Ion microbeam applications in semiconductors

Microbeam techniques and applications to semiconductor analysis are briefly reviewed. Special microbeam requirements and limitations for channeling analysis using MeV He microbeams are discussed, including conditions to minimise beam damage to Si and GaAs. Finally, channeling contrast microscopy is described, together with the application of this technique to the analysis of phase transformations and impurity redistribution in locally laser annealed Si.     

Ion radiation damage in copper

Transmission electron microscopy techniques have been used to study dislocation loop type damage as a function of depth in copper single crystals irradiated with MeV Cu, Ni and He ions at room temperature. By comparing the location of the peak in the experimental depth profiles with calculated damage energy curves, the electronic stopping powers of Cu and Ni ions in copper were deduced. The deduced electronic stopping powers have been compared with those predicted by Lindhard et al., Bricc, and the Northcliffe and Schilling tables. It was found that the deduced stopping powers agreed well with the Northcliffe and Schilling values corrected for Z₂ oscillations by the method proposed by Ward et al. In the case of 1 MeV He ions, good agreement was obtained between the observed damage peak position and that calculated using the experimental electronic stopping of Ziegler and Chu and that of White and Mueller.     

Time Resolved Ion Beam Induced Current measurements on MOS capacitors using a cyclotron microbeam

As overlayers on electronic devices become progressively thicker, radiation effects microscopy using traditional microbeams (with ion energies up to a few tens of MeVs) is becoming less and less viable. To penetrate to the sensitive regions of these devices, much higher energies, several hundreds of MeVs are necessary. These high energies are available only from cyclotrons. A nuclear microprobe has been developed on the AVF cyclotron of the Takasaki Ion Accelerators for Advanced Radiation Applications (TIARA) facility. In this paper we will present the first results using 260 MeV Ne and 520 MeV Ar microbeams to perform Time Resolved Ion Beam Induced Current (TRIBIC) measurements on Metal-Oxide-Semiconductor (MOS) capacitors. The results will be compared to data taken with a traditional 15 MeV O microbeam.     

Heavy-ion microbeam system for cell irradiation at Kyoto University

We have developed a heavy-ion microbeam system for cell irradiation that uses an 8-MV tandem Van de Graaff accelerator at Kyoto University. Using a pair of apertures as the final collimator, microbeams of carbon, fluorine, and silicon were extracted to the atmosphere with few background particles. We used a thin transmission scintillator and a photomultiplier detector to accurately measure the number of extracted particles. To examine beam spreading, the beam profile was measured by observing tracks of an irradiated CR-39 track detector. The two disks with holes which were added to the collimating apertures reduced background radiation due to secondary X-rays and electrons from the apertures.     

Ion beam radiation effects in monazite

Monazite is a potential matrix for conditioning minor actinides arising from spent fuel reprocessing. The matrix behavior under irradiation must be investigated to ensure long-term containment performance. Monazite compounds were irradiated by gold and helium ions to simulate the consequences of alpha decay. This article describes the effects of such irradiation on the structural and macroscopic properties (density and hardness) of monazites LaPO₄ and La_0.73Ce_0.27PO₄. Irradiation by gold ions results in major changes in the material properties. At a damage level of 6.7 dpa, monazite exhibits volume expansion of about 8.1%, a 59% drop in hardness, and structure amorphization, although Raman spectroscopy analysis shows that the phosphate-oxygen bond is unaffected. Conversely, no change in the properties of these compounds was observed after He ion implantation. These results indicate that ballistic effects predominate in the studied dose range.     

Progress of in-air microbeam system at the Wakasa Wan Energy Research Center

Modifications of an in-air microbeam system at the Wakasa Wan Energy Research Center designed to improve its performance are described. In the previous setup, a silicon nitride membrane (area: 1 × 1 mm²; thickness: 100 nm) was used for the beam exit window and the distance between the window and the sample was restricted to ?1.7 mm. Due to this restriction, the beam spot size obtained using the previous setup was 13 × 13 μm². To reduce the beam spot size, the beam exit window was replaced by a silicon nitride membrane (area: 3 (horizontal) × 2 (vertical) mm²; thickness: 200 nm). In this setup, the sample can be moved as close as 0.7 mm to the window, enabling a beam spot size of 7 × 6 μm² to be achieved. An additional Si-PIN X-ray detector was installed to estimate the relative number of beam particles. It detects X-rays from the beam exit window. The number of the X-rays from the beam exit window (which is proportional to the number of beam particles) is used for quantitative analysis and for online monitoring of the beam current. This system has the potential to be used for simultaneous particle-induced X-ray emission (PIXE) and particle-induced gamma-ray emission (PIGE) measurements and for studying dental medicine.     

Nanosecond pulsed proton microbeam

We show the preparation of a pulsed 20 MeV proton beam at the Munich tandem accelerator which offers a fluence of more than 1 × 10⁹ protons/cm² being deposited in a beam spot smaller than 100 μm in diameter and within a time span of 0.9 ns fwhm. Such a beam is produced by an ECR type proton source using charge exchange in cesium vapor to obtain a beam of negative hydrogen of high brightness that is bunched, chopped, accelerated and then focused by the superconducting multipole lens of the microprobe SNAKE. Single beam pulses are generated in order to irradiate cell samples or tissue and to measure their biological effect in comparison to continuous proton or X-ray irradiation.     

早期微束的发展及其在细胞辐射生物学中的应用

介绍了研究细胞辐射生物学效应的早期微束装置,总结了在单细胞定位定量辐射中所得到的一系列研究成果,并分析了这些微束装置存在的局限性,为微束装置的设计提供了借鉴和参考。     

Improved high energy microbeam techniques

The University at Albany ion scanning microprobe has been used for many industrial applications in thin films. Of prime importance for rapid analysis, the beam should be set-up and in-use very shortly after the beam is turned on. Rapid optical and electronic tune-up methods are discussed. Standard 1–2 micron, 2 MeV helium or proton beams are generally used with RBS (Rutherford Backscattering) and PIXE (Particle Induced X-ray Emission) to obtain composition analysis in one- or two-dimensions. We demonstrate the use of 3-dimensional analysis in thin films, wherein film thickness is the third dimension.     

Heavy ion microbeam vacuum requirements

Transport of heavy ions through an ion microbeam focusing system can be affected by insufficient vacuum within the beam transport tube. Due to interactions of heavy ions with atoms of residual gas in the vacuum tube of a microbeam facility, the angular, lateral and energy spreading of an ion beam increases prior to focusing, creating a beam halo. This beam halo can produce undesirable effects in some applications of ion microbeam techniques. In order to model this effect, the ion beam angular spread in residual gas has been approximated by Sigmund’s theoretical predictions for small-angle ion multiple scattering (MS), while ion energy loss straggling distributions have been applied for studying the energy spread. The extent of the beam halo has been estimated by combining the results of these calculations with ion optics calculations. Recommendations concerning microbeam focusing due to the vacuum conditions are given for different heavy ions in the MeV energy range.     

CEFR辐射监测系统

介绍了研制的数字化网络化CEFR辐射监测系统的构成,描述了部分监测仪器的结构特点,详细论述了处理组件和计算机的控制与数据处理功能。     

The single-particle microbeam facility at CEA-Saclay

Low dose and non-targeted effect studies continue to attract the attention of a growing number of radiobiologists. Experimental setups based on light ion microbeams constitute a tool of choice for this kind of investigations. However, a careful attention must be given to experimental conditions, as setup-induced stress levels should be well below those induced by the irradiation itself. Here, we present the current status of the single-particle microbeam facility that has been developed these last years at the nuclear microprobe of Saclay. The driving idea was to build a facility in which local irradiation studies are performed in an environment close to cellular biology standards. This facility includes unique features, such as (i) a compact setup that allows easy access and vertical irradiation mode, (ii) a collimated beam that can be mechanically positioned under the desired cells at a very fast speed, avoiding the requirement of a focusing element and (iii) a controlled environment (temperature, CO₂, humidity) that allows performing of very long term experiments on cultured cells.Fluorescent techniques are implemented and permit in situ monitoring of cellular responses to irradiations.Several radiobiological studies are already underway and this will be illustrated with recent results regarding DNA damage and reactive oxygen species signaling time courses following targeted irradiations.     

Slit scattering in a microbeam set-up

Slit scattering of beam particles in a microbeam set-up becomes significant for low current applications and thus limits its lateral resolution and application potential. In this work, the angular and energy distributions of beam particles interacting with cylindrically shaped slit-jaws of different radii, surface roughnesses, and materials are calculated numerically, employing the computer code SRIM. To quantitatively investigate their effect on the beam spot quality of a microbeam set-up, a quality factor is proposed as an index to evaluate the effect of slit-scattered particles on the beam spot. The results of the investigation reveal a high sensitivity of slit scattering in relation to the slit-jaw surface roughness.     

兰州重离子研究装置周围环境的放射性监测

叙述了对兰州重离子研究装置周围环境中土壤,植物和水中总α,总β放射性的监测情况。给出了测量结果,并进行了初步评价,连续７年的监测表明,ＨＩＲＦＬ周围环境样品的放射性都在本底水平,装置的运行未对环境造成污染。     

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 μm² at Ljubljana ion microprobe has been used to scan the surface of the pigments. PIXE mapping of Al K 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.     

The Columbia University proton-induced soft x-ray microbeam

A soft X-ray microbeam using proton-induced X-ray emission (PIXE) of characteristic titanium (K_α 4.5 keV) as the X-ray source has been developed at the Radiological Research Accelerator Facility (RARAF) at Columbia University. The proton beam is focused to a 120 μm × 50 μm spot on the titanium target using an electrostatic quadrupole quadruplet previously used for the charged particle microbeam studies at RARAF. The proton induced X-rays from this spot project a 50 μm round X-ray generation spot into the vertical direction. The X-rays are focused to a spot size of 5 μm in diameter using a Fresnel zone plate. The X-rays have an attenuation length of (1/e length of ∼145 μm) allowing more consistent dose delivery across the depth of a single cell layer and penetration into tissue samples than previous ultrasoft X-ray systems. The irradiation end station is based on our previous design to allow quick comparison to charged particle experiments and for mixed irradiation experiments.     

Biological studies using mammalian cell lines and the current status of the microbeam irradiation system,SPICE

The development of SPICE (single-particle irradiation system to cell), a microbeam irradiation system, has been completed at the National Institute of Radiological Sciences (NIRS). The beam size has been improved to approximately 5 μm in diameter, and the cell targeting system can irradiate up to 400–500 cells per minute. Two cell dishes have been specially designed: one a Si₃N₄ plate (2.5 mm × 2.5 mm area with 1 μm thickness) supported by a 7.5 mm × 7.5 mm frame of 200 μm thickness, and the other a Mylar film stretched by pressing with a metal ring. Both dish types may be placed on a voice coil stage equipped on the cell targeting system, which includes a fluorescent microscope and a CCD camera for capturing cell images. This microscope system captures images of dyed cell nuclei, computes the location coordinates of individual cells, and synchronizes this with the voice coil motor stage and single-particle irradiation system consisting of a scintillation counter and a beam deflector. Irradiation of selected cells with a programmable number of protons is now automatable. We employed the simultaneous detection method for visualizing the position of mammalian cells and proton traversal through CR-39 to determine whether the targeted cells are actually irradiated. An immuno-assay was also performed against γ-H2AX, to confirm the induction of DNA double-strand breaks in the target cells.     

Development of a real-time beam current monitoring system for microbeam scanning-PIXE analysis using a ceramic channel electron multiplier

Microbeam scanning-PIXE (micro-PIXE) analysis is a useful method for obtaining information of multi-elemental distribution in samples by two-dimensional images of sample surfaces such as mammalian cells, tissues, and other environmental monitoring species. In addition to elemental distribution information, quantitative analysis is in demand for further investigations of environmental and biomedical studies concerning heavy metals accumulated in terms of cells and sub-cellular organelles. To make quantitative analysis possible, a real-time beam monitoring system that gives a precise number of ions, and an output independent from a sample that enables one to keep a beam resolution of micrometer size is required. In this paper, we report on the development of beam current monitoring. The beam current was monitored using a ceramic channel electron multiplier (CEM) to detect secondary electrons induced from a 50 nm thick carbon film (10 μg/cm²). This carbon film was attached to a sample holder, which was set at the targeted sample position. The output value of the CEM was proportional to the Faraday cup installed just after the sample position. The beam resolution was measured using off-axis STIM by scanning a copper grid, and was estimated at 1.79 and 1.72 μm for the horizontal and vertical directions, respectively, sufficient for routine micro-PIXE analysis.     

Detectors for microbeam applications at medium ion energy

Nuclear microprobes with excellent lateral resolution can be realized using a liquid metal ion source and electrostatic einzel lens system in a few hundred keV energy range. In case of ion beam analysis it is better to provide a special detector for Rutherford Backscattering (RBS) analysis or elastic recoil detection. Good mass and depth resolutions should be attained while keeping the damage caused by the beam at tolerable level. Two solutions are considered in the present work: (1) toroidal electrostatic analyzer combined with simultaneous Time-of-Flight (TOF) measurement for mass identification; (2) TOF measurement only, using a large area microchannel plate. Both solutions can be combined with 2D position sensitive anode plates for excellent performance. In case of the first solution, it is possible to distinguish the different mass atoms by the scattering angle where their peak in the angular distribution appears. Similarly to the energy distribution at a fixed scattering angle the angular distribution at a fixed energy represents mass and depth distribution. In case of the second solution the huge acceptance angle will make it possible to analyze submicron spot size without serious beam effects and both heavy and light elements can be investigated.