keV In Silicon Research Articles

Effective attenuation length of keV photoelectrons in silicon measured by transmission through thin membranes

We use 9 nm and 15 nm thin membranes for determining the effective attenuation length of photoelectrons in silicon. One side of silicon membranes was covered with a thin film of aluminium and exposed to X-rays with energies from 3 to 8 keV. We recorded Al 1s and 2s photoelectrons that were (a) emitted from the Al film directly and (b) transmitted through the membranes. With the help of the ratio of both yields, we obtained values for the effective attenuation length (EAL) of electrons with kinetic energies up to 7.9 keV in silicon. The experimentally determined EAL values are smaller than obtained from different predictive equations. Using a power law fit EAL(k,p)=kEkinp to the experimental and predicted EAL values we find that mainly different is the pre-factor of the power law, k, while the exponent, p, i.e. the dependence on kinetic energy Ekin is represented well. Our study underlines the feasibility of using membranes for investigating surfaces under (near) ambient pressure conditions by photoelectron spectroscopy and points out the advantages of employing hard X-rays.

A novel mechanism of ultrathin SOI synthesis by extremely low-energy hot O+ implantation

Extremely low-energy oxygen implantations at 10 keV in silicon were challengingly performed to directly synthesize ultrathin silicon-on-insulator (SOI) structure separated by a buried oxide (BOX) layer. We quantitatively investigated the optimum condition and the formation mechanism of homogeneous and continuous stoichiometric SOI/BOX structure. In this study, oxygen ions were implanted into Si(0 0 1) substrates with keeping the temperatures at 500, 800, and 1000 °C with ion-fluences from 0.5 to ions cm−2. These samples were then postannealed at high temperatures from 950 to 1150 °C in Ar ambient for several hours. We found that ultrathin stoichiometric SOI/BOX structure with less than 20 nm thick was synthesized by oxygen implantation with an ion dose of ions cm−2 from 500 °C to 800 °C followed by annealing at a significantly low temperature of 1050 °C for 5 h. According to the RBS-channeling analysis, the crystallinity was excellent as quality as that of the SOI structure formed by a wafer-bonding method. We found that the BOX layer was finally formed around the deeper end of the oxygen distribution in the as-implanted sample, though the depth of the BOX formation was much deeper than the projected range of oxygen and the damage peak of silicon. The formation process of the SOI/BOX structure proposed so far could not be applicable to the present conditions for ultrathin SOI/BOX synthesis by extremely low-energy implantation followed by low-temperature annealing. We thus suggested a novel mechanism of the ultrathin SOI/BOX synthesis as follows. The mechanism during the thermal treatment was demonstrated that the recrystallization of the damaged Si layers induced by ion irradiation took place from the very surface with relatively less irradiation-damages toward deeper layers with sweeping interstitial oxygen atoms, and the condensed oxygen atoms finally synthesized the stoichiometric BOX layer.

A Linear Mode Avalanche Photodiode for Ion Detection in the Energy Range 5–250 keV

We investigated the response linearity and the energy resolution of a silicon based reach-through avalanche photodiode (APD) for low energy ions ranging from 5 keV to 250 keV. We found that space charge affects the APD gain, and that this could be compensated by applying a simple correction formula to the measured pulse height distributions. The comparison between former theoretical or experimental studies and our results showed that there was no evidence of additional performance degradation within the tested energy range in terms of the linearity and the energy resolution compared to conventional non-avalanching silicon detectors. Thanks to the low noise level (equivalent to 0.9 keV in silicon) at the room temperature even for a large detection area (15 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ), APDs would be potentially used for detection of low-energy ions in various environments such as space plasma physics, particle physics, and many industrial applications.

Anomalous Uphill Diffusion and Dose Loss of Ultra-Low-Energy Implanted Boron in Silicon during Early Stage of Annealing

Uphill diffusion of boron implanted with 0.5 keV in silicon was investigated under nonamorphizing implant conditions. Postimplantation annealing at temperatures above 400°C induces the uphill diffusion of boron, which can be observed in an initial stage of annealing. The uphill diffusion is significantly suppressed by additional Si implantation into the boron implant region, suggesting that the uphill diffusion is mediated by the excess free self-interstitials during the annealing. Also, the uphill diffusion causes severe dose loss of implanted boron to the Si/SiO2 interface.

TRIM-DYNAMIC applied to marker broadening and SIMS depth profiling

The collisional mixing of thin metal markers in silicon is investigated with the computer program TRIM-DYNAMIC (T-DYN). This code assumes that, at high dose irradiation, the substrate Si or Ge will get fully amorphized, and the recoil atom can stop in any position after slowing down below a certain final energy E f (taken here as 3 eV). In order to avoid chemical effects, the system of a Au marker in a silicon matrix was chosen for the TRIM simulation. The results are in good agreement with the experimental findings, as compiled in the review article by Paine and Averback [Nucl. Instr. and Meth. B 7/8 (1985) 666]. Similar collisional mixing effects occur in the process of SIMS or AES depth profiling and cannot be avoided. Examples are given here for a thin film of antimony, which was vapor deposited on silicon and covered by amorphous silicon, and an arsenic implant of 0.5 keV in silicon which was known to exhibit no channeling tails. The analysing beam was 1 keV Ar + incident at 45°. Good agreement was found between the T-DYN simulations and the experimental results obtained with SIMS measurements using modern depth profiling equipment.

Measurements of Fano factors in silicon and germanium in the low-energy X-ray region

Estimates of Fano factors have been made in the low-energy X-ray region for both silicon and germanium (109 eV to 5.9 keV for silicon and 183 eV to 5.9 keV for germanium). The measurements are based on observations on a large number of X-ray detectors taking into account the effects of incomplete charge collection. The values at an X-ray energy of 5.9 keV are 0.1161 ± 0.0001 and 0.1057 ± 0.0002, respectively, for silicon and germanium at cryogenic temperatures. The values are found to converge and increase to about 0.15 at 183 eV. Comparisons are made with theoretical predictions and the difficulties of making measurements in the 100 eV region are discussed.

Temperature dependence of planar channeling radiation in silicon, germanium, and beryllium between 12 and 330 K

The temperature dependence of planar channeling radiation of 62.8 MeV electrons has been studied for silicon, germanium, and beryllium. The measurements have been performed using an uncollimated low-emittance cw beam from the superconducting electron linac S-DALINAC at the Technische Hochschule Darmstadt. Energies and linewidths of transitions between transverse bound states have been determined in the energy range between 40 and 230 keV for silicon and beryllium at temperatures between 12 and 330 K, and for germanium between 12 and 223 K. From the shift of the transition energies with temperature the mean thermal vibrational amplitudes of the atoms transverse to the channeling planes are determined by comparison with calculations using the many-beam formalism. Within experimental errors no directional dependence of the vibrations is observed. For silicon a Debye temperature of (535.2\ifmmode\pm\else\textpm\fi{}8.5) K at 12 K and (519.0\ifmmode\pm\else\textpm\fi{}10.8) K at 300 K has been derived. For germanium an increase from (232.7\ifmmode\pm\else\textpm\fi{}12.8) K at 12 K to (292.0\ifmmode\pm\else\textpm\fi{}16.4) K at 223 K is observed. Planar channeling radiation spectra from a beryllium crystal taken at 12, 220, and 300 K have been analyzed the same way yielding a Debye temperature of (1060\ifmmode\pm\else\textpm\fi{}50) K.

An optical bridge reflectometer for sensitive measurement of ion implantation dose

An instrument is described that can be used to monitor, with unprecedented sensitivity, changes in the optical reflectivity due to crystailine damage incurred during ion implantation. It is shown that at the shot-noise limit, changes in the optical reflectivity of silicon as small as 5·10−7 can be measured in a 10 Hz bandwidth with a signal-to-noise ratio of 100, corresponding to an extrapolated uniform implantation dose of 5·108 cm−2 for 11B+ at 50 keV in silicon.

Silicon-on-insulator structures by SIMOX and SIMNI procedures studied by Raman scattering and Rutherford backscattering

Oxygen and nitrogen ions were implanted at 150 keV and 200 keV in silicon to form buried insulating layers for silicon-on-insulator structures. Rutherford backscattering and Raman scattering measurements were performed to investigate the crystallinity and residual stress of the top silicon layers. Single crystalline silicon layers on buried insulating layers were found to have residual stresses of 0.7–2.0 kbar after annealing at 1200–1300° C for 2–6 h.

Depth distributions of low-energy 4He implanted in solids

Concentration profiles of 4He implanted with energies of 0.25–80 keV in silicon have been measured. The method employed-ion beam sputter erosion in conjunction with the mass spectrometric detection of sputter released He atoms-offers several advantages over other techniques used for helium analysis: He depth distributions in very near-surface regions (< 10 nm) of solids are determined with a detection sensitivity of 5 × 10 18 He atoms/cm 3 in Si. Furthermore, a depth resolution of 3.1 nm is demonstrated as deduced from the measured interface width between an undoped and a He doped layer. Over the energy regime investigated the experimentally determined values of the mean projected range and the range straggling agree very well with theoretical data for amorphous silicon.

Matter in superstrong magnetic fields

The behaviour of condensed matter in superstrong magnetic fields of the order of 1012–1015 G is investigated, i.e., binding energies of atoms in condensed matter are calculated by a variational method. The cohesive energy, i.e., the difference between the binding energies of free atoms and of atoms in condensed matter, is also calculated, and results are obtained for hydrogen, helium, carbon, oxygen, silicon, and iron atoms.For a magnetic field of 1012 G, we obtain binding energies for atoms in condensed matter of 0.2 keV for hydrogen, 0.7 keV for helium, 4.5 keV for carbon, 7.4 keV for oxygen, 20.0 keV for silicon, and 59.0 keV for iron. For a magnetic field of 1014 G, we get corresponding binding energies of 1.2 keV for hydrogen, 3.9 keV for helium, 27.0 keV for carbon, 44.9 keV for oxygen, 121.5 keV for silicon, and 366 keV for iron. For a magnetic field of 1012 G, we obtain cohesive energies of 0.04 keV for hydrogen, 0.10 keV for helium, 0.36 keV for carbon, 0.51 keV for oxygen, 1.4 keV for silicon, and 2.8 keV for iron. For a magnetic field of 1014 G, we get corresponding cohesive energies of 0.16 keV for hydrogen, 0.40 keV for helium, 1.9 keV for carbon, 3.0 keV for oxygen, 7.3 keV for silicon, and 19.4 keV for iron.

Measurement of average projective ranges of ions with energies of hundreds and thousands of keV in silicon using the resistance technique

An experimental determination of the average projective ranges Rp of accelerated ions in silicon, based on the measurement of the specific resistivity profile in irradiated samples is described. The theoretical aspects of the method related to the determination of the radiation-induced defect concentration profile and values of Rp from the above measurements, are discussed. New experimental data in silicon on the ranges of ions of hydrogen, deuterium, and helium with energies between 0.1 and 6.3 MeV/nucleon and the ions of boron, nitrogen, and phosphorus with energies from 0.03 to 0.7 MeV/nucleon are presented. The results obtained are compared with the respective theoretical values and with the experimental data. [Russian Text Ignored.]

Ranges in silicon of ions with atomic numbers 62 ⩽ Z1 ⩽ 66 at 100 keV

The ranges of ions with atomic numbers 62 ⩽ Z 1 ⩽ 66 at 100 keV in silicon have been measured. Both the projected range and standard deviation are found to vary smoothly with Z 1.