardment. In general, the use of sub-keV O2+ beams at the glancing incidence (above 80°) favored a thinner altered layer, a short surface transient, a minimal apparent shift in depth profiles, a better depth resolution (not for B in Si), a good sputter rate, but a poor yield of the positive secondary ions. To address the issues with the low ion yield, we identified optimal cluster ions for common dopant such as boron and nitrogen. Good sensitivity was achieved for analyses of boron in Si by detecting BO2− as the characteristic secondary ion. A parallel study published elsewhere suggested SiN− as an ideal candidate for detection of nitrogen in ultrathin oxynitride [Z. X. Jiang et al., Surf. Interface Anal. (in press)]. For analyses of thin SiGe films in Si at glancing incidence, detection of Ge+ provided fairly good sensitivity. Applications of an O2+ beam at 250eV 83° for analyses of shallow boron implant demonstrated superior accuracy in the measured near-surface boron distribution. Also the characterization of thin SiGe films exhibited excellent depth resolving power for Ge in Si although the ion yield of Ge+ was low.

Application of r.f. plasma ultrashallow nitrogen ion implantation for pedestal oxynitride layer formation

The study examines the possibility of fabrication of pedestal oxynitride layers for high-k gate stacks by means of nitrogen implantation from r.f. plasma alone or followed immediately by the plasma oxidation process. The obtained layers were characterized by means of ellipsometry, X-ray photoelectron spectroscopy (XPS) and ultra low energy secondary ion mass spectrometry (ULE-SIMS). The results of electrical characterization of NMOS Al-gate test structures fabricated with the investigated layers used as a gate dielectric are also discussed. Presented results seem to be very promising and presented methods allow to form ultrathin pedestal oxynitride layers with good properties (e.g. breakdown behavior) and we believe that presented method—ultrashallow nitrogen plasma implantation with plasma oxidation may be seriously considered for future VLSI technologies.

Low energy electron-excited nanoscale luminescence spectroscopy studies of intrinsic defects in HfO2 and SiO2–HfO2–SiO2–Si stacks

Low energy electron-excited nanoscale (LEEN) luminescence spectroscopy and secondary ion mass spectrometry have been used to probe the defect states and chemical composition in as-deposited relatively thick (∼100nm) HfO2 films and in SiO2∕HfO2∕SiO2∕Si (5nm∕15nm∕5nm) heterojunction stacks grown by plasma enhanced chemical vapor deposition including as well changes in bonding and defects after high temperature (900°C) annealing. LEEN measurements of optical transitions in the thicker HfO2 films are assigned to defect-associated radiative transitions centered at approximately 2.7, 3.4, 4.2 and 5.5eV. These spectra exhibited significant changes in as-deposited films (300°C) and after a 900°C anneal in forming gas (N2∕H2). Qualitative differences in LEEN spectra of stacked films are correlated with (i) formation of Hf silicate during deposition of the HfO2 film onto the SiO2 substrates in the as-deposited films, and (ii) a chemical phase separation of these Hf silicates into a heterogeneous mixture SiO2 and HfO2 nanocrystallites after the 900°C anneal.

Determination of the surface segregation ratio of P in Si(1 0 0) during solid-source molecular beam epitaxial growth

The surface segregation ratio as a function of growth temperature of a dopant is a fundamental property that must be known for that dopant to be used in device applications. Using low energy secondary ion mass spectrometry, a precise determination of the segregation ratio of P in Si(1 0 0) in the temperature interval from 380 °C to 650 °C has been made. The values of the surface segregation ratios determined are substantially less than previously reported. It has been observed that the source of the P dopant as well as the temperature during growth influences the segregation of P. Using a GaP decomposition source, the deposited P has been shown to be fully electrically active in the whole growth temperature interval by measurement of the carrier concentration profiles using spreading resistance profiling.

Thin epitaxial Si films as a passivation method for Ge(1 0 0): Influence of deposition temperature on Ge surface segregation and the high-k/Ge interface quality

Epitaxial fully strained Si films are known to form an effective passivation of the Ge(1 0 0) surface. However, we show using low-energy secondary ion mass spectrometry (SIMS) that considerable Ge surface segregation occurs for Si films grown from SiH 4 at 500 °C. In this study, we develop an alternative deposition process at 350 °C using Si 3H 8 which significantly decreases the Ge peak at the Si surface. We attribute this strong reduction mainly to the fact that growth at 350 °C from trisilane proceeds below the Si–H desorption temperature. Charge pumping measurements on n-type Ge devices show a reduction by approximately a factor three in the high-k/substrate interface trap density for the samples with 350 °C Si passivation, compared to those using a Si passivation deposited at 500 °C.

RF-plasma source qualification and compositional characterisation of GaNAs superlattices using SIMS

The potential of GaAs-based dilute nitride alloys, such as GaNAs and GaInNAs, for use in long-wavelength telecommunication applications has led to intensive research into their growth and physical properties. In order to produce high quality GaNAs-based devices it is essential that the material and growth source is fully characterised. In this paper, we present a study of MBE grown dilute GaN x As 1− x ( x ≈ 0.01) structures grown using two different nitrogen RF-plasma sources. The samples have been characterised using low energy secondary ion mass spectrometry (SIMS), whilst the attributes of the RF-plasma sources have also been fully assessed with this analytical technique. The study shows that low energy SIMS is essential in order to fully characterise the structure and purity of the GaNAs superlattices grown and can also assist in qualification of the RF-plasma source used for growth.

Ultra low energy SIMS depth profiling of sub-1.5 nm silicon oxynitride films

Silicon oxynitride is one of the most researched silicon-based dielectric currently used in IC fabrication. Properties of the oxynitride films can be modified to achieve desirable functions by specific engineering of thickness and stoichiometry. In the case of gate stacks, considerable progress has been made in optimising the properties of oxynitride dielectrics in order to reduce boron penetration and dielectric leakage with respect to pure SiO 2, allowing sub-2 nm dielectrics. In this study ultra low energy (ULE) secondary ion mass spectrometry (SIMS) has been used to assess a range of ultra thin (<1.5 nm) silicon oxynitride films containing varied amounts of nitrogen (up to 18 at.%) and the results have been compared with shallow angle surface X-ray photoelectron spectroscopy (XPS). Despite the limited number of atomic layers available for probing, this investigation indicates that both techniques are capable of extracting useful and reliable chemical and physical information from these oxynitride films. Critical parameters such as stoichiometry and film thickness have been evaluated, whilst consistency between the two techniques is also addressed.

Application of ultra low energy (ULE) SIMS to emerging diamond technologies

AbstractWe report ultra low energy secondary ion mass spectrometry (ULE‐SIMS) analysis of a single crystal boron delta–doped diamond layer with normal incidence O2+ beam at incident energies of 300 eV, 500 eV and 1 keV. The diamond layer was epitaxially grown using a chemical vapor deposition (CVD) method on a synthetic single crystal diamond substrate grown using a high‐temperature, high‐pressure technique. The good crystalline quality of the homoepitaxal boron delta–doped layer has allowed the study of the ULE‐SIMS measurement process.In contrast to the case of silicon, the transient effects on the sputter yield are very weak: we obtained a differential shift of 0.6 nm/keV—smaller than the depth measurement uncertainty (i.e. the initial erosion rate is marginally slower).The boron ion yield is independent of the incident energy and the decay length is almost so (3.0, 3.1 and 3.5 nm for 300 eV, 500 eV and 1 keV respectively), reflecting a good depth resolution possibly limited by sample structure.The erosion rate is energy independent over a wide range, but carbon ion yields are both energy and boron concentration dependent for high boron concentrations, proportional to (YB+)0.85. For this reason, care is needed with the boron quantification when the boron content is high. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Quantitative analysis of the Ge concentration in a SiGe quantum well: comparison of low-energy RBS and SIMS measurements

The germanium concentration and the position and thickness of the quantum well in molecular beam epitaxy (MBE)-grown SiGe were quantitatively analyzed via low-energy Rutherford backscattering (RBS) and secondary ion mass spectrometry (SIMS). In these samples, the concentrations of Si and Ge were assumed to be constant, except for the quantum well, where the germanium concentration was lower. The thickness of the analyzed quantum well was about 12 nm and it was situated at a depth of about 60 nm below the surface. A dip showed up in the RBS spectra due to the lower germanium concentration in the quantum well, and this was evaluated. Good depth resolution was required in order to obtain quantitative results, and this was obtained by choosing a primary energy of 500 keV and a tilt angle of 51 degrees with respect to the surface normal. Quantitative information was deduced from the raw data by comparing it with SIMNRA simulated spectra. The SIMS measurements were performed with oxygen primary ions. Given the response function of the SIMS instrument (the SIMS depth profile of the germanium delta (delta) layer), and using the forward convolution (point-to-point convolution) model, it is possible to determine the germanium concentration and the thickness of the analyzed quantum well from the raw SIMS data. The aim of this work was to compare the results obtained via RBS and SIMS and to show their potential for use in the semiconductor and microelectronics industry. The detection of trace elements (here the doping element antimony) that could not be evaluated with RBS in low-energy mode is also demonstrated using SIMS instead.

Characterization of nitrogen distribution in HfO2 with low energy secondary ion mass spectrometry

Accurate characterization of the nitrogen distribution in a thin HfO2 film is important for process development on the nitridation of HfO2. Low energy secondary ion mass spectrometry (LESIMS) is potentially the technique of choice, thanks to the combined strength of high depth resolution and high detection sensitivity. By using a 250 eV, 60° O2+ primary beam and detecting NO−30 and O2−32 secondary ions, SIMS analysis was capable of profiling nitrogen in HfO2 with very short surface transient and minimal matrix effect across the HfO2–Si interface. This particular condition also exhibited desirable low yield of Si− secondary ions, i.e., minimal contribution of Si−30 to NO−30 through mass interference. Applications of this technique revealed incorporation of nitrogen at high levels in the top part of a HfO2 film by the modified magnetic type (MMT) plasma nitridation. The data also suggested loss of nitrogen near the top of an HfO2 film but no depletion across the interface between HfO2 and the interfacial as a result of the post nitridation anneal in O2.

Low energy RBS and SIMS analysis of the SiGe quantum well

The Ge concentration in a MBE grown SiGe and the depth of the quantum well has been quantitatively analysed by means of low energy Rutherford backscattering (RBS) and secondary ion mass spectrometry (SIMS). The concentrations of Si and Ge were supposed to be constant, except for the quantum well, where the nominal germanium concentration was at 5%. Quantitative information was deduced out of raw data by comparison to SIMNRA simulated spectra. With the knowledge of the response function of the SIMS instrument (germanium delta (δ) layer) and using the model of forward convolution (point to point convolution) it is possible to determine the germanium concentration and the thickness of the analysed quantum well out of raw SIMS data.

Influence of regrowth conditions on the hole mobility in strained Ge heterostructures produced by hybrid epitaxy

Strained Ge p-channel heterostructures have been produced using a hybrid-epitaxy method, which allows the advantages offered by different growth techniques to be exploited. Chemical vapor deposition of thick strain-tuned virtual substrates has been combined with growth of the active layers by solid-source molecular beam epitaxy. This paper discusses optimization of the regrowth conditions, to achieve a high hole mobility, and correlates structural characterization with electrical measurements. Initial ex situ chemical cleaning of the virtual substrate was found to be essential for successful regrowth. Structural analysis, using cross-sectional transmission electron microscopy and atomic force microscopy, showed that the regrowth temperature significantly affects the growth mode of the active layers and that planar growth was only achieved below 400°C. Samples with Ge channels from 8to30nm thick were analyzed with plan view transmission electron microscopy to study the formation of misfit dislocations and estimate the degree of relaxation—two effects detrimental to hole transport properties. For intermediate thickness layers, postgrowth annealing at 650°C was found to significantly improve the hole mobility, by eliminating point defects but not leading to substantial relaxation. As a result, the mobility was found to almost double at room temperature and increase fourfold at 10K. The level of diffusion and interface integrity, for both the as-grown and annealed structures, has been investigated using low energy secondary ion mass spectrometry.

Secondary ion mass spectrometry characterization of source/drain junctions for strained silicon channel metal–oxide–semiconductor field-effect transistors

As complementary metal–oxide–semiconductor (CMOS) devices approach the sub-100-nm dimensions in accordance with Moore’s Law, several major technical barriers exist with the formation of ultrashallow junctions. Strained silicon CMOS devices have the advantages of higher carrier mobility and high current drive. The use of silicon germanium substrates for strain in the silicon channel presents many challenges for CMOS integration including maintaining the channel strain and effect on shallow source/drain (SD) junctions. Low energy secondary ion mass spectrometry (SIMS) has been used to study boron and arsenic diffusion behavior in strained silicon and in SiGe. In addition, diffusion of germanium from the relaxed SiGe into the strained silicon layer will be discussed in relationship with SD implant and annealing. SIMS experimental results will also be compared to theoretical simulation results.