Coupled diffusion of impurity atoms and point defects in silicon crystals (original) (raw)
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Atomistic analysis of defect evolution and transient enhanced diffusion in silicon
Journal of Applied Physics, 2003
Kinetic Monte Carlo simulations are used to analyze the ripening and dissolution of small Si interstitial clusters and ͕113͖ defects, and its influence on transient enhanced diffusion of dopants in silicon. The evolution of Si interstitial defects is studied in terms of the probabilities of emitted Si interstitials being recaptured by other defects or in turn being annihilated at the surface. These two probabilities are related to the average distance among defects and their distance to the surface, respectively. During the initial stages of the defect ripening, when the defect concentration is high enough and the distance among them is small, Si interstitials are mostly exchanged among defects with a minimal loss of them to the surface. Only when defects grow to large sizes and their concentration decreases, the loss of Si interstitials through diffusion to the surface prevails, causing their dissolution. The presence of large and stable defects near the surface is also possible when the implant energy is low-small distance to the surface-but the dose is high enough-even smaller distance among defects. The exchange of Si interstitials among defects sets a interstitial supersaturation responsible for the temporary enhancement of the diffusivity of interstitial diffusing dopants. The transitory feature of the enhancement is well correlated to the extinction of the Si interstitial defects.
Model of High-Temperature Diffusion of Interstitial Silicon Atoms in Silicon
American Journal of Applied Sciences, 2009
Problem statement: Correct description of the anomalous phenomena determined by selfpoint defects in implanted silicon desires knowledge of their properties. Interstitial Si atoms themselves display anomalies in their behavior and firstly in existence of two very different values of the diffusion coefficient. Approach: We analyzed experimental results and proposed the model of diffusion of interstitial Si atoms in silicon in two shapes. Results: At low saturation Si atoms diffuse as isolated atoms with a low diffusion coefficient (~10 −12 cm 2 sec −1 at 900°C). At high supersaturation interstitial atoms diffused as Si-Si pairs, which had lower activation energy of migration and higher diffusion coefficients (~10 −7 cm 2 sec −1). Conclusion: The high diffusivity pairs were formed when two Si atoms hit in the same interstice. The atoms were not bound to one another by covalent bond. In a pair atoms were retained by a potential relief of the crystal.
Physical Review B, 2015
We study point-defect diffusion in crystalline silicon using the kinetic activation-relaxation technique (k-ART), an off-lattice kinetic Monte Carlo method with on-the-fly catalog building capabilities based on the activation-relaxation technique (ART nouveau), coupled to the standard Stillinger-Weber potential. We focus more particularly on the evolution of crystalline cells with one to four vacancies and one to four interstitials in order to provide a detailed picture of both the atomistic diffusion mechanisms and overall kinetics. We show formation energies, activation barriers for the ground state of all eight systems, and migration barriers for those systems that diffuse. Additionally, we characterize diffusion paths and special configurations such as dumbbell complex, di-interstitial (IV-pair+2I) superdiffuser, tetrahedral vacancy complex, and more. This study points to an unsuspected dynamical richness even for this apparently simple system that can only be uncovered by exhaustive and systematic approaches such as the kinetic activation-relaxation technique.
Time evolution of the depth profile of {113} defects during transient enhanced diffusion in silicon
Applied Physics Letters, 2003
The evolution of {113} defects as a function of time and depth within Si implantgenerated defect profiles has been investigated by transmission electron microscopy. Two cases are considered: one in which the {113} defects evolve into dislocation loops, and the other, at lower dose and energy, in which the {113} defects grow in size and finally dissolve. The study shows that dissolution occurs preferentially at the near-surface side of the defect band, indicating that the silicon surface is the principal sink for interstitials in this system. The results provide a critical test of the ability of physical models to simulate defect evolution and transient enhanced diffusion.
Fast diffusion mechanism of silicon tri-interstitial defects
Physical Review B, 2005
Molecular dynamics combined with the nudged elastic band method reveals the microscopic selfdiffusion process of compact silicon tri-interstitials. Tight-binding molecular dynamics paired with ab initio density functional calculations speed the identification of diffusion mechanisms. The diffusion pathway can be visualized as a five defect-atom object both translating and rotating in a screw-like motion along 111 directions. Density functional theory yields a diffusion constant of 4 × 10 −5 exp(−0.49 eV/kBT) cm 2 /s. The low-diffusion barrier of the compact tri-interstitial may be important in the growth of ion-implantation-induced extended interstitial defects.
Dependence of transient enhanced diffusion on defect depth position in ion implanted silicon
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1989
Transient enhanced diffusion of phosphorus in silicon has been investigated for implants below and above the threshold for complete amorphization. In the first case, a strong enhanced diffusion, proportional to the amount of damage produced, has been observed. The extent of the phenomenon is practically independent of the damage depth position. On the contrary, the formation of extended defects at
Nucleation, growth and dissolution of extended defects in implanted Si: impact on dopant diffusion
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1999
Transient Enhanced Diusion (TED) of boron in silicon is driven by the large supersaturations of self-interstitial silicon atoms left after implantation which also often lead to the nucleation and subsequent growth, upon annealing, of extended defects. In this paper we review selected experimental results and concepts concerning boron diusion and/or defect behavior which have recently emerged with the ion implantation community and brie¯y indicate how they are, or will be, currently used to improve``predictive simulations'' softwares aimed at predicting TED. In a ®rst part, we focuss our attention on TED and on the formation of defects in the case of``direct'' implantation of boron in silicon. In a second part, we review our current knowledge of the defects and of the diusion behavior of boron when annealing preamorphised Si. In a last part, we try to compare these two cases and to ®nd out what are the reasons for some similarities and many dierences in defect types and thermal evolution depending on whether boron is implanted in crystalline or amorphous silicon. While rising many more questions, we propose a``thermodynamical'' vision of the nucleation and growth of clusters and extended defects and stress the interactions between these defects and the free Si self-interstitial atoms which surround them and are the source for TED in all cases. A pragmatic approach to the simulation of TED for various experimental conditions is proposed.
Diffusion and lifetime engineering in silicon
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1993
elusion mechanisms in crystalline silicon are reviewed emphasizing the role played by the structural defects like vacancies and self-interstitials. These defects control the diffusion process of some transition metals, such as Au and Pt, which undergo fast long-range diffusion as interstitials and become substitutional by replacing a Si atom in a kick-out reaction. The influence of boundary conditions and sample surfaces on the concentration profiles of these metals are analysed in detail. These profiles can be precisely tailored using ion-implantation to achieve a low fluence diffusion source. Pine tuning of the metal profiles is shown to improve greatly the trade-off between dynamic and static characteristics of some silicon power devices like metal-oxide-semiconductor field effect transistors. Moreover, the possibility to obtain a preferential reduction of lifetime by metal doping in a selected area of a semiconductor device is demonstrated.
Modeling of defects, dopant diffusion and clustering in silicon
Journal of Computational Electronics, 2014
Ion implantation is a very well established technique to introduce dopants in semiconductors. This technique has been traditionally used for junction formation in integrated circuit processing, and recently also in solar cells fabrication. In any case, ion implantation causes damage in the silicon lattice that has adverse effects on the performance of devices and the efficiency of solar cells. Alternatively, damage may also have beneficial applications as some studies suggest that small defects may be optically active. Therefore it is important an accurate characterization of defect structures formed upon irradiation. Furthermore, the technological evolution of electronic devices towards the nanometer scale has driven the need for the formation of ultra-shallow and low-resistive junctions. Ion implantation and thermal anneal models are required to predict dopants placement and electrical activation. In this article, we review the main models involved in process simulation, including ion implantation, evolution of point and extended defects and dopant-defect interactions. We identify different regimes at which each type of defect is more relevant and its inclusion in the models becomes crucial. We illustrate in some examples the use of atomistic modeling techniques to gain insight into the physics involved in the processes as well as the relevance of the accuracy of models.