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.     

Gettering layer for oxygen accumulation in the initial stage of SIMOX processing

A cavity layer or nano-bubble layer introduced by He implantation before the oxygen implantation collects the implanted oxygen and increases the oxygen concentration. The average size and density of the oxygen precipitates formed in the initial stage of the separation-by-implanted-oxygen (SIMOX) process is conform with the size and density of the cavities pre-formed by He implantation and annealing. The gettering ability of the cavity layer for oxygen is directly related to the area of the internal surface of the cavities. A nano-bubble layer accumulates oxygen in a very narrow range occurring between the damage maximum, D_P, and the mean projected ion range, R_P. Such a nano-bubble layer is most efficient in oxygen gettering due to their larger area of the internal surface and the small size of the oxide precipitates initially formed at the bubbles.     

X-ray irradiation of ion-implanted MOS capacitors

He⁺ ion-implanted metal-oxide-semiconductor (MOS) capacitors with two different oxide thickness have been irradiated by X-rays and the depth distribution of the implant damage in the Si–SiO₂ structures have been examined. The efficiency of X-ray annealing of electronic traps caused by implantation and changes in charge populations are reported. The experiment shows that (in the case when defects introduced by implantation are located at the Si–SiO₂ interface) only defects corresponding to the deep levels in the Si can be affected by X-ray irradiation. When defects introduced by ion implantation are located deeper within the Si substrate complete annealing of these defects is observed.     

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.     

Post-annealing temperature dependence of blistering in high-fluence ion-implanted H in Si 〈1 0 0〉

This study examined the influence of post-annealing temperature on blister formation and growth in ion-implanted H in Si 〈1 0 0〉. Ion energy levels of 40 and 100 keV and fluences of 2 × 10¹⁶ and 5 × 10¹⁶ cm⁻² were investigated. Post-annealing treatments were performed using the furnace annealing (FA) method with temperatures ranging from 200 to 600 °C for a duration of 1 h. Raman scattering spectroscopy (RSS), optical microscopy (OM), secondary ion mass spectrometry (SIMS), atomic force microscopy (AFM), and cross-sectional transmission electron microscopy (XTEM) were employed to explore the mechanisms behind the smart cut technique. The results revealed that variations among the transformation of the VH₃ (or V₂H₆) defect complex phase into the Si(1 0 0):H bonding configuration phase (RSS results), the appearance of optically detectable blisters and craters (OM results), the average depth of craters (AFM results), the trapping of hydrogen atoms and gettering of oxygen atoms (SIMS results), and the damaged microstructures (XTEM results) against post-annealing temperature were in close correspondence. It was also found that the optimal post-annealing temperature for blister formation and growth was 550 °C.     

Enhanced defects recombination in ion irradiated SiC

Point defects induced in SiC by ion irradiation show a recombination at temperatures as low as 320 K and this process is enhanced after running current density ranging from 80 to 120 A/cm².Ion irradiation induces in SiC the formation of different defect levels and low-temperature annealing changes their concentration. Some levels (S₀, S_x and S₂) show a recombination and simultaneously a new level (S₁) is formed.An enhanced recombination of defects is besides observed after running current in the diode at room temperature. The carriers introduction reduces the S₂ trap concentration, while the remaining levels are not modified. The recombination is negligible up to a current density of 50 A/cm² and increases at higher current density. The enhanced recombination of the S₂ trap occurs at 300 K, which otherwise requires a 400 K annealing temperature. The process can be related to the electron-hole recombination at the associated defect.     

Defect- and strain-enhanced cavity formation and Au precipitation at nano-crystalline ZrO2/SiO2/Si interfaces

Defect- and strain-enhanced cavity formation and Au precipitation at the interfaces of a nano-crystalline ZrO₂/SiO₂/Si multilayer structure resulting from 2 MeV Au⁺ irradiation at temperatures of 160 and 400 K have been studied. Under irradiation, loss of oxygen is observed, and the nano-crystalline grains in the ZrO₂ layer increase in size. In addition, small cavities are observed at the ZrO₂/SiO₂ interface with the morphology of the cavities being dependent on the damage state of the underlying Si lattice. Elongated cavities are formed when crystallinity is still retained in the heavily-damaged Si substrate; however, the morphology of the cavities becomes spherical when the substrate is amorphized. With further irradiation, the cavities appear to become stabilized and begin to act as gettering sites for the Au. As the cavities become fully saturated with Au, the ZrO₂/SiO₂ interface then acts as a gettering site for the Au. Analysis of the results suggests that oxygen diffusion along the grain boundaries contributes to the growth of cavities and that oxygen within the cavities may affect the gettering of Au. Mechanisms of defect- and strain-enhanced cavity formation and Au precipitation at the interfaces will be discussed with focus on oxygen diffusion and vacancy accumulation, the role of the lattice strain on the morphology of the cavities, and the effect of the binding free energy of the cavities on the Au precipitation.     

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.     

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.     

Dwell-time dependence of the defect accumulation in focused ion beam synthesis of CoSi2

Cobalt disilicide microstructures were formed by 70 keV Co²⁺ focused ion beam implantation into Si(1 1 1) at substrate temperatures of about 400°C and a subsequent two step annealing (600°C, 60 min and 1000°C, 30 min in N₂). It was found that the CoSi₂ layer quality strongly depends on the pixel dwell time and the implantation temperature. Only for properly chosen parameters continuous CoSi₂ layers could be obtained. Scanning electron microscopy and Rutherford backscattering/channelling investigations were carried out combined with a special preparation technique for structures which are smaller than the analysing beam. The quality of the CoSi₂ layers which is correlated to the damage was investigated as a function of dwell-time (1–250 μs) and target temperature (355–415°C). The results show that the irradiation damage increases with the dwell-time. The Si top layer was amorphized for longer dwell-times although the substrate temperature was always above the critical temperature for amorphization of about 270°C according to the model of Morehead and Crowder. For the high current density of a focused ion beam (1–10 A/cm²) the damage creation rate is higher than the rate of dynamic annealing.     

Defects in carbon and oxygen implanted p-type silicon

Both oxygen and carbon ion implantation are frequently used to form either insulating buried SiO₂ or SiC layer for various purposes. This creates a renewal of the interest in defects produced during such implantation processes. In the present paper we report on deep level transient spectroscopy studies of defect states occurring in boron-doped p-type silicon after high dose C⁺ and CO⁺ ion implantation and subsequent thermal annealing. It is shown that the predominant defect created during the implantation is in both cases related to silicon selfinterstitial clusters, which upon annealing at higher temperatures evolve to extended structural defects.     

Photoluminescence induced by Si implantation into Si3N4 matrix

Up to the present, photoluminescence (PL) was obtained from near stoichiometric or amorphous Si nitride films (SiN_x) after annealing at high temperatures. As a consequence, the existence of PL bands has been reported in the 400–900 nm range. In the present contribution, we report the first PL results obtained by Si implantation into a stoichiometric 380 nm Si₃N₄ film. The Si excess is obtained by a 170 keV Si implantation at different temperatures with a fluence of Φ = 10¹⁷ Si/cm². Further, we have annealed the samples in a temperature range between 350 and 900 °C in order to form the Si precipitates. PL measurements were done using an Ar laser as an excitation source, and a broad PL band basically centered at 910 nm was obtained. We show that the best annealing condition is obtained at T_a = 475 °C for the samples implanted at 200 °C, with a PL yield 20% higher than the obtained at room temperature implantation. Finally, we have varied the implantation fluence and, consequently, the Si nanocrystals size. However, no variation was observed nor in the position neither in the intensity of the PL band. We concluded that the PL emission is due to radiative states at the matrix and the Si nanocrystals interface, as previously suggested in the literature.     

Low-temperature relaxation processes in cold-worked zirconium

The internal friction and modulus relaxation spectrum of high-purity polycrystalline zirconium has been studied between 77 K and room temperature. Low (1 Hz) and high (50 kHz) frequency measurements are reported after room- and low-temperature tensile deformation. Three relaxation peaks appeared, called P₁, P₂ and P₃. The variation of these with the measuring frequency, amount of cold work and annealing of the specimen at temperatures above that of deformation was investigated. The peak P₁ appeared in the range 80 to 90 K at 1Hz after cold work at 80 K and dissappeared on heating the specimen above 200 K. P₂ appeared either after deformation at room temperature or at low temperature if followed by an annealing process above 200 K: this peak is a very wide one at low frequencies (1 Hz) with its maximum at about 150 K. P₃, generated by cold-working the specimen at 80 K, proved to be very unstable and recovered while being measured at 1 Hz: its physical origin is still uncertain. The recovery of the modulus defect after deformation at 80 K showed three stages, coincident with those of resistivity reported in the literature. The peak p₁ is considered to be due to the relaxation of dislocations against intrinsic lattice barriers, the peak P₂ to the interaction of point defects with dislocations.     

Xenon-ion-induced and thermal mixing of Co/Si bilayers and their interplay

Studies on ion-irradiated transition-metal/silicon bilayers demonstrate that interface mixing and silicide phase formation depend sensitively on the ion and film parameters, including the structure of the metal/Si interface. Thin Co layers e-gun evaporated to a thickness of 50 nm on Si(1 0 0) wafers were bombarded at room temperature with 400-keV Xe⁺ ions at fluences of up to 3 × 10¹⁶ cm⁻². We used either crystalline or pre-amorphized Si wafers the latter ones prepared by 1.0-keV Ar-ion implantation. The as-deposited or Xe-ion-irradiated samples were then isochronally annealed at temperatures up to 700 °C. Changes of the bilayer structures induced by ion irradiation and/or annealing were investigated with RBS, XRD and HRTEM. The mixing rate for the Co/c-Si couples, Δσ²/Φ = 3.0(4) nm⁴, is higher than the value expected for ballistic mixing and about half the value typical for spike mixing. Mixing of pre-amorphized Si is much weaker relative to crystalline Si wafers, contrary to previous results obtained for Fe/Si bilayers. Annealing of irradiated samples produces very similar interdiffusion and phase formation patterns above 400 °C as in the non-irradiated Co/Si bilayers: the phase evolution follows the sequence Co₂Si → CoSi → CoSi₂.     

Point defects induced in ion irradiated 4H–SiC probed by exciton lines

The defects produced in 4H–SiC epitaxial layers by irradiation with a 200 keV H⁺ ion beam in the fluence range 6.5 × 10¹¹–1.8 × 10¹³ ions/cm² are investigated by Low Temperature Photoluminescence (LTPL–40 K).The defects produced by ion beam irradiation induce the formation of some sharp lines called “alphabet lines” in the photoluminescence spectra in the 425–443 nm range, due to the recombination of excitons at structural defects.From the LTPL lines intensity trend, as function of proton fluence, it is possible to single out two groups of peaks: the P₁ lines (e, f, g) and the P₂ lines (a, b, c, d) that exhibit different trends with the ion fluence. The P₁ group normalized yield increases with ion fluence, reaches a maximum at 2.5 × 10¹² ions/cm² and then decreases. The P₂ group normalized yield, instead, exhibits a formation threshold at low fluence, then increases until a maximum value at a fluence of 3.5 × 10¹² ions/cm² and decreases at higher fluence, reaching a value of 50% of the maximum yield.The behaviour of P₁ and P₂ lines, with ion fluence, indicates a production of point defects at low fluence, followed by a subsequent local rearrangement creating complex defects at high fluence.     

Effects of the density of collision cascades: Separating contributions from dynamic annealing and energy spikes

We present a quantitative model for the efficiency of the molecular effect in damage buildup in semiconductors. Our model takes into account only one mechanism of the dependence of damage buildup efficiency on the density of collision cascades: nonlinear energy spikes. In our three-dimensional analysis, the volume of each individual collision cascade is divided into small cubic cells, and the number of cells that have an average density of displacements above some threshold value is calculated. We assume that such cells experience a catastrophic crystalline-to-amorphous phase transition, while defects in the cells with lower displacement densities have perfect annihilation. For the two limiting cases of heavy (500 keV/atom ²⁰⁹Bi) and light (40 keV/atom ¹⁴N) ion bombardment of Si, theory predictions are in good agreement with experimental data for a threshold displacement density of 4.5 at.%. For intermediate density cascades produced by small 2.1 keV/amu PF_n clusters, we show that dynamic annealing processes entirely dominate cascade density effects for PF₂ ions, while energy spikes begin contributing in the case of PF₄ cluster bombardment.     

Gettering of copper impurity in silicon by aluminum precipitates and cavities

Al precipitates as well as cavities (or open-volume defects) are known for their ability to getter impurities within Si. In order to compare their relative gettering strength we produced both Al precipitates and cavities at different depths within one Si wafer. This was done by H+ and Al+ implantation with different energies and subsequent annealing process, resulting in Al-Si alloy and cavities at depth of 300 nm and 800 nm, respectively. Cu was then implanted with an energy of 70 keV to a fluence of 1 X 1014 / cm". The Cu implanted samples were annealed at temperature from 700C to 1200C. It was found that Cu impurities were gettered primarily by the precipitated Al layer rather than by cavities at the temperature of 700~1000C, while gettering of Cu occured in both regions at the temperature of 1200C. The secondary ion mass spectrometry and transmission electron microscopy analyses were used to reveal the interaction between Cu impurities and defects at different trap sites.     

Effects of environment on annealing behavior of In+ implanted c-axis sapphire

Single crystal samples of 〈0001〉α-Al₂O₃ were implanted with 360 keV indium ions of doses of 1 × 10¹⁶ and 3 × 10¹⁶ ions/cm², at room temperature (RT). The implanted samples were annealed isothermally in air or in flowing high purity argon ambient at 900°C for 2 or 12 h. The damage and thermal annealing were evaluated using Rutherford Backscattering Spectrometry and Channeling (RBS-C) and X-ray Diffraction (XRD). Amorphization of sapphire was not observed, despite damage energy densities up to 105 dpa (displacements per atom obtained from TRIM code calculation) for the Al sublattice, which indicated that self-annealing was severe during In ion implantation of sapphire at RT. RBS-C measurement revealed differences in the annealing characteristics of the implanted indium ions that depended on the annealing environment. The XRD spectrum indicated the presence of the In₂O₃ phase in the subsurface region of the sample after annealing in air.     

Damage buildup and the molecular effect in Si bombarded with PFn cluster ions

We study the molecular effect (ME) in damage accumulation in Si bombarded at room temperature with atomic P and F and cluster PF_n (n = 2 and 4) ions with an energy of 2.1 keV/amu. Correct ion irradiation conditions for unambiguous studies of the ME are discussed. Rutherford backscattering/channeling spectrometry results show that the damage buildup behavior strongly depends on the cluster ion size, and the ME efficiency increases rapidly with increasing the number of atoms in cluster ions. Moreover, the ME efficiency decreases with increasing the defect generation rate, indicating that dynamic annealing processes, rather than nonlinear energy spikes, play a major role in the ME for these irradiation conditions.     

Light particle irradiation effects in Si nanocrystals

Si nanocrystals, formed by Si ion implantation into SiO₂ layers and subsequent annealing at 1150°C, were irradiated at room temperature either with He⁺ions at energies of 30 or 130 keV, or with 400 keV electrons. Transmission electron microscopy (TEM) and photoluminescence (PL) studies were performed. TEM experiments revealed that the Si nanocrystals were ultimately amorphized (for example at ion doses ∼10¹⁶ He cm⁻²) and could not be recrystallized by annealing up to 775°C. This contrasts with previous results on bulk Si, in which electron- and very light ion-irradiation never led to amorphization. Visible photoluminescence, usually ascribed to quantum-size effects in the Si nanocrystals, was found to decrease and vanish after He⁺ ion doses as low as 3 × 10¹²–3 × 10¹³ He cm⁻² (which produce about 1 displacement per nanocrystal). This PL decrease is due to defect-induced non-radiative recombination centers, possibly situated at the Si nanocrystal/SiO₂ interface, and the pre-irradiation PL is restored by a 600°C anneal.