Papers by Keyword: Self-Interstitial

Abstract: The contributions of vacancies and self-interstitials to silicon (Si) self-diffusion are a matter of debate since many years. These native defects are involved in dopant diffusion and the formation of defect clusters and thus influence many processes that take place during Si single crystal growth and the fabrication of silicon based electronic devices. Considering their relevance it is remarkable that present data about the properties of native point defects in Si are still limited and controversy. This work reports recent results on the properties of native point defects in silicon deduced from self-diffusion experiments below 850°C. The temperature dependence of silicon self-diffusion is accurately described by contributions due to vacancies and self-interstitials assuming temperature dependent vacancy properties. The concept of vacancies whose thermodynamic properties change with temperature solves the inconsistency between self-and dopant diffusion in Si but further experiments are required to verify this concept and to prove its relevance for other material systems.

Abstract: Vacancies (and probably also self-interstitials) in silicon appear to exist in several forms (atomic configurations) some of them being fast diffusers and other slow diffusers. The data on enhanced self-diffusivity under proton irradiation, on vacancy and oxide precipitate profiles installed by Rapid Thermal Annealing, and on the self-diffusivity under equilibrium conditions suggest that there are at least two kinds of vacancy: 1) V_w - a fast-diffusing localized vacancy manifested in electron irradiated samples (Watkins vacancy), 2) V_s - a slow-diffusing extended vacancy manifested under hot proton irradiation. In RTA experiments, these two species behave as one equilibrated subsystem of a moderate effective diffusivity intermediate between those of V_w and V_s. There is also strong evidence in favor of a third kind of vacancy: V_f a fast extended species, which controls the grown-in voids in silicon crystals.

Abstract: Local density approximation (LDA) +U within the framework of density functional theory (DFT) was used to study the properties of vacancy and self-interstitial atom (SIA) in δ-Pu. The results show that mono-vacancy, di-vacancy and tri-vacancy existing in δ-Pu shift rightward the f shell peak of the projected density of states (PDOS), the peak values of mono-vacancy and di-vacancy decrease, while the peak value of tri-vacancy increases. The saddle point during vacancy migration shifts leftward the f shell peak of PDOS, and the peak value decreases. The octahedral SIA, the tetrahedral SIA, the split SIA shift leftward the f shell peak of PDOS, and the peak values decreases. Finally, the recombination behavior of vacancy and SIA were studied at both the spin-restricted and the spin-unrestricted level, SIA migrates to vacancy site, and exhibits a tendency to forming the perfect fcc structure.

Abstract: In dislocation-free silicon, intrinsic point defects – either vacancies or self-interstitials, depending on the growth conditions - are incorporated into a growing crystal. Their incorporated concentration is relatively low (normally, less than 1014 cm-3 - much lower than the concentration of impurities). In spite of this, they play a crucial role in the control of the structural properties of silicon materials. Modern silicon crystals are grown mostly in the vacancy mode and contain many vacancy-based agglomerates. At typical grown-in vacancy concentrations the dominant agglomerates are voids, while at lower vacancy concentrations there are different populations of joint vacancy-oxygen agglomerates (oxide plates). Larger plates – formed in a narrow range of vacancy concentration and accordingly residing in a narrow spatial band – are responsible for the formation of stacking fault rings in oxidized wafers. Using advanced crystal growth techniques, whole crystals can be grown at such low concentrations of vacancies or self-interstitials such that they can be considered as perfect.

Abstract: The study of fast diffusion processes in materials requires short isothermal annealing treatments combined with an accurate temperature measurement. The paper discusses the special demands on rapid thermal annealing (RTA) devices in diffusion research and how these can be met in practice. The scientific impact of RTA for diffusion research in semiconductors is demonstrated by several examples dealing with fast impurities in Ge and Si.

Abstract: The time dependence of thermal donor (TD) concentration, N(t), during annealing at 450oC was measured in samples cut from a single slab of silicon containing bands of grown-in microdefects of different types. An enormous impact of the microdefect type on the kinetic curve was observed. Samples from the interstitial region showed simple linear rise in N(t). The samples from an inner part of the vacancy region showed a complicated oscillating variation with an abrupt disappearance of the TDs at some moment followed by an immediate restoration of a linear rise. In samples from the marginal H-band of the vacancy region, an initial anneal does not produce TDs. However if this anneal was followed by a quench, subsequent anneals produce a linear rise in N(t). On the other hand, if the sample was slowly cooled, the subsequent production of TDs remained almost negligible. These observed peculiarities are accounted for by enhanced TD growth in the presence of self-interstitials (I) - due to IO species serving as vehicles for oxygen transport.

Abstract: Interstitial iron and iron-acceptor pairs are well studied but undesirable defects in Si as they are strong recombination centers which resist hydrogen passivation. Thermal anneals often result in the precipitation of Fe. Relatively little information is available about the interactions between Fe and native defects or common impurities in Si. We present the results of first-principles calculations of Fe interactions with native defects (vacancy, self-interstitial) and common impurities such as C, O, H, or Fe. The goal is to understand the fundamental chemistry of Fe in Si, identify and characterize the type of complexes that occur. We predict the configurations, charge and spin states, binding and activation energies, and estimate the position of gap levels. The possibility of passivation is discussed.

Abstract: Oxygen precipitation in Si is a complex set of processes which has been studied over many years. Here we review theoretical work relating to the precipitation process. At temperatures around 450°C oxygen atoms become mobile and form a family of thermal double donors. The structure of these defects and the origin of their electrical activity is discussed. At temperature around 650°C these donors disappear and there is a growth of SiO2 precipitates along with rod like defects which are extended defects involving Si interstitials. At higher temperatures these collapse into dislocation loops. The structure and electrical properties of the rod like defect are described and compared with those of dislocations.

Abstract: Nitrogen in silicon is known to affect dramatically the properties of voids. A plausible mechanism could be vacancy trapping by nitrogen interstitial species, mostly by the minor monomeric species (N1) with only a negligible contribution of the major dimeric species (N2). However, a more careful analysis of the published data shows that in Czochralski silicon no vacancy trapping occurs at the void formation stage (around 1100oC). The implication is that the trapping reaction, V + N1, although favoured thermodynamically, is of a negligible rate. Therefore, the nitrogen effect on voids in Czochralski Si is entirely due to nitrogen adsorption at the void surface. Quite a different mechanism operates in Float-Zoned crystals where voids are formed at lower T. Here vacancy trapping by N2 seems to be responsible for void suppression.

Abstract: The electronic properties and structure of a complex incorporating a self-interstitial (I) and two oxygen atoms are presented by a combination of deep level transient spectroscopy (DLTS), infrared absorption spectroscopy and ab-initio modeling studies. It is argued that the IO2 complex in Si can exist in four charge states (IO− 2 , IO02 , IO+ 2 , and IO++ 2 ). The first and the second donor levels of the IO2 complex show an inverted location order in the gap, leading to a E(0/ + +) occupancy level at Ev + 0.255 eV. Activation energies for hole emission, transformation barriers between different structures, and positions of LVM lines for different configurations and charge states have been determined. These observables were calculated by density-functional calculations, which show that they are accounted for if we consider at least two charge-dependent defect structures.