Accurate hydrogen depth profiling by reflection elastic recoil detection analysis

A technique to convert reflection elastic recoil detection analysis spectra to depth profiles, the channel-depth conversion, was introduced by Verda et al. [Nucl. Instr. and Meth. B 183 (2001) 401]. But the channel-depth conversion does not correct for energy spread, the unwanted broadening in the energy of the spectra, which can lead to errors in depth profiling. A work in progress introduces a technique that corrects for energy spread in elastic recoil detection analysis spectra, the energy spread correction [Nucl. Instr. and Meth. B 187 (2002) 383]. Together, the energy spread correction and the channel-depth conversion comprise an accurate and convenient hydrogen depth profiling method.     

Unique capabilities of heavy ion elastic recoil detection with gas ionization detectors

Specific aspects of heavy ion elastic recoil detection (ERD) with gas ionization detectors have been studied using representative measurements. A particular strength of the technique is the detection and direct quantification of elements with atomic numbers in the range Z=2–8, which are often not accessible with other ion beam techniques. Within the wider spectrum of analytical techniques in materials science, heavy ion ERD has unique capabilities, when the particular problem requires in addition the analysis of heavy elements or hydrogen detection. Whenever only heavy element analysis or only hydrogen profiling is of interest, alternative techniques tend to be superior.     

Efficiency enhancements to Monte Carlo simulation of heavy ion elastic recoil detection analysis spectra

Monte Carlo (MC) simulation can be used to simulate heavy ion elastic recoil detection analysis spectra, including the broadening and tailing effects of multiple and plural scattering, although it is very costly in terms of computer time. In this work, kinematic relationships and experimental parameters are exploited to implement efficiency improvements in the MC modeling process. For thin films, incident ions that pass through the sample without undergoing a significant scattering event need not be tracked. Ions that might generate a detectable scattered or recoiled ion are predicted by generating, in advance, the impact parameters which will define its path. Light recoiled target atoms may be dealt with in the same way. For heavy atoms, however, the probability of large angle scattering events is so high that the paths of most recoil atoms are dominated by several scattering events with large angular deflections.     

High resolution elastic recoil detection analysis of polystyrene depth profiles using carbon ions

The resolution of conventional elastic recoil detection (ERD) is enhanced by using ions which are efficiently stopped by matter. We describe an ERD experiment using a 2.4 MeV carbon ion beam which has a surface resolution of 80 Å FWHM in polystyrene. The maximum analysable depth for this geometry is 1000 Å. We show that by cumulating spectra with a low enough dose on different points of the same sample it is possible to avoid a substantial beam-induced modification of the true depth profile. The technique is demonstrated with experiments showing the decrease in the surface segregation of deuterated polystyrene (dPS) as a function of its molecular weight (Mw) in films of blends of deuterated and protonated polystyrene.     

3D hydrogen profiling by elastic recoil detection analysis in transmission geometry

An analytical procedure and a simulation-optimization algorithm are described for hydrogen determination based on elastic recoil detection induced by low-energy ⁴He ions ( 3 MeV) using transmission geometry. Hydrogen concentration depth profiles can be derived from the experimental recoil spectra for a depth range of up to 6 μm with a resolution better than 40 nm at the surface. The method is applied to thin polyimide films irradiated by high-energy heavy ions. The 3D hydrogen distribution is determined with a ⁴He⁺ mubeam. A high-hydrogen-concentration zone below the surface is shown. The hydrogen distribution is seen to evolve during the ⁴He⁺ irradiation.     

Elastic recoil detection analysis on the ANSTO heavy ion microprobe

The heavy ion microprobe at the Australian Nuclear Science and Technology Organisation is capable of focussing heavy ions with an ME/q² of up to 100 amu MeV. This makes the microprobe ideally suited for heavy ion elastic recoil detection analysis (ERDA). However, beam currents on a microprobe are usually very small, which requires a detection system with a large solid angle. We apply microbeam heavy ion ERDA using a large solid angle ΔE−E telescope with a gas ΔE detector to layered structures. We demonstrate the capability to measure oxygen and carbon with a lateral resolution of 20 μm, together with determination of the depth of the contamination in thin deposited layers.     

Energy and depth resolution in elastic recoil coincidence spectrometry

Elastic recoil coincidence spectrometry was implemented into the analytical ion beam simulation program DEPTH. In the calculations, effective detector geometry and multiple scattering effects are considered. Mott’s cross section for the identical, spin zero particles is included. Spectra based on the individual detector signal and summing the energy of the recoiled and scattered particles originating from the same scattering events can also be calculated. To calculate this latter case, the dependency of the energy spread contributions had to be reconsidered.     

Reliability,detection limit and depth resolution of the elastic recoil measurement of hydrogen

Reliability, detection limit and depth resolution were studied in the elastic recoil measurement of hydrogen mainly in silicon compounds by bombardment with argon ions accelerated up to 50 MeV. For the quantitative determination of hydrogen, recoil silicon atoms proved to serve satisfactorily as an internal monitor. The detection limit was shown to be about 1 to 2×10¹² (atoms/cm² for hydrogen on surface and about 1 wt. ppm for hydrogen in bulk. The depth resolution was found to be about 50 nm in most silicon compounds.     

Mass selection and depth profiling by coincident recoil detection for nuclei in the middle mass region

The possibilities of coincident elastic recoil detection for mass analysis around mass 64 have been investigated at the GSI heavy-ion microprobe. Partial separation between the stable isotopes ⁶³Cu and ⁶³Cu has been obtained using a pair of position-sensitive detectors accepting both scattered projectiles and recoils between 38° and 52°. Total energy spectra gated by the peaks in the mass spectrum show small differences. For the surface nearest to the detectors depth resolution is better than 25 nm.     

用符合弹性前冲法测量硅中的氧含量及其分布

采用２７ＭｅＶ的＾１２Ｃ５＾５＋作为入射粒子，采用符合弹性前冲方法测量了５．６μｍ的硅样品中氧的含量及其深度分布。实验结果表明，采用＾１２Ｃ与＾１６Ｏ符合弹性前冲方法分析硅样品中的氧，其最小探测限可达２０×１０＾－６，深度分辨率为－４５０ｎｍ。该方法对于厚样品，尤其比常规弹性前冲优越。     

Depth resolution and recoil cross section for analyzing hydrogen in solids using elastic recoil detection with 4He beam

Two aspects of the elastic recoil detection technique for analyzing H and D are described; i) experimental factors which effectively limit the depth resolution in Al film, and ii) determination of the recoil cross section for H(⁴He, ⁴He)H and D(⁴He, ⁴He)D reactions in the range of 1.5–3.0 MeV energy of ⁴He. Both experimental and theoretical estimates of the depth resolution are presented and are in good agreement each other. The theoretical estimate therefore provides a reliable guide to find optimum resolution conditions. The recoil cross section for H is more than double the theoretical Rutherford scattering value and that for D becomes greater than 30 times Rutherford near the resonance energy of 2.1 MeV ⁴He.     

A method for analysis and profiling of boron,carbon and oxygen impurities in semiconductor wafers by recoil atoms in heavy ion beams

A method based on identification of recoil atoms in heavy ion beams, by using a (ΔE, E) measuring system, is described. The two parameter (ΔE, E) spectra, obtained with the aid of a computer, shows a good separation between carbon and oxygen recoils originating from a 300 μ;m thick silicon wafer bombarded with a 70 MeV sulphur beam. Profiling depths 10–20 μm and sensitivities close to 10¹⁶ atoms/cm are estimated.     

Ion beam induced damage in InP during heavy-ion elastic recoil detection analysis

Heavy-Ion Elastic Recoil Detection Analysis (HIERDA) is an analytical technique which has undergone rapid development in the past few years with the availability of high-energy Tandem accelerators for materials science applications. HIERDA has found application in the study of various semiconductor systems, particularly III–V compounds. The technique employs a high-energy heavy-ion analysing beam to knock constituent nuclei from the target material and a time of flight and energy (ToF-E) detector system to extract mass and depth of origin information from these recoiling nuclei. Present work examines the sample damage produced in InP under typical analysis conditions. The depth distribution of damage induced by an ¹²⁷I analysing beam of varying energy (54–98 MeV) and dose (10¹³−2 × 10¹⁴ ions/cm²) in InP has been examined using RBS channelling, and cross-sectional TEM.     

Positron spectroscopy in elastic and dissipative heavy ion collisions

A new magnetic transport system, the Tori spectrometer, which is able to measure positrons and electrons simultaneously, has been used to study the dynamics of collisions between very heavy ions via their influence on the positron and δ-electron spectra. While these spectra obtained in coincidence to elastic scattering agree well with theory based on pure Rutherford trajectories, those observed in coincidence to dissipative collisions can only be described by calculations taking into account a time delay in the collision process. A quantitative analysis gives an estimation for the nuclear contact time in the U + U collision.     

Hydrogen behavior in gasochromic tungsten oxide films investigated by elastic recoil detection analysis

Changes in the composition and crystalline structure of gasochromic tungsten oxide films resulting from the incorporation of hydrogen were investigated; the oxide films were prepared by reactive RF magnetron sputtering on SiO₂ and glassy carbon substrates simultaneously. X-ray diffraction analysis of the deposited films at 600 °C showed a uniaxial oriented structure in the (0 1 0) plane of monoclinic WO₃ for both substrates. The elastic recoil detection analysis (ERDA) and Rutherford backscattering spectroscopy (RBS) for the films on glassy carbon revealed that the hydrogen impurity was uniformly distributed up to a concentration of 0.24 H/W. The Pd-coated films on SiO₂ turned blue when they were exposed to a mixture of Ar and 5% H₂ gases. When the sample became colored, the hydrogen concentration in the film increased to 0.47 H/W and the crystalline structure of the film changed from monoclinic to tetragonal. These results indicated that the gasochromic coloration of the tungsten oxide films coincided with incorporation of hydrogen atoms into the crystalline lattice, corresponding to the formation of hydrogen tungsten bronze (H_xWO₃).     

Measurement of He and H depth profiles in tungsten using ERDA with medium heavy ion beams

Elastic recoil detection analysis method (ERDA) with medium heavy analyzing ion beam and its application for the simultaneous measurement of light elements in a very heavy substrate is presented. The availability of cross section data and the method of cross section calculation for recoiled particles are discussed. Different ion species for analyzing beam are discussed with respect to the cross-section data availability, sensitivity of the method, and the depth resolution. Calculations of depth resolution for each element and maximum depth of analysis for tungsten substrate are presented. The influence of the detector geometry and multiple scattering effects on the depth resolution is discussed. An example spectrum measured on tungsten implanted with He seeded D plasma is shown.     

SIMS depth profiling of multilayer metal-oxide thin films — improved accuracy using a xenon primary ion

Multilayer thin films containing silver and copper, sandwiched in a metal oxide, have been depth profiled by secondary ion mass spectrometry (SIMS) using primary ions of differing mass, energy and chemical reactivity. These results were compared for accuracy with those obtained by Rutherford backscattering spectrometry (RBS). The use of O₂⁺ or O^? as primary ions resulted in severe distortion of the silver ion intensity distribution in the SIMS profile of a ZnO/Ag/ZnO thin film on glass; O₂⁺ bombardment at energies from 3–10 keV resulted in the detection of silver at the glass interface, while the use of O^? caused the silver to be detected closer to the outer surface than expected from RBS results. Primary beams of Ar⁺ and Xe⁺ gave progressively more accurate results for the Zn/Ag/Zn distribution; Xe⁺ at 5.0 keV energy produced profiles that agreed within 10% of RBS-derived values. The same beam conditions, used to profile a double silver layer in ZnO, resulted in some discrepancy in the position of the inner layer, compared to RBS results, and this was attributed to an enhanced sputter rate in the oxide under the outside metal film. Depth profiling of TiO₂/Cu/TiO₂ films with oxygen also resulted in significant distortion of the perceived position of the metal layer, and this was again significantly improved using Xe⁺ primary ions of 6–9 keV energy. The distorting effects of oxygen bombardment can be understood in terms of a migration of metal ions in an electrostatic field created by a charged surface. Ionization of the metallic layer is enhanced by the use of oxygen. By contrast, the use of rare gases reduces the production of ions from the metallic layer which can migrate prior to the onset of sputtering.     

Optimizing NRA depth profiling using Bayesian experimental design

Nuclear reaction analysis with ³He holds the promise to derive Deuterium depth profiles up to large depths from a set of measurements with different energies. Unfortunately, the extraction of the depth profile from the measured data is very sensitive to the quality of the data and the commonly chosen set of equispaced energies is in hindsight often noticeably inferior to other choices. However, recent advances in Bayesian experimental design together with increased computing power allow to optimize the measurement strategy ‘on-the-fly’, taking into account the results of previous measurements to select the best energy for the next measurement and to compute the expected information gain from further measurements. As example depth profiling of Deuterium in tungsten is presented and the results of the different measurement strategies are compared.     

Thin film depth profiling using simultaneous particle backscattering and nuclear resonance profiling

We report an important extension to the DataFurnace code for Ion Beam Analysis which allows users to simultaneously and self-consistently analyse Rutherford (RBS) or non-Rutherford (EBS) elastic backscattering together with particle-induced gamma-ray (PIGE) spectra. We show that the code works correctly with a well-known sample. Previously it has not been feasible to self-consistently treat PIGE and RBS/EBS data to extract the depth profiles. The PIGE data can be supplied to the code in the usual way as counts versus beam energy, but the differential cross-sections for the PIGE reaction are required. We also compared the results obtained by the new routine with high resolution narrow resonance profiling (NRP) simulations obtained with the stochastic model of energy loss.     

Characterization of optical coatings by Rutherford backscattering spectrometry and elastic recoil detection analysis

The thicknesses of optical coatings vary between a few hundred Å and a few μm. Ion-beam techniques are ideally suited for probing this thickness range and in this work we discuss the use of Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA) for characterizing optical coatings such as ZnS, YF₃,Y₂O₃, C and Ge on silicon and germanium substrates. A general evaluation of the favourable features as well as the limitations of RBS and ERDA ion beam analysis for characterizing optical coatings is given.