Oxygen and hydrogen accumulation at buried implantation-damage layers in hydrogen- and helium-implanted Czochralski silicon

Oxygen and hydrogen accumulations at buried implantation-damage layers were studied after post-implant-ation annealing of hydrogen- and helium-implanted Czochralski (Cz) silicon. Hydrogen implantation was carried out at energies E=180 keV and doses D=2.7×10¹⁶ cm^-2, and helium implantation at E=300 keV and D=10¹⁶ cm^-2. For comparison hydrogen implantation was also done into float-zone (Fz) silicon wafers. Post-implantation annealing at 1000 °C was done either in H₂ or N₂ atmosphere. Hydrogen and oxygen concentration profiles were measured by secondary ion mass spectroscopy (SIMS). It is shown that the ambient during annealing plays a significant role for the gettering of oxygen at buried implantation-damage layers in Cz Si. For both hydrogen and helium implantations, the buried defect layers act as rather effective getter centers for oxygen and hydrogen at appropriate conditions. The more efficient gettering of oxygen during post-implantation annealing in a hydrogen ambient can be attributed to a hydrogen-enhanced diffusion of oxygen towards the buried implantation-damage layers, where a fast oxygen accumulation occurs. Oxygen concentrations well above 10¹⁹ cm^-3 can be obtained. From the comparison of measurements on hydrogen-implanted Cz Si and Fz Si one can conclude that at the buried defect layers hydrogen is most probably trapped by voids and/or may be stable as immobile molecular hydrogen species. Therefore hydrogen accumulated at the defect layers, and is preserved even after high-temperature annealing at 1000 °C. Received: 3 July 2000 / Accepted: 11 July 2000 / Published online: 22 November 2000     

EPR study of radiation-induced defects in carbonate-containing hydroxyapatite annealed at high temperature

Radiation-induced (γ or UV) paramagnetic defects in carbonate-containing hydroxyapatite (HAP) annealed at high (600–950 °C) temperature were studied by EPR. The complex spectra reveal the presence of different paramagnetic species. Their contributions were found to be strongly dependent on the annealing temperature as well as microwave power, thus, by the adjustment of experimental conditions some of the components can be eliminated that allowed to record EPR spectra caused by no more than two types of paramagnetic defects. All experimental spectra were analyzed using computer simulation. The parameters of the paramagnetic defects detected were determined, and the centers models were discussed. It was found that high-temperature annealing influences essentially the formation of radiation-induced defects in HAP. The СО₃³⁻, О⁻ centers and oxygen vacancy V_O⁻ were shown to be the main stable γ-induced defects in the HAP annealed at high temperatures. New paramagnetic defect with the parameters g_|| = 2.002, g_⊥ = 2.0135 was detected and tentatively identified as an O-related radical. The γ-induced EPR response from СО₃³⁻ radicals was found to be more intense than response from CO₂⁻ in non-annealed HAP. UV-irradiation was found to create smaller amounts of paramagnetic defects in comparison with γ-rays. Besides, oxygen vacancy V_O⁻ was not observed, while two other centers (СО₃⁻ and the center of unknown nature) appear in the UV-induced EPR spectra.     

Hydrostatic pressure effects on oxygen-related irradiation-produced defects in silicon

Abstract

Hydrostatic pressure has been used as a variable to investigate the E_c-0.164 eV acceptor level for the oxygen-vacancy (O—V) defect in γ-ray irradiated Si, and the annealing/formation of oxygen-related defects in neutron-irradiated Si. The acceptor level is found by deep level transient spectroscopy to move closer to the conduction band and away from the valence band at rates of 3.9 meV/kbar and 2.4 meV/kbar, respectively, i.e., the level moves higher in the gap. There is also a relatively large inward (outward) breathing mode lattice relaxation (4.6±1.2 ų/electron) accompanying electron emission (capture) from this level. Both results reflect the antibonding nature of the level and are qualitatively consistent with the Watkins—Corbett model for the O—V defect. The annealing rate was found by infrared absorption to increase with pressure for the O—V defect at 350°C with a derived activation volume of ?4.5 ų/defect, where the negative sign implies inward relaxation (contraction) on annealing. Pressure has relatively little effect on annealing of the C—Si—O C(3) defect which is interstitial in nature, but strongly favors the formation of the dioxygen (2 oxygen atoms per vacancy, i.e., O₂—V) defect. The intensity of the O₂—V band after annealing at 20 kbar is 5 times higher than that following similar annealing at 0 kbar. Additionally, this intensity at 20 kbar is higher than that achievable by any isochronal or isothermal annealing steps at 0 kbar. These annealing/formation results are discussed qualitatively in terms of models for the various defects.     

Structure, electrical and magnetic properties, and the origin of the room temperature ferromagnetism in Mn-implanted Si

The structure and the electrical and magnetic properties of Mn-implanted Si, which exhibits ferromagnetic ordering at room temperature, are studied. Single-crystal n- and p-type Si wafers with high and low electrical resistivities are implanted by manganese ions to a dose of 5 × 10¹⁶ cm^?2. After implantation and subsequent vacuum annealing at 850°C, the implanted samples are examined by various methods. The Mn impurity that exhibits an electric activity and is incorporated into the Si lattice in interstitial sites is found to account for only a few percent of the total Mn content. The main part of Mn is fixed in Mn₁₅Si₂₆ nanoprecipitates in the Si matrix. The magnetization of implanted Si is found to be independent of the electrical resistivity and the conductivity type of silicon and the type of implanted impurity. The magnetization of implanted Si increases slightly upon short-term postimplantation annealing and disappears completely upon vacuum annealing at 1000°C for 5 h. The Mn impurity in Si is shown to have no significant magnetic moment at room temperature. These results indicate that the room temperature ferromagnetism in Mn-implanted Si is likely to be caused by implantation-induced defects in the silicon lattice rather than by a Mn impurity.     

Positron annihilation in electron-irradiated n-type gap crystals

Abstract

The defects in n-GaP crystals irradiated by 2.3 MeV electrons up to 1 × 10¹⁹ cm^?2 at RT were studied by means of positron annihilation (angular correlation) and electrical property measurements. It was found that positrons are trapped in some radiation-induced vacancy-type defects (acceptors) but that the effect saturates at high electron fluences (D1 × 10¹⁸ cm^?2). The trapping rate in irradiated samples increases with temperature in the range 77–300 K. Post-irradiation isochronal annealing reveals the positron traps clustering at about 200–280°C. All positron sensitive radiation-induced defects disappear upon annealing up to 500°C.     

Electron and nuclear spin dynamics in plastically deformed silicon crystals enriched in isotope 29Si

Paramagnetic defects of a new type with a concentration of about 10¹⁵ cm^?3 are shown to be generated during the plastic deformation of isotope-rich (72%, 76% ²⁹Si) silicon crystals at a temperature of 950°C. The electron paramagnetic resonance (EPR) spectra of these defects are anisotropic and have a significant width (up to 1 kOe). The nonuniform broadening of the EPR lines is caused by the variation of the internal magnetic field in correlated defect clusters. The nuclear magnetic resonance (NMR) spectra of the deformed crystals consist of Pake doublets split by nuclear spin-spin interaction. The broadening of the NMR spectra is caused by nuclear dipole-dipole relaxation.     

Secondary defects in low-energy As-implanted Si

14 /cm² dose of As ions followed by both isochronal and isothermal annealing. The elementary defects generated first during solid-phase epitaxial recovery of implantation-induced amorphous layers at temperatures of 550 °C and/or 600 °C are {311} defects 2–3 nm long. They are considered to be transformed into {111} and {100} defects after annealing at temperatures higher than 750 °C. These secondary defects show the opposite annealing behavior to the dissolution and growth by the difference of their depth positions at 800 °C. This phenomenon is explained by the diffusion of self-interstitials contained in defects. With regard to the formation and dissolution of defects, there is no significant difference between the effects of rapid thermal annealing (950 °C for 10 s) and furnace annealing (800 °C for 10 min). Received: 14 November 1997/Accepted: 16 November 1997     

Defect recovery behavior of neutron irradiated molybdenum and tungsten of two purity levels

Abstract

The recovery behavior of radiation-induced defects during post-irradiation annealing was studied on molybdenum and tungsten specimens of two different purity levels. An electrical resistivity measurement technique at liquid nitrogen boiling temperature (～77°K) was used. Irradiation of both materials was conducted in Oak Ridge Research reactor at reactor ambient temperature (～70°C). The accumulative neutron fluence received was 7.3E+19 neutrons cm^?2 (E_n>l MeV) and 5.1E+20 neutrons cm^?2 (thermal). It was found that the number of recovery stages appeared to be independent of either the material or the impurity content. The stages are then believed to be due to the recovery of intrinsic defects and the recovery mechanisms are most likely the same for molybdenum and tungsten on the homologous temperature scale.     

Irradiation effects in II-VI compounds

Abstract

A summary of published results on electron energy threshold measurements in II–VI compounds, and their interpretation in terms of damage on the metal and chalcogenide sublattices, is given. EPR results in irradiated II–VI compounds are also reviewed. These include the F⁺ center in ZnS; ZnO, and BeO and new results on the zinc vacancy (V) in ZnSe. For the zinc vacancy, optical absorption bands at 4680Å and 8850Å are identified with V^? and a band at 5000Å is tentatively assigned to V^?. The activation energy for anneal of the vacancy is measured to be 1.26±.06 eV, and this is tentatively identified as the activation energy for vacancy motion. An EPR spectrum produced in a 20.4 °K irradiation is tentatively identified as a zinc vacancy-interstitial pair. Complete annealing occurs for this defect in the range 60–100 °K.     

Investigation of silicon doped by zinc ions with a large dose

The formation of nanoparticles in СZn-Si(100) implanted with ⁶⁴Zn⁺ ions using a dose of 5 × 10¹⁶ cm^–2 and an energy of 50 keV at room temperature with subsequent thermal processing in oxygen at temperatures ranging from 400 to 900°C is studied. The surface topology is investigated with scanning electron (in the secondary emission mode) and atomic force microscopes. The structure and composition of the near-surface silicon layer are examined using a high-resolution transmission electronic microscope fitted with a device for energy dispersive microanalysis. An amorphized near-surface Si layer up to 130 nm thick forms when zinc is implanted. Amorphous zinc nanoparticles with an average size of 4 nm are observed in this layer. A damaged silicon layer 50 nm thick also forms due to radiation defects. The metallic zinc phase is found in the sample after low-temperature annealing in the range of 400–600°C. When the annealing temperature is raised to 700°C, zinc oxide ZnO phase can form in the near-surface layer. The complex ZnO · Zn₂SiO₄ phase presumably emerges at temperatures of 800°C or higher, and zinc-containing nanoparticles with lateral sizes of 20–50 nm form on the sample’s surface.     

Effect of double annealing on the critical parameters of highly textured YBa2Cu3O6.9

The effect of low-temperature treatment (200°C) and subsequent annealing at 930°C on the critical parameters of highly textured YBa₂Cu₃O_6.9 is studied. The structural defects that are formed during the low-temperature decomposition of this compound into phases with different oxygen contents and during interaction with atmospheric moisture are shown to deteriorate the superconducting properties. After annealing at T = 930°C and subsequent oxidation, superconductivity is restored and the formed defects are partly retained and serve as effective pinning centers, including the case of high magnetic fields. The stresses induced by the low-temperature treatment lead to primary recrystallization at T = 930°C, which results in the disappearance of texture and an isotropic state of the material in high fields.     

Temperature dependence of oxidation rate in clean Ge(111)

The temperature dependence of the sticking coefficient of oxygen on a clean Ge(111) surface has been investigated over a wide temperature range from 300 to 1100 °K using three methods. In the interval 300–600 °K a flash technique was used, the desorbed germanium oxide being detected by the time of flight mass-spectrometer. In the range from 500 to 1000 °K the sticking coefficient was measured from the pumping speed of oxygen by the sample surface, and in the range from 800 to 1100 °K the temperature dependence of the etching speed by oxygen was determined.The measured temperature dependence of the sticking coefficient is complex. It increases between 300 and 400 °K, remaining virtually constant from 400 to 500 °K with a new increase in the range from 500 to 1000 °K. A rapid fall in the sticking coefficient was observed at temperatures above 1000 °K.The dependence of the adsorption coverage on exposure has also been obtained for sample temperatures of 300, 350, 400 and 500 and 600 °K. The form of the adsorption curves differs considerably from a theoretical one based on a decrease in the sticking coefficient with coverage given by s = s₀(1 ? θ)². At 600 °K the sticking coefficient decreases more slowly than predicted by this equation. On the contrary, at 300 °K it begins to decrease rapidly at low coverages less than 0.1 of a monolayer.To explain the results it is assumed that oxygen molecules adsorb on the surface structural defects. At 300 °K such defects may be in the form of steps or other morphological disturbances on the surface, and above 500 °K they are probably equilibrium thermal defects, for example, surface vacancies.     

Annealing of γ-ray irradiated lithium compensated p-type silicon

Abstract

Annealing behavior of electrical properties and photoluminescence spectra both at 77 °K in electron-irradiated melt-grown n-GaAs were investigated. Defects electrically active in the Hall mobility and carrier removal anneal through two stages centered at 250° and 460 °K. From the temperature dependence of carrier concentration the existence of a defect level located near 0.15 eV below the conduction band is supposed. Several emission bands are resolved at 1.51, 1.47, 1.415, 1.305 and ～1.2 eV in photoluminescence experiments. Electron irradiation (1.5–2.0 MeV) causes a remarkable decrease in emission intensity of 1.51 and ～1.2 eV bands. Recovery of emission intensity occurs remarkably when samples are annealed to 520 °K which would correspond to the 460 °K annealing stage for carrier concentration and Hall mobility. The 250 °K annealing stage is not observed in photoluminescence experiments. The 1.415 eV peak appears clearly after irradiation and grows remarkably with the 520 °K annealing, especially in Si-doped samples, resulting in large reverse annealing. This band is tentatively speculated to be a complex of Si on As site with As vacancy. Moreover, in samples doped with Te a new emission band at 1.305 eV (9500 Å) is observed after 470°–620 °K annealing.     

Enhanced photosensitivity in sol–gel derived 20GeO2:80SiO2 thin films

We investigate the photosensitivity of binary 20GeO₂:80SiO₂ (germanosilicate) inorganic films. The samples have been fabricated by the sol–gel spin-coating method and the densification has been performed by rapid thermal annealing at various temperatures ranging from 500 °C to 1000 °C. The –OH absorption bands in the Fourier-transform infrared (FTIR) spectra and the refractive-index data show that the films annealed below 900 °C are porous and the films annealed at 900 °C and above are dense. An ultraviolet (UV) KrF laser at 248 nm has been used to induce the change in the refractive index of the samples. We have achieved a large refractive-index change (Δn) of 0.0098 after UV illumination in excess of 1 min for our dense germanosilicate films. This UV-induced refractive-index change is attributed to the formation of GeE’/SiE’ centers from Ge–Ge/Si–Si (neutral oxygen monovacancy) and Ge²⁺ centers and to the creation of oxygen deficiency related defects. From our experiments, the oxygen deficiency related defects correspond to the absorption band at 620–740 cm^-1 in the FTIR spectra and these are the defects which make a large contribution to Δn. The attenuation coefficient of the as-deposited and UV-illuminated dense samples is about 0.42 dB/cm at 1550 nm. For porous samples, UV exposure has densified the samples to some extent. PACS 82.50.Hp; 71.23.Cq; 81.20.Fw     

Absorption measurements in neutron irradiated silicon

Silicon samples have been neutron irradiated at 76 °K with fluences sufficient to allow measurement of the 1.7 μ divacancy band at 76 °K. The growth of the divacancy concentration and the recovery of the edge absorption were studied as a function of annealing temperature between 76 °K and 550 °K. Immediately after irradiation the divacancy concentration is about 25 per cent of its maximum value which is attained at 330 °K, the temperature at which the divacancies begin to anneal out. Increases in the 1.7 μ band intensity and recovery of the edge absorption can also be achieved at 76 °K by illuminating the sample with intense sub-bandgap light or white light. The experimental results suggest a neutron-induced cluster model in which the cluster is a vacancy-rich region whose annealing characteristics are controlled by the liberation and motion of vacancies. The injection effects can be explained by analogy to the charge state dependent mobility of the Si vacancy.     

Structural and photoluminescence properties of silicon nanocrystals embedded in SiC matrix prepared by magnetron sputtering

Si nanocrystals (NCs) embedded in an SiC matrix were prepared by the deposition of Si-rich Si_1?xC_x/SiC nanomultilayer films using magnetron sputtering, subsequently followed by thermal annealing in the range of 800～1200 °C. As the annealing temperature increases to 1000 °C, Si NCs begin to form and SiC NCs also start to emerge at the annealing temperature of 1200 °C. With the increase of annealing temperature, two photoluminescence (PL) peaks have an obvious redshift. The intensity of the low-energy PL peak around 669～742 nm gradually lowers, however the intensity of high-energy PL peak around 601～632 nm enhances. The low-energy PL peak might attribute to dangling bonds in amorphous Si (a-Si) sublayers, and the redshift of this peak might be related to the passivation of Si dangling bonds. Whereas the origin of the high-energy PL peak may be the emergence of Si NCs, the redshift of this peak correlates with the change in the size of Si NCs.     

The observation of high concentrations of arsenic anti-site defects in electron irradiated n-type GaAs by X-band EPR

N-type GaAs doped with sulphur (2.8 × 10¹⁸ cm^-3) has been subjected to 2 MeV electron irradiation in stages at room temperature and examined by the EPR technique. When the free carrier absorption is first eliminated no EPR signal is detected. After further irradiation, the spectrum of the As anti-site defect appears, grows and subsequently saturates at a concentration of about 10¹⁸ cm^-3. The saturation concentration is about one third of [n] in most samples. The defects are stable on annealing to 500°C but are not observed in various irradiated p-type samples. It is suggested that grown-in defects such as [V_Ga-As_Ga-V_Ga] capture Ga interstitials during the irradiation and are thereby converted to the simpler anti-site defect.     

Influence of oxygen on the ion-assisted regrowth of deposited Si layers

Summary The ion-assisted regrowth of chemical-vapour deposited Si films onto (100) Si substrates is reported. The regrowth was induced by a 600 keV Kr⁺⁺ beam at doses in the range (2·10¹⁵÷6·10¹⁵)/cm² and at a dose rate of 1·10¹²/cm²s. The target temperature was set at 450°C. During irradiations the crystal-amorphous interface velocity was measuredin situ by monitoring the reflectivity of a He-Ne laser light focused onto the sample surface. After irradiation some samples were also analysed by Rutherford backscattering in combination with the channelling effect and by transmission electron microscopy. The growth rate of deposited layers depends on the cleaning procedure performed prior to deposition,i.e on the total amount of oxygen present at the deposited layer/substrate interface. Moreover, twinned material is observed in the recrystallized layers and its concentration is strongly dependent on substrate cleaning. These phenomena are explained in terms of a decrease in the ion-assisted growth rate in the presence of high oxygen concentrations. The data are discussed and compared with those obtained during pure thermal annealing. To speed up publication, the authors of this paper has agreed to not receive the proofs for correction.     

Oxygen diffusion barriers using a new sacrificial design concept for future high-density memory devices

We emphasize the importance of the new design concept for diffusion barriers in high-density memory capacitors. RuTiN and RuTiO films are proposed as sacrificial oxygen diffusion barriers. They showed much lower sheet resistance up to 800 °C than various barriers including binary and ternary nitrides, reported by others. The contact resistance for both the Pt/RuTiN/TiSi_x/n⁺⁺poly-plug/n⁺channel layer/Si and the Pt/RuTiO/RuTiN/TiSi_x/n⁺⁺poly-plug/n⁺channel layer/Si contact structures, the most important electrical parameter for the diffusion barrier in the bottom-electrode structure of capacitors, exhibited values as low as 5 kΩ, even after annealing up to 750 °C. When each RuTiN and TiN film is inserted as a glue layer between the bottom electrode Pt layer in the CVD–BST simple stack-type structure, the thermal stability of the RuTiN glue layer is observed to be 150 °C higher than that of the TiN glue layer. Moreover, the capacitance of the PVD–BST simple stack-type structure with a TiN glue layer initially degrades after annealing at 500 °C, and thereafter failed completely. In the case of RuTiN and the RuTiO/RuTiN glue layers, however, the capacitance continuously increased up to 550 °C. These new experimental results accommodate the introduction of the sacrificial design concept of diffusion barriers against oxygen in high-density memory capacitors. Received: 6 February 2002 / Accepted: 4 March 2002 / Published online: 26 February 2003 RID="*" ID="*"Corresponding author. Fax: +82-31/360-4545, E-mail: dongsoo.yoon@hynix.com     

Radiation-induced defects in annealed carbonate-containing hydroxyapatite

The effect of preliminary (before irradiation) annealing of synthetic carbonate-containing hydroxyapatite powders on the formation of paramagnetic centers under γ-ray and ultraviolet irradiation has been investigated. Annealing of the samples has been performed in the temperature range from 100 to 700°C. It has been found that electron paramagnetic resonance spectra of radiation-induced defects depend substantially on the annealing temperature. The paramagnetic centers CO ₂ ^? dominate in the samples annealed to 250°C (γ-ray irradiation) and 500°C (ultraviolet irradiation). In the samples annealed above 400°C, other defects, in particular, the O^? and CO ₃ ^3? centers, play a significant role. Annealing at some temperatures leads to an increase in the radiation sensitivity of the material. The observed effects can be associated with the escape of molecular water from the annealed hydroxyapatite samples and with the corresponding transformation of the defect subsystem of the material.