Primary Ion Beam Energy Research Articles

Signal oscillations in helium scattering by bismuth atoms in the low energy range

Low Energy Ion Scattering (LEIS) analysis of bismuth selenide (Bi2Se3), a strong 3D topological insulator, revealed oscillations of the detected signal in dependence on primary ion beam energy. Bismuth is a part of the group of elements where oscillatory behaviour was already noticed, such as gallium, indium, or lead. Generally, it is ascribed to quasi-resonant charge exchange processes between primary ion and target atom. Moreover, clear differences exist between data for target atoms in elemental form and for atoms in compound form. A study of Bi signal yields in different material forms was performed for primary He+ projectiles within the energy range from 0.50 to 6.00 keV. A foil of pure Bi, Bi2Se3, Bi2O3 and thin Bi films deposited on several substrates (SiO2, CuOx) by Molecular Beam Epitaxy were analysed. The energy shift in the position of oscillations was observed when the oxygen atoms were present at the surface and bonded to Bi atoms. A description of the Bi ion yield variation is provided to facilitate the quantification process in LEIS.

Bismuth, by high-sensitivity low energy ion scattering

Low energy ion scattering is an analytical technique with extreme surface sensitivity. It enables qualitative and quantitative elemental analysis of the outermost atomic layer. Straightforward quantification is possible by using well-defined reference samples, as the measured signal is related to known surface atomic concentration. Bi, like Pb, exhibits strong oscillatory behavior of backscattered ion yield when primary ion beam energy is varied. Here, we present the spectra of bismuth obtained by scattering of 4He+ ions in a wide range of energies (0.5–6.0 keV). These should cover a regularly used range of energies for He analysis and serve as standards or reference spectra for analysis of bismuth if the scattering angle is 145° or similar. For this purpose, high-purity foil cleaned by ion sputtering was used. The sensitivity of the instrument in use (high-sensitivity low energy ion scattering spectrometer) is defined by the 3 keV 4He+ spectrum of copper. The related atomic sensitivity and relative sensitivity factors are determined.

Determining the oxygen detection limit with magnetic sector dynamic secondary ion mass spectrometry (SIMS)

Dynamic SIMS is often used in evaluating the concentration of impurities in solids because of its high sensitivity and depth profiling capabilities with good depth resolution and high throughput. Continuous ion beam sputtering with a high-density primary beam provides high sensitivity and reduced background contribution from residual gases within the analytical chamber. Numerical simulations along with the data acquired in the real depth profiling experiment show a good agreement of the simple model, assuming that the surface uptake of the oxygen under Cs bombardment depends on the Cs surface retention concentration. In cases where high depth resolution is desired, requiring a low primary ion beam energy, a background subtraction option will help provide better detection limits. It is proposed to perform the background subtraction based on the difference between the continuous and interleaving sputtering modes of dynamic SIMS. The experiments performed on different instruments using different sputtering rate conditions (and different impact energies) show the power function dependence of oxygen detection limit on the reversed sputter rate variation or sputtering beam density. The proposed detection limit dependence curve can be used for analytical specifications benchmarking in most magnetic sector SIMS instruments.

Molecular depth profiling by wedged crater beveling.

Time-of-flight secondary ion mass spectrometry and atomic force microscopy are employed to characterize a wedge-shaped crater eroded by a 40-keV C(60)(+) cluster ion beam on an organic film of Irganox 1010 doped with Irganox 3114 delta layers. From an examination of the resulting surface, the information about depth resolution, topography, and erosion rate can be obtained as a function of crater depth for every depth in a single experiment. It is shown that when measurements are performed at liquid nitrogen temperature, a constant erosion rate and reduced bombardment induced surface roughness is observed. At room temperature, however, the erosion rate drops by ∼(1)/(3) during the removal of the 400 nm Irganox film and the roughness gradually increased to from 1 nm to ∼4 nm. From SIMS lateral images of the beveled crater and AFM topography results, depth resolution was further improved by employing glancing angles of incidence and lower primary ion beam energy. Sub-10 nm depth resolution was observed under the optimized conditions on a routine basis. In general, we show that the wedge-crater beveling is an important tool for elucidating the factors that are important for molecular depth profiling experiments.

State selective detection of sputtered Al neutrals by resonant laser ionization SNMS

It is important to optimize the resonance ionization efficiency of the sputtered particle by evaluating the internal energy of it. And also the dependence of the change of the internal energy of it on primary ion species and accelerating voltages was investigated. For this study, we developed proto-type resonance laser ionization SNMS instrument, which is a quadrupole SIMS apparatus combined with a wavelength tunable laser. The internal energy of the sputtered aluminum atoms, which has lowly lying excited state (112 cm −1) on the ground state, was monitored. As the results, the internal energy of the sputtered aluminum atoms was not influenced by the change of the surface work function and primary ion beam energy at all. On the contrary, the density on lowly lying excited state drastically increased due to the existence of the oxygen on aluminum surface.

Ultrashallow profiling using secondary ion mass spectrometry: Estimating junction depth error using mathematical deconvolution

As implant energies get lower and lower, significant errors can be present in junction depth measurements in secondary ion mass spectrometry (SIMS) ultrashallow depth profiling. Primary beam ion mixing is one of the main sources of errors leading to overestimation of junction depths in SIMS measurements. In this article, we systematically study the correlations between the implant profile trailing edge, junction depth and primary ion beam energy for low energy boron and arsenic implants. Using a mathematical deconvolution model proposed by Yang and Odom [Mater. Res. Soc. Symp. Proc. 669, J4–16 (2001)], we are able to estimate the error of the junction depth and consistently improve the accuracy of junction depth measurements using SIMS.

Characterization of interfaces in nanoscale semiconductor devices by optimization of depth resolution in SIMS depth profiling

Optimization of depth resolution in secondary ion mass spectrometry (SIMS) depth profiling has been carried out prior to characterization of different nanoscale semiconductor devices based on Si, GaAs and SiGe. The optimization of depth resolution was carried out by adjusting different experimental parameters like primary ion beam energy, ion mass, angle of incidence, sputter rate, etc. Such adjustments control the basic processes like recoil mixing, cascade mixing or penetration depth which in turn control the depth resolution Δ z. Certified reference material Ta 2O 5/Ta was used as standard to optimize the parameters and the actual experiments were performed keeping them in view. Various nanoscale semiconductor devices were characterized for their interfaces, e.g.: 1. InP/InGaAs/InP… quantum well (QW) structures. 2. Si x N y / n-GaAs structures with NH 3 plasma pre-treatment of GaAs for MIS devices. 3. Ga 2O 3(Gd 2O 3)/Si 0.74Ge 0.26/Si structures for MIS devices. 4. Ga 2O 3(Gd 2O 3)/GaAs structures for MOS devices. 5. Au/GaN/Si schottky diodes. 6. Ge/Si bilayer films for swift heavy ion beam induced interface-mixing experiment. It has been observed that Cs + primary ion beam with 10–11 keV energy gives Δ z ∼2–3 nm for most of the depth profiles while O 2 + with 7 keV energy can also give Δ z of similar order (∼2 nm) in some of the systems depending on ion–matrix interaction and secondary ion yield response.

The energy spectra of secondary ions sputtered from Si and SiGe by ultra-low-energy primary ions

Several SiGe alloys of various compositions were bombarded with ultra-low-energy primary ions, and the energy spectra of the resulting secondary ions were studied. We report here on the effects of alloy composition and primary ion beam energy on the spectra. It was found that the shape of the Si + and Ge + energy spectra are strongly dependent on the Ge fraction. The high energy tail on the spectra increases with Ge alloy percentage, whilst the peak position remains the same regardless of sample composition, primary beam energy or the mass of the secondary ion. It was also found that for low primary beam energies there is a narrowing of the atomic energy spectra so that atomic and molecular characteristics are indistinguishable.

Oxygen beam SIMS depth profiling of Si1−xGex layers: transient processes

AbstractCharacterization of shallow dopant profiles near surfaces and interfaces in Si1−xGex layers by secondary ion mass spectroscopy (SIMS) is a challenge in advanced Si‐based technologies. In standard SIMS, quantification with confidence is possible only in the dynamic steady state of the measurement after completing a transient period. Therefore, we analyse the transient processes during oxygen bombardment and sputtering of epitaxial Si1−xGex layers, which were grown by low‐pressure chemical vapour deposition (LPCVD) with different compositions (0 < x < 0.75). We show that a drop of the Ge+ secondary ion yield near the end of the transient period in epitaxial Si1−xGex layers extends this period in comparison with pure Si. We demonstrate that the drop is a function of layer composition and bombardment parameters, such as primary ion beam energy and erosion rate. We show that an interfacial transient period after crossing a Si/Si1−xGex interface can be neglected if the formation of the oxygen‐beam‐induced altered layer is completed within the Si cap layer before reaching the interface between the cap and the Si1−xGex layer. This allows reliable quantification of dopant spikes within a few nanometers near to interfaces. By means of computer modelling we describe secondary ion emission kinetics and simulate the dynamics of structural and compositional changes in the subsurface region of Si1−xGex alloys caused by interaction with oxygen beams. Experimental and theoretical time dependencies for secondary ion yields are in good accordance; the dependence of the Ge+ intensity drop on the Ge concentration is simulated and experimentally proved. Copyright © 2002 John Wiley & Sons, Ltd.

Ion Beam Deposited Gmr Materials

ABSTRACTIon beam sputter deposition (IBSD) techniques for deposition of giant magnetoresistance (GMR) films have been studied using an automated IBSD system designed and built in-house. We have studied the properties of Fe/Cr multilayers deposited using either Ar or Xe ions with the primary ion beam energy varying from 500 eV to 1100 eV. The films were characterized using transmission electron microscopy (TEM), atomic force microscopy (AFM), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), magnetization measurements, and magnetoresistance measurements. The maximum value of GMR obtained was 49% (measured at 10K). For the Cr spacer thickness layer chosen, this GMR ratio is larger than the values reported for polycrystalline Fe/Cr multilayers deposited by magnetron sputtering. In general, we have found that GMR ratios for the Fe/Cr multilayers increase with decreasing primary ion beam energy, and are greater for films deposited using Xe ions than for films deposited using Ar ions. We explain the observed effects on the basis of energy distributions of sputtered atoms and backscattered working gas atoms (neutrals). The energy distributions were calculated using TRIM (Transport of Ions in Matter) software based on the Monte Carlo method.

Primary beam energy dependence of properties in ion beam sputtered spin–valve films

Spin–valve films with the structure Ta/NiFe/FeCo/Cu(18–30 Å)/FeCo/FeMn–70 Å/Ta were deposited using a Veeco ion beam deposition (IBD) system, model IBD-350. The physical properties of these spin–valve films as a function of primary ion beam energy have been studied in a primary ion beam energy range of 600–1500 eV. Xe was used as the working gas. The optimal ion beam energy range for the best spin-valve performance has been found to be around 600 eV. Giant magnetoresistance (GMR) values of ΔR/R∼8% have been measured for the spin–valve films deposited in this energy range. A strong dependence on beam energy of magnetic properties for these spin–valve films has been observed in the energy range from 600 to 1500 eV. ΔR/R for spin–valve films with a Cu layer thickness of 22 Å decreases from 7.5% at 600 eV monotonically to 6.1% at 1500 eV with increasing ion beam energy. Interlayer coupling field increases from 20 Oe at 600 eV to 37 Oe at 1500 eV. Further reduction in the interlayer coupling field to 13 Oe and an increase in ΔR/R to 8% have been achieved by depositing the free layer at 1000 eV and the rest of the layers at 600 eV. These are consistent with the improvement in crystallographic orientation and crystallinity of these spin–valve films.

Thickness and energy dependence of secondary ion emissions from Langmuir–Blodgett films

Using Cd arachidate films formed on Ag and Si substrates, secondary ion intensities were investigated by TOF-SIMS. The intensities of [M+H] +, [M+Cd] + and Ag cationized ions from samples on the Ag and Si substrates were found to change as a function of LB film thickness, as well as the primary beam energy. The intensities of [M+H] + and [M+Cd] + were seen to be (1) the highest at a one-layer LB film, (2) to decrease as the LB film becomes thicker, (3) change slightly with the primary ion beam energy. On the other hand, the intensities of Ag cationized secondary ions were almost constant with the changes of LB thickness and the energy of the primary ion beam, after normalized by Ag + intensity. The results were discussed in terms of the energy transfer of the primary beam to the LB films, the property of the substrate materials, and the strength of chemical bondings.

Profiling Shallow As Implants with Low‐energy Cs Bombardment on a Modified Cameca IMS-4f

The inability to decouple primary ion beam energy and incidence angle in Cameca-type magnetic sector SIMS instruments makes profiling shallow As implants (⩽20 keV), using typical Cs+ bombardment conditions and negative secondary ion detection, problematic. A Cameca IMS-4f has been modified to lower the Cs+ primary beam impact energy by concomitant decreases in primary ion beam energy and sample potential. Evaluation of the instrument's performance after modification shows about a 35% improvement in depth resolution as defined by the decay length, λ, of a 20 keV As implant profile. This is accompanied by a decrease in useful yield, resulting from the lower sample potential, of about a factor of eight. Comparison of Cameca IMS-4f data from a 5 keV As implant with data obtained on a quadrupole-based instrument suggests that the Cameca's fixed incidence angle at low energy is the limiting factor to further improvements in depth resolution. Nevertheless, the ease and relatively low cost of modification makes this an attractive approach to increasing the range and flexibility of existing Cameca SIMS instruments. © 1997 John Wiley & Sons, Ltd.

Profiling Shallow As Implants with Low-energy Cs Bombardment on a Modified Cameca IMS-4f

The inability to decouple primary ion beam energy and incidence angle in Cameca-type magnetic sector SIMS instruments makes profiling shallow As implants (≥20 keV), using typical Cs + bombardment conditions and negative secondary ion detection, problematic. A Cameca IMS-4f has been modified to lower the Cs+ primary beam impact energy by concomitant decreases in primary ion beam energy and sample potential. Evaluation of the instrument's performance after modification shows about a 35% improvement in depth resolution as defined by the decay length, λ, of a 20 keV As implant profile. This is accompanied by a decrease in useful yield, resulting from the lower sample potential, of about a factor of eight. Comparison of Cameca IMSD-4f data from a 5 keV As implant with data obtained on a quadrupol-based instrument suggests that the Cameca's fixed incidence angle at low energy is the limiting factor to further improvements in depth resolution. Nevertheless, the ease and relatively low cost of modification makes this an attractive approach to increasing the range and flexibility of existing Cameca SIMS instruments.

Atomic force microscopy (AFM) of the topography of silicon surfaces exposed to ion beams

Reactive ion beams such as O2+and Cs+are used in Secondary Ion Mass Spectrometry (SIMS) to analyze solids for trace impurities. Primary beam properties such as energy, dose, and incidence angle can be systematically varied to optimize depth resolution versus sensitivity tradeoffs for a given SIMS depth profiling application. However, it is generally observed that the sputtering process causes surface roughening, typically represented by nanometer-sized features such as cones, pits, pyramids, and ripples. A roughened surface will degrade the depth resolution of the SIMS data. The purpose of this study is to examine the relationship of the roughness of the surface to the primary ion beam energy, dose, and incidence angle. AFM offers the ability to quantitatively probe this surface roughness. For the initial investigations, the sample chosen was <100> silicon, and the ion beam was O2+.Work to date by other researchers typically employed Scanning Tunneling Microscopy (STM) to probe the surface topography.

Ultra Shallow Junction Formation Using Diffusion from Silicides: I . Silicide Formation, Dopant Implantation and Depth Profiling

Shallow junctions have been fabricated in a silicide‐As‐diffusion‐source process using implantation of and As into thin silicides of cobalt, titanium, nickel, palladium, and platinum with emphasis on . Ge‐implantation was used in an attempt to amorphize the silicide prior to the boron introduction and thereby eliminate the possible channeling of boron in the polycrystalline silicide. Cross‐section transmission electron microscopy (TEM) shows that Ge implantation created a heavily damaged layer of 10 nm in the silicide, which was restored to a polycrystalline state after annealing at 900°C for 10 s. For shallow boron depth profiling using secondary ion mass spectroscopy (SIMS), careful selection of the primary ion beam energy and angle was necessary to minimize ion beam mixing and shadowing due to surface roughness. The boron profile in a thick , 300 nm, measured deeper than in a thin , 50 nm, demonstrating the effect of SIMS shadowing. The effect of Ge‐implantation on boron profiles was within the depth measurement error, indicating that no pronounced channeling had taken place in the silicide. Implant depths measured by SIMS agree well with those calculated by TRIM near the peak, but large deviations exist at the tail.

Incident ion energy effects on the secondary Rh + ion kinetic energy and azimuthal angle distributions from Rh{111}

The nature of the collision cascade initiated by a bombarding ion beam strongly depends upon the kinetic energy of the ion beam. As the incident ion beam energy is lowered, the changes in the collision cascade cause a reduction in the total ejected particle yield, the ion fraction of the ejected particles, and the fraction of ejected clusters. We present the azimuthal angle and kinetic energy distributions of secondary Rh + ions from a clean Rh{111} sample bombarded with 250 and 3000 eV Ar + ion beams. These distributions show features associated with the lattice atomic arrangement and a previously unreported secondary ionization mechanism which arises from damage to the electronic structure of the lattice. The azimuthal angle and kinetic energy distributions exhibit substantial changes at low primary ion beam energy due to the diminution of the collision cascade.

Primary ion beam energy effects on secondary ion emission from Ni(001)c(2 × 2)-CO: Classical dynamics calculations and sims

The variation of the SIMS spectra of Ni(001)c(2 × 2)-CO induced by bombardment of Ar + primary ions with kinetic energy between 300 and 1200 eV has been examined in detail. The purpose of the study is to examine the influence of primary ion energy on a number of experimental observables and to test the accuracy of classical dynamics calculations for neutral particles in predicting the experimental results for ejected ions. The calculations were performed using two extreme forms of the Ar + -substrate interaction potential to examine the sensitivity of the results to the parameters that need to be included in the model. We find excellent agreement between the NiCO +/Ni + ion yield ratio measured between 300–1200 eV Ar + ion energy and the computational results if the Molière form of the ion-substrate potential is used and if the calculated results are corrected by including an image force. The calculated angular distributions of the ejected particles also agree well with those observed experimentally. From the calculations we see that the extent of CO fragmentation relative to the amount of molecular CO ejection is roughly constant in the 300–1200 eV beam energy range with a slight increase seen at lower (~ 300 eV) energies. The implications of these results are discussed in terms of our ability to study the chemistry and structure of surfaces with SIMS.

Primary ion beam energy effects on secondary ion emission from Ni(001)c(2×2)-CO: Classical dynamics calculations and SIMS

Primary ion beam energy effects on secondary ion emission from Ni(001)c(2×2)-CO: Classical dynamics calculations and SIMS

Oscillatory scattered ion yields from nonconductive materials

Oscillatory scattered ion yields have been measured for He + scattering from Pb and Bi in nonconductive compounds using a flood of low energy electrons for surface charge neutralization. Surface charge equilibration is sufficiently rapid to allow direct recording of the scattered ion yield curves at scan rates in which the primary ion beam energy and current are increasing at rates of 25 eV/s and several nA/s, respectively.