The solid phase crystallization of chemical vapor deposited amorphous silicon films onto oxidized silicon wafers, induced either by thermal annealing or by ion beam irradiation at high substrate temperatures, has been extensively developed and it is reviewed here. We report and discuss a large variety of processing conditions. The structural and thermodynamical properties of the starting phase are emphasized. The morphological evolution of the amorphous towards the polycrystalline phase is investigated by transmission electron microscopy and it is interpreted in terms of a physical model containing few free parameters related to the thermodynamical properties of amorphous silicon and to the kinetical mechanisms of crystal grain growth. A direct extension of this model explains also the data concerning the ion-assisted crystal grain nucleation.

Crystal grain nucleation in amorphous silicon

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 crystal-to-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 paper 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 ...

https://www.ele.uva.es/~mmm/papers/2004_Pelaz_JAP_96.pdf

Ion-beam-induced amorphization and recrystallization in silicon

In this article, we show how the well-known one-phonon confinement model can be improved to determine the diameter of silicon nanocrystalline spheres from the optical phonon wave-number shift, even using a physical-meaning weighting function. We show that the fundamental parameter is the knowledge of the phonon dispersion. The accuracy of our approach is supported by experimental data obtained by selective UV Raman scattering on nanocrystalline silicon thin films produced by size-selected silicon cluster beam deposition.

Improved one-phonon confinement model for an accurate size determination of silicon nanocrystals

On annealing a boron implanted Si sample at similar to800 degreesC, boron in the tail of the implanted profile diffuses very fast, faster than the normal thermal diffusion by a factor 100 or more. ...

Transient enhanced diffusion of Boron in Si

Semiconductor industry has increasingly resorted to strain as a means of realizing the required node-to-node transistor performance improvements. Straining silicon fundamentally changes the mechanical, electrical (band structure and mobility), and chemical (diffusion and activation) properties. As silicon is strained and subjected to high-temperature thermal processing, it undergoes mechanical deformations that create defects, which may significantly limit yield. Engineers have to manipulate these properties of silicon to balance the performance gains against defect generation. This paper will elucidate the current understanding and ongoing published efforts on all these critical properties in bulk strained silicon. The manifestation of these properties in CMOS transistor performance and designs that successfully harness strain is reviewed in the last section. Current manufacturable strained-silicon technologies are reviewed with particular emphasis on scalability. A detailed case study on recessed silicon germanium transistors illustrates the application of the fundamentals to optimal transistor design.

Fundamentals of silicon material properties for successful exploitation of strain engineering in modern CMOS manufacturing

Extended defects are often found after ion implantation and annealing of silicon and they are known to affect dopant diffusion. The article reviews the structure and energetics of the most often found extended defects and describes the mechanisms by which all these defects grow in size and transform during annealing. Defects grow by interchanging the Si atoms they are composed of and thus maintain large supersaturations of free Si interstitials in the region. A model has been developped to describe such an evolution in presence of a free surface. It is shown that after low energy implantation, the surface of the wafer may recombine large amounts of these free Si interstitials, driving defects into dissolution before transformation into more stable forms.

Extended defects in shallow implants

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...

Formation energies and relative stability of perfect and faulted dislocation loops in silicon

Transient Enhanced Diffusion (TED) of boron in silicon is driven by the large supersaturations of self-interstitial silicon atoms left after implantation which also often lead to the nucleation and subsequent growth, upon annealing, of extended defects. In this paper we review selected experimental results and concepts concerning boron diffusion and/or defect behavior which have recently emerged with the ion implantation community and briefly indicate how they are, or will be, currently used to improve “predictive simulations” softwares aimed at predicting TED. In a first part, we focuss our attention on TED and on the formation of defects in the case of “direct” implantation of boron in silicon. In a second part, we review our current knowledge of the defects and of the diffusion behavior of boron when annealing preamorphised Si. In a last part, we try to compare these two cases and to find out what are the reasons for some similarities and many differences in defect types and thermal evolution depending on whether boron is implanted in crystalline or amorphous silicon. While rising many more questions, we propose a “thermodynamical” vision of the nucleation and growth of clusters and extended defects and stress the interactions between these defects and the free Si self-interstitial atoms which surround them and are the source for TED in all cases. A pragmatic approach to the simulation of TED for various experimental conditions is proposed.

Nucleation, growth and dissolution of extended defects in implanted Si: impact on dopant diffusion

In this letter, we report the results obtained on polycrystalline silicon thin films using Raman spectrometry in resonance with the silicon direct band gap. First, we show that accurate information about crystallites can be obtained in these experimental conditions, without any deconvolution of Raman spectra. Second, we apply the technique to estimate the mechanical stress of polycrystalline silicon thin films.

Resonant Raman scattering in polycrystalline silicon thin films

In this paper TEM investigations have been carried out on typical EOR defects found in Ge-amorphized (001) wafers (Ge → Si, 150 keV, 2×1015 ions/cm2) after thermal annealing (RTA, 1000°C, 10 s). These defects consist of medium sized (10–50 nm) dislocation loops that have been characterized by conventional electron microscopic techniques. Most of them (~ 75%) are circular faulted Frank loops with b = a 3〈111〉 vectors. The remaining (~ 25%) loops are perfect elongated hexagon-shaped loops: they have nearly t(111⊃ habit planes, with b = a 2〈101〉 vectors. Hence, it is possible to deduce from only one TEM image the number of Si atoms available in the loops as well as the density of the loops for different implantation or annealing conditions. This is needed for optimization of process conditions.

B. de Mauduit

Papers

Extended defects in shallow implants

Formation energies and relative stability of perfect and faulted dislocation loops in silicon

Nucleation, growth and dissolution of extended defects in implanted Si: impact on dopant diffusion

Resonant Raman scattering in polycrystalline silicon thin films

Identification of EOR defects due to the regrowth of amorphous layers created by ion bombardment