Ultra Low Energy Secondary Ion Research Articles

Strain Tuning in Graded SiGe on Insulator: Interplay between Local Concentration and Nonmonotonic Lattice Evolution after Ge Condensation

Germanium condensation has proven to be a reliable route for obtaining smoothly graded composition SiGe layers with good reproducibility and reduced defect density. The process is known as a crucial tool to induce well-defined strain on Si or SiGe layers with potential use in semiconductor devices. In this work, we show that starting from a low concentration Si0.92Ge0.08 layer grown on top of a crystalline Si(001) on SOI substrates, we can reach desirable concentration with a nonmonotonic interplay on in-plane and out-of-plane strain. The Ge concentration is evaluated by a combination of ultralow energy secondary ion mass spectroscopy (ULE-SIMS) and synchrotron X-ray measurements (diffraction and reflectivity). After the evaluation of Ge content, the strain-sensitive process of rolling up tubes from the flat layers is used and combined with X-ray diffraction to provide a concise scenario of the strain evolution along an in-growth oxidation series, pointing out the conditions that maximize strain, as well as its fading, as the Ge content rises.

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.

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.

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.

Calibration of boron concentration in CVD single crystal diamond combining ultralow energy secondary ions mass spectrometry and high resolution X-ray diffraction

In this work, we combine ultralow energy secondary ion mass spectrometry (uleSIMS) and high resolution X-ray diffraction (HRXRD) for the analysis of boron doped single crystal diamond. CVD layers of nominal boron concentrations 1.3 · 10 21 At/cm 3, 2.0 · 10 21 At/cm 3, 6.9 · 10 21 At/cm 3 and 3.8 · 10 22 At/cm 3 have been characterized by uleSIMS at 1 keV, 500 eV and 300 eV using normal incidence O 2 + and by HRXRD. We show that the enhancement of 12C + signal as a function of boron concentration observed in uleSIMS analysis of heavily doped layers compared to intrinsic diamond is due to a change in the ionization probability for carbon rather than to a change in erosion rate or post-ionization in the gas phase. For this reason, calibrating the boron concentration using a relative sensitivity factor (RSF) derived from an implanted reference material, which will naturally have a different ionization probability for carbon, is not accurate and a calibration curve needs to be obtained from an independent analysis technique such as nuclear reaction analysis (NRA). Simulation and measurement of HRXRD 113 asymmetric and 004 symmetric reflections have confirmed that the layers grew coherently to the substrate. The peak strain in the samples has been obtained from the HRXRD patterns by comparison between simulation and experiments, being ∼ 0.41 · 10 − 3 , ∼ 0.43 · 10 − 3 and ∼ 1.30 · 10 − 3 for the first three samples. The peaks in the experimental profiles are broad compared to the simulations of uniform layers, which is explained by the graded composition of the layers, shown by the uleSIMS profiles.

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 & Sons, Ltd.

Determination of the erosion rate in the transient region of an ultralow energy secondary ion mass spectrometry profile using medium energy ion scattering

A method which allows the erosion rate to be established from the earliest stages of an ultralow energy secondary ion mass spectrometry (ule-SIMS) profile is described. Using the technique of medium energy ion scattering (MEIS), this method provides data which enables an accurate depth scale to be established from a depth of a few nanometers onwards. The method is applicable for a thin amorphous layer at the surface or a heavy element marker in the near-surface region, and enables the erosion rate as a function of SIMS ion dose to be established for particular bombardment conditions. The erosion rate obtained is used to calibrate the depth and intensity scales of implant profile measured using ule-SIMS and to interpret the near-surface distribution. In this article we demonstrate this methodology using a Ge preamorphized Si(001) surface with a 1 keV boron implant. The altered layer formed by the primary SIMS O2+ incorporation and the redistribution of Ge in the samples used, are also described. Based on the Ge redistribution results, the possibility of adapting this method for determining erosion rates in crystalline silicon and silicon surface recession measurements, is also discussed.

Quantitative determination of dopant dose in shallow implants using the low energy x-ray emission spectroscopy technique

A technique using low energy x-ray emission spectroscopy (LEXES) is used to determine the dose of shallow implanted dopants. This technique is nondestructive and dopant selective. This technique can provide absolute dose values. CAMECA has developed specific instrumentation called the shallow probe which adapts the LEXES technique to the requirements of the semiconductor industry in terms of sensitivity and reproducibility of dose measurements. This work reports the performance of the shallow probe applied to a wide variety of boron, phosphorus, and arsenic implants into silicon wafers. Measured doses are compared to both ultralow energy secondary ion mass spectrometry and implanter tool values.

Ultra low energy SIMS, XTEM and X-ray diffraction methods for the characterization of a MBE grown short period (SinGem)16 superlattices

The structural parameters (the layer thickness, interface roughness) for a 16-period (SinGem) superlattice grown by solid source molecular beam epitaxy (MBE) on Si(001) substrates were determined by high-resolution X-ray diffraction (HRXRD), X-ray reflectivity (XRR) and cross-sectional transmission electron microscopy (XTEM). The results were compared to the data obtained by ultra-low energy secondary ion mass spectrometry (ULE SIMS) method, using a 280 eV O2+ probe at 20° to normal incidence. The differences in layer thickness values obtained from HRXRD, XRR and XTEM, ULE SIMS data, are explained in terms of significant microroughness at both the Si/Ge and Ge/Si interfaces. The n and m values were also determined by X-ray diffraction methods.

Transient phenomena and impurity relocation in SIMS depth profiling using oxygen bombardment: pursuing the physics to interpret the data

High detection sensitivity in bulk analysis or depth profiling by secondary ion mass spectrometry (SIMS) can only be achieved, for positively charged ions, if the nearsurface regions of the sputter eroded sample are fully oxidized. Using oxygen primary ions, a stationary oxidation state is established after some time of bombardment during which period the sputtering yield decreases and the ionization probability increases. The physical and chemical processes occurring during the transient period are reviewed with emphasis on the results for impurity analysis in silicon, i.e. the matrix material that has been studied most thoroughly in the past. The transient decrease in sputtering yield gives rise to a depth scale offset and an associated apparent shift of impurity profiles towards the surface. The effect is largest at normal beam incidence, ca. 1 nm /keV (O + 2 ), in which case silicon is fully oxidized. The transition depth, i.e. the depth sputtered before achieving a stable ion yield is about twice as large and increases as the impact angle is turned away from normal. The shift and the depth scale offset can be measured safely using thin (delta) layers of isotopically pure tracers, for example 30 Si in 28 Si. Boron delta layers can serve as secondary standards because this impurity behaves almost the same as the host silicon atoms. The profile shift observed with other common dopants may contain contributions due to unidirectional relocation, often driven by segregation away from the surface. At O + 2 energies below about 0.7 keV the transition depths fall below the thickness of typical native oxides, so that the transient changes in sputtering yield and ionization probability can disappear. The transient phenomena may be described by a simple sputtering-oxidation model that connects the depth scale offset to other observable parameters like the initial and final sputtering yield, the transition fluence and the oxide thickness.