A. Saint

The Leipzig high-energy ion nanoprobe: A report on first results

Abstract The high-energy ion nanoprobe LIPSION at the University of Leipzig has been operational since October 1998. Its magnetic quadrupole lens system, arranged as a separated Russian quadruplet, has been developed by the Microanalytical Research Centre (MARC), Melbourne. The ultrastable single-ended 3.5 MV SINGLETRON™ accelerator (High Voltage Engineering Europa) supplies H+ and He+ ion beams with a beam brightness in the range of 10–20 A rad −2 m −2 eV −1 [D.J.W. Mous, R.G. Haitsma, T. Butz, R.-H. Flagmeyer, D. Lehmann, J. Vogt, Nucl. Instr. and Meth. B 130 (1997) 31]. Due to this high brightness, the excellent optical properties of the focusing system of the nanoprobe and the suppression of mechanical vibrations, lateral resolutions of 100 nm for the low current mode (STIM) and 340 nm at a current of 10 pA (PIXE, RBS, SEI modes) were achieved. Further improvements are expected.

High resolution imaging with high energy ion beams

Abstract The limits to high spatial resolution and the requirements for its achievement are discussed. A decade of evolution in high energy ion microscopy is reviewed, the principles, performances and possibilities of the many techniques are discussed. The resultant extreme demands placed upon the microprobe system are described. Finally, possibilities of, requirements for and progress towards nanometre resolution are reviewed.

Ion Beam Induced Charge Collection (IBICC) microscopy of ICs: Relation to Single Event Upsets (SEU)

Abstract Single event upset (SEU) imaging is a new diagnostic technique recently developed using Sandias nuclear microprobe. This technique directly images, with micron resolution, those regions within an integrated circuit which are susceptible to ion-induced malfunctions. Such malfunctions are an increasing threat to space-based systems which make use of current-generation 1C designs. A complementary technique to SEU imaging involves measurement of the charge collection volumes within integrated circuits; charge collection is the underlying physical process responsible for single event phenomena. This technique, which we term ion beam induced charge collection (IBICC), has been used here and elsewhere to generate micron resolution maps of the charge collection response of integrated circuits. In this paper, we demonstrate the utility of combining the SEU imaging and IBICC techniques in order to gain a better understanding of single event upset phenomena. High resolution IBICC images are used to extract more detailed information from charge collection spectra than that obtained from conventional broad-area ion exposures, such as from radioactive sources. Lastly, we suggest the application of IBICC as a replacement for electron beam induced conduction/current (EBIC) measurements. As reductions in circuit feature size continue in the submicron regime, IBICC could certainly prove to be a technologically valuable replacement for EBIC and an important business opportunity for all nuclear microprobe facilities.

Submicron STIM tomography reconstruction techniques

Abstract One-dimensional projections of ion energy loss have been converted to areal density using tabulated stopping powers in a scanning transmission ion microscopy (STIM) reconstruction of a test object, displaying a spatial resolution of 0.37 μm. Location and registration of the centre of areal mass density in each projection provides a means of overcoming (a) the misalignment of the specimen rotation axis with the centre of the scan path and (b) deviations of the specimen from its precession around the axis of rotation. Multiplicative algebraic reconstruction technique (ART), filtered backprojection and maximum-entropy algorithms for the reconstruction of the object are considered. Maximum entropy is shown to produce an image with the least number of artifacts. However, when time considerations are taken into account, it is found that filtered backprojection is the preferred algorithm for a tomographic reconstruction.

Channeling scanning transmission ion microscopy

Scanning transmission ion microscopy (STIM) has been used, in conjunction with channeling, to explore transmission channeling in 50‐μm‐thick epitaxially grown n‐type silicon with 3.9 MeV H+ beam currents of 0.1 fA focused to spot sizes of less than 200 nm. The technique is extremely efficient, causes negligible damage, and is capable of very high resolution. High‐resolution images of crystal damage were obtained with this first demonstration of channeling contrast in STIM.

Ion-beam-induced charge-collection imaging of CMOS ICs

Charge collection regions of the Sandia TA670 16-Kbit SRAM have been directly imaged using a technique we call ion-beam-induced charge-collection (IBICC) imaging. During the IBICC measurement, the integrated circuit is connected through its power (VDD) or ground (VSS) pins to a charge sensitive preamp whose output is pulse-height analyzed while the IC is exposed to a scanned 0.1-μm resolution microbeam of heavy ions. The IC, in effect, functions as its own detector of the magnitude of charge collected following a heavy-ion strike. In this work, we examine the effect on IBICC imaging of varying power supply bias over a range of 0 to 15 V. Comparison of the IBICC image with the design layout for this integrated circuit unambiguously identifies source and drain regions of n-channel transistors and drain regions of p-channel transistors in the memory array. We were not able to image p-channel source regions in either the VDD or VSS configuration. This result is clearly explained on the basis of the IC design. Comparison of IBICC images with previously measured single-event-upset (SEU) images of the TA670 provide a more complete understanding of the mechanisms that govern single-event upset in this SRAM. IBICC holds great promise as a diagnostic tool to quantify the underlying charge collection processes that are responsible for single event upset in complex integrated circuits. It can also be applied to device failure analysis in a manner similar to EBIC, with potentially higher resolution.

A comparative study of the radiation hardness of silicon carbide using light ions

6H-silicon carbide (SiC) schottky diodes were irradiated at room temperature (RT) with proton, alpha and carbon particles to fluences in the range of 108–1013 ions/cm2. Both radiative and non-radiative traps are generated due to damage caused by the incident ions. Ionluminescence performed at RT revealed that radiative traps with photon emission energy of 2.32 eV appear after radiation. Electroluminescence measurement indicated that at RT the influence of non-radiative defects dominated over the radiative ones. Ion beam induced charge collection was used to investigate the charge collection efficiency of these diodes. Reduction in the charge pulse height is compared with calculation of non-ionising energy loss (NIEL). NIEL is a good measure of the displacement damage introduced in SiC materials by ionising particles. There is no significant difference in the radiation hardness of n-type and p-type 6H-SiC schottky diodes when irradiated with 2 MeV alpha particles.

Secondary electron emission from boron-doped diamond under ion impact: Applications in single-ion detection

The secondary electron emission from a 2 μm thick boron-doped diamond film under ion (4.6–7.7 MeV He+)impact is reported. The yield under ions impact is found to be remarkably high, stable over a period of many months, and independent of which side of the film (i.e., growth or substrate side) is exposed to the ion flux. By taking advantage of the high secondary-electron yield, the passage of each ion through the film could be detected with an efficiency of close to 100%, which to the best of our knowledge is the highest efficiency recorded to date for any thin-film window. This finding has an immediate application in single-ion irradiation systems where a thin vacuum window is required to allow extraction of an ion beam from the vacuum into air and at the same time offer 100% efficiency for the detection of the passage of the ion through the window.

STIM tomography: a three-dimensional high resolution imaging tool

Abstract The ion microprobes now found in many accelerator laboratories were developed to perform quantitative elemental microanalysis with high sensitivity. The rapid evolution on this instrument of new computer based techniques has led to the development of high resolution quantitative 3D ion microtomography. This technique offers unique opportunities to examine internal structure of microscopic specimens.

New problems in nuclear microprobe analysis of materials

Abstract Advanced materials are being evaluated for use as novel radiation detectors and microelectronic devices, including, potentially, synthetic diamond radiation-hard detectors for high-energy physics experiments and tissue equivalent dosimeters. Use of a nuclear microprobe has allowed spatially resolved electrical properties of the detector material to be measured. However quantitative analysis requires good models for charge collection mechanisms by ion beam induced charge (IBIC). In fact, nuclear microprobe analysis is playing an increasingly prominent role in the analysis of detector materials and devices by IBIC, with secondary roles also being played by ionoluminescence (IL) and the traditional techniques of Rutherford backscattering and particle induced X-ray emission. In this paper, many recent applications are reviewed and some examples of applications of the nuclear microprobe to the study of new materials and devices are presented. Some of these applications involve wide band gap materials, such as GaN, as well as novel detectors for radiation dosimetry in cancer therapy, photovoltaic devices and other microelectronic devices.