From point defects to dislocation loops: A comprehensive modelling framework for self-interstitial defects in silicon (original) (raw)
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Stability of defects in crystalline silicon and their role in amorphization
Physical Review B, 2001
Using molecular-dynamics simulation techniques, we have investigated the role that point defects and interstitial-vacancy complexes have on the silicon amorphization process. We have observed that accumulation of interstitial-vacancy complexes in concentrations of 25% and above lead to homogeneous amorphization. However, we have determined the basic properties of the interstitial-vacancy complex, and showed that it is not as stable at room temperature as previously reported by other authors. From our simulations we have identified more stable defect structures, consisting of the combination of the complex and Si self-interstitials. These defects form when there is an excess of interstitials or by incomplete interstitial-vacancy recombination in a highly damaged lattice. Unlike the interstitial-vacancy complex, these defects could survive long enough at room temperature to act as embryos for the formation of extended amorphous zones and/or point defect clusters.
Formation energies and relative stability of perfect and faulted dislocation loops in silicon
Journal of Applied Physics, 2000
Engineering of boron-induced dislocation loops for efficient room-temperature silicon light-emitting diodes J. Appl. Phys. 97, 073512 (2005); 10.1063/1.1866492 Defect evolution of low energy, amorphizing germanium implants in silicon A study of the relative thermal stability of perfect and faulted dislocation loops formed during annealing of preamorphized silicon wafers has been carried out. A series of transmission electron microscopy experiments has been designed to study the influence of the ion dose, the annealing ambient and the proximity of a free surface on the evolution of both types of loops. Samples were implanted with either 150 keV Ge ϩ or 50 keV Si ϩ ions to a dose of 2ϫ10 15 cm Ϫ2 and annealed at 900°C in N 2 , N 2 O, and O 2 . The calculations of formation energy of both types of dislocation loops show that, for defects of the same size, faulted dislocation loops ͑FDLs͒ are more energetically stable than perfect dislocation loops ͑PDLs͒ if their diameter is smaller than 80 nm and vice versa. The experimental results have been analyzed within the framework of the Ostwald ripening of two existing populations of interstitial defects. It is found that the defect ripening is nonconservative if the surface is close to the end of range defect layer or if the sample is oxidized during annealing. In both cases, the knowledge of the formation energy of both types of dislocation loops allows a realistic estimate of the interstitial flux towards and from the surface, respectively, during annealing, in agreement with the experimental results. During a conservative ripening process, a direct correspondence exists between the formation energy of the two defect families and the number of atoms bound to them. In this case, the relative stability of FDLs and PDLs depends on the initial supersaturation of Si interstitial atoms created during implantation.
Complexity of Small Silicon Self-Interstitial Defects
Physical Review Letters, 2004
The combination of long-time, tight-binding molecular dynamics and real-time multiresolution analysis techniques reveals the complexity of small silicon interstitial defects. The stability of identified structures is confirmed by ab initio relaxations. The majority of structures were previously unknown, demonstrating the effectiveness of the approach. A new, spatially extended tri-interstitial ground state structure is identified as a probable nucleation site for larger extended defects and may be key for the compact-to-extended transition.
Stability of Si-Interstitial Defects: From Point to Extended Defects
Physical Review Letters, 2000
Trends in the growth of extended interstitial defects are extracted from extensive tight-binding and ab inito local density approximation simulations. With an increasing number of interstitials, the stable defect shape evolves from compact to chainlike to rodlike. The rodlike ͕311͖ defect, formed from (011) interstitial chains, is stabilized as it grows, elongating in the chain direction. Accurate parametrization of the defect-formation energy on the number of interstitials and interstitial chains, together with the anisotropy of the interstitial capture radius, enables macroscopic defect-growth simulations.
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.
Structural transformations from point to extended defects in silicon: A molecular dynamics study
Physical Review B, 2008
We use classical molecular dynamics simulation techniques to study how point defects aggregate to form extended defects in silicon. We have found that ͗110͘ chains of alternating interstitials and bond defects, a generalization of the Si di-interstitial structure, are metastable at room temperature but spontaneously transform into ͕311͖ defects when annealed at higher temperatures. Obtained atomic configurations and energetics are in good agreement with experiments and previous theoretical calculations. We have found a ͕311͖ structural unit which consists of two interstitial chains along ͗110͘ but arranged differently with respect to the known ͕311͖ units.
Arxiv preprint cond-mat/ …, 1996
We perform total energy calculations based on the tight-binding Hamiltonian scheme (i) to study the structural properties and energetics of the extended {311} defects depending upon their dimensions and interstitial concentrations and (ii) to find possible mechanisms of interstitial capture by and release from the {311} defects. The generalized orbital-based linear-scaling method implemented on Cray-T3D is used for supercell calculations of large scale systems containing more than 1000 Si atoms. We investigate the {311} defects systematically from few-interstitial clusters to planar defects. For a given defect configuration, constant temperature MD simulations are performed at 300-600 K for about 1 psec to avoid trapping in the local minima of the atomic structures with small energy barriers. We find that interstitial chain structures along the 011 direction are stable interstitial defects with respect to isolated interstitials. The interstitial chains provide basic building blocks of the extended {311} defects, i.e., the extended {311}defects are formed by condensation of the interstitial chains side by side in the 233 direction. We find successive rotations of pairs of atoms in the {011} plane are mechanisms
Precipitation and extended defect formation in silicon
physica status solidi (c), 2005
The impact of self-interstitials and strain on the critical size for nucleation of incoherent precipitates is well-known. A factor that has been neglected so far is the incorporation of intrinsic point defects of the host matrix in the precipitate itself. It is shown that this can have an important impact both on the critical size and on the precipitated phase. The theoretical results are illustrated for the case of oxygen precipitation in silicon. The growing precipitate can also cause the nucleation of extended lattice defects such as dislocations and stacking faults in the surrounding matrix. A model is presented to predict stacking fault nucleation.
The Role of Incomplete Interstitial-Vacancy Recombination on Silicon Amorphization
Simulation of Semiconductor Processes and Devices 2001, 2001
We investigate the role that point defects and interstitial-vacancy pairs have on the Si amorphization process using molecular dynamics techniques. We show that accumulation of interstitial-vacancy pairs in concentrations of 25% and above lead to homogeneous amorphization. We identify very stable defect structures, consisting of the combination of the pair and Si self-interstitials, which form when there is an excess of interstitials or by incomplete interstitialvacancy recombination in a highly damaged lattice. These defects could survive long enough at room temperature to act as embryos for the formation of extended amorphous zones and/or point defect clusters.
Modeling of the Ostwald ripening of extrinsic defects and transient enhanced diffusion in silicon
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2002
We present an atomistic simulation of the Ostwald ripening of extrinsic defects (clusters, {1 1 3}s and dislocation loops) which occurs during annealing of ion implanted silicon. The model describes the capture and emission of Si interstitial atoms to and from extrinsic defects of sizes up to thousands of atoms and includes a loss term due to the flux of interstitials to the recombining surface. Key input parameters of the simulation are the variations of the formation energy and of the capture efficiency with the size of the different defects. This model shows that the kinetics of the wellknown dissolution of {1 1 3} defects is only driven by the recombination efficiency at the surface and the distance from the defects to the sample surface. We have subsequently used this model to study defect evolution in low and ultra low energy (ULE) B implanted Si during annealing. Defect dissolution occurs earlier and at smaller sizes in the ULE regime. Consequently, TED is mostly characterized by its ''pulse'' component which occurs at the very beginning of the anneal. Ó