Evelyne Lampin

Modeling of the transient enhanced diffusion of boron implanted into preamorphized silicon

We present a physically based modeling of the transient enhanced diffusion (TED) of boron implanted into preamorphized silicon. We start by describing the nucleation and growth of a supersaturation of Si interstitial atoms into dislocation loops. Our modeling of the nucleation and growth of the dislocation loops is divided into three distinct stages: the nucleation, the “pure growth,” and the Ostwald ripening. The implementation of this modeling into the process simulator IMPACT-4 allows one to correctly predict the size and density evolutions of the dislocation loops observed by transmission electron microscopy for a variety of annealing times and temperatures. This simulation also gives access to the concomitant behavior of the free Si interstitials atoms responsible for TED. Implementation of this model into IMPACT-4 shows that TED in preamorphized Si can be simulated for a variety of experimental conditions by assuming boron diffusion occurs through the coupling of boron atoms with this fast evolving ...

Molecular dynamics simulation of the recrystallization of amorphous Si layers : Comprehensive study of the dependence of the recrystallization velocity on the interatomic potential

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 annealed afterward 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.

Thermal conductivity from approach-to-equilibrium molecular dynamics

We use molecular dynamics simulations to study the thermal transport properties of a range of poor to good thermal conductors by a method in which two portions are delimited and heated at two different temperatures before the approach-to-equilibrium in the whole structure is monitored. The numerical results are compared to the corresponding solution of the heat equation. Based on this comparison, the observed exponential decay of the temperature difference is interpreted and used to extract the thermal conductivity of homogeneous materials. The method is first applied to bulk silicon and an excellent agreement with previous calculations is obtained. Finally, we predict the thermal conductivity of germanium and α-quartz.

Graphene buffer layer on Si-terminated SiC studied with an empirical interatomic potential

The atomistic structure of the graphenebuffer layer on Si-terminated SiC is investigated using a modified version of the environment-dependent interatomic potential. The determination of the equilibrium state by the conjuguate gradients method suffers from a complex multiple-minima energy surface. The initial configuration is therefore modified to set the system in specific valleys of the energy surface. The solution of minimal energy forms a hexagonal pattern composed of stuck regions separated by unbonded rods that release the misfit with the SiC surface. The structure presents the experimental symmetries and a global agreement with an ab initio calculation. It is therefore expected that the interatomic potential could be used in classical molecular dynamics calculations to study the graphene growth.

Prediction of boron transient enhanced diffusion through the atom-by-atom modeling of extended defects

The modeling of the atom-by-atom growth of extended defects is coupled to the diffusion equations of boron by transferring the free interstitial supersaturation calculated with a defect model into a process simulator. Two methods to achieve this coupling (equilibrium method and fully coupled method, respectively) are presented and tested against a variety of experimental conditions. They are first applied to a transient enhanced diffusion experiment carried out on a structure containing several B delta-doped layers, in which the amount of diffusion of the different layers is accurately predicted. The fully coupled method is then used to simulate the diffusion of ultrashallow B-implanted profiles. This work definitely demonstrates the relevance of accurate physical defect models for the successful design of ultrashallow junctions in future generations of integrated circuits.

Silicon dry oxidation kinetics at low temperature in the nanometric range: Modeling and experiment

Kinetics of silicon dry oxidation is investigated theoretically and experimentally at low temperature in the nanometer range where the limits of the Deal and Grove model become critical. Based on a fine control of the oxidation process conditions, experiments allow the investigation of the growth kinetics of nanometric oxide layer. The theoretical model is formulated using a reaction rate approach. In this framework, the oxide thickness is estimated with the evolution of the various species during the reaction. Standard oxidation models and the reaction rate approach are confronted with these experiments. The interest of the reaction rate approach to improve silicon oxidation modeling in the nanometer range is clearly demonstrated.

Solid phase epitaxy amorphous silicon re-growth: some insight from empirical molecular dynamics simulation

The modelling of interface migration and the associated diffusion mechanisms at the nanoscale level is a challenging issue. For many technological applications ranging from nanoelectronic devices to solar cells, more knowledge of the mechanisms governing the migration of the silicon amorphous/crystalline interface and dopant diffusion during solid phase epitaxy is needed. In this work, silicon recrystallisation in the framework of solid phase epitaxy and the influence on orientation effects have been investigated at the atomic level using empirical molecular dynamics simulations. The morphology and the migration process of the interface has been observed to be highly dependent on the original inter-facial atomic structure. The [100] interface migration is a quasi-planar ideal process whereas the cases [110] and [111] are much more complex with a more diffuse interface. For [110], the interface migration corresponds to the formation and dissolution of nanofacets whereas for [111] a defective based bilayer reordering is the dominant re-growth process. The study of the interface velocity migration in the ideal case of defect free re-growth reveals no difference between [100] and [110] and a decrease by a mean factor of 1.43 for the case [111]. Finally, the influence of boron atoms in the amorphous part on the interface migration velocity is also investigated in the case of [100] orientation.

Physics-based diffusion simulations for preamorphized ultrashallow junctions

In recent years there have been major advances in our understanding of the energetics, Ostwald ripening and transformations between various types of extended self-interstitial defect in Si and Ge ion-implanted silicon. As a result we can now predict the detailed time- and temperature-dependent supersaturation of interstitials during thermal evolution of these defects. This opens the way to predictive simulation of transient enhanced diffusion and dose loss in preamorphized ultrashallow junctions, where dopant movement is driven by free interstitials emitted by self-interstitial “end-of-range” defects. We present recent progress on this topic, emphasizing novel effects in highly doped ultrashallow junctions. Two key influences – the chemical pump effect due to the high concentration of dopants in ultrashallow junctions, and the ‘long hop’ behaviour of the dopant – are discussed in detail. The paper concludes by presenting simulation results that explain the recent observation of ‘uphill diffusion’ of B ultrashallow junction profiles.

Diffusion and activation of dopants in silicon and advanced silicon-based materials

A quantitative description of the transient diffusion and activation of boron during post-implantation annealing steps is one of the most challenging tasks in the simulation of silicon doping processes. In industrially relevant situations, simulations needs to address diffusion at extrinsic concentrations, the agglomeration of self-interstitials, and the formation of boron-interstitial clusters. This paper describes the experimental work performed or used to calibrate model parameters as independently as possible. The combined model is then applied to ultra-shallow junction formation by annealing boron implanted into crystalline or preamorphized silicon. In comparison to bulk silicon, much less is known about diffusion of dopants in SiGe and germanium which are considered as technological options for future technology nodes. Therefore, dedicated experiments were performed to clarify open points in the diffusion behaviour of dopants in these materials.

Modelisation of extended defects to simulate the transient enhanced diffusion of boron

Abstract Process conditions to create ultra-shallow junctions for silicon devices are known to result in a transient enhanced diffusion (TED) of boron. The diffusion of boron is due to its coupling with silicon self-interstitials. An anomalous behavior of these atoms is responsible for the boron TED. More precisely, it has been experimentally evidenced that a great amount of excess Si interstitials is created after implantation and that a part of this supersaturation precipitates into extended defects during annealing. A modelisation of this phenomenon is presented, aimed at enlarging the predictness of the process simulations, such as in the simulator IMPACT-4, and at increasing the understanding of boron TED. The continuous description of the nucleation, ‘pure growth’ and Ostwald ripening of one kind of extended defects, dislocation loops, is exposed. The comparison of the calculated sizes and densities of dislocation loops with their experimental values validates the modelisation. It was demonstrated that the concomitant evolution of silicon free interstitials results in the right amount of boron diffusion. TED is correctly simulated throughout the annealing thanks to this enhancement of the physical basis of IMPACT-4.