Ion Beam Analysis Methods Research Articles

Depth Profiling by Ion Beams Analysis Techniques for the Characterization of Interdiffusion in Multilayered Au-Al Systems

Ion beam analysis (IBA) methods were used for the characterization of interdiffusion in thin Au-Al multilayered systems. Conventional RBS with a high depth resolution at the specimen surface and at the interfaces (e.g. 14 nm in the depth of 255 nm) was used for gold depth profiling. In contrast to gold, the depth resolution of the aluminium distributions is limited even when the signals are in a background-free region of the spectrum. In addition, the aluminium depth profiles were measured using the resonant nuclear reaction 27 Al(p, γ) 28 Si at 992 keV with a high depth resolution of 5 nm at the specimen surface. High-energy backscattering spectroscopy with 7.6 MeV 4 He ions was used to investigate light element contaminantions (depth resolved), e.g. oxygen, at the specimen surface, the Ao-Al interfaces and at the Au/C interface.

Determination of the hydrogen sensitivity and depth resolution of medium-energy, time-of-flight, forward-recoil spectrometry

Medium energy time-of-flight forward recoil spectrometry has been developed recently as a complement to conventional ion beam analysis methods such as nuclear reaction analysis and elastic recoil detection. Here we report measurements of the minimum detectable surface concentration and near surface depth resolution for hydrogen by forward recoil spectrometry using a number of beam species and energies. The primary physical limitations encountered in these measurements are identified and discussed. Using an 810 keV Ar 3+ beam, H on a carbon substrate can, in principle, be detected at areal densities as low as 1 × 10 13 H/cm 2. A 540 keV O 2+ beam has been found to be a suitable choice for depth profiling of H in Si achieving a resolution of approximately 6 nm near the surface. Examples are given which demonstrate the utility of the technique for hydrogen profiling.

In situ analysis of thin film deposition process using time of flight (TOF) ion beam analysis methods

The use of non-destructive, in situ methods for the characterization of thin film growth phenomena is the key both to obtaining a better understanding of thin film growth processes and to the development of more reliable deposition procedures, especially for complex layered structures involving multi-phase materials. However, surface characterization methods that utilize either electrons (e.g. AES or XPS) or low energy ions (SIMS) for the signal require an ultra-high vacuum (UHV) environment and utilize instrumentation which obstructs line of sight access to the substrate. These methods are therefore incompatible with line of sight deposition methods and thin film deposition processes which introduce gas, either as an intrinsic part of the deposition procedure or in order to produce the desired composition. We have developed a means of differentially pumping both the ion beam source and detectors of a TOF ion beam surface analysis spectrometer that does not interfere with the deposition process and permits compositional and structural analysis of the growing film in the present system, at pressures up to several mTorr. Higher pressures are feasible with modified source-detector geometry. In order to quantify the sensitivity of Ion Scattering Spectroscopy (ISS) and Direct Recoil Spectroscopy (DRS), we have measured the signal intensity for stabilized clean metals in a variety of gas environments as a function of the ambient gas species and pressure, and ion beam species and kinetic energy. The results are interpreted in terms of collision cross sections which are compared with known gas phase scattering data and provide an apriori basis for the evaluation of time-of-flight ion scattering and recoil spectroscopies (ToF-ISARS) for various industrial processing environments which involve both inert and reactive gases. The cross section data for primary ion-gas molecule and recoiled atom-gas molecule interactions are also provided, from which the maximum operating pressure in any experimental configuration can be obtained.

Roughness determination of plasma-modified surface layers with atomic force microscopy

Graphite surfaces exposed to the deuterium plasma in the TEXTOR tokamak were characterized in detail by means of scanning probe microscopy, ion beam analysis and colorimetry methods. The aim is to study the composition and structure of thin layer deposits formed on surfaces subjected to the tokamak plasma. The surface roughness was measured and parametrized in terms of fractal dimension and scaling constant. Several different methods for the fractal analysis of plasma-exposed surfaces have been critically evaluated. The main emphasis of this paper is on the correlation between surface roughness (fractal parameters), the amount of deposited atoms and the layer thickness.

Theoretical approximations for depth resolution calculations in IBA methods

One of the most important parameters in depth profiling using ion beam analysis (IBA) is depth resolution. Theoretical approximations are presented that lead to relatively fast calculations for the following contributions: energy and angular spread of the beam; geometric spread caused by finite beam size and detector's solid angle; energy straggling and multiple scattering in the sample; effect of the absorber foil; energy resolution of the detection method and resonance width in resonance methods. Multilayered multi-elemental targets are also considered and the different contributions are composed statistically by a method that takes into account the peculiar shapes of the corresponding probability densities. A computer code, DEPTH, successfully demonstrated the speed and reliability of the calculations.

A highly sensitive method for rare-earth element analysis using ionoluminescence combined with PIXE

In Ion Beam Analysis (IBA), a beam of energetic particles (a few MeV/amu) is normally employed. Particle induced X-ray emission (PIXE) is one of the well-established IBA methods for accurate element analysis with the capabilities of a low detection limits and the absolute quantification for many elements. Nevertheless, for intermediate elements, including rare-earth elements (REEs), the experimental detection limits of PIXE in analysis of some geological materials are too high. The IonoLuminescence (IL) method is a sensitive analytical method for REE analysis based on the facts that the luminescence emission lines for REEs are characterised by narrow peak, stable position and high yields in a variety of minerals. Thus, similar to PhotoLuminescence (PL) and CathodoLuminescence (CL), the IL can be employed as a sensitive method for REE study. In the present work, synthetic minerals such as zircon and calcite separately doped various single REE were studied by combined IL and PIXE. An apatite standard sample containing several REEs was also investigated. The IL detection limits of most REE elements involved were estimated much lower than those offered by PIXE.

Hydrogen diffusion in a-Si:H stimulated by intense illumination.

Hydrogenated amorphous silicon (a-Si:H) films have been thermally annealed at temperatures in the range 220-270 °C for 24-48 h either under intense visible light illumination (4-16 W/cm2) or in the dark. After each annealing, the hydrogen-concentration profile was measured with Rutherford-backscattering-spectrometry and elastic-recoil-detection-analysis ion-beam analysis methods. A model is proposed which shows that, in good agreement with our results, the hydrogen-diffusion constant DH is proportional to the power of illumination and also proportional to the loosely bonded hydrogen concentration. Other consequences of the model are discussed. © 1994 The American Physical Society.

IBA study of the growth mechanisms of very thin silicon oxide films: the effect of wafer cleaning

The growth mechanisms of very thin silicon oxide films formed during rapid thermal oxidation were studied using ion beam analysis and 18O isotopic tracing methods. In this paper we report on the effects of different cleaning procedures of silicon wafers prior to oxidation in dry oxygen (16O2 followed by 18O2) on the growth mechanisms and kinetics. Typical oxide thicknesses ranging from 0.2 to 10 nm were studied. The 18O and 16O isotopic profiles were determined by ion beam analysis methods, namely: the 18O(p, α)15N narrow resonance at 151 keV, and the 18O(p, α)15N and the 16O(d, p)17O reactions associated with step-by-step chemical dissolution. The profiles could be related to current theories on the initial stages of thermal growth of silicon oxide layers allowing us to draw some conclusions regarding the role of surface cleaning of the silicon wafers on the formation of silicon fragments in the volume of the very thin oxide layer. The influence of rapid thermal processing parameters like temperature, time and oxygen partial pressure on the growth mechanisms were also studied and discussed here.

Theoretical calculation of the depth resolution of IBA methods

One of the most important parameters in depth profiling via ion beam analysis (IBA) is the depth resolution. Unfortunately its approximations in the literature are not general and theoretically well based. To fill this gap and help our decisions when selecting the suitable IBA method, a relatively fast and accurate algorithm was developed and implemented in a PC-code called DEPTH. The code takes into account the following effects: (1) energy and angular spread of the beam, (2) geometrical spread caused by the finite beam spot and detector solid angle, (3) straggling and multiple scattering in the sample, (4) the width of the resonance (in resonance methods), (5) absorber foil (if any) and (6) energy resolution of detection method. The energy distribution contributions coming from multiple scattering are taken into account with their statistical dependence and non-Gaussian shape. The effect of the absorber foil is approximated with its transfer function.

Enhancement of hydrogen diffusion in a-Si:H through intense illumination

Hydrogenated amorphous Silicon (a-Si:H) films have been thermally annealed at temperatures in the range 220°C to 270°C for 48 hours, either under intense visible light illumination (15 watts/cm 2) or in the dark. After each annealing, the hydrogen concentration profile was measured with RBS-ERDA ion beam analysis methods. Substantial enhancement of the hydrogen diffusion constant D was observed in the illuminated samples. To our knowledge, this is the first observation of this effect directly in a-Si:H films. Our results are in agreement with others obtained with a-Si:H/a-Si:D/a-Si:H sandwiches by SIMS (Secondary Ion Mass Spectroscopy).

Trapping of deuterium in beryllium

The thermal release of deuterium (D) implanted into beryllium and the internal redistribution between traps at different depths was studied using ion-beam analysis methods. These methods allow surface effects and trapping to be characterized independently which is difficult from measurements of thermal release alone. At low concentrations D is trapped at lattice damage and is thermally detrapped around 450°C. Transport simulations indicate that the energy barrier for detraping is about 2.3 eV. At high concentrations D precipitates into gas bubbles. Release of D from the bubbles occurs by permeation from high pressure D 2 gas inside the bubbles through the Be lattice to the surface. The permeability of D through Be determined from these experiments was about 2×10 5 D/(cm s atm 1/2 ) at 600°C, seven orders of magnitude smaller than the value calculated from published solubility and diffusivity data. The oxidized Be surface did not limit the D release.

Analysis of diffusion in polymers by forward recoil spectrometry

We demonstrate that an ion beam analysis method that detects the energies of forward recoiling deuterons can be used to measure concentration profiles and tracer diffusion coefficients D* of a deuterated polymer (d-polystyrene) diffusing into its hydrogenated analog. The D*’s decrease as M−2 as predicted by the reptation theory of polymer diffusion and agree in magnitude with both the theory and marker displacement measurements of D* in the same system.

Backscattering techniques for the measurement of stable isotope abundances and tracers

Prompt ion beam analysis methods can be used to measure the isotopic composition of materials. When applied using microbeams of charged particles they have the potential to measure the spatial distribution of isotopes. The value of Rutherford backscattering for isotope measurement is examined both from the point of view of the measurement of stable isotope abundances and the spatial distribution of stable isotope tracers. Parametes which affect the mass resolution and sensitivity are examined including incident particle energy and mass, scattering angle, energy spread of the incident beam, detector resolution and solid angle effects. Experimental measurement of the isotopic abundances of several elements are presented including magnesium, nickel and silver. A variety of incident ions and energies and different detection systems are used. The limitations of the method are discussed and its extension to nuclear microprobe application, with its spatial tracer determination capabilities, is appraised.

Lattice location and trapping of hydrogen implanted in FCC metals

Hydrogen implantation in fcc metals is studied by ion-beam analysis methods. The lattice location and long-range migration are carried out after low-temperature implantation defects is found.

Applications of the scattering spectrometry with fast protons (5–8 MeV) and heavy ions (15–25 MeV) to special analysis problems

The combination of proton and heavy ions beams for light element or “deep interface” analysis problems, high mass or depth resolution questions, respectively, provides a versatile extension of the more conventional ion beam analysis methods. Similar to the 4He + -backscattering, computer analysis of heavy ion data is possible with good success using approximation polynomials for the energy loss values tabulated by Northcliffe and Schilling. Applications of the analysis with protons (5–8 MeV) to the Nb+H, Nb 3Sn+Si and Nb 3Au systems and of heavy ion (16–20 MeV) backscattering to CrCuAu-layers, NbSn diffusion couples and sputtered Nb 3Ge layers are presented.