Ion Microbeam Research Articles

Analysis of heavy-ion induced charge collection mechanisms in SOI circuits

Focused ion microbeam and broadbeam heavy-ion experiments on capacitors and SRAMs are used to investigate charge collection in SOI devices. Charge collection in capacitors and ICs can be induced by displacement currents caused by the release of charge in the substrate. The magnitude of charge collection depends on the geometry, gate surface area and oxide thickness of the device. It is mainly induced by the diffusion of carriers generated in the silicon bulk, which induces a voltage drop under the oxide surface. Carrier diffusion in low-doped silicon creates coupling effects between MOS elements separated by up to hundreds of microns. However, because of charge sharing effects, charge collection by displacement currents (by itself) does not appear to significantly affect SEU sensitivity in SOI devices. p–n junctions are far less sensitive to charge sharing effects than neighboring MOS structures. A mechanism that can significantly increase the SEU saturation cross section in SOI devices is charge release in non-ideally doped drain regions (not heavily doped throughout the silicon film). Carriers released in drain regions can drift or diffuse into the body region and be amplified by parasitic bipolar effects. By heavily doping drain junctions throughout the silicon film, drain strike sensitivity can be significantly reduced. For this case, SEU sensitivity can be limited to gate (body) strikes and by reducing parasitic bipolar effects using body ties, SOI circuits can be fabricated that are very hard to single event effects. These results have important implications on the soft-error reliability of SOI and other oxide-isolated structures, e.g., DRAMs. For SOI SRAMs, it is possible that the additive effects of charge collection by displacement currents and charge released in drain regions may lead to SEU. For trench DRAMs, the retention capacitors are particularly sensitive to charge released in the substrate. Charge collection in retention capacitors by displacement currents can lead to multiple bit upsets (MBUs) in DRAMs, thus significantly degrading the soft-error reliability of DRAMs.

Development of single-ion hit techniques and their applications at TIARA of JAERI Takasaki

At TIARA facility in JAERI Takasaki, the single-ion hit technique combined with heavy ion microbeam has evolved in conjunction with developments in applied research such as the study of single-ion irradiation effects in semiconductors or biological cells. This technique is the most effective tool for the investigation of individual phenomena induced by single-ion injections to local areas of those samples, which have micron-scale structures. Adding a feature of position detection for the study of single event effects in semiconductor nano- or quantum devices is regarded as the next stage in the development of the single-ion hit technique.

Ion beam analysis of functional layers for CuInSe 2 solar cells deposited on polymer foils

In this study various functional layers and stacks of layers up to complete CuInSe 2 (CIS) solar cells produced on polyimide foils by the Solarion company in a roll to roll process using sputter and evaporation techniques were investigated by means of RBS and PIXE using He + and H + broad ion beams and microbeams in order to optimize the deposition parameters. The ITO front contact layer deposited on a polyimide foil of 200 mm width showed a very good homogeneity of the thickness and composition across the polyimide substrate. The elemental composition was found to be identical to the sputter target taking into account that the Sn concentrations in the ITO films were found to be underestimated by a factor of 1.8 when using PIXE. The individual layers of a complete CIS solar could be analysed with a combination of RBS and PIXE under some reasonable assumptions. With microbeam scans the granular structure of the CIS film could be imaged. Furthermore, from elemental profiles extracted along scratches in the absorber layer it was found that only 75% of the CIS absorber layer thickness were selenized which explains the Se-deficiency observed in the broad beam measurements.

Ferromagnetic microstructures in highly oriented pyrolytic graphite created by high energy proton irradiation

In this study ferromagnetic microstructures were created in highly oriented pyrolitic graphite (HOPG) by proton microbeam irradiation. For this purpose, spots of 1, 2 × 2 and 3.5 × 3.5 μm 2 were irradiated with ion fluences ranging from 3.1 × 10 16 to 4.7 × 10 19 cm −2 using 2.25 MeV proton and 1.5 MeV helium ion microbeams. As calculated by SRIM2003 simulations, the corresponding defect densities in the near surface region are between 3 × 10 19 and 4 × 10 22 cm −3 for the proton irradiation. The irradiated spots, which were characterized with atomic force microscopy (AFM) and magnetic force microscopy (MFM), show a clear swelling of the HOPG crystal proportional to the ion fluence. Strong magnetic force gradients were found even for the lowest proton fluences. Contrary to the topography, the magnetic force gradient changes after the application of a magnetic field. This rules out that the magnetic signals arise from topographical changes. Therefore, the MFM measurements reveal the existence of ferromagnetic domains in localized, disordered HOPG regions. On the contrary, helium ion irradiation of HOPG leads to much weaker magnetic signals only, which indicates that hydrogen plays a significant role in the formation of the magnetic moments and ordering. Very recently, the existence of ferromagnetism in ion beam irradiated HOPG was confirmed by SQUID measurements.

Improving of Irradiation Efficiency of the JAERI-Takasaki Heavy Ion Microbeam Cell Irradiation System (III)

Improving of Irradiation Efficiency of the JAERI-Takasaki Heavy Ion Microbeam Cell Irradiation System (III)

The PTB single ion microbeam for irradiation of living cells

At the PTB's ion accelerators, a new microbeam facility is now in operation that is capable of delivering single ions, for example, to the nuclei of individual living cells. The wide range of proton and 4He 2+ ion energies affords LET-values between 3 and 200 keV/μm. A beam diameter of less than 2 μm outside the vacuum system has been measured and a targeting accuracy of better than 2 μm has been determined. In contrast to other microbeam facilities operated for radiobiological research using mechanical collimators in front of the target to define the beam, the PTB facility utilises beam focusing by quadrupole magnets. The microbeam has a unique ion optical design that incorporates a 90° bending magnet in the beam transport system. This design has the advantage of providing a microbeam basically without scattered particles. Every ion reaching the target is detected by a thin scintillating foil and a photomultiplier tube with efficiency close to 100%. Presently up to 1500 single cells per hour can be automatically irradiated with a chosen number of particles. Procedures and results of first cell irradiations are described as an example.

Resolution improvement for a maskless microion beam reduction lithography system

A maskless ion projection lithography technique called maskless microion beam reduction lithography (MMRL) has been developed at Lawrence Berkeley National Laboratory. As a candidate for a next generation lithography system, MMRL is designed to achieve sub-70 nm resolution. By adding a 100 μm diam limiting aperture at the focal plane of the ion beam, an aperture angle of 0.56 mrad [corresponding to numerical aperture (NA)=5.6×10−4] at the image plane has been obtained. Small NA can decrease the geometrical and axial chromatic aberrations of the MMRL system. Thus resolution better than 150 nm has been obtained. Simulation results indicate that the resolution can be further improved by decreasing the aperture diameter and minimizing the limiting aperture induced aberrations. Meanwhile, the single-shot exposure time can still be as low as 193 ms at NA≈10−5 if the high brightness ion source design is employed in the MMRL system.

Ion microbeam diagnostics with scintillators for application of deep lithography with particles

We have developed two techniques for microscopic particle beam imaging and dose measurement, both based on scintillators. One employs a scintillating fiberoptic plate to display the two-dimensional beam transversal profile, the other makes use of a small scintillator optically coupled to a compact photomultiplier. We have proved the possibility of detection from single beam particles up to several nanoampere currents. Both the devices are successfully being exploited for on-line control of low and very low intensity proton beams, down to a beam size of <50 /spl mu/m in the framework of deep lithography with protons oriented to the production of optical microcomponents.

Focusing of MeV ion beams by means of tapered glass capillary optics

We present evidence of the focusing effects of fine glass capillary optics for MeV He ion beams. The glass capillary optics are formed by a puller as to have inlet diameters of about 1 mm and outlet diameters of submicrons. The total length of the optics is about 50 mm. Impingent MeV ions to such optics are reflected by the inner wall several times, in a very similar process to the so-called surface channeling. The majority of incident ions are lost by the dechanneling, or large-angle scattering process, however, a part of them, actually about 1% more or less, is emitted through the outlet without significant energy loss. Compared with the conventional micro-ion beam facilities, the present method is certainly simple and lowcost, thus providing an easy method of submicron Rutherford backscattering spectrometry or particle induced x-ray emission analyses. In addition, if the ion species are extended to heavier elements, the present method provides versatile maskless ion implantation techniques.

Irradiation of single mammalian cells with a precise number of energetic heavy ions – Applications of microbeams for studying cellular radiation response

A single cell irradiation system has been developed for targeting cells individually with a precise number of high-LET heavy ions to elucidate radiobiological effects of single heavy ions and to investigate the interaction of damages produced by separate events. The system has been installed at a high-energy collimated heavy-ion microbeam apparatus under a vertical beam line of the JAERI-Takasaki AVF-cyclotron. Using the heavy ion microbeam apparatus, mammalian cells are irradiated in the atmosphere with a single or precise number of heavy ions, 13.0 MeV/u 20Ne or 11.5 MeV/u 40Ar. Positional data of the individual cells are obtained at an off-line microscope before irradiation, then the cells are targeted and irradiated semi-automatically using the on-line microscope of the microbeam apparatus according to the obtained data. The number of ions penetrating the cells attached on the ion track detector CR-39 were counted with a plastic scintillator-photomultiplier tube assembly and a constant fraction discriminator. Immediately after the irradiation, the position and the number of ion tracks traversed the cell was detected with etching of CR-39 from the opposite side of the cell with alkaline-ethanol solution at 37 °C. The growths of the cells were observed individually up to 60 h after irradiation. The continuous observation of the individual cell growth indicated that a single ion traversal of a cell nucleus resulted in complete growth inhibition of the irradiated cells.

Reconstruction of low-count step-like signals in ion microbeam analysis

The evaluation of experimental data of ion microbeam analysis is often hindered by low counts/pixel statistics of elemental or tomographic images available within limited acquisition time, mainly at low elemental concentrations. In this contribution we present a method based on a non-linear iterative deconvolution scheme, designed to recover step-like profiles with forcibly low counts. To demonstrate its performance and effectiveness, the algorithm was applied for measured one-dimensional profiles with a micrometre resolution, generated by Rutherford backscattering spectrometry (μRBS) at the ATOMKI scanning nuclear microprobe facility. The method can be extended to solve the analogous two-dimensional problem, giving an improvement of nuclear microscopic methods, like channelling contrast microscopy (CCM).

Design of a focusing high-energy heavy ion microbeam system at the JAERI AVF cyclotron

For bio-medical applications of single-ion hit techniques such as radio-microsurgery, a focused high-energy heavy ion microbeam was designed and installed as a vertical beam line connected to the AVF cyclotron ( K=110) facility at JAERI Takasaki. By extracting a heavy ion microbeam into atmosphere, living cells can be irradiated with an accuracy smaller than typical cellular sizes. In addition, a high-speed automatic targeting and single-ion irradiation system was combined with a two-dimensional microbeam scanning system allowing more than 1000 targets per minute to be hit within a set field of view. Such high speeds targeting is necessary when examining statistically significant trends in cell irradiation studies within feasible time constraints. A real-time single-ion hit position detecting system was also designed to further increase the reliability of such irradiations.

Characterization of refractive index changes of silica glass induced by ion microbeam

Distributions of structural and refractive index changes of silica irradiated by H + microbeam were studied by optical and atomic force microscopes (AFM). The AFM measurements on the microbeam irradiated area show the formation of a groove on the surface. In addition, a cross sectional observation on the surface parallel to the incident plane reveals surface deformation along the ion tracks, which is deepest at the projected range of ions. Taking into account the possible structural changes of silica induced by energy deposition calculated by TRIM, the measured topological changes at the front and side surfaces result from internal compaction of silica glass. Refractive index changes were estimated from the Lorentz–Lorenz relationship using the distribution of the internal compaction estimated by the AFM measurements.

A comparison of heavy ion and picosecond laser microbeams for investigating single event transients in InGaAs on InP photodetectors

The MeV ion and laser microbeams are the two most commonly used tools for examining the spatial and temporal dependence of charge collection processes that lead to single event phenomena in semiconductor devices. In this paper, we perform a detailed comparison of the fundamental differences that exist between the two methods for examining single event transients in InGaAs photodetectors. In particular, we compare results collected by transient laser and ion beam induced current for several ion species.

The design and application of ion microbeams for irradiating living cells and tissues

The range of radiobiological experiments requiring microirradiation techniques continues to expand and diversify, creating ever-greater challenges for the designers of such systems. A versatile microbeam for radiation biology must excel in a number of areas. For studies of intracellular cell signalling where it may be of interest to target just the cytoplasm or nuclear membrane, targeting accuracies of micron or less are desirable. Other studies may use endpoints that are rare enough to require the irradiation of hundreds of thousands of cells in order to observe and quantify the effects. Inevitably, this means automating the cell finding, aligning and irradiation steps in order to achieve high cell throughputs. For investigations related to radiation risk, the effect of single particle traversals are paramount, therefore particle counting and single particle delivery are essential. A number of improvements have been implemented to the Gray Cancer Institute charged-particle microbeam, to extend its versatility and to meet these challenges. Specifically, improvements to the speed, alignment accuracy and environmental control have enabled investigations related to cell signalling, low-dose hypersensitivity, genomic instability and the visualisation of DNA repair to be successfully addressed.

Hydrogen redistribution in titanium due to bending stress studied by micro ERDA

The influence of bending stress on the hydrogen behaviour in titanium was investigated by elastic recoil detection analysis with a heavy ion microbeam (micro ERDA) and X-ray diffraction (XRD). The samples were made by hydrogen ion implantation into polished pure titanium sheets. Three-dimensional hydrogen distributions were obtained by scanning the microbeam over the sample using the depth information of ERDA. Inhomogeneous hydrogen distributions in the titanium were observed which vary with the depth. With mechanical bending of the samples the inhomogeneities increased in varied grade. The surface hydrogen loaded by surface polishing is stable, whereas the implanted hydrogen located inside of the sample is mobile under bending. These different hydrogen behaviours are relevant to the chemical states of hydrogen. Different titanium hydrides are formed by the different loading methods. An relatively unknown titanium-dihydride phase (TiH 2(x)) with a tetragonal texture was identified by XRD in the depth region of implanted hydrogen. It is less stable than the normal titanium-dihydride phase (TiH 2(δ)) observed in the surface region. The change of hydrogen distribution is related to the dehydrogenation of the TiH 2(x) and TiH(γ) under bending.

Characterization of ion-implanted silica glass by micro-photoluminescence and Raman spectroscopy

We evaluated structural changes in silica glass induced by ion microbeam using microscopic photoluminescence (PL) and Raman scattering measurements. Microbeams (1.7 MeV H +) were scanned over the sharp right-edges of the silica substrates with a fluence of 1×10 17 cm −2, then two PL bands of silica at 540 and 650 nm were observed at the irradiated region. The PL bands show different lateral and depth distributions. The distribution of the 540 nm PL is in good agreement with that of the refractive index changed region. The lateral distribution of the 650 nm band is broader by 1.5 times than those of the 540 nm PL and the refractive index changed region. The microscopic Raman scattering measurements show an increased intensity of 606 cm −1 peak associated with compaction at the microbeam irradiated regions.

Radiosurgery using heavy ion microbeams for biological study: Fate mapping of the cellular blastoderm-stage egg of the silkworm, Bombyx mori

We investigated the effects of heavy ions on embryogenesis of the silkworm, Bombyx mori using a collimated heavy ion microbeam from the vertical beam line of an AVF-cyclotron. Eggs were exposed to carbon ions at the cellular blastoderm stage. Microbeams were found to be extremely useful for radio-microsurgical inactivation of nuclei or cells in the target site. Spot irradiation caused abnormal embryos, which showed localized defects such as deletion, duplication and fusion, depending on dose, beam size and site of irradiation. The location and frequency of defects on the resultant embryos were closely correlated to the irradiation site. Based on this correlation, a fate map was established for the Bombyx egg at the cellular blastoderm stage.

Comparison of the ion induced charge collection in Si epilayer and SOI devices

It is known that the single-event phenomena (SEP) are the malfunction of micro electronics devices caused by the impact of an energetic heavy ion. Improving the tolerance of devices to the SEP requires a better understanding of basic charge collection mechanisms on the timescales of the order of picoseconds. In order to better elucidate these mechanisms, we measure the fast transient current resulting from heavy ion strikes with a fast sampling data collection system and a heavy ion microbeam line at JAERI. In this paper we report on differences in both the transient current and charge collection from 15 MeV carbon ions on silicon-on-insulator, Si epilayer and bulk p +n junction diodes and charge transportation under MeV ion injection is discussed.

Radiation damage on 6H-SiC Schottky diodes

The radiation damage production rate in SiC Schottky diodes was studied by measuring the ion beam induced charge (IBIC) from a 2 MeV He + ion microbeam. Two 30 μm diameter SiC Schottky diodes with a Ni Schottky contact were fabricated on 5 μm thick epilayers of both n-type and p-type 6H-SiC. An area of 10 μm × 10 μm on each Schottky diode was irradiated by a scanned 2 MeV He + ion beam focused to less than 1 μm in diameter with a dose range from 1 × 10 9 to 1 × 10 13 ions/cm 2. Before and after He + ion beam irradiation, IBIC spectra were measured at the irradiated area. From these spectra, the relationship between the IBIC peak shift and the He + ion beam dose was measured. For the n-type and p-type diodes, the IBIC pulse height was found to decrease from the initial height by 27% at 7.6 × 10 11 ions/cm 2 irradiation and 29% at 1.1 × 10 11 ions/cm 2, respectively.