Endotaxial growth of InSb nanocrystals at the bonding interface of the In+ and Sb+ ion implanted SOI structure

Growth of InSb nanocrystals at the Si/SiO₂ bonding interface of silicon-on-insulator (SOI) structures has been studied as a function of the annealing temperature. SOI structures with the ion implanted regions above and below the bonding interface were produced as a result of the hydrogen transfer of the Sb⁺ ion implanted silicon layer from first silicon substrate to the In⁺ ion implanted SiO₂ layer thermally-grown on the second silicon substrate. Rutherford backscattering spectrometry and high-resolution transmission electron microscopy (XTEM) were used to study the properties of the prepared structures. Up-hill diffusion of In and Sb atoms from the implantation regions toward the bonding interface as well as subsequent interface-mediated growth of InSb nanocrystals were observed as the annealing temperature achieved 1100 °C. The strain minimizing orientations of the Si and InSb lattice heteropairs were obtained from XTEM analysis of the grown nanocrystals.     

Electrically active defects in BF2+ implanted and germanium preamorphized silicon

Ultra-shallow p⁺-n junctions have been formed using 15 keV/10¹⁵ cm⁻² BF₂⁺ implantation into both Ge⁺-preamorphized and crystalline 〈1 0 0〉 silicon substrates. Rapid thermal annealing (RTA) for 15 s at 950°C was used for dopant electrical activation and implantation damage gettering. The electrically active defects present in these samples were characterized using Deep Level Transient Spectroscopy (DLTS) and isothermal transient capacitance (ΔC(t, T)). Two electron traps were detected in the upper half of the band gap at, respectively, E_c - 0.20 eV and E_c - 0.45 eV. They are shown to be related to Ge⁺ implantation-induced damage. On the other hand, BF₂⁺ implantation along with RTA give rise to a depth distributed energy continuum which lies within the forbidden gap between E_c - 0.13 eV and E_c - 0.36 eV. From isothermal transient capacitance (ΔC(t, T)), reliable damage concentration profiles were derived. They revealed that preamorphization induces not only defects in the regrown silicon layer but also a relatively high concentration of electrically active defects as deep as 3.5 μm into the bulk.     

Peculiarities of defect generation in Si+-implanted GaAs (2 1 1)

Peculiarities of the defect generation during implantation of (2 1 1) GaAs with Si⁺ ions and doses below the amorphisation dose of GaAs have been investigated by X-ray diffraction, the secondary ion mass-spectroscopy (SIMS) and transmission electron microscopy. It was shown, that in such implanted layers less radiation defects will be formed and these defects are more easily annealed by rapid photon annealing (RPA) than in (1 0 0)-oriented wafers.     

Vacancy-type defects near Al surface studied by slow positron annihilation spectroscopy before and after He implantation

The vacancy-type defects He_nV_m near Al surface before and after He⁺ implantation and their evolutions with annealing temperatures and aging time have been investigated by mono-energy slow positron annihilation spectroscopy (SPAS) with S parameters. The results show that many vacancies are produced during the sample preparation process, which can be re-occupied by Al atoms during annealing, Al⁺ and MeV He⁺ implantation. S parameters denote the concentration and size of He_nV_m clusters induced by He⁺ implantation in Al. The higher fluence of He implanted, the larger S parameters will be, indicating more He_nV_m clusters produced. S parameters decrease with the increase of annealing temperatures until the fastest change temperature, and then an opposite or minor change occurs depending on the fluence of He implanted in Al, showing that the concentration and size of He_nV_m clusters will vary with the annealing temperatures. Aged at RT for some time, the concentration and mean size of He_nV_m clusters in Al will get smaller and larger, respectively, resulting in the decrease of S parameters with the aging time. In conclusions, the evolution of vacancy-type defects He_nV_m near Al surface after He⁺ implantation depends on the annealing temperatures, He concentration and aging time.     

Surface analytical studies of ion-implanted uni-directionally aligned silicon nitride for tribological applications

Uni-directionally aligned silicon nitride, which exhibits both high strength and high toughness, was implanted with B⁺, N⁺, Si⁺ and Ti⁺ ions at a fluence of 2 × 10¹⁷ ions/cm² and an energy of 200 keV. The effect of ion implantation on the surface structure of the uni-directionally aligned silicon nitride has been studied, in terms of surface analyses such as atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS) and X-ray absorption near edge structure (XANES). It was clarified that the ion-implanted layer was amorphized and the implantation profile showed good agreement with that estimated from a TRIM simulation. It was found that BN and TiN were formed in B⁺- and Ti⁺-implanted Si₃N₄, respectively. There was a slight difference in ion implantation depth among different structures of Si₃N₄, considered to be due to differences in ion channeling.     

Effects of Li ion implantation energies on the structure, photoluminescence, and ferromagnetism properties of (Li, Co) co-implanted ZnO films

Room temperature ferromagnetism was observed in (Li, Co) co-implanted ZnO films. The implantation energy for Co ions was 400 keV, while for Li ions were 50, 100 and 200 keV, respectively. The ion implantation induced defects and disorder has been observed by the XRD, PL and TEM experiments. For the co-implanted ZnO films with Li ion implantation energies of 100 and 200 keV, the band energy emission disappears and the defect related emission with wavelength of 500-700 nm dominates, which can be attributed to defects introduced by implantation. Co-implanted ZnO Films with Li ion implantation energies of 200 keV show a saturation magnetization value (M_S) of over 9 × 10⁻⁵ emu and a positive coercive field of 60 Oe. The carrier concentration is not much improved after annealing and in the order of 10¹⁶ cm⁻³, which suggests that FM does not depend upon the presence of a significant carrier concentration. The origin of ferromagnetism behavior can be explained on the basis of electrons and defects that form bound magnetic polarons, which overlap to create a spin-split impurity band.     

Measuring the generation lifetime profile modified by MeV H+ ion implantation in silicon

A silicon wedge mask with thickness varying from approximately 5 μm to a few hundred μm has been used for converting the depth distribution of defect concentration induced by 4 MeV H⁺ ion implantation in silicon to a lateral scale on the surface, i.e. the distance from the edge of the wedge mask. Thus, using proper devices fabricated on bulk Si prior to ion implantation, depth profiles of the generation lifetime of minority charge carriers and of the different defect densities can be measured by the transient capacitance method and by Deep Level Transient Spectroscopy (DLTS), respectively. The distribution of lifetime follows well that of the implantation induced vacancies calculated by the TRIM code in the applied dose range (from 1 × 10¹⁰ to 3 × 10¹¹ H⁺/cm²). The correlation between implantation dose and lifetime decrease is also discussed.     

Spatial distribution of defects in ion-implanted and annealed Si: The RP/2 effect

Gettering of metal impurities in ion-implanted Si occurs midway between the surface and the projected ion range, R_P, after annealing at temperatures in the range of 700–1000°C and vanishes at higher temperatures. This phenomenon, called the R_P/2 effect, seems to be a common feature of ion-implanted and annealed Si. The gettering ability of the damage at R_P/2 is commensurate with or may exceed that of the damage at R_P. The defects around R_P/2 acting as gettering sites have not yet been identified by other analysis techniques. They are formed after ion implantation in the process of defect evolution during annealing and, probably, consist of small complexes of intrinsic defects (vacancies or/and self-interstitials).     

Nanometer-thick SGOI structures produced by Ge+ ion implantation of SiO2 films and subsequent hydrogen transfer of Si layers

Nanometer-thick silicon-germanium-on-insulator (SGOI) structures have been produced by the implantation of Ge⁺ ions into thermally grown SiO₂ layer and subsequent hydrogen transfer of silicon film on the Ge⁺ ion implanted substrate. The intermediate nanometer-thick Ge layer has been formed as a result of the germanium atom segregation at the Si/SiO₂ bonding interface during annealing at temperatures 800–1100 ^оС. From a thermodynamic analysis of Si/Ge/SiO₂ system, it has been suggested that the growth of the epitaxial Ge layer is provided by the formation of a molten layer at the Si/SiO₂ interface due to the Ge accumulation. The effect of germanium on the hole mobility in modulation-doped heterostructures grown over the 3–20 nm thick SGOI layers was studied. An increase in the Hall hole mobility in SGOI-based structures by a factor of 3–5 was obtained in comparison with that in respective Ge-free SOI structures.     

The evolution of He+ irradiation-induced point defects and helium retention in nuclear graphite

The atomic-level study of point defect evolution in nuclear graphite is essential for a deep understanding of irradiation-induced property changes. The evolution of helium ion irradiation-induced point defects and helium retention in nuclear graphite ETU-10 and ETU-15 were studied by positron annihilation Doppler broadening (PADB) experiments and thermal desorption spectroscopy (TDS) measurements. The graphite samples were implanted with 10¹⁵, 10^16_, and 10¹⁷ cm^?2 of 200 keV He⁺ at operation temperatures below 373 K. Frenkel pairs were created during ion irradiation and they annihilated during annealing. Three stages of interstitial-monovacancy annihilation are suggested. At low temperatures, the initial annihilation would be refined only to the recombination of intimate metastable Frenkel pairs. When temperature increases, the annihilation would expand to a larger extent that isolate interstitials and vacancies annihilate with each other. In the case of high doses irradiation, vacancy clusters form at elevated temperatures. The retention and release of helium is tightly related to the evolution of the defects, especially the vacancies. The small over-pressured He-V clusters (He_nV) are thought to be the most possible form of helium retention under irradiation.     

Efficiency of formation of radiation defects in silicon upon implantation of silicon and phosphorus ions

Accumulation and annealing of radiation defects in silicon and in the heavily phosphorus doped silicon layers implanted with Si⁺ or P⁺ ions have been studied by the X-ray diffraction method. The observed differences in the introduction rates of stable radiation defects are due to the differences between the intensities of annihilation processes determined by charge states of defects.     

Relaxation of strain during solid phase epitaxial growth of Ge+ ion implanted layers in silicon

Formation of Si_1−xGe_x-alloy layers by solid phase epitaxial growth (SPEG) of Ge⁺ ion implanted silicon has been studied. The ion implantations were performed with 40, 100, 150, 200 and 300 keV ⁷⁴Ge⁺ ions and various ion doses. The SPEG of the ion implanted layers was carried out in a conventional furnace at 850°C for 20 min under a flow of nitrogen gas. The Si_1−xGe_x-alloy layers were characterised by Rutherford backscattering spectrometry and transmission electron microscopy (TEM). For a given ion energy, a Si_1−xGe_x-alloy layer with no observable extended defects can be manufactured if the ion dose is below a critical value and strain-induced defects are formed in the alloy layer when the ion dose is equal to or above this value. The critical Ge⁺ ion dose increases with ion energy, while the critical maximum Ge concentration decreases. For ion energies ⩽150 keV, the defects observed in the alloy layers are mostly stacking faults parallel to the {1 1 1} planes. For higher ion energies, 200 keV and above, the majority of defects in the alloy layer are hairpin dislocations. In the whole ion energy range, the critical ion dose and the depth position of the nucleation site for the stacking faults obtained from the measurements are in good agreement with theoretical predictions. Extended defects are formed in the alloy layer during the SPEG when the regrowth of the crystalline/amorphous interface has reached the depth position in the crystal where the accumulated strain energy density is equal to the critical value of 235 mJ/m².     

As–Al recoil implantation through Si3N4 barrier layer

Al recoil implantation have been shown to be a possible alternative to direct Al ion implantation to avoid usual problems linked with Al sources. Poor efficiency of the recoil + annealing process is observed if no barrier or an oxyde screen layers are used. This problem can be solved using a Si₃N₄ screen layer. Then, P–N and N⁺/P/N structures can be obtained with deep low doped P-well with reduced thermal budget.     

Proton beam induced luminescence of silicon dioxide implanted with silicon

Light emission from a silicon dioxide layer enriched with silicon has been studied. Samples used had structures made on thermally oxidized silicon substrate wafers. Excess silicon atoms were introduced into a 250-nm-thick silicon dioxide layer via implantation of 60 keV Si⁺ ions up to a fluence of 2 × 10¹⁷ cm⁻². A 15-nm-thick Au layer was used as a top semitransparent electrode. Continuous blue light emission was observed under DC polarization of the structure at 8-12 MV/cm. The blue light emission from the structures was also observed in an ionoluminescence experiment, in which the light emission was caused by irradiation with a H₂⁺ ion beam of energy between 22 and 100 keV. In the case of H₂⁺, on entering the material the ions dissociated into two protons, each carrying on average half of the incident ion energy. The spectra of the emitted light and the dependence of ionoluminescence on proton energy were analyzed and the results were correlated with the concentration profile of implanted silicon atoms.     

Stability of defects created by high fluence helium implantation in silicon

Stability of extended defects created by high fluence helium implantation (50 keV, 5 × 10¹⁶ cm⁻²) from room temperature to 800 °C has been studied using transmission electron microscopy. Our results clearly show that the cavities behave as good sinks for interstitial type defects generated during ion implantation, leading in some cases to the cavity dissolution. A three-dimensional “phase diagram” related to the formation and evolution of interstitial-type defects is also proposed. It is plotted in terms of quantity of damage, annealing time and implantation temperature.     

The production of non linear damage under molecular ion implantation

Germanium atomic (Ge₁) and molecular ions (Ge₂) of equivalent energy are implanted in silicon at an elevated temperature. The ion induced damage has been characterized by RBS channeling (RBS/C) and positron annihilation spectroscopy. The RBS/C studies indicate that the molecular ion implantation has produced more defects in the near surface regions compared to the atomic ion implantation. This paper reports a first time observation of an enhanced production of vacancy related defects in silicon implanted with molecular ions.     

Comparative study of damage production in ion implanted III–V-compounds at temperatures from 20 to 420 K

The damage evolution in ion implanted InP, GaAs, GaP and InAs is studied as a function of the ion fluence in the temperature range 20–420 K using various ion masses. It is shown that the macroscopic behaviour can be described in terms of critical temperatures T_c which depend on the ion mass and on the dose rate for a given material. At temperatures T_I< T_c amorphization is obtained by direct impact amorphization and the growing of the amorphous zones. However, athermal in-cascade annealing is observed even at 20 K, which is the more pronounced the lighter the ion is. This indicates the influence of the density of the primary cascades on defect recombination. Around T_c intrinsic defects are mobile leading to an equilibrium between defect production and annealing over a broad dose region. Amorphization at very large ion fluences is the consequence of complex processes which are influenced by the high ion concentration and the formation of dislocation bands near the end of range. Using an empirical formula which describes the ion mass and dose rate dependence of the critical temperature, the damage evolution for certain implantation conditions becomes predictable.     

Structural studies of silicon oxynitride layers formed by low energy ion implantation

Silicon oxynitride (Si_xO_yN_z) layers were synthesized by implanting ¹⁶O₂⁺ and ¹⁴N₂⁺ 30 keV ions in 1:1 ratio with fluences ranging from 5 × 10¹⁶ to 1 × 10¹⁸ ions cm⁻² into single crystal silicon at room temperature. Rapid thermal annealing (RTA) of the samples was carried out at different temperatures in nitrogen ambient for 5 min. The FTIR studies show that the structures of ion-beam synthesized oxynitride layers are strongly dependent on total ion-fluence and annealing temperature. It is found that the structures formed at lower ion fluences (∼1 × 10¹⁷ ions cm⁻²) are homogenous oxygen-rich silicon oxynitride. However, at higher fluence levels (∼1 × 10¹⁸ ions cm⁻²) formation of homogenous nitrogen rich silicon oxynitride is observed due to ion-beam induced surface sputtering effects. The Micro-Raman studies on 1173 K annealed samples show formation of partially amorphous oxygen and nitrogen rich silicon oxynitride structures with crystalline silicon beneath it for lower and higher ion fluences, respectively. The Ellipsometry studies on 1173 K annealed samples show an increase in the thickness of silicon oxynitride layer with increasing ion fluence. The refractive index of the ion-beam synthesized layers is found to be in the range 1.54-1.96.     

Thermal annealing behavior of hydrogen and surface topography of H2+ ion implanted tungsten

Tungsten (W) has been proposed as a plasma-facing material in fusion reactors due to its outstanding properties. Degradation of the material properties is expected to occur as a result of hydrogen (H) isotope permeation and trapping in W. In this study, two polycrystalline W plates were implanted with 80 keV H₂⁺ ions to a fluence of 2 × 10²¹ H⁺/m² at room temperature (RT). Time-of-flight secondary ion mass spectrometry (ToF-SIMS), focused ion beam (FIB), and scanning electron microscopy (SEM) were used for sample characterization. The SIMS data shows that H atoms are distributed well beyond the ion projected range. Isochronal annealing appears to suggest two H release stages that might be associated with the reported activation energies. H release at RT was observed between days 10 and 70 following ion implantation, and the level was maintained over the next 60 days. In addition, FIB/SEM results exhibit H₂ blister formation near the surface of the as-implanted W. The blister distribution remains unchanged after thermal annealing up to 600 ?C.     

Defects remaining in MeV-ion-implanted and annealed Si away from the peak of the nuclear energy deposition profile

Damage has been observed in MeV-ion-implanted Si away from the maximum of the nuclear energy deposition profile, mainly around the half of the projected ion range, R_P/2. Cu gettering has been used for the detection of irradiation defects which are formed during annealing at temperatures between 700°C and 1000°C. This damage is primarily created by the implanted ions on their trajectory and consists of intrinsic defects remaining so small that they have not yet been resolved. These defects undergo a defect evolution during annealing which results in a decrease of the width of the damage layer with increasing temperature and prolonged time of the annealing.