Self-ion Implantation Research Articles

High thermal stability of vacancy clusters formed in MeV Si-self-ion-implanted Si

We have shown that considerable vacancy defects, introduced by MeV Si self-ion implantation, can survive a 900°C∕5min annealing for gate formation. By analyzing the trap-limited Si interstitial diffusion, we have characterized these vacancy clusters. Furthermore, we show that the remaining vacancies are sufficient to reduce B diffusion. The study suggests that MeV ion implantation, a promising approach for ultrashallow junction formation in metal-oxide-semiconductor device fabrication, can be inserted before gate formation (involving high temperature annealing) to avoid irradiation damage on gate structures.

Neutron-enhanced annealing of radiation damage formed by self-ion implantation in silicon

The annealing effect of neutron irradiation has been observed for radiation damage in self-ion implanted silicon. Si samples implanted with (0.5–2)×1015Si∕cm2 were neutron irradiated at 400°C with the total number of displacements of 8.8×10−3dpa. A heavily disordered (not amorphized) sample clearly showed damage annealing enhanced by the neutron irradiation. The annealing efficiency (the ratio of annealed defects to atomic displacements) was calculated to be 1.3 defects/displacement. This annealing efficiency was compared with the results of previous ion beam annealing studies.

Formation and in situ dynamics of metallic nanoblisters inGa+ implanted GaN nanowires

The formation of voids and bubbles in the energetic ion implantation processis an important issue in material science research, involving swelling inducedembrittlement of materials in nuclear reactors, catalytic activities in the nanoporesof the bubble, etc. We report here the formation and in situ dynamics ofmetallic nanoblisters in GaN nanowires under self-ion implantation using aGa+ focused ion beam. High-resolution transmission electron microscopes equipped withelectron energy loss spectroscopy and energy filtering are used to identify the constituentsof the blister. In situ monitoring, with focused ion beam imaging, revealed the translationand rotation dynamics of the blisters.

Mechanism of nanoblister formation in Ga+ self-ion implanted GaN nanowires

The formation of voids and bubbles during ion implantation is an important area of material research. Void and bubble formation can result in swelling and embrittlement of metallic or semiconducting materials, and increase catalytic effects in the nanopores of the bubble. Here, we report the observation of metallic nanoblister formation in GaN nanowires under self-ion implantation using a Ga+ focused ion beam. The mechanism of the blister formation was resolved using high-resolution transmission electron microscopy equipped with electron energy loss spectroscopy and plasmon imaging.

Damage accumulation in Si during high-dose self-ion implantation

Accumulation and annealing of damage in Si implanted with self-ions to high doses were investigated using a combination of grazing incidence diffuse x-ray scattering, high-resolution x-ray diffraction scans, and transmission electron microscopy. During implantation at 100°C, small vacancy and interstitial clusters formed at low doses, but their concentrations saturated after a dose of ≈3×1014cm−2. The concentration of Frenkel defects at this stage of the implantation was ≈1×10−3. At doses above 1×1015cm−2, the concentration of implanted interstitial atoms began to exceed the Frenkel pair concentration, causing the interstitial clusters to grow, and by ≈3×1015cm−2, these clusters formed dislocation loops. Kinematical analysis of the rocking curves illustrated that at doses above 1×1015cm−2 the “plus one” model was well obeyed, with one interstitial atom being added to the dislocation loops for every implanted Si atom. Measurements of Huang scattering during isochronal annealing showed that annealing was substantial below 700°C for the specimens irradiated to lower doses, but that little annealing occurred in the other samples owing to the large imbalance between interstitial and vacancy defects. Between 700 and 900°C a large increase in the size of the interstitial clusters was observed, particularly in the low-dose samples. Above 900°C, the interstitial clusters annealed.

Modification of mechanical properties of silicon nanocantilevers by self-ion implantation

Nanoscale silicon beams (∼3 μm long, 250 nm wide, and 193 nm thick) were implanted with Si ions at energies of 100 and 35 keV and a dose of 1×1015 ions/cm2 and then tested using an atomic force microscope. The Young’s modulus of fully amorphous silicon nanostructures (thus formed at 100 keV) was measured to be 134.5 GPa, and the modulus of bimaterial silicon nanostructures (amorphous and single crystal formed at 35 keV energy) was measured to be 150.3 GPa. Thus, the fundamental mechanical properties of 3D silicon nanostructures can be controllably modified using ion implantation at nanometer scale. This has major implications for nanoelectromechanical systems and related devices.

Atomistic simulation of defects evolution in silicon during annealing after low energy self-ion implantation

Defects evolution in silicon during annealing after low energy Si + implantation is simulated by atomistic method in this paper. Distribution of implanted dopants and defects is simulated by molecular dynamic method. The experimental results published by Stolk et al. (J Appl Phys 81 (9) (1991) 6031) are simulated to verify the models and parameters applied here. The annealing after low energy (5 kev) Si + implantation is studied by simulation. Although the damage field is only 10 nm under the surface in this case and thus surface annihilation has important impact on defects evolution, the experimental results are reproduced by the simulation. The analysis indicates that the Ostwald ripening can suppress the surface annihilation obviously in the case of low energy implantation.

Mechanical properties of ion-implanted amorphous silicon

We used nanoindentation coupled with finite element modeling to determine the mechanical properties of amorphous Si layers formed by self-ion implantation of crystalline Si at approximately 100 K. When the effects of the harder substrate on the response of the layers to indentation were accounted for, the amorphous phase was found to have a Young’s modulus of 136 ± 9 GPa and a hardness of 10.9 ± 0.9 GPa, which were 19% and 10% lower than the corresponding values for crystalline Si. The hardness agrees well with the pressure known to induce a phase transition in amorphous Si to the denser β–Sn-type structure of Si. This transition controls the yielding of amorphous Si under compressive stress during indentation, just as it does in crystalline Si. After annealing 1 h at 500 °C to relax the amorphous structure, the corresponding values increase slightly to 146 ± 9 GPa and 11.6 ± 1.0 GPa. Because hardness and elastic modulus are only moderately reduced with respect to crystalline Si, amorphous Si may be a useful alternative material for components in Si-based microelectromechanical systems if other improved properties are needed, such as increased fracture toughness.

Effect of self-ion bombardment on the corrosion behavior of zirconium

In order to study the influences of self-ion bombardment on the aqueous corrosion behavior of zirconium, specimens were implanted by zirconium ions with a fluence range from 1 × 10 15 to 2 × 10 17 ions/cm 2 at about 170 °C, using MEVVA source at an extracted voltage of 50 kV. The valence of the surface layer was analyzed by X-ray photoemission spectroscopy (XPS); the thickness of the oxide film was measured by Auger electron spectroscopy (AES). Three-sweep potentiodynamic polarization measurement was employed to value the aqueous corrosion resistance of zirconium in a 1N H 2SO 4 solution. Glancing angle X-ray diffraction (GAXRD) was employed to examine the phase transformation due to the self-ion implantation in the oxide films. It was found that the aqueous corrosion behavior of zirconium implanted with 5 × 10 16 Zr ions/cm 2 is the best in all the samples. The natural corrosion potentials of all the bombarded samples are more negative than that of the as-received zirconium. The tendency is probably that the natural corrosion potential declines with raising the bombarded fluences. Finally, the mechanism of the corrosion behavior of the self-ion implanted zirconium is discussed.

Effects of Self-Ion Implantation on the Thermal Growth of He-Induced Cavities in Silicon

Effects of Self-Ion Implantation on the Thermal Growth of He-Induced Cavities in Silicon

Formation of nanoscale voids and related metallic impurity gettering in high-energy ion-implanted and annealed epitaxial silicon

We have examined nanovoid formation, Fe gettering, and Fe clustering phenomena occurring in epitaxial silicon layers implanted with MeV Si ions. Insights into these phenomena as a function of depth have been gained from detailed analyses by Z-contrast imaging in conjunction with electron energy-loss spectroscopy. Our work has shown at the nanoscale structural and chemical levels that the defects produced by MeV self-ion implantation between the surface and the ion projected range Rp (i.e., in the so-called Rp/2 region) are voids, which provide extremely efficient and aggressive metallic impurity gettering. It has been proposed that the gettering does not occur via chemisorption or silicidation layering on the internal surface of the void walls, as in the well-known case of helium-induced cavities, but rather proceeds in a mode of metal–metal atom binding in the vicinity of the Rp/2 voids.

Effect of ion implantation induced defects on optical attenuation in silicon waveguides

The effect of ion implantation induced defects on optical attenuation in silicon waveguides has been investigated for MeV self-ion implantation. A lower limit of 1200 dB cm−1 for a dose of 1×1014 cm−2 has been measured. The results can be approximated by a simple analytical expression and hence extended to a wider range of implantation species, doses and energies.

Relating Nanostructures to Mechanical Properties in Ion-Implanted Materials

AbstractIon implantation was used to form high densities (~1019 /cm3) of small oxide precipitates in Ni in order to investigate the strength mechanism produced by such highly refined structures. Nanometer-size precipitates of Al2O3 and NiO are found to block dislocation motion in the Ni matrix, producing yield strengths up to 4.6 GPa, more than twice that of hardened bearing steel. Dispersion strengthening theory, developed for micrometer-size precipitates and spacings, was found to account quantitatively for the yield strengths produced by nanometer-size oxides as well. Nanoindentation plus finite-element modeling was used to quantify the mechanical properties of implanted metal layers, and was extended to examination of amorphous Si layers formed by self-ion implantation. The amorphous phase was found to have a yield strength of 4.45 ± 0.20 GPa, Young's modulus of 144 ± 7 GPa, and hardness of 10.3 ± 0.4 GPa. The modulus and hardness are reduced by 10% and 15%, respectively, from those of crystalline Si.

Finite Element Modeling of Nanoindentation Measurements of Crystalline and Amorphous Si

ABSTRACTNanoindentation testing of amorphous Si layers, formed by self-ion implantation, has been performed, and their mechanical properties compared to crystalline Si. The data was analyzed using finite element modeling of the indentation measurement, allowing the properties of the thin amorphous layers to be separated from those of the underlying material. By modeling the materials as isotropic, elastic-plastic solids with the Mises yield criterion, the amorphous Si is shown to have a hardness about 15% lower than crystalline Si and an elastic modulus about 10% lower. Electron and atomic force microscopies of the indents indicate that the amorphous Si does not undergo phase changes during indentation, and that it may be somewhat more ductile than crystalline Si.

Boron segregation to extended defects induced by self-ion implantation into silicon

The evolution of boron segregation to extended defects during thermal annealing was studied with secondary ion mass spectrometry and cross-sectional transmission electron microscopy. Czochralski Si wafers with a boron concentration of 3×1017 cm−3 were implanted with 50 keV Si ion for doses from 5×1013 to 2×1015 cm−2 and then annealed at 720, 820, or 870 °C in nitrogen ambient for various annealing times. The evolution of boron segregation peaks to three types of dislocation loops, end-of-range (EOR) dislocation loops, clamshell defects, and Rp (the projected range) defects, is closely related to the evolution of dislocation loops. As annealing temperature and time increase, the boron segregation peaks grow, remain stable, and then disappear together with the dislocation loops. For lower temperature annealing, the boron segregation peaks grow more slowly and reach higher peak concentrations. In addition to the boron segregation to dislocation loops, boron segregation to {311} defects was also found. The boron segregation peak to {311} defects is unstable and dissolves completely after annealing at 820 °C for 10 min. An analytic model for the boron segregation to EOR dislocation loops was developed under equilibrium condition by taking account of the average radius and area density of the EOR dislocation loops. The boron segregation energy to the EOR dislocation loops was found to be 0.75 eV. The evolution of the boron segregation peak was explained with the analytic model. The experimental boron segregation profiles can be well reproduced with the analytic model.

Vacancy defects in solid-phase epitaxial grown layers of self-implanted Si

A method for preparing shallow dopant distributions via solid-phase epitaxial growth (SPEG) following amorphization by low-energy Si self-ion implantation leaves defects that can lead to unwanted dopant impurity diffusion. The double implant method for SPEG [O. W. Holland et al., J. Electron. Mater. 25, 99 (1996)] uses both low- and high-energy Si self-ion implantation to remove most of the interstitials. Nevertheless, we find that measurable crystalline imperfections remain following the SPEG annealing step. Measurements of defect profiles using variable-energy positron spectroscopy show that there are divacancy-impurity complexes in the SPEG layer and V6 and larger vacancy clusters near the SPEG-crystalline interface. These measurements should be useful for modeling the diffusion of dopant atoms and for fine tuning the double implant parameters.

Low-energy excitations in amorphous films of silicon and germanium

We present measurements of internal friction and shear modulus of amorphous Si $(a\ensuremath{-}\mathrm{Si})$ and amorphous Ge $(a\ensuremath{-}\mathrm{Ge})$ films on double-paddle oscillators at 5500 Hz from 0.5 K up to room temperature. The temperature- independent plateau in internal friction below 10 K, which is common to all amorphous solids, also exists in these films. However, its magnitude is smaller than found for all other amorphous solids studied to date. Furthermore, it depends critically on the deposition methods. For $a\ensuremath{-}\mathrm{Si}$ films, it decreases in the sequence of electron-beam evaporation, sputtering, self-ion implantation, and hot-wire chemical-vapor deposition (HWCVD). Annealing can also reduce the internal friction of the amorphous films considerably. Hydrogenated $a\ensuremath{-}\mathrm{Si}$ with 1 at.% H prepared by HWCVD leads to an internal friction more than two orders of magnitude smaller than observed for all other amorphous solids. The internal friction increases after the hydrogen is removed by effusion. Our results are compared with earlier measurements on $a\ensuremath{-}\mathrm{Si}$ and $a\ensuremath{-}\mathrm{Ge}$ films, none of which had the sensitivity achieved here. The variability of the low-energy tunneling states in the $a\ensuremath{-}\mathrm{Si}$ and $a\ensuremath{-}\mathrm{Ge}$ films may be a consequence of the tetrahedrally bonded covalent continuous random network. The perfection of this network, however, depends critically on the preparation conditions, with hydrogen incorporation playing a particularly important role.

Recent developments in hot wire amorphous silicon

We present measurements of low temperature internal friction (Q−1) of amorphous silicon (a-Si) films designed to probe how their structure and formation affect low temperature vibrational properties. All a-Si films, whether produced by e-beam evaporation, sputtering, Si self-ion implantation, or chemical vapor deposition (CVD) show the well-known temperature-independent plateau (Q0−1) common to all amorphous solids. For hydrogenated amorphous silicon (a-Si:H) with about 1 at.% H produced by hot wire CVD; however, the internal friction is nearly three orders of magnitude less than any known amorphous material. For this material we find that Q−1 depends on H concentration (CH), and on deposition conditions. For CH>2 at.%, both a peak and a sharp transitional feature appear in Q−1 between 5 and 40 K. We identify the feature as H2, presumably in microvoids, undergoing a phase transition at the freezing point.

An Experimental Study of Ion Beam and ECR Hydrogenation of Self-Ion Implantation Damage in Silicon by Admittance Spectroscopy and X-Ray Triple Crystal Diffractometry

An Experimental Study of Ion Beam and ECR Hydrogenation of Self-Ion Implantation Damage in Silicon by Admittance Spectroscopy and X-Ray Triple Crystal Diffractometry

Detection of Metastabile Defective Regions in Ion-Implanted Silicon by Means of Metal Gettering

ABSTRACTHigh-energy, self-ion implantation has been used to form deep gettering layers in Si. Subsequently samples have been contaminated with Cu and subjected to heat treatment. The residual defects act as gettering centres for Cu. The decoration of defects byCu making them detectable by secondary ion mass spectromety analysis. Metastable defect complexes have been detected which, because of their small size, are not directly detectable by other analytical techniques such as transmission electron microscopy and MeV-particle channeling. These defects are probably of interstitial type and have been found mainly midway between the sample and the projected ion range, i.e. around Rp/2. The gettering ability of these small defect complexes may largely exceed that of the post-anneal damage at the projected i.e range, Rp. The results obtained demonstrate that by means of metal gettering the formation, growth and dissolution of very small defect complexes in ion-implanted Si can be studied.