Investigation of avalanche silicon detectors for low energy single ion implantation applications

Avalanche silicon photodiodes have potential applications to detect low energy single ions for counting single ion impacts in shallow implant depths for the deterministic doping of nanoscale electronic devices. This paper reports the investigation of avalanche photodiode detectors in the linear operation mode for detection of 0.5–2 MeV helium ions. The measured charge gain was found to be up to 100 depending on bias voltage. The charge gain was found to saturate at a level that correlated with the ion stopping depth in silicon. The measured charge gain for energetic ions, which have a well-defined depth in a silicon substrate for the deposition of ionization energy, is compared with that of X-rays and photons, which deposit the ionization energy over a wider range of depth. This allowed the identification of a suitable structure for an avalanche photodiode optimised for the detection of sub-10 keV heavy ions with an internal charge gain above 10 achievable. This offers significant advantages over conventional PIN devices where the signals from such ions would be lost in the noise.     

Experimental stopping powers of Al,Mg, F and O ions in ZrO2 in the 0.1–0.6 MeV/u energy range

The study of the stopping and range of heavy ions (Z > 3) in matter isdsc cfddc of both fundamental and practical interest as heavy ions find increasing usage in a wide range of ion beam based techniques. While semi-empirical formulations like the widely used SRIM code can predict the stopping powers of hydrogen and helium in many elemental and compound targets over a wide range of energies quite well, their predictive accuracy for heavy ions is not as good. This is mainly due to the lack of heavy ion experimental stopping power data on which such codes are based. We present results of measurements performed using a Time of Flight–Energy spectrometer to determine the stopping powers of O, F, Mg and Al ions in the oxide ceramic ZrO₂ within the 0.1–0.6 MeV/u energy range. Possible SRIM correction (or correlation) factors for F, Mg and Al ions were extracted from quantitative comparisons of experimental and predicted stopping power values.     

Empirical approach to the description of spectral performance degradation of silicon photodiodes used as particle detectors

The spectral deterioration of Hamamatsu S5821 silicon photodiodes for ion types and energies frequently used in Ion Beam Analysis was investigated. Focused proton beams with energies 430 keV and 2 MeV were applied to generate radiation damage via an area selective ion implantation in unbiased diodes at room temperature. The variations of spectroscopic features were measured “in situ” by Ion Beam Induced Current (IBIC) method as a function of fluence, within the 10⁹–5 × 10¹² ion/cm² range and diode bias voltages, between 0 and 100 V.An empirical model has been developed to describe the radiation damage. Equations are derived for the variations of the normalized peak position and peak width. The derived empirical equations are physically correct, as far as they account for the superposition of the influence of charge carrier trapping by native and radiation-induced defects and for the effect of charge carrier velocity saturation with electric field strength, as well.     

High-speed processing with Cl2 cluster ion beam

Cluster ion beam processes can produce high rate sputtering with low damage compared with monomer ion beam processes. Cl₂ cluster ion beams with different size distributions were generated with controlling the ionization conditions. Size distributions were measured using the time-of-flight (TOF) method. Si substrates and SiO₂ films were irradiated with the Cl₂ cluster ions at acceleration energies of 10–30 keV and the etching ratio of Si/SiO₂ was investigated. The sputtering yield increased with acceleration energy and was a few thousand times higher than that of Ar monomer ions. The sputtering yield of Cl₂ cluster ions was about 4400 atoms/ion at 30 keV acceleration energy. The etching ratio of Si/SiO₂ was above eight at acceleration energies in the range 10–30 keV. Thus, SiO₂ can be used as a mask for irradiation with Cl₂ cluster ion beam, which is an advantage for semiconductor processing. In order to keep high sputtering yield and high etching ratio, the cluster size needs to be sufficiently large and size control is important.     

Comparative study of transient current induced in SiC p+n and n+p diodes by heavy ion micro beams

N⁺p and p⁺n diodes were fabricated on p- and n-type 6H–SiC substrates with epitaxial layers, respectively. The charge induced in the diodes by 9 MeV oxygen (O) and nickel (Ni) ions was measured using Transient Ion Beam Induced Current (TIBIC) to clarify the capability of these diodes as particle detectors. As a result of the TIBIC measurements using 9 MeV O, the Charge Collection Efficiency (CCE) of around 83% was obtained for both p⁺n and n⁺p diodes. Since the CCE value includes the consumption of incident ion energy in an Al electrode and the n⁺ (p⁺) region as well as the decay of charge in the measurement system, the CCE value obtained in this study indicates that SiC n⁺p as well as p⁺n diodes are suitable for particle detectors. On the other hand, in the case of 9 MeV Ni ion irradiation, the CCE for both n⁺p and p⁺n diodes decreases due to the Auger recombination in dense electron–hole pairs.     

Helium-implanted CLAM steel and evolutionary behavior of defects investigated by positron-annihilation spectroscopy

China Low Activation Martensitic (CLAM) steel has been chosen as the primary candidate structural material for the first wall/blanket for fusion reactor. The excessive helium irradiation induced damage of CLAM steel at high temperatures and the evolution of defects were investigated in this paper. The samples were homogeneously implanted with 1e + 17 ions/cm² and 100 keV of helium at room temperature, 473, 673, and 873 K. Irradiation induced damage of CLAM steel and the annealing behavior of defects were probed by slow positron beam Doppler broadening technique. Helium implantation produced a large number of vacancy-type defects which bound with helium and formed helium–vacancy complexes. Target atoms’ displacement capacity was strengthened with rising irradiation temperatures, so the S parameter increased with increasing irradiation temperatures, and helium–vacancy complexes were main defects after helium implantation at damage layers. Helium bubbles would be unstable and the desorption of helium bubbles would promote the density of defects above 673 K. By analyzing the curves of S–W and annealing tests of irradiated specimen, it suggested that there werenot only one type of defect in damage layers. Though helium–vacancy complexes were primary defects after helium implanted, introducing excessive helium might also generated other point defects or dislocation loops in the material.     

SHI induced re-crystallization of Ge implanted SiO2 films

Ge nanocrystals embedded in SiO₂ matrix have been synthesized by swift heavy ion irradiation of Ge implanted SiO₂ films. In the present study, 400 keV Ge⁺ ions were implanted into SiO₂ films at dose of 3 × 10¹⁶ ions/cm² at room temperature. The as-implanted samples were irradiated with 150 MeV Ag¹²⁺ ions with various fluences. Similarly 400 keV Ge⁺ ions implanted into Silicon substrate at higher fluence at 573 K have been irradiated with 100 MeV Au⁸⁺ ions at room temperature (RT). These samples were subsequently characterized by XRD and Raman to understand the re-crystallization behavior. The XRD results confirm the presence of Ge crystallites in the irradiated samples. Rutherford backscattering spectrometry (RBS) was used to quantify the concentration of Ge in the SiO₂ matrix. Variation in the nanocrystal size as a function of ion fluence is presented. The basic mechanism of ion beam induced re-crystallization has been discussed.     

Development of a TOF-ERDA measurement system for analysis of light elements using a He beam

A time-of-flight ERDA (TOF-ERDA) measurement system has been developed for the analysis of light elements. He ions are used for the incident beam, and recoil light ions are detected with the system. The system consists of a time detector and a silicon detector, and energy and velocity of recoil ion are measured simultaneously. The depth resolution of 21.6 ± 2.2 nm (FWHM) has been obtained by an ERDA measurement of a thin carbon layer onto a silicon wafer using a 5.7 MeV He beam. The mass resolution is better than 1 for elements up to oxygen. Maximum detectable depth of carbon in a PET film is about 650 nm. An ERDA measurement of implanted carbon in a silicon wafer has been demonstrated.     

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.     

The effect of displacement damage on deuterium retention in ITER-grade tungsten exposed to low-energy,high-flux pure and helium-seeded deuterium plasmas

Samples prepared from polycrystalline ITER-grade tungsten were damaged by irradiation with 20 MeV W ions at room temperature to a fluence of 1.4 × 10¹⁸ W/m². Due to the irradiation, displacement damage peaked near the end-of-range, 1.35 μm beneath the surface, at 0.89 displacements per atom. The damaged as well as undamaged W samples were then exposed to low-energy, high-flux (10²² D/m² s) pure D and helium-seeded D plasmas to an ion fluence of 3 × 10²⁶ D/m² at various temperatures. Trapping of deuterium was examined by the D(³He,p)⁴He nuclear reaction at ³He energies varied from 0.69 to 4.0 MeV allowing determination of the D concentration at depths up to 6 μm. It has been found that (i) addition of 10% helium ions into the D plasma at exposure temperatures of 440–650 K significantly reduces the D concentration at depths of 0.5–6 μm compared to that for the pure plasma exposure; (ii) generation of the W-ion-induced displacement damage significantly increases the D concentration at depths up to 2 μm (i.e., in the damage zone) under subsequent exposures to both pure D and D–He plasmas.     

A simple way to analyze infrared reflectivity spectra of p-type Hg0.78Cd0.22Te implanted in various conditions

Different ion-implanted p-type Hg_0.78Cd_0.22Te samples were analyzed by infrared reflectivity in the 2–20 μm wavelength range. We show how to derive some characteristic values of the free carriers induced by ion implantation from simple models of the implanted samples. For low energy implantations (Al (320 keV)) an excess of electrons with concentration n⁺ ≈ 5 × 10¹⁷ cm⁻³ for doses 10¹² and 10¹⁴ ions cm⁻² is observed between the surface and the projected range R_p of the ions, in agreement with the well-known change of type of the free carriers induced by the ion implantation in this kind of samples. High energy α particle (0.8 and 2 MeV, 10¹⁴ ions cm⁻²) implantations lead to a pronounced inhomogeneous concentration of free electrons with n⁺ ≈ 9.2 × 10¹⁶ cm⁻³ between the surface and R_p where a negligible amount of defects due to the nuclear energy loss is formed, and n⁺ ≈ 1.6 × 10¹⁷ cm⁻³ between R_p and R_p + ΔR_p, ΔR_p being the longitudinal straggling, where the defect production rate through the nuclear energy loss mechanism is maximum.     

Ge and Ti post-ion acceleration from laser ion source

Laser ion sources (LIS) are employed with success to generate, in vacuum, Ge and Ti ion beams with high current, ion energy, charge states and directivity.Nanoseconds infrared laser pulses, with intensities of the order of 10¹⁰ W/cm², induce high ablation in Ge and Ti targets. Ions are produced in vacuum with energy distribution following the Coulomb–Boltzmann-shifted distribution and they are ejected mainly along the normal to the target surface. The free ion expansion process occurs in a constant-potential chamber placed at 30 kV positive voltage. An electric field of 5 kV/cm was used to accelerate the ions emitted from the plasma at INFN-LNS laser facility. Time-of-flight technique is employed to measure the mean ion energies of the post-accelerated particles. Ion charge states and energy distributions were measured through an ion energy spectrometer.     

Stopping force and straggling of 0.6–4.7 MeV H,He and Li ions in the polyhydroxybutyrate foil

Stopping force and straggling of 0.6–3.5 MeV ¹H ions, 2.0–4.7 MeV ⁴He ions and 1.4–4.4 MeV ⁷Li ions in the polyhydroxybutyrate (PHB) foil were measured by means of a transmission technique. The measured stopping forces are in well agreement with the SRIM 2008 calculation and the ICRU Report tables, except for the lower energy region. The obtained energy loss straggling deviates from the Bohr’s value by as much as 23.6% for the energies under study. The validity of the Bragg’s rule has also been demonstrated in the stopping force and straggling for ¹H, ⁴He and ⁷Li ions in the PHB foil.     

Deuterium and helium retentions of V–4Cr–4Ti alloy used as first wall of breeding blanket in a fusion reactor

The deuterium and helium retention properties of V–4Cr–4Ti alloy were investigated by thermal desorption spectroscopy (TDS). Ion energies of deuterium and helium were taken at 1.7 and 5 keV, respectively. The retained amount of deuterium in the sample irradiated at 380 K increased with the ion fluence and was not saturated to fluence of up to 1 × 10²³ D/m². For the irradiation at 773 K, 0.1% of implanted deuterium was retained at the highest fluence. For the helium ion irradiation at room temperature, three groups of desorption peaks appeared at around 500, 850, and 1200 K in the TDS spectrum. In the lower fluence region (<1 × 10²¹ He/m²), the retained helium desorbed mainly at around 1200 K. With increasing fluence, the amount desorbed at 500 K increased. Total amount of retained helium in the samples saturated at fluence up to 5 × 10²¹ He/m² and saturation level was 2.7 × 10²¹ He/m².     

Effect of a body-tie structure fabricated by partial trench isolation on the suppression of floating body effect induced soft errors in SOI SRAM investigated using nuclear probes

Soft errors induced by proton, helium and oxygen ion irradiations were measured as a function of distance between a body electrode under partial trench isolation and a metal pad connected to a tungsten via for the first metal layer of a silicon-on-insulator (SOI) static random access memory. Abnormal drain charges induced by ion irradiations with various distances in the SOI metal oxide semiconductor field effect transistor were simulated to be compared with the experimental results. The soft errors were found to depend on the distance between the body electrode and the metal pad in the case of the abnormal drain charge, which is induced by incident ions, lower than the critical charge of the SRAM cells. The soft errors did not depend on the distance for the abnormal drain charges higher than the critical charge.     

Ion beam mixing in uranium nitride thin films studied by Rutherford Backscattering Spectroscopy

Thickness, composition, concentration depth profile and ion irradiation effects on uranium nitride thin films deposited on fused silica have been investigated by Rutherford Backscattering Spectroscopy (RBS) using 2 MeV He⁺ ions. The films were prepared by reactive DC sputtering at the temperatures of ?200 °C, +25 °C and +300 °C. A perfect 1U:1N stoichiometry with a layer thickness of 660 nm was found for the film deposited at ?200 °C. An increase of the deposition temperature led to an enhancement of surface oxidation and an increase of the thickness of the mixed U–N–Si–O layers at the interface. The sample irradiation by 1 MeV Ar⁺ ion beam with ion fluence of about 1.2–1.7 × 10¹⁶ ions/cm² caused a large change in the layer composition and a large increase of the total film thickness for the films deposited at ?200 °C and at +25 °C, but almost no change in the film thickness was detected for the film deposited at +300 °C. An enhanced mixing effect for this film was obtained after further irradiation with ion fluence of 2.3 × 10¹⁶ ions/cm².     

Annealing of ion implanted 4H–SiC in the temperature range of 100–800 °C analysed by ion beam techniques

Ion implantation induced damage formation and subsequent annealing in 4H–SiC in the temperature range of 100–800 °C has been investigated. Silicon Carbide was implanted at room temperature with 200 keV ⁴⁰Ar ions with two implantation fluences of 4 × 10¹⁴ and 2 × 10¹⁵ ions/cm². The samples were characterized by Rutherford backscattering and nuclear reaction analysis techniques in channeling mode using 2.00 and 4.30 MeV ⁴He ion beams for damage buildup and recovery in the Si and C sublattices, respectively. At low ion fluence, the restoration of the Si sublattice is evident already at 200 °C and a considerable annealing step occurs between 300 and 400 °C. Similar results have been obtained for the C sublattice using the nuclear resonance reaction for carbon, ¹²C(α,α)¹²C at 4.26 MeV. For samples implanted with the higher ion fluence, no significant recovery is observed at these temperatures.     

Fabrication of nanowires by varying energy microbeam lithography using heavy ions at the TIARA

In TIARA facility of Japan Atomic Energy Agency (JAEA) Takasaki, we have produced three-dimensional micro/nano-structures with high aspect ratio using cross linking process based on negative resist such as SU-8 by a technique of mask less ion beam lithography. By bombarding high energy heavy ions such as 450 MeV Xe²³⁺ to SU-8, on the other hand, it appeared that a nanowire could be produced just with a single ion hitting. Then we tried to produce nanowires, of which both ends were fixed in the three-dimensional structure. This paper shows a preliminary experiment for this purpose using a combination of 15 MeV Ni⁴⁺ ion microbeam patterning and the 450 MeV ¹²⁹Xe²³⁺ hitting on SU-8.     

Elastic scattering of 7Li + 27Al at several angles in the 7–11 MeV energy range

Elastic cross sections for the ⁷Li + ²⁷Al system were measured at laboratory energies between 7 and 11 MeV in steps of 0.25 MeV, and angles between 135° and 170° in steps of 5°. Excitation functions for the elastic scattering were measured using an array of eight Si surface-barrier detectors whereas a solid-state telescope was used to estimate and subtract background from other reactions. Contamination from α particles arising from the ⁷Li breakup process at E_lab ? 10 MeV makes the use of these energies inadvisable for RBS applications. The present results are compared with previous data obtained at 165° (E_lab ? 6 MeV), 140° and 170° (E_lab ? 8 MeV). The experimental data were analyzed in terms of the Optical Model. Two different energy-independent potentials were found. These optical potentials allow an interpolation with physical meaning to other energies and scattering angles. The experimental cross sections will be uploaded to the IBANDL database.     

Ion channeling investigation of oxygen sublattice in YBa2Cu3O7 crystal film

The features of the oxygen sublattice in a crystal YBa₂Cu₃O₇ are investigated by channeling technique. It has been measured the angular dependence of resonant reaction yield of 3.055 MeV He⁺ ions channeled from oxygen nuclei along 〈0 0 1〉 direction. The best agreement of the calculated angular dependence of the reaction yield with experimental data is achieved with the assumption that the oxygen sublattice is partly disordered. About 20% of oxygen atoms are situated in the plane (1 1 0) randomly; the oxygen atoms in oxygen chains are displaced from crystal sites at ∼0.3 Å in the (1 1 0) plane.