B. Colombeau

Formation energies and relative stability of perfect and faulted dislocation loops 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+ or 50 keV Si+ ions to a dose of 2×1015 cm−2 and annealed at 900 °C in N2, N2O, and O2. The calculations of formation energy of both types of dislocation loops show that, for defects of the same size, faulted dislocation loops (FDLs) are more energetically stable than perfect dislocation loops (PDLs) 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...

Kinetic study of group IV nanoparticles ion beam synthesized in SiO2

Abstract Most studies concerning group IV (Si, Ge) ion beam synthesized nanocrystals in SiO 2 have shown that a link exists between the observed physical properties and the characteristics of the “populations” of nanoparticles (size-distribution, density, volume fraction). The aim of this paper is to study the influence of the initial supersaturation and annealing conditions on these characteristics. For this, experimental methods have been developed, that allow accurate statistical studies. Different transmission electron microscopy (TEM) imaging conditions have been tested and the most adequate ones have been identified for each system. An original method for the measurement of the density of precipitates embedded in an amorphous matrix has been developed and tested for Ge precipitates in SiO 2 and has permitted to evidence a conservative Ostwald ripening during annealing. The kinetic behavior of Si nanoparticles has also been studied by coupling TEM measurements and “atomistic” simulations. During annealing, the growth of these nanoparticles is very slow but their size significantly increases when increasing the initial Si excess. Simulations are in perfect agreement with experiment when taking into account interaction effects between particles.

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.

Influence of the annealing ambient on the relative thermal stability of dislocation loops in silicon

In this work, we have studied the relative stability of perfect (PDLs) and faulted (FDLs) dislocation loops formed during annealing of preamorphised silicon. In particular, we have investigated the effect of the annealing ambient (N2, O2) on their thermal evolution. Transmission Electron Microscopy analysis shows that after short annealing times FDLs are the more stable defects if the ripening process is conservative or if the surface acts as a sink for Si interstitial atoms. On the contrary, when the surface injects Si atoms (oxidising conditions) or for long annealing times under conservative conditions, PDLs are stabilised. We have calculated the formation energies of these defects as a function of their sizes and we have found that a stability inversion occurs for sizes of about 80 nm. All the experimental results presented here are explained by making use of these calculations.

Simulations of the ripening of 3D, 2D and 1D objects

Abstract This paper presents simulations aimed at predicting the kinetic evolution during annealing of nanoparticles and extended defects having different geometry. This versatile model describes the capture and emission of single atoms by clusters. Within this approach, nanoparticles and defects only differ through their formation energies and capture cross-sections. This model has been applied to three particular cases relevant to semiconductor processing (i) spherical Si nanocrystals embedded in a SiO 2 matrix; (ii) plate-shaped dislocation loops; and (iii) {311} planar defects in Si. Transmission electron microscopy (TEM) observations have been carried out on each system to measure the evolution of the size-histograms, mean radius and precipitate density during annealing. The simulation results well compared with the experimental data.

Effect of the Ge preamorphization dose on boron diffusion and defect evolution in silicon

Abstract In this paper, we study the effect of the Ge+ preamorphization dose on boron diffusion and on the thermal evolution of end of range (EOR) defects during annealing. Amorphizations were carried out by implanting Ge+ at 150 keV to doses ranging from 1×1015 to 8×10 15 ions/cm 2 . Boron was subsequently implanted at 3 keV with a dose of 1×10 14 ions/cm 2 . Rapid thermal annealing (RTA) was performed for various time/temperature combinations in nitrogen ambient. Secondary ion mass spectroscopy (SIMS) and transmission electron microscopy (TEM) were used to study boron diffusion and defect evolution, respectively. We have found that after a given annealing, both the defect size and boron diffusivity are independent on the Ge ion dose. Increasing this dose only results in an increase of the defect density. These results are discussed and definitely show that EOR defects are involved in a quasi-conservative Ostwald ripening process during annealing. The diffusive behavior of boron suggests that the coupling of boron atoms with the “mean field” of Si interstitial atoms in dynamical equilibrium with the defects is responsible for transient enhanced diffusion (TED).

Atomistic simulations of extrinsic defects evolution and transient enhanced diffusion in silicon

In this letter, a physically based model describing the kinetic evolution of extrinsic defects during annealing is presented. The fundamental concepts of Ostwald ripening and formation energy of extrinsic defects are combined in this model, which has been tested against some classical experiments concerning ~i! transient enhanced diffusion ~TED! of dopants in conjunction with the dissolution of

On the Energetics of Extrinsic Defects in Si and their Role in Nonequilibrium Dopant Diffusion

113% defects and~ii ! the ‘‘pulsed’’ TED observed in the case of ultralow energy implants where the surface acts as a strong sink for the silicon interstitial atoms. We show that a full understanding of the formation and the evolution of extended defects leads to a correct prediction of dopant enhanced diffusion in all experimental conditions.

Annealing Behavior of Locally Confined Dislocation Loops Under Inert And Oxidizing Ambient

In this paper, we discuss the mechanisms by which small clusters evolve through “magic” sizes into {113} defects and then, at sufficiently high dose levels, transform into dislocation loops of two types. This ripening process is mediated by the interchange of free Si(int)s between different extended defects, leading to a decrease of their formation energy. The calculation of the supersaturation of free Si-interstitials in dynamical equilibrium with these defects shows a hierarchy of levels of nonequilibrium diffusion, ranging from supersaturations S of about 10 6 in the presence of small clusters, through 10 3 in the presence of {113} defects, to S in the range 100 down to 1 as loops are formed, evolve and finally evaporate. A detailed analysis of defect energetics has been carried out and it is shown that Ostwald ripening is the key concept for understanding and modelling defect interactions during TED of dopants in silicon.

Thermal evolution of interstitial defects in implanted silicon

In this work, we report data for the growth kinetics of locally confined dislocation loops organized within lines of controlled dimension and periodicity. The dislocation loop lines were formed in the crystalline substrate after local Si implantation and annealing in predefined areas. The distance between the lines ranges between 0.2 νm to 5 μm. It is shown that the kinetics of the DLs depends on the distance between them. When the distance is less than 1 μm, the DLs behave in a similar fashion like those grown in a continuous layer, under inert and oxidizing conditions. However, when the distance between the lines is increased (eg. 5 μm), the behavior of the loops is changed. Fast dissolution of the dislocations loops is observed during annealing in inert ambient, due to enhanced interstitial losses, while under oxidizing conditions the loops grow faster.