Microscopic Description of the Irradiation-Induced Amorphization in Silicon (original) (raw)
Related papers
The role of the bond defect on silicon amorphization: a molecular dynamics study
Computational Materials Science, 2003
We have studied the influence of the so called ''bond defect'' in the silicon amorphization process using molecular dynamics simulation techniques. The bond defect consists in a local distortion of the silicon lattice with no excess or deficit of atoms, and it can be formed during ion-beam irradiation. Even though the bond defect lifetime is too short to justify damage accumulation at usual implantation temperatures, we have observed however that the interaction between close bond defects can generate more stable structures which behave as the amorphous pockets created by ion irradiation. We have seen as well that the recombination of a given amount of damage created by bond defect accumulation depends of its spatial distribution.
Atomistic modeling of ion beam induced amorphization in silicon
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2004
Ion beam induced amorphization in Si has attracted significant interest since the beginning of the use of ion implantation for the fabrication of Si devices. Nowadays, a renewed interest in the modeling of amorphization mechanisms at atomic level has arisen due to the use of preamorphizing implants and high dopant implantation doses for the fabrication of nanometric-scale Si devices. In this work, we briefly describe the existing phenomenological and defect-based amorphization models. We focus on the atomistic model we have developed to describe ion beam induced amorphization in Si. In our model, the building block for the amorphous phase is the bond defect or IV pair, whose stability increases with the number of surrounding IV pairs. This feature explains the regrowth behavior of different damage topologies and the kinetics of the crystalline to amorphous transition. The model provides excellent quantitative agreement with experimental results.
Ion-beam-induced amorphization and recrystallization in silicon
Journal of Applied Physics, 2004
Ion beam induced amorphization in Si has attracted significant interest since the beginning of the use of ion implantation for the fabrication of Si devices. A number of theoretical calculations and experiments were designed to provide a better understanding of the mechanisms behind the crystalto-amorphous transition in Si. Nowadays, a renewed interest in the modeling of amorphization mechanisms at atomic level has arisen due to the use of preamorphizing implants and high dopant implantation doses for the fabrication of nanometric-scale Si devices. In this review we will describe the most significant experimental observations related to the ion-beam-induced amorphization in Si and the models that have been developed to describe the process. Amorphous Si formation by ion implantation is the result of a critical balance between the damage generation and its annihilation. Implantation cascades generate different damage configurations going from isolated point defects and point defect clusters in essentially crystalline Si to amorphous pockets and continuous amorphous layers. The superlinear trend in the damage accumulation with dose and the existence of a ion-mass depending critical temperature above which it is not possible to amorphize, are some of the intriguing features of the ion-beam-induced amorphization in Si. Phenomenological models were developed in an attempt to explain the experimental observations, as well as other more recent atomistic models based on particular defects. Under traditional models, amorphization is envisaged to occur through the overlap of isolated damaged regions created by individual ions (heterogeneous amorphization) or via the build-up of simple defects (homogeneous amorphization). The development of atomistic amorphization models requires the identification of the lattice defects involved in the amorphization process and the characterization of their annealing behavior. Recently, the amorphization model based on the accumulation and interaction of bond defects or IV pairs has been shown to quantitatively reproduce the experimental observations. Current understanding of amorphous Si formation and its recrystallization, predictive capabilities of amorphization models and residual damage after regrowth are analyzed.
Molecular dynamics simulation of ion-beam-amorphization of Si, Ge and GaAs
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2002
We use molecular dynamics simulations to study ion-irradiation-induced amorphization in Si, Ge and GaAs using several different interatomic force models. We find that the coordination number is higher, and the average bond length longer, for the irradiated amorphous structures than for the molten ones in Si and Ge. For amorphous GaAs, we suggest that longer Ga-Ga bonds, also present in pure Ga, are produced during the irradiation. In Si the amorphization is found to proceed via growth of amorphous regions, and low energy recoils are found to induce athermal recrystallization during irradiation. Ó
Atomistic simulations of resistance to amorphization by radiation damage
Physical Review B, 2006
We use molecular-dynamics simulations to study processes related to resistance to amorphization by radiation damage. We simulate high-energy radiation events in SiO 2 , GeO 2 , TiO 2 , Al 2 O 3 , and MgO, and find that simulation results match the experiments. We discuss the difference between the damage that the structures along this series can support. We find that for the same material, activation barriers for damage recovery can strongly depend on the degree of structural damage. We observe that the effect of resistance to amorphization is primarily governed by the relaxation processes at the time scales of several picoseconds. On this time scale, we observe two distinct relaxation processes, reversible elastic deformation around the radiation cascade and recovery of the in-cascade damage of high topological disorder. Finally, we discuss how resistance to amorphization is related to interatomic interactions and to the nature of the chemical bond.
Amorphization processes in electron and/or ion-irradiated silicon
Physical Review Letters, 1987
Amorphization has been studied in electron-(e~) and ion-irradiated Si. Si irradiated at < 10 K with 1.0-or 1.5-MeV Kr + became amorphous at < 0.4 displacement per atom (dpa), whereas Si irradiated at 10 K to a fluence of ~ 14 dpa of 1-MeV e ~, in an electron microscope, failed to amorphize. However, Si subjected to a simultaneous e ~ and Kr + in situ irradiation at < 10 K to a Kr + fluence of 1.5 dpa retained crystallinity. The critical ratio, at < 10 K, of the e ~ to Kr + ion displacement rates to maintain a degree of crystallinity is ~ 0.5. Atomistic models for these phenomena are presented.
Monte Carlo modeling of amorphization resulting from ion implantation in Si
Computational Materials Science, 2003
We propose an atomistic model to describe the damage generation during ion irradiation in Si and its evolution upon anneal. We have included new features to the classical models used to describe damage in crystalline Si, that allow us to extend the atomistic approach to the modeling of continuous amorphous layers. The elementary units to describe the defective lattice are Si interstitials, vacancies and the bond defect, which is a local distortion of the lattice without any excess or deficit of atoms. More complex defect structures can be formed by the coalescence of these elementary units. The competition between the damage generation and its annihilation determines the damage accumulation that eventually may lead to amorphous layers. The same model is used for amorphizing and non-amorphizing implants, and the amorphization is the result of the simulation itself and not established as an input parameter.
The mechanism of ion induced amorphisation in Si
Damage build up and amorphization in Si, induced by 25 keV Si$_5^-$ cluster ions and similar mass Cs$^-$ ions have been studied using transmission electron microscopy and channeling Rutherford back-scattering spectrometry. The threshold dose for amorphisation is found to be just below sim15\sim 15sim15 eV/atom with saturation occurring above 17 eV/atom. Amorphisation is seen to be a nucleation and growth process with the direct impact mechanism suppressed by recoil induced recrystallization. At a dose above the amorphization threshold, unlike the lower dose case, the amorphous-to-crystalline (a/c) interface is found to be smooth. The smooth a/c interface, as seen for a high dose, indicates a transition to a stress relaxed amorphous phase in line with earlier observations.
Ion beam induced recrystallization of amorphous silicon: A molecular dynamics study
Journal of Applied Physics, 1996
We use molecular dynamics techniques to study the ion beam induced enhancement in the growth rate of microcrystals embedded in an amorphous silicon matrix. The influence of the ion beam on the amorphous-to-crystal transformation was separated into thermal annealing effects and defect production effects. Thermal effects were simulated by heating the sample above the amorphous melting point, and damage induced effects by introducing several low energy recoils in the amorphous matrix directed at the crystalline grain. In both cases, the growth rate of the microcrystals is enhanced several orders of magnitude with respect to the pure thermal process, in agreement with experimental results. The dynamics of the crystallization process and the defect structures generated during the growth were analyzed and will be discussed.
Journal of Applied Physics, 2007
The molecular dynamics method is applied to simulate the recrystallization of an amorphous / crystalline silicon interface. The atomic structure of the amorphous material is constructed with the method of Wooten, Winer and Weaire. The amorphous on crystalline stack is afterwards annealed on a wide range of temperature and time using five different interatomic potentials : Stillinger-Weber, Tersoff, EDIP, SW115 and Lenosky. The simulations are exploited to systematically extract the recrystallization velocity. A strong dependency of the results on the interatomic potential is evidenced and explained by the capability of some potentials (Tersoff and SW115) to correctly handle the amorphous structure while other potentials (Stillinger-Weber, EDIP and Lenosky) lead to the melting of the amorphous. Consequently, the interatomic potentials are classified according to their ability to simulate the solid or the liquid phase epitaxy.