Ion Microbeam Research Articles

Spatial distribution measured by the modulation transfer function

Spatial distributions in ion micro-beam and IBA experimental practice are regularly characterized through the parameters of FWHM and tail area percentage (TF, tail fraction). Linear and stationary transducer theory allows these distributions to be described in the Fourier-dual frequency space, and provides an indirect method to evaluate them through measurement of the modulation transfer function (MTF). We suggest direct measurement of MTF by employing bar pattern grids, similar to those used for calibration of radiological equipment. Assuming spatial distributions of the form exp(−(| αx|) η ), we are able to relate the MTF measurements to the more popular FWHM and TF. This new approach to determine spatial resolution can become a standard for use by the micro-beam community.

Ion and X-ray micro-beam induced charge collection and their applications in CVD diamond detector characterisation

We have used a micrometer size X-ray beam generated from a synchrotron light source at the European Synchrotron Radiation Facility (ESRF) in Grenoble and a 2 MeV proton micro-beam at the Italian National Laboratory (LNL) of Legnaro to image the electronic transport properties of a CVD diamond detector developed within the CERN RD42 collaboration. The focused X-rays or protons are scanned over the device surface, and the induced current or charge pulse is measured and plotted on two dimensional maps. Due to the polycrystalline nature of the material, the maps are not homogeneous and both the techniques show structures ascribable to diamond grains. It was found that the uniformity of the maps depends on the lateral scale (binning) and on the analytical depth of the micro-probes.

In situ monitoring of polyimide windows for external ion microbeams

Damage of polyimide windows for external ion microbeams was monitored by analyzing backscattering protons from the window. A 1.5 MeV proton microbeam focused to approximately 50 × 50 μm 2 was transmitted through the polyimide window from vacuum to oxygen atmosphere. The changes in backscattering spectra of the window were monitored as a function of irradiation dose up to 2 × 10 18 H +/cm 2. For comparison, the polyimide window was irradiated in vacuum in the same way as the oxygen case. The backscattering spectra drastically changed in the case of oxygen. We observed that the carbon spectrum width, corresponding to the thickness of the window, substantially decreased with increasing the irradiation dose. The in situ monitoring of backscattering protons demonstrated the ability to detect the damage of the window and to predict the rupture of the window.

Ion microbeam facility at the Wakasa Wan Energy Research Center

Two microbeam lines for an ion microprobe and a cell irradiation have been installed in a 5 MV tandem accelerator at the Wakasa Wan Energy Research Center (WERC), Japan. In the ion microprobe beam line, a magnetic quadrupole doublet is equipped for focus of the ion beam on the target point in a scattering chamber. It is utilized for the ion microprobe analysis such as particle induced X-ray emission and Rutherford backscattering spectroscopy. The beam spot size was obtained to be 0.8 μm ( x) × 0.6 μm ( y) (FWHM) for a beam current of 1 pA, and to be 2.0 μm ( x) × 2.5 μm ( y) (FWHM) for a beam current of 140 pA. In the cell irradiation beam line, a beam is extracted in air through a glass capillary with a 10 μm inner diameter in the vertical direction. A total dose to the cell is measured with a silicon surface barrier detector mounted under the sample stage.

Observation of single-ion induced charge collection in diode by a heavy ion microbeam system

In order to study the phenomena of single event upset (SEU), investigations of properties of single event transient current (SETC) in micro-scale semiconductor devices are in progress at the JAERI Takasaki heavy ion microbeam single-ion hit system. Irradiation damage effects are noticeable problems in SETC measurement, especially when a device is irradiated continuously by high-energy heavy ions in an area of 1 μm level. On the other hand, confined irradiation damages in such narrow localized area can be a useful landmark to indicate how large area or region of the device to be concerned with charge collection events. This information is very important for designing micro-scale devices with high SEU tolerance. When a micro-scale test device of silicon carbide (SiC) pn diode was irradiated by single 12 MeV nickel ions with a beam spot size of 1 μm in FWHM, successive irradiation damage effects were observed in the form of attenuation of the current pulse heights and the amount of total charge collected. The lateral extent of charge collection induced by every ion injection was evaluated by analyzing these data. The extent of charge collection in depth direction will be also discussed in conjunction with the thickness of the sensitive layer and the range of the projectiles.

Time-resolved ion beam-induced charge collection measurement of minority carrier lifetime in semiconductor power devices by using Gunn's theorem

Ion microbeam techniques like ion beam-induced charge collection (IBICC) are very powerful methods in order to investigate and to map the transport properties in different technologically important semiconductors and in particular in materials proposed for nuclear detection. Time-resolved ion beam-induced charge collection (TRIBICC) represents a further improvement with respect to more traditional IBICC, since it can supply not only the charge collection efficiency (and through it data on mobility and trapping time of carriers in drift regions) but also the time behaviours of the charge collection. For long collection times, this means to gather information, also about diffusion lengths and lifetimes of carriers in the diffusion regions, which are always present in undepleted electronic devices, in particular power devices, and which are of paramount importance as inputs for simulation codes. By TRIBICC, in fact, some difficulties could be avoided in analysis of data collected in cases when lifetimes and shaping times of electronic chain are similar, and the sensitivity of the method is worse. In order to suitably analyse TRIBICC data, a theoretical model should be available: in general, Ramo's theorem is used, but its validity in cases when space charge is present is questionable. A more general and powerful method is presented in this work by using Gunn's theorem and a particular formulation of the generation function in order to solve the adjoint of the continuity equation in the time-dependent case. An application of this method to a commercial power device is presented and discussed.

Development of an ion microbeam system for irradiating single plant cell[s

An ion microbeam system for irradiating single plant cells was developed to analyze exact biological effects of ion beams. Tobacco BY-2 protoplasts were used as a model of single plant cells. Protoplasts were cultured in thin agarose medium on a specially designed irradiation-vessel, which has a CR-39 nuclear track detector (a 100-micrometer thick sheet). The colony formation rate of unirradiated protoplasts was 22.7 +/- 6.7% (mean +/- SE of 3 different experiments) after a month of culture. Protoplasts were irradiated with programmed numbers of 18.3 MeV/u carbon ions that had been collimated by a 20-micrometer phi micro-aperture. After the irradiation, the positions within the protoplasts that were hit with ions were accurately determined by etching the CR-39 sheet in 13.4M KOH solution at 27 degrees centigrade for 9 h. The hit rate of the carbon ion microbeam, i.e., the percent of the ion particles that hit the protoplast that they were aimed at, was 56.9 +/- 2.4% (mean +/- SE of 7 different replications).

Comparison of SETs in bipolar linear circuits generated with an ion microbeam, laser light, and circuit simulation

Generally good agreement is obtained between the single-event output voltage transient waveforms obtained by exposing individual circuit elements of a bipolar comparator and operational amplifier to an ion microbeam, a pulsed laser beam, and circuit simulations using SPICE. The agreement is achieved by adjusting the amounts of charge deposited by the laser or injected in the SPICE simulations. The implications for radiation hardness assurance are discussed.

Charge collection in SOI capacitors and circuits and its effect on SEU hardness

Focused ion microbeam and broadbeam heavy-ion experiments on capacitors and SRAMs are used to investigate increased saturation upset cross sections recently observed in some silicon-on-insulator (SOI) integrated circuits (ICs). Experiments performed on capacitors show a very strong bias and oxide thickness dependence for charge collection. In combination with three-dimensional (3-D) simulations, these data suggest that the mechanism for charge collection in capacitors is due to perturbation of the substrate electric fields by charge deposition in the substrate. For substrates biased in depletion, these perturbations induce displacement currents through the oxide. Charge collection by displacement currents can be substantially reduced or mitigated by using heavily doped substrates. Experiments performed on SRAMs also show enhanced charge collection from displacement currents. However, experimental data and 3-D simulations show that for SRAMs, a second mechanism also contributes to charge collection. The 3-D simulations suggest that the charge collection results from drain and body-tie heavy-ion strikes within a few tenths of a micron of the body-to-drain junctions. These charge collection mechanisms can substantially reduce the SEU hardness and soft-error reliability of commercial SOI ICs.

Non-destructive 3D-characterization of Zn 2-2x Cu x In x S 2-thin films with ion beam analysis.

Thin layers of ZnS-CuInS(2) mixed crystals (called ZCIS) are promising absorber materials for thin film solar cell applications. The ZCIS-films investigated in this study were grown on (001)GaP, SiO(2) and CeO(2)/Al(2)O(3) with different elemental compositions by Pulsed Laser Deposition (PLD). In order to optimize the sample preparation process a quantitative three-dimensional (i.e. laterally and depth resolved) determination of the compositions and thicknesses of the ZCIS-films is needed. It is demonstrated how this difficult analytical task can be addressed with ion microbeam analysis. For this purpose the films have been analysed non-destructively by means of Rutherford Backscattering Spectrometry (RBS) and Particle Induced X-ray Emission (PIXE) using a 2 MeV He(+) ion microbeam at the high-energy ion nanoprobe LIPSION. A large variation in film thickness caused by particulates deposited on the film was observed. The elemental compositions of the film and the particulates have been determined and compared with the target composition. The deviations found varied substantially for the individual elements. It could be concluded from these measurements, that the quality of the sintered PLD-target is of crucial importance for the roughness of the films. Furthermore concentration-depth-profiles of the individual elements have been derived non-destructively by means of RBS.

Microstructure analysis of metal-effect coatings

The microstructure of a system of metal-effect coatings was studied with respect to the types of metal falkes used, their dispersion and their orientation. Some indirect and some direct methods were applied on the same silver metallic acrylic coatings and blue metallic acrylic coatings, prepared with various amounts of different types of metallic flakes. Indirect methods were used to measure the influence of coating microstructure on their optical properties. Diffuse reflectance in D/8° geometry at various incidence planes was measured in order to detect the tilted flakes. Gonio-spectrophotometry was used to evaluate the lightness flop. The angular dependence of specularly reflected infrared light was used to detect the effect of optical screening. SEM micrographs of metallic flakes in the dry coating were obtained on plasma-etched surfaces where the parameters of the flake/binder geometry were quantified. A three-dimensional distribution of aluminum in upper layers of coating was determined by ion microbeam analysis, where the vertical resolution was higher than the lateral resolution. Vertical grouping of flakes was detected and their inclination angle was determined. The advantages of applied methods are discussed and compared.

Charge collection studies of SOI diodes

Charge collection measurements on SOI diodes have been performed with heavy ion microbeam and pulsed focused laser. Both irradiation techniques show that no electrical coupling occurs. However, laser measurements show an optical coupling effect when irradiation occurs close to the isolation trench. Qualitative electromagnetic simulations have been performed to confirm and describe the optical coupling.

High-resolution X-ray spectroscopy for copper and copper oxides and a new WDX system using an ion microbeam

High-resolution Cu L X-ray spectra from Cu, Cu 2O and CuO targets induced by MeV H, He, C and F ions have been measured. High-resolution Cu Lα 1,2 and Lβ 1 X-ray spectra from Cu, Cu 2O and CuO targets induced by 2.0 MeV focused protons have been also measured. It is shown that high-resolution X-ray spectra are sensitive to the chemical states of the emitting projectile and target atoms. The Cu Lα 1,2 and Lβ 1 X-ray spectra were compared with Cu 2p XPS spectra to investigate the atomic and electronic structures and electron excitation and relaxation processes in Cu and its compounds. High-resolution X-ray spectroscopy with a microbeam is found to be useful for analysis of the chemical environment of atoms of interest in the near surface region of bulk and particle samples.

Radiation effects and surface deformation of silica by ion microbeam

Radiation effects induced by ion microbeam were studied by a confocal microspectroscopy and an atomic force microscopy (AFM). We investigate two significant radiation effects, defect generation and compaction, which were ascribed to electronic ( E elec) and nuclear stopping powers ( E nucl), respectively. Photoluminescence mapping of nonbridging oxygen hole centers at 650 nm reveals the defect formation along the tracks of ions. The surface deformation measured by AFM depends on the width of irradiated by microbeam. Confinement effects from the interface of irradiated and nonirradiated regions are taken into account for the understanding of the correlation between the surface deformations and internal compactions.

Investigation of the radiation hardness on semiconductor devices using the ion micro-beam

Variation of the ion beam induced charge (IBIC) pulse heights due to ion irradiation was investigated on a Si pn diode and a 6H-SiC Schottky diode using a 2 Mev He + micro-beam. Each diode was irradiated with a focused 2 MeV He + micro-beam to a fluence in the range of 1×10 9–1×10 13 ions/cm 2. Charge pulse heights were analyzed as a function of the irradiation fluence. After a 2 MeV ion irradiation to the Si pn junction diode, the IBIC pulse height decreased by 15% at 9.2×10 12 ions/cm 2. For the SiC Schottky diode, with a fluence of 6.5×10 12 ions/cm 2, the IBIC pulse height decreased by 49%. Our results show that the IBIC method is applicable to evaluate irradiation damage of Si and SiC devices and has revealed differences in the radiation hardness of devices dependent on both structural and material.

Analysis of metallic pigments by ion microbeam

Metallic paints consist of metallic flakes dispersed in a resinous binder, i.e. a light-element polymer matrix. The spatial distribution and orientation of metallic flakes inside the matrix determines the covering efficiency of the paint, glossiness, and its angular-dependent properties such as lightness flop or color flop (two-tone). Such coatings are extensively used for a functional (i.e. security) as well as decorative purpose. The ion microbeam analysis of two types of silver paint with imbedded metallic flakes has been performed to determine the spatial distribution of the aluminum flakes in paint layer. The average sizes of the aluminum flakes were 23 μm (size distribution 10–37) and 49 μm (size distribution 34–75), respectively. The proton beam with the size of 2×2 μm 2 at Ljubljana ion microprobe has been used to scan the surface of the pigments. PIXE mapping of Al Kα map shows lateral distribution of the aluminum flakes, whereas the RBS slicing method reveals tomograms of the flakes in uppermost 7 μm of the pigment layer. The series of point analysis aligned over the single flake reveal the flake angle in respect to the polymer matrix surface. The angular sensitivity is well below 1 angular degree.

Lateral micro-ion beam induced charge characterization of chemical vapor deposition diamond

A lateral micro-ion beam induced charge technique has been used to obtain the charge collection efficiency (CCE) profiles at different biases applied on the growth electrode of chemical vapor deposition (CVD) diamond. A new linear model, only related to characteristic parameters (mobility×lifetime product) of CVD diamond, was reasonably proposed and checked by fitting the CCE profile. The results confirm that: (1) this CVD diamond is similar to a n–p junction film with bulk volume p type on the substrate side at the positive bias applied on the growth side; (2) in the case of negative bias, space charge on both sides may arise from donors/acceptors of the film and electrons/holes injected from the growth/substrate side, but in the middle no space charge exists due to the electron–hole neutralization.

In situ RBS study of the kinetics of galena thermal oxidation by means of 4He external micro-beam

In situ RBS measurements with an external He ion micro-beam have been performed on galena heated at temperatures varying from 400°C to 600°C, to study dynamically its oxidation kinetics. At each temperature, a millimetre-sized crystal is placed in a specially built oven directly facing the exit window of the beam. The thickness of the oxidised layer is measured every 2 min by means of the lead signal in the RBS spectrum, using a 3 MeV 4 He 2+ external focused beam (about 100 μm). We infer the diffusion mechanism from the growth of a phase, which is more or less stable when increasing temperature. This probing beam allows one to characterise layers of thickness extending from about 100–2000 nm.

Chemical state analysis of Cu, Cu 2O and CuO with WDX using an ion microbeam

The possibility of chemical state analysis with a wavelength-dispersive X-ray spectrometer system for particle-induced X-ray emission (WDX-PIXE) using a light ion microbeam is described. High-resolution Cu Lα 1,2 and Lβ 1 X-ray spectra from Cu, Cu 2O and CuO targets are measured using this spectrometer system. The incident microbeam is focused 2.0 MeV protons with a beam size of 100(H)×30(V) μm 2. The Cu L X-ray spectra show two clear main peaks and their satellites. The main peaks are the Lα 1,2 and the Lβ 1 diagram lines, respectively. Due to a high detection efficiency of our spectrometer equipped with a position-sensitive detector for soft X-rays, the intensity ratio Lβ 1/Lα 1,2 is observable, which is the lowest for pure Cu metal, and the largest for CuO. Moreover, the Lα 1,2 X-ray spectrum for CuO shows a large shoulder at the high energy side of the main peak, which is considered to be due to the chemical bonding between Cu and O atoms. The results show that this system can be used for chemical state analysis for various compound materials and for analyzing small areas of materials or small particles.

Observation of radiation damage induced by single-ion hits at the heavy ion microbeam system

A single-ion hit system combined with the JAERI heavy ion microbeam system can be applied to observe individual phenomena induced by interactions between high-energy ions and a semiconductor device using a technique to measure the pulse height of transient current (TC) signals. The reduction of the TC pulse height for a Si PIN photodiode was measured under irradiation of 15 MeV Ni ions onto various micron-sized areas in the diode. The data containing damage effect by these irradiations were analyzed with least-square fitting using a Weibull distribution function. Changes of the scale and the shape parameters as functions of the width of irradiation areas brought us an assumption that a charge collection in a diode has a micron level lateral extent larger than a spatial resolution of the microbeam at 1 μm. Numerical simulations for these measurements were made with a simplified two-dimensional model based on this assumption using a Monte Carlo method. Calculated data reproducing the pulse-height reductions by single-ion irradiations were analyzed using the same function as that for the measurement. The result of this analysis, which shows the same tendency in change of parameters as that by measurements, seems to support our assumption.