Thermal evolution of defects produced by implantation of H, D and He in Silicon

Despite decades of study, voids in silicon produced by implantation of H or He followed by annealing continue to be a topic of interest. There are two key applications: gettering of heavy metal impurities, and “ion cutting” used in silicon-on-insulator fabrication. Positron annihilation is one of the few techniques that can probe the vacancies and vacancy clusters that are the precursors to void formation. Data from recent studies will be discussed, including (I) isotopic substitution, in which comparisons of H vs. D implantation permit examination of the impact of primary point defects vs. chemical effects. Remarkable differences exist between H and D in blistering of silicon - ion doses 2-3 times higher are required for blistering with D than with H, despite a higher rate of primary defect production for D; (II) the effect of annealing temperature ramp-rate, in which we show that ramp-rate has a significant impact on residual defects, despite which it is so disregarded as to often be omitted from published reports; and (III) comparisons with electron microscopy which suggest that positron annihilation can be insensitive to large voids. In these studies, positron annihilation augments data from techniques including ion channelling, Raman scattering and electron microscopy; the suite of techniques allows elucidation of the interplay between implanted impurities and the vacancies and interstitials created by implantation.     

Elementary atomistic mechanism of crystal plasticity

The simulation of loaded crystal behavior under relaxation is carried out. Typical local structural distortions named protodefects, which give rise to conventional lattice defects, are discovered. The dynamics of atomic displacements that govern protodefect nucleation is studied in detail. A local expansion of atomic volume induces protodefect formation.     

Precursor effects of the Rhombohedral-to-Cubic Phase Transition in Indium Selenide

We report on the observation of precursor effects of the rhombohedral-to-cubic phase transition in Indium Selenide (InSe) with several experimental techniques. The pressure at which these precursor defects are first observed depends on the sensitivity of the experimental technique. In transport measurements, which are very sensitive to low defect concentrations, precursor effects are observed 5 to 6 GPa below the phase transition pressure whereas in X-ray diffraction measurements precursor effects are only observed 2 GPa below the phase transition pressure. We report optical absorption measurements, in which the precursor effects are shown by the growth and propagation of dark linear defects appearing 3 GPa below the phase transition pressure. On the base of a simple model of the stress field around edge dislocations, we attribute the darkening of the InSe samples to local phase transitions to a high-pressure modification along linear dislocations. These results agree with room-pressure and high-pressure Raman spectra of samples compressed up to 7-8 GPa, which show new phonon lines not corresponding to the low-pressure phase.     

Kinetics of Nitrogen Indiffusion in Czochralski Silicon Annealed in Nitrogen Ambient

By means of low-temperature （10 K） Fourier transform infrared absorption spectroscopy, the kinetics of nitrogen indiffusion in Czochralski （CZ） silicon annealed at 1150-1250℃ in nitrogen ambient is investigated. Moreover, the nitrogen diffusivities in CZ silicon at elevated temperatures deduced herein are in good agreement with those previously obtained in float-zone silicon, thus leading to the conclusion that the nitrogen indiffusion in CZ silicon at elevated temperatures is via nitrogen pairs.     

Interaction of Point Defects with Twin Boundaries in Copper

The interaction between small vacancy clusters and twin boundaries in copper is studied by using many-body potential developed by Ackland et aL for fcc metals. The interaction energies of single-, di- and tri-vacancy clusters with （111） and （112） twin boundaries are computed using well established simulation techniques. For （111） twins the vacancy clusters are highly repelled when they are on the adjacent planes, and are attracted when they are away from the boundary. In the case of （112） twins, vacancy clusters are more attracted to the boundary when they are near the boundary as compared to away from it. Vacancy clusters on both the sides of the boundary are also investigated, and it is observed that the clusters energetically prefer to lie on the off-mirror sites as compared to the mirror position across the twin.     

Hydrothermal synthesis of ZnO nanobelts and gas sensitivity property

The ZnO nanobelts were synthesized by a hydrothermal method. The XRD spectrum indicates that the sample is wurtzite (hexagonal) structured ZnO with lattice constants of , . SEM and TEM images show the nanobelts to have lengths of 10-20 μm, widths of 50-500 nm, thicknesses of about 30-60 nm, and growth direction of [0001]. Gas sensitivity experiments on ZnO nanobelts were carried out under different temperatures. The results indicated high sensitivities with an operating temperature of only 220 ^°C for the oxidative gas O₂, and 305 ^°C for the gas N₂. The mechanism of gas sensitive effects is analyzed in detail.     

The silicon vacancy in SiC

The isolated silicon vacancy is one of the basic intrinsic defects in SiC. We present new experimental data as well as new calculations on the silicon vacancy defect levels and a new model that explains the optical transitions and the magnetic resonance signals observed as occurring in the singly negative charge state of the silicon vacancy in 4H and 6H SiC.     

Existence and atomic arrangement of microtwins in CdTe epilayers grown on GaAs (211) B substrates

Selected area electron diffraction pattern (SADP) and high-resolution transmission electron microscopy (HRTEM) measurements were carried out to investigate the existence and the atomic arrangement of microtwins in CdTe epilayers grown on GaAs (211) B substrates by using molecular beam epitaxy. The SADP results showed that an epitaxial relationship between the CdTe epilayer and the GaAs substrate was formed. The lattice of the CdTe (211) tilts about 2° with respect to the GaAs (211) B substrate about the CdTe [110]∥GaAs [110] common zone axis. The HRTEM images showed that microtwins were formed in the CdTe epilayers. A possible atomic arrangement of the microtwins is presented on the basis of the HRTEM result. The present observations can help to improve understanding of the microstructural properties in CdTe epilayers grown on GaAs substrates.     

Dopant diffusion and segregation in semiconductor heterostructures: Part 1. Zn and Be in III-V compound superlattices

chemical effect on the neutral species; and (ii) a Fermi-level effect on the ionized species, because, in addition to the chemical effect, the solubility of the species also has a dependence on the semiconductor Fermi-level position. For Zn and Be in GaAs and related compounds, their diffusion process is governed by the doubly-positively-charged group III element self-interstitials (I²⁺ _III), whose thermal equilibrium concentration, and hence also the diffusivity of Zn and Be, exhibit also a Fermi-level dependence, i.e., in proportion to p². A heterojunction consists of a space-charge region with an electric field, in which the hole concentration is different from those in the bulk of either of the two layers forming the junction. This local hole concentration influences the local concentrations of I²⁺ _III and of Zn^- or Be^-, which in turn influence the distribution of these ionized acceptor atoms. The process involves diffusion and segregation of holes, I²⁺ _III, Zn^-, or Be^-, and an ionized interstitial acceptor species. The junction electric field also changes with time and position. Received: 20 August 1998/Accepted: 23 September 1998     

Dopant diffusion and segregation in semiconductor heterostructures: Part 2. B in GexSi1-x/Si structures

x Si_1-x/Si heterostructures have been obtained. Here the chemical effects seem to be of less importance. The Fermi-level effect determines the ionized boron solubilities in Ge_xSi_1-x and in Si, as well as the thermal equilibrium concentration of the singly-positively-charged crystal self-interstitials I⁺ which governs the boron diffusion process. The junction carrier concentration affects the concentration of I⁺ and solubility of B in the region and hence controls B diffusion across the heterojunction. Received: 20 August 1998/Accepted: 23 September 1998     

Computer simulation of intrinsic defects in YAlO3 single crystal

Computer simulation techniques were used to investigate intrinsic defects in YAlO₃ single crystal. A set of short-range potential parameters were derived using a relaxed fitting procedure incorporating with the known crystal properties. These parameters were then applied within the framework of the shell model. The simulation results reveal that oxygen Frenkel disorder and the antisite defect of Al ion substituting the Y ion dominate the intrinsic defects in YAlO₃. An analysis of redox reactions corroborate that the oxidation is most likely to occur via forming interstitial oxygen, while the oxidation via filling oxygen vacancies and reduction reaction may predominate at high temperature. The activation energy of oxygen vacancy migration on conduction was also studied.     

Molecular dynamics simulations of the interaction between 60° dislocation and self-interstitial cluster in silicon

Molecular dynamics simulations are performed to investigate the interaction between 60° shuffle dislocation and tetrainterstitial (I₄) cluster in silicon, using Stillinger-Weber (SW) potential to calculate the interatomic forces. Based on Parrinello-Rahman method, shear stress is exerted on the model to move the dislocation. Simulation results show that the I₄ cluster can bend the dislocation line and delay the dislocation movement. During the course of intersection the dislocation line sections relatively far away from the I₄ cluster accelerate first, and then decelerate. The critical shear stress unpinning the 60° dislocation from the I₄ cluster decreases as the temperature increases in the models.     

Growth of α-Al2O3:C crystal with highly sensitive optically stimulated luminescence

In this work, an α-Al₂O₃:C crystal was directly grown by the temperature gradient technique (TGT) using Al₂O₃ and graphite powders as the raw materials. The optical, optically stimulated luminescence (OSL) properties and dosimetric characteristics of as-grown crystal were investigated. As-grown α-Al₂O₃:C crystal shows strong absorption band at 205, 230 and 256 nm. Three-dimensional thermoluminescence (TL) emission spectrum of the crystal shows a single emission peak at ∼415 nm. The OSL decay curve can be fitted to two exponentials, the faster component and the slower component. The OSL response of the crystal shows a linear-sublinear-saturation characteristic. As-grown α-Al₂O₃:C crystal shows excellent linearity in the dose range from 5×10⁻⁶ to 50 Gy. For doses higher than the saturation dose (100 Gy), the OSL sensitivity decreases as the dose increases.     

Annealing behaviour of high-dose-implanted nitrogen in InP

Concentration profiles of nitrogen in vacuum-annealed p- and n-type single-crystal (1 0 0) InP implanted with 1 × 10¹⁶ 30 keV¹⁵N⁺ ions cm^–2 have been studied by Secondary Ion Mass Spectrometry (SIMS) and Nuclear Resonance Broadening (NRB) techniques. Damage induced by the nitrogen implantation was studied by Rutherford Backscattering Spectrometry (RBS) and channeling. Annealing the samples led to loss and redistribution of nitrogen in the temperature range from 575 to 675 °C. At temperatures from 575 to 600 °C, rapid migration of nitrogen towards the sample surface was observed. The n-type InP material had a very dominant tendency for surface nitrogen build-up, whereas the p-type material had a markedly smaller surface peak in the nitrogen distribution. The surface peak in n-type material is due to sulphur acting partly as a diffusion barrier. SIMS analyses showed sulphur build-up on the surface in the course of annealing. At temperatures from 600 to 675 °C, the nitrogen profiles of n- and p-type InP were similar. A small loss of nitrogen was observed at 625–675 °C. Two different recovery stages were observed at 575–600°C and at 625–650 °C. The corresponding activation energies for nitrogen loss are 2.9 and 3.0 eV, respectively.     

Characterization of vacancy-related defects introduced into silicon during heat treatment by deep-level transient spectroscopy and gamma-ray diffraction techniques

Vacancy-related defects introduced into n-Si during annealing or aluminium diffusion at high temperature (1000–1250°C) have been studied. Different ambients (argon, nitrogen, vacuum and chlorine-containing atmosphere) were used to create a vacancy supersaturation during heat treatments. Three deep-level centers whose formation is governed by the presence of vacancies have been identified. They were characterized by the following temperature dependences of the thermal emission rate:e3 = 7.92 × 10⁷ T ² × exp(– 0.455/kT),e ₅ = 2.64 × 10⁶ T ² × exp( – 0.266/kT),e ₇ = 7.26 × 10⁶ T ² × exp (– 0.192/kT). The influence of different factors, such as heat-treatment conditions, concentration of oxygen and doping level in initial crystals, on center formation was studied. An asymmetric diffuse-ray scattering was observed near the surface of a crystal irradiated by thermal neutrons and annealed in a chlorine-containing atmosphere. This scattering is related to the formation of structural defects of the vacancy type. In the same region of the crystal, the concentration of the E7 center was one order of magnitude higher than that of other deep-level centers. Comparison of the-ray diffraction and deeplevel transient spectroscopy (DLTS) data suggests that the formation of the center occurs under the conditions of Si supersaturation with vacancies.     

45 nm CMOS technology with low temperature selective epitaxy of SiGe

This paper describes the advanced embedded silicon germanium (eSiGe) technologies to apply the 45 nm node CMOS fabrication technology. There are three key techniques as follows. The first technique is a low temperature of epitaxial growth at 550 °C to suppress staking faults in eSiGe layer. The second one is a controlling of recess shape for eSiGe. Sigma(Σ)-shaped recess is applied, because the strain force on the channel of MOSFET is increased effectively by narrowing spacing between source and drain. The third one is to apply particular surface cleaning treatment before the epitaxial growth, to get the excellent SiGe crystallinity. We demonstrated the drain current of I_on = 725 μA/μm and I_off = 100 nA/μm for PMOSFET using above these techniques.     

Useful vacancies: Positron beam interrogation of fluorine-vacancy complexes in semiconductor device structures

The formation, migration and agglomeration in silicon of fluorine-vacancy complexes have been monitored by single-detector Doppler broadening spectroscopy. After electronics engineers found that fluorine ion implantation effectively eliminated the transient-enhanced diffusion of dopants in the creation of ultra-shallow junctions, a vital step in the further miniaturization of device structures, positron beams have played a pivotal role in providing an insight into the mechanisms underlying this phenomenon, being able to detect FV complexes in implanted and annealed samples. Secondary Ion Mass Spectrometry has provided complementary information on fluorine concentrations so that the nature of the F_mV_n complexes can be further assessed. New results on Si and SiGe structures are presented.     

Ordered zinc-vacancy induced Zn0.75Ox nanophase structure

Using transmission electron microscopy, a new nano-phase structure of Zn_0.75O_x induced by Zn-vacancy has been discovered to grow on wurtzite ZnO nanobelts. The superstructure grows epitaxial from the surface of the wurtzite ZnO nanobelts and can be fitted as an orthorhombic structure, with lattice parameters a′=2a, and c′=c, where a and c are the lattice parameters of ZnO. The superstructured phase is resulted from high-density Zn vacancies orderly distributed in the ZnO matrix. This study provides direct observation about the existence of Zn-vacancies in ZnO.     

Doping mechanism of optical-damage-resistant ions in lithium niobate crystals

The doping mechanism of optical-damage-resistant ions (Mg²⁺, Zn²⁺, In³⁺, Sc³⁺, Hf⁴⁺, and Zr⁴⁺) in the lithium niobate crystallographic frame is quantitatively studied from the chemical bond viewpoint. Calculated results show that optical-damage-resistant ions have a strong interaction with the lithium niobate matrix, which is quantitatively evaluated by the deviation between normal and calculated valence states and the global instability index. All optical-damage-resistant ions first substitute Nb_Li and then Li ions, they change their dopant occupancies from Li to Nb sites at the same global instability index value 0.1055. On the basis of such a quantitative interaction, the doping mechanism of these ions is finally derived. Furthermore, a criterion in searching for new optical-damage-resistant ions is also proposed.     

High elastic modulus in b-axis-oriented single crystal V2O5

The elastic moduli of V₂O₅ are of great importance for the assessment of the buildup of strain during thin-film growth as well as for the analysis of defect generation and propagation. The usually rather small crystal dimensions make a precise experimental determination of the elastic constants highly challenging and only very little is known about the temperature dependent strain evolution. Here large V₂O₅ single crystals grown with different parameter sets are investigated by ultrasonic pulse experiments and by sampled continuous wave ultrasound spectroscopy. The elastic modulus C₂₂ is determined to be 220 GPa at room temperature. Temperature dependent investigations of the elastic behavior show that ultrasonic experiments are suitable for highly sensitive detection of oxygen-deficient phases in rapidly grown samples. In addition they indicate the presence of temperature dependent elastic instabilities in inhomogeneous samples.