Influence of the beam current density distribution on the spatial resolution of a nuclear microprobe

The paper discusses the effect of nonuniform distribution of the ion beam phase density on the nuclear microprobe resolution. The deconvolution of the beam brightness distribution parameters was performed on the base of the beam current distribution measurements in the object collimator plane. This information gives a possibility to define the ion distribution in the phase set for a beam to be transformed by the probe-forming system into the target plane. A criterion for selecting the optimum collimator dimensions was the highest beam current for the fixed beam spot size (FWHM). This approach, with allowance for the initial distribution, makes it possible to obtain a higher beam current intensity at the center of the spot.     

Early works on the nuclear microprobe for microelectronics irradiation tests at the CEICI (Sevilla, Spain)

Particle radiation effects are a fundamental problem in the use of numerous electronic devices for space applications, which is aggravated with the technology shrinking towards smaller and smaller scales. The suitability of low-energy accelerators for irradiation testing is being considered nowadays. Moreover, the possibility to use a nuclear microprobe, with a lateral resolution of a few microns, allows us to evaluate the behavior under ion irradiation of specific elements in an electronic device. The CEICI is the new CEnter for Integrated Circuits Irradiation tests, created into the facilities at the Centro Nacional de Aceleradores (CNA) in Sevilla-Spain. We have verified that our 3 MV Tandem accelerator, typically used for ion beam characterization of materials, is also a valuable tool to perform irradiation experiments in the low LET (Linear Energy Transfer) region.     

First direct-write lithography results on the Guelph high resolution proton microprobe

The recently completed high-resolution proton microprobe at the University of Guelph is Canada’s first one-micron nuclear microprobe, which represents the country’s state-of-the-art technology for various nuclear microprobe applications, e.g. direct-write microlithography. Its probe-forming system is comprised of a triplet Oxford Micro beams magnetic quadrupole lenses, along with high-precision objective slits. High energy protons coming off a 3 MV particle accelerator can achieve a nominal resolution of one micro and a beam current of several hundred of picoamperes when arriving at the target. This proton probe is ideal for the use of direct-write lithography with the incorporation of a magnetic scanning system and motorized sample stage.Preliminary lithography results have been obtained using spin-coated PMMA photoresist as specimen. The beam spot size, beam range and straggling inside the substrate and the exposure conditions are investigated by using scanning electron microscopy. This facility is the first in Canada to perform focused direct-write ion beam lithography, which is ideal for modification and machining of polymer and semiconductor materials for biological, microfluidic and ultimate lab-on-chip applications.     

Status and future development of ion sources for on-line mass separators

The status is given of ion sources for on-line mass separators with examples of recent developments on element availability, ionization efficiency, speed and selectivity. Since the target and the ion source are most often integrated, a discussion is included of the progress in the most important methods used to bring the nuclear reaction products out of the target and into the active region of the source. A number of novel, more advanced target and ion source systems have recently emerged and may in the future offer new possibilities for existing machines. Selected examples will be given for: (1) new release and delay studies, (2) selective resonant laser ionization, (3) electron cyclotron resonance (ECR) ion sources, (4) chemical reactions inside the ion source, (5) ion sources with bunched beam release. In view of the planned new facilities with post-acceleration of radioactive ion beams or on-line to high intensity low repitition rate accelerators, a number of future requirements of the ion sources are discussed.     

Charge sharing in multi-electrode devices for deterministic doping studied by IBIC

Following a single ion strike in a semiconductor device the induced charge distribution changes rapidly with time and space. This phenomenon has important applications to the sensing of ionizing radiation with applications as diverse as deterministic doping in semiconductor devices to radiation dosimetry. We have developed a new method for the investigation of this phenomenon by using a nuclear microprobe and the technique of Ion Beam Induced Charge (IBIC) applied to a specially configured sub-100 μm scale silicon device fitted with two independent surface electrodes coupled to independent data acquisition systems. The separation between the electrodes is comparable to the range of the 2 MeV He ions used in our experiments. This system allows us to integrate the total charge induced in the device by summing the signals from the independent electrodes and to measure the sharing of charge between the electrodes as a function of the ion strike location as a nuclear microprobe beam is scanned over the sensitive region of the device. It was found that for a given ion strike location the charge sharing between the electrodes allowed the beam-strike location to be determined to higher precision than the probe resolution. This result has potential application to the development of a deterministic doping technique where counted ion implantation is used to fabricate devices that exploit the quantum mechanical attributes of the implanted ions.     

High brightness sources for MeV microprobe applications

State of the art MeV ion microprobe facilities are now approaching current density limitations on targets imposed by the fundamental nature of conventional gaseous ion sources. With a view to addressing this problem efforts are under way which have the ultimate objective of developing high brightness Li liquid metal ion sources suitable for MeV ion microprobe applications. Prototype Li⁺ and Ga⁺ liquid metal ion sources have been designed, fabricated and are undergoing preliminary testing. This paper describes the first total emittance and brightness measurements of a Ga liquid metal ion source. The effect of the geometry of the ion extraction system is investigated and the brightness data are compared to those of a radio frequency ion source.     

A new generation of single-ended Van de Graaff accelerators for ion implantation and ion beam analysis

High voltage Engineering Europa B.V., The Netherlands developed a new generation of single-ended Van de Graaff accelerators for ion implantation and ion beam analysis. The new HVEE Van de Graaff accelerators are equipped with a unique (patented) ion source exchange system capable of handling four lands of ion sources, mass separation at high voltage level and an X-ray intensity suppression system. The accelerators are able to produce a large variety of continuously, homogeneous and highly collimated mass-analyzed ion beams of several hundred μA in the energy range from 50 keV up to l MeV (l MV model) or from 100 keV up to 2 MeV (2 MV model), using singly charged ions, whereby the maximum energy can be easily reached and maintained without conditioning and virtually no X-rays are produced. Combined with two dedicated end stations (one for ion beam analysis using RBS, channeling, NRA and PIXE, and one with an automatic wafer-handling system for both single-wafer implantation and batch processing), these systems are very suitable for research as well as industrial applications.     

Improved resolution and sensitivity on the ANSTO microprobe and it’s application to μ-PIXE

We report on the improved spatial resolution of the ANSTO heavy ion microprobe, achieved through the use of a higher brightness ion source for hydrogen. The improved resolution will be demonstrated for applications of μ-PIXE.With the higher brightness source, a 3 μm resolution was achieved for μ-PIXE elemental analysis. This is illustrated in high resolution images of nickel (Ni)-hyperaccumulating Hybanthus floribundus subsp. floribundus leaf tissues, where individual cells were clearly visible in the acquired elemental images. The higher resolution images illustrated that Ni was localised in epidermal cell walls.     

Analysis of the characteristics of the plasma of an RF driven ion source for a neutral beam injector

A radio frequency(RF)driven ion source is a very important component of a neutral beam injector for large magnetic confinement fusion devices.In order to study the key technology and physics of an RF driven ion source for a neutral beam injector in China,an RF ion source test facility was developed at the Institute of Plasma Physics,Chinese Academy of Sciences.In this paper,a two-dimensional fluid model is used to simulate the fundamental physical characteristics of RF plasma discharge.Simulation results show the relationship of the characteristics of plasma(such as electron density and electron temperature)and RF power and gas pressure.In order to verify the effectiveness of the model,the characteristics of the plasma are investigated using a Langmuir probe.In this paper,experimental and simulation results are presented,and the possible reasons for the discrepancies between them are given.This paper can help us understand the characteristics of RF plasma discharge,and give a basis for further R&D for an RF ion source.     

在线低能气体离子源

材料中氦和氢积累可引起材料性能的恶化甚至失效。为研究材料内氦和氢的存在形式、氦与氢及缺陷的相互作用、气泡的形成和演变过程以及各种因素的影响,建立一套离子束能量最高20keV的潘宁型气体离子源引出和聚焦系统,与200kV透射电镜联机,在离子注入现场原位观察氦和氢不同注入浓度下材料内部的微观结构及变化过程。对离子源进行氦离子的起弧、引出和聚焦测试。离子源在15–60mA放电电流范围内稳定地工作。在5×10–3Pa和1.5×10–2Pa工作气压下,放电电压约380V和320V。低气压下引出离子束流比高气压下大,且引出束流随放电电流和吸极电压的增加而增加。等径三圆筒透镜有显著聚焦作用,在距透镜出口150cm处,离子束流密度提高一个量级以上。能量10keV左右的氦离子获得束流密度约200nA·cm–2的离子束,可满足多种材料进行在线离子注入和原位电镜观测的需要。     

Ion-beam-induced-charge characterisation of particle detectors

Ion-beam-induced-charge collection (IBIC) in a nuclear microprobe has been used to characterise detectors for the measurement of particles over a median energy range (100 keV–1 MeV). Three standard detector devices have been studied: a PIPS detector with a buried (ion-implanted) junction structure, a Schottky barrier junction device and a PN-junction photodiode. A 2.0 MeV focussed helium ion beam was used to probe the active area of each device with a spatial resolution 1–2 μm, to quantify the thickness of the dead layer, the charge collection response and the reduction in charge collection efficiency induced by ion-beam damage.     

Mapping ion beam induced current changes in a commercial MOSFET

We demonstrate a novel nuclear microprobe imaging and analysis modality for micrometre-scale field effect transistor devices probed with focused beams of MeV ions. By recording the drain current as a function of time during ion irradiation it is possible to identify current transients induced by the passage of single ions through the sensitive structures of the device. This modality takes advantage of the fact that the ionization produced by the passage of a single ion acts in an equivalent way to a transient change in the gate bias which therefore modulates the drain current as a function of time. This differs from the traditional ion beam induced charge technique where the ionization drifts in an internal electric field and induces a single charge pulse in an electrode applied to the device. Instead a richer variety of phenomena are observed, with different time constants which depend on the proximity of the ion strike to the channel of the device. The signals may be used to examine device function, radiation sensitivity or to count ion impacts within the channel.     

Simulation studies on two-frequency RF gun

Photocathode RF gun is widely used for particle accelerators as an electron source.When driving an RF electron gun at the fundamental frequency and a higher harmonic frequency simultaneously with proper field ratio and relative phase,it generates electron beams of ultralow emittance and a linear longitudinal phase space distribution.Such a gun provides high quality electron beam with low energy spread,small traverse emittance and high brightness.In this paper,the RF design of a 1.5 cell cavity is presented.Simulation results of beam dynamics for the two-frequency gun and a standard single-frequency RF gun are also shown in this paper.In addition,bunch compression with a two-frequency gun is explored.     

Microbeam complex at TIARA: Technologies to meet a wide range of applications

Since 1990 R&Ds of microbeam technology has been progressed at the TIARA facility of JAEA Takasaki. In order to meet a wide variety of ion beam applications, analysis, radiation effect studies, or fabrication in regions of micro- or nano-structures, three different types of ion microbeam systems were developed. In these systems, high-spatial resolutions have been achieved and techniques of micro-PIXE, single ion hit and particle beam writing (PBW) were also developed for these applications. Microbeams, on the other hand, require the highest quality of beams from the accelerators, the cyclotron in particular, which was an important part of the microbeam technology of TIARA. In this paper, the latest progress of the ion microbeam technology and applications are summarized and a future prospect of them is discussed.     

Characterization and calibration of a SSNTD for heavy-ion detection and strangelet search in cosmic rays

A commercially available grade of polymer was investigated for its suitability as a solid state nuclear track detector (SSNTD) to look for rare events in cosmic rays at very high mountain altitudes. It was identified to be polyethylene terephthalate (PET) and found to have a higher detection threshold compared to many other widely used SSNTDs. Hence it is particularly suited for rare event search in cosmic rays by eliminating the dominant low Z background. Systematic studies were carried out to determine the ideal etching condition. Also the charge response of PET was studied using various ion beams from accelerators. The results of such studies were combined to obtain the calibration curve for PET as SSNTD, by which one can identify and characterize charged particles.     

The design of a versatile scanning proton microprobe of high resolution and efficiency

The designer of a scanning proton (or nuclear) microprobe must make many decisions, some of which may be compromises. There is a wide range of lens types and configurations. Microprobe performance will depend on performance of the accelerator and its ion source, on stability and control of the lens current supply, on the nature of the microprobe supports, on the vacuum system, on magnetic shielding and connection to the accelerator.There are many possible modes of observation and analysis to be considered when the specimen chamber is designed and a versatile chamber should make provision for most of them. They include optical microscopy of front and back surfaces of the specimen, secondary electron imaging, X-Ray imaging, channelling contrast microscopy, Rutherford backscattering and forward scattering, nuclear reaction analysis and scanning transmission ion microscopy in brightfield and darkfield modes.Microprobe performance will also inevitably depend on the ease of operation and the extent to which the operator has been considered in the overall design and layout of the microprobe. The equally important considerations involved in data collection and analysis are discussed in a second paper.     

Proton beam micromachined resolution standards for nuclear microprobes

The quest for smaller spot sizes has long been the goal of many nuclear microprobe groups worldwide, and consequently there is a need for good quality resolution standards. Such standards have to be consistent with the accurate measurement of state-of-the-art nuclear microbeam spot sizes, i.e. 400 nm for high current applications such as Rutherford backscattering spectrometry and proton-induced X-ray emission, and 100 nm for low current applications such as scanning transmission ion microscopy or ion beam-induced charge. The criteria for constructing a good quality nuclear microprobe resolution standard is therefore demanding: the standard has to be three dimensional with a smooth surface, have an edge definition better than the state-of-the-art beam spot resolutions, and exhibit vertical side walls. Proton beam micromachining (PBM) is a new technique of high potential for the manufacture of precise 3D microstructures. Recent developments have shown that metallic microstructures (nickel and copper) can be formed from these microshapes. Prototype nickel PBM resolution standards have been manufactured at the Research Centre for Nuclear Microscopy, NUS and these new standards are far superior to the 2000 mesh gold grids currently in use by many groups in terms of surface smoothness, vertical walls and edge definition. Results of beam resolution tests using the new PBM standards with the OM2000 microprobe end station/HVEE Singletron system have yielded spot sizes of 290 nm×450 nm for a 50 pA beam of 2 MeV protons.     

金属真空弧离子源引出强流离子束的数值模拟

为了引出更高强度、更高亮度的铀离子束,以满足重离子研究中心(Gesellschaft für SchwerionenforschungmbH,GSI)重离子同步加速器的需求,本文用三维的计算机程序KOBRA3-INP对金属真空弧离子源(Metalvapor vacuum arcion source,MEVVA)引出强流铀离子束在引出系统和后加速系统中的动力学特性进行了研究,讨论了离子源发射束流密度对引出束性能的影响.结果表明,束流损失主要发生在引出系统和后加速系统之间的漂移区;在假设漂移区束流被空间电荷中和的情况下,模拟结果和实验结果符合;在发射束流密度为180-230 mA/cm2范围内,经后加速的束流强度变化不大.     

Recent Advances in DC Methods of Particle Acceleration

Four recent developments have contributed significantly to broadening the scope of dc particle-acceleration systems: 1. Tandem principle of utilizing the generated high-voltage several times; 2. Insulating-core transformer for generating high-voltage dc power; 3. Inclined-field acceleration tube that minimizes the "total voltage effect, a previous limitation of dc acceleration systems; 4. Ion-source and beam-optical designs to increase useful ion intensities and to improve efficiency of transporting accelerated dc beams. These developments are currently being incorporated, in various combinations, into several dc accelerator designs, including: a. Sub-Mev electron and positive-ion accelerators with high beam power; b. Tandem Van de Graaff accelerators with at least 10 million-volt potential; c. Powerful Tandem accelerator at moderate voltage and very high current. Typical systems arising out of these advances are described in the light of applications now being exploited in research and industry.     

Investigation of Arc Regulation of Hot Cathode Ion Source with Langmuir Probe

The neutral beam injector (NBI) is one of the main plasma heating methods for nuclear fusion devices. For the hot cathode high current ion source, the arc current and beam current tends to increase during the beam pulse. In order to gets long pulse beam extraction, the arc regulation technology is employed. The Langmuir probes are installed on the experimental advanced superconducting tokamak-NBI ion source, to feedback control the arc discharge and beam extraction. The experimental results show that, the long pulse of 100 s ion beam is extracted with beam energy of 30 keV with arc regulation. More the results are presented in this paper.