Maria Aboy

• University of Valladolid

The improved radiation hardness of p-type Si detectors is hindered by the radiation-induced acceptor removal process, which is not fully understood yet. Through atomistic modeling of displacement damage and dopant interactions, we analyze the acceptor removal under neutron irradiation, providing physical insight into its microscopic origin. Our res...

Intra-die device variation due to pattern layout effects associated with the development of ultra-fast annealing processes is one of the major scaling challenges for advanced CMOS devices. In this paper, we show that an excellent and universal correlation can be established between on-die device variation and a new reflectance characterization tech...

The effective dopant concentration in p-type Si detectors reduces with irradiation fluence at low fluences due to the acceptor removal process, which degrades detector performance and shortens its lifetime. This effect has been experimentally characterized and parametrized, but its microscopic origin is still unknown. We use atomistic simulations t...

Emergent alternative Si processes and devices have promoted applications outside the usual processing temperature window and the failure of traditional defect kinetics models. These models are based on Ostwald ripening mechanisms, assume pre-established defect configurations and neglect entropic contributions. We performed molecular dynamics simula...

Due to the intrinsic features of laser annealing treatments in semiconductors, i.e., localized irradiation with a space- and time-dependent thermal field that leads to far-from-equilibrium conditions, experimental analysis can reveal only specimen postirradiation characteristics. In order to understand how the laser-irradiated system evolves and re...

By using classical molecular dynamics simulations and a novel technique to identify defects based on the calculation of atomic strain, we have elucidated the detailed mechanisms leading to the anomalous generation and growth of {001} loops found after ultra-fast laser annealing of ion-implanted Si. We show that the building block of the {001} loops...

We used classical molecular dynamics simulations to reproduce basic properties of Si, Ge and SiGe using different empirical potentials available in the literature. The empirical potential that offered the better compromise with experimental data was used to study the surface stability of these materials. We considered the (100), (100)2x1 and (111)...

The construction of realistic atomistic models for amorphous solids is complicated by the fact that they do not have a unique structure. Among the different computational procedures available for this purpose, the melting and rapid quenching process using molecular dynamics simulations is commonly employed as it is simple and physically based. Neve...

We combine focused experiments with molecular dynamics simulations to investigate in detail the formation of {0 0 1} loops in nanosecond laser-annealed silicon. We demonstrate that at temperatures close to the melting point, self-interstitial rich silicon is driven into dense liquid-like droplets that are highly mobile within the solid crystalline...

Several atomistic techniques have been combined to identify the structure of defects responsible for X and W photoluminescence lines in crystalline Si. We used kinetic Monte Carlo simulations to reproduce irradiation and annealing conditions used in photoluminescence experiments. We found that W and X radiative centers are related to small Si self-...

We used atomistic simulation tools to correlate experimental transmission electron microscopy images of extended defects in crystalline silicon with their structures at an atomic level. Reliable atomic configurations of extended defects were generated using classical molecular dynamics simulations. Simulated high-resolution transmission electron mi...

Ultrafast laser annealing of ion implanted Si has led to thermodynamically unexpected large {001} self-interstitial loops, and the failure of Ostwald ripening models for describing self-interstitial cluster growth. We have carried out molecular dynamics simulations in combination with focused experiments in order to demonstrate that at temperatures...

The modeling of self-interstitial defects evolution is key for process and device optimization. For a self-interstitial cluster of a given size, several configurations or topologies exist, but conventional models assume that the minimum energy one is instantaneously reached. The existence of significant energy barriers for configurational transitio...

We performed a characterization of the energetic and structural features of amorphous Si using classical molecular dynamics simulations. We generated amorphous Si samples from different procedures: quenching liquid silicon, accumulating the damage generated by subsequent energetic recoils, and accumulating point defects. The obtained energetic and...

We review atomistic modeling approaches for issues related to ion implantation and annealing in advanced device processing. We describe how models have been upgraded to capture physical mechanisms in more detail as a response to the accuracy demanded in modern process and device modeling. Implantation and damage models based on the binary collision...

In this work we propose a methodology to analyze the elastic energy interaction at the atomic level between Si self-interstitials and extended defects in crystalline Si. The representation of this energy in maps in 2D planes shows the anisotropic nature of the elastic interaction. This elastic energy maps can be used to understand diffusion traject...

We have used atomistic simulations to identify and characterize interstitial defect cluster configurations candidate for W and X photoluminescence centers in crystalline Si. The configurational landscape of small self-interstitial defect clusters has been explored through nanosecond annealing and implantation recoil simulations using classical mole...

We have studied the early stages of self-interstitial clustering in silicon using molecular dynamics simulation techniques. We have generated silicon samples of over 200,000 atoms where we introduced a 0.5% extra concentration of self-interstitials. Then samples were annealed at several temperatures. During the simulations we observed the formation...

Requirements for the manufacturing of electronic devices at the nanometric scale are becoming more and more demanding on each new technology node, driving the need for the fabrication of ultra-shallow junctions and finFET structures. Main implantation strategies, cluster and cold implants, are aimed to reduce the amount of end-of-range defects thro...

New criteria are presented for the classification and statistical analysis of defects from irradiation cascades that allow a more detailed description of the diversity of damage, especially amorphous regions. Classical molecular dynamics simulations are used to analyze the damage produced by 2 keV Si recoils annealed at 1000 K for 1 ns. Based on a...

Defect evolution and dopant activation dynamics in boron implanted silicon under excimer laser irradiation is investigated by means of continuous model and kinetic Monte Carlo (KMC) simulations [1,2]. The thermal problem has been solved within the phase-field methodology. Dopant activation efficiency in the solid phase has been measured in a wide r...

We propose an atomistic model to describe extended {311} defects in silicon. It is based on the combination of interstitial and bond defect chains. The model is able to accurately reproduce not only planar {311} defects but also defect structures that show steps, bends, or both. We use molecular dynamics techniques to show that these interstitial a...

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...

We investigate the correlation between dopant activation and damage evolution in boron-implanted silicon under excimer laser irradiation. The dopant activation efficiency in the solid phase was measured under a wide range of irradiation conditions and simulated using coupled phase-field and kinetic Monte Carlo models. With the inclusion of dopant a...

Molecular dynamics simulation techniques are used to analyze damage production in Ge by the thermal spike process and to compare the results to those obtained for Si. As simulation results are sensitive to the choice of the inter-atomic potential, several potentials are compared in terms of material properties relevant for damage generation, and th...

We present an extended model for B clustering in crystalline or in preamorphized Si and with validity under conditions below and above the equilibrium solid solubility limit of B in Si. This model includes boron-interstitial clusters (BICs) with BnIm configurations—complexes with n B atoms and m Si interstitials—larger (n > 4), and eventually more...

The demanding requirements for low power devices are stimulating new technological schemes. Cluster and cold implants have arisen as new strategies for dopant incorporation oriented to the formation of amorphous regions with reduced end-of-range defects. In this work we have used different atomistic simulation techniques to study the phenomena invo...

Ion implantation is a technique commonly used in the fabrication of semiconductor devices. The introduction of ions generates a large concentration of defects in the Si lattice. The presence of these defects can adversely affect the device performance. Conversely, in more recent years, ion induced defects have opened the possibility of new Si based...

In order to fulfill the stringent requirements for ultra- shallow junction formation and proper defect removal needed for future Si devices, molecular and cold implants have arisen as new technological strategies for dopant incorporation. In this work we have used different atomistic simulation techniques within a multiscale scheme to study the phe...

The removal of residual defects beyond the amorphous/crystalline interface is essential for device optimization. Modeling of associated processes involves detailed description of damage generation mechanisms, dynamic annealing during implant and defect evolution during subsequent thermal processing. The thermal spike mechanism, which is responsible...

We present an atomistic model that describes the evolution of ion induced damage ranging from individual defects to continuous amorphous layers. The elementary units used to reproduce the defective zones are Si interstitials, vacancies and the IV pair, which is a local distortion of the Si lattice without any excess or deficit of atoms. More comple...

Boron implantation into preamorphized Si, followed by low temperature solid phase epitaxial (SPE) regrowth produces high activation combined with low diffusion. However, in the presence of high B concentrations, the activation obtained after the SPE regrowth only can reach concentrations in the order of a few times 1020 cm-3, and even more deactiva...

Ion implantation continues being the dominant technique to introduce dopants in Si devices. With the device feature size in the nanometer scale, the accurate and detailed description of as-implanted dopant and damage profiles is becoming key as advanced annealing techniques are almost diffusionless. The demanding requirements for ultrashallow junct...

In this work we describe the basis of different atomistic simulation techniques and their application for process modeling. We analyze the influence of implant flux on the position of the amorphous/crystalline interface and the amount of residual damage. We also illustrate the challenges for doping narrow finFET devices. Atomistic modeling is used...

In this paper we discuss from an atomistic point of view some of the issues involved in the modeling of electrical characteristics evolution in silicon devices as a result of ion implantation and annealing processes in silicon. In particular, evolution of electrically active dose, sheet resistance and hole mobility has been investigated for high B...

The co-implantation of F and B in pre-amorphized Si has been proved to be beneficial for the fabrication of ultrashallow junctions due to a remarkable reduction of B diffusion. This is attributed to the presence of fluorine-vacancy (F–V) complexes after regrowth, acting as annihilation centers for Si interstitials. Whereas the resulting F profile i...

Kinetic Monte Carlo simulations have been used to investigate mechanisms for boron clustering in crystalline and preamorphized Si. We have extended previous boron-interstitial cluster models to include larger and more stable complexes in order to reproduce boron cluster evolution at very high boron concentrations. We have investigated the stoichiom...

We use classical molecular dynamics simulation techniques to study how point defects aggregate to form extended defects in silicon. We have found that <110> chains of alternating interstitials and bond defects, a generalization of the Si di-interstitial structure, are metastable at room temperature but spontaneously transform into (311) defects whe...

We focus this work on multi-scale modeling of the ion-beam-induced amorphization and recrystallization in Si, although our scheme can be applied to other materials. We use molecular dynamics to study the formation mechanisms of amorphous regions. We have observed that along with energetic ballistic collisions that generate Frenkel pairs, low energy...

Atomistic process models are beginning to play an important role as direct simulation approaches for front-end processes and materials, and also as a pathway to improve continuum modeling. Detailed insight into the underlying physics using ab-initio methods and classical molecular dynamics simulations will be needed for understanding the kinetics o...

We use classical molecular dynamics simulation techniques to study the regrowth behavior of amorphous pockets in Si. We demonstrate that crystallization depends on the morphology of the pocket-crystal interface. Although our simulated amorphous pockets had not any excess nor deficit of atoms with respect to perfect crystal, after regrowth we found...

We investigate the influence of the buried Si/SiO2 interface in Silicon-on-insulator (SOI) substrates on B electrical activation by comparing experimental data and atomistic simulations in bulk Si and SOI materials. In crystalline Si, the effect of the Si/SiO2 interface on the formation of B clusters is practically negligible because they are forme...

The fabrication of small Si devices brings up complex physical mechanisms, whose modeling requires a multiscale approach. We illustrate the case of ion implantation and annealing in Si. Ab initio calculations and molecular dynamics simulations provide defect energetics and the physical basis for defect formation and annihilation mechanisms. Binary-...

Kinetic Monte Carlo simulations of B diffusion and activation in preamorphized Si during annealing after solid phase epitaxial regrowth have been used to provide insight into the mechanisms that drive these phenomena. Simulations show that the presence of an initially high active B concentration along with a Si interstitial supersaturation set by e...

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 fabrica...

With devices shrinking to nanometric scale, process simulation tools have to shift from continuum models to an atomistic description of the material. However, the limited sizes and time scales accessible for detailed atomistic techniques usually lead to the difficult task of relating the information obtained from simulations to experimental data. T...

We have analyzed the as-implanted damage produced in silicon by B, Si and Ge ions using molecular dynamics (MD) simulations. Implantations were carried out at 50K to avoid damage migration and annealing. In order to make a statistical study of the damage features, we have simulated hundreds of independent cascades for each ion for the same nuclear...

The solid phase epitaxial regrowth (SPER) technique achieves active B concentrations up to a few times 1020cm−3 after low-temperature recrystallization process, while higher B concentration regions remain immobile forming electrically inactive B clusters during SPER. Kinetic Monte Carlo simulations on B diffusion and activation in preamorphized Si...

We use kinetic nonlattice Monte Carlo atomistic simulations to investigate the physical mechanisms for boron cluster formation and dissolution in complementary metal-oxide semiconductor (MOS) processing, and the role of Si interstitials in the different processes. For this purpose, B implants in crystalline Si as well as B implants in preamorphized...

We present a technique which allows the direct determination of defect structures and energetics in the molecular dynamics framework. Due to its computational simplicity, it can be applied during the actual molecular dynamics simulation. This allows the monitoring of the evolution of the defect properties as a function of time and/or temperature. W...

In this paper we discuss some of the issues involved in the modeling of damage evolution, dopant diffusion and electrical activation as a result of ion implantation and annealing processes in Si. Dopant diffusion and activation during thermal anneal is complicated by the presence of the damage generated by the energetic impinging ion. Of particular...

We present kinetic nonlattice Monte Carlo atomistic simulations to investigate the role of Si interstitials in B cluster dissolution. We show that the presence of Si interstitials from an oxidizing anneal stabilize B clusters and slow down B cluster dissolution, compared to anneal in inert ambient. We have also analyzed the influence of injected Si...

In this work, we investigate the effect of Ge amorphization and low temperature regrowth on the activation and deactivation of boron in the source and drain region, transistor channel and polycrystalline gate. It is concluded that amorphization of silicon offers important advantages for boron activation enhancement and junction depth control. Simul...

Solid phase epitaxial regrowth of pre-amorphizing implants has received significant attention as a method to achieve high dopant activation with minimal diffusion at low implant temperatures and suppress channelling. Therefore, a good understanding of the amorphization and regrowth mechanisms is required in process simulators. We present an atomist...

Boron cluster formation and dissolution in high concentration B profiles and the role of Si interstitials in these processes are analyzed by kinetic non-lattice Monte Carlo atomistic simulations. For this purpose, we use theoretical structures as simplifications of boron implants into preamorphized Si, followed by low-temperature solid phase epitax...

Kinetic non-lattice Monte Carlo atomistic simulations are used to analyze the ion beam induced defect evolution. This is studied in terms of the probabilities of emitted interstitials being recaptured by other defects or in turn, being annihilated at the surface. In this way, the ripening and dissolution of interstitial defects can be explained as...

We use kinetic nonlattice Monte Carlo atomistic simulations to investigate the physical mechanisms for boron cluster formation and dissolution at very high B concentrations, and the role of Si interstitials in these processes. For this purpose, high-dose, low-energy B implants and theoretical structures with fully active box shaped B profiles were...

A multi-scale modeling, from ab-initio calculations, through Monte Carlo diffusion simulators, to the continuum models, is necessary to describe the complexity of dopant and defect interactions for process simulators. The advantages that make continuum simulators the standard in industrial applications are maintained only on the basis of the simpli...

We have investigated the atomistic mechanism behind the irradiation-induced amorphization in Si using molecular dynamics simulation techniques. The microscopic description of the process is based on the defect known as bond defect or IV pair. IV pairs recombine very fast when isolated, but if they interact to each other they survive longer times an...

Kinetic Monte Carlo simulations are used to analyze the ripening and dissolution of small Si interstitial clusters and {113} 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...

We propose an atomistic model to describe the evolution of the damage generated by irradiation in Si, going from isolated point defects to the formation of continuous amorphous layers. The elementary units used to reproduce the defective zones are Si interstitials, vacancies and the bond defect, which is a local distortion of the Si lattice without...

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 t...

Liquid−liquid equilibria (LLE) temperatures for systems of acetic anhydride with hexane, heptane, octane, decane, cyclohexane, and methylcyclohexane have been measured between 314 K and the upper critical solution temperature (UCST). The coexistence curves were determined visually. They have a rather horizontal top, and their symmetry depends on th...

We have carried out molecular dynamics simulations of monatomic B and octadecaborane cluster implantations into Si in order to make a comparative study and determine the advantages and drawbacks of each approach when used to fabricate shallow junctions. We have obtained and analyzed the doping profiles and the amount and morphology of the damage pr...