B. de Mauduit

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...

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

Abstract 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.

Resonant Raman scattering in polycrystalline silicon thin films

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.

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

Abstract 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.

TRANSIENT ENHANCED DIFFUSION OF BORON IN PRESENCE OF END-OF-RANGE DEFECTS

The presence of a supersaturation of Si self-interstitials in ion implanted silicon has been shown to be the origin of several physical phenomena such as transient enhanced diffusion (TED) of boron, the formation of extended defects at the projected range of implanted atoms at doses below the amorphization threshold, and the formation of end-of-range (EOR) defects in the case of a preamorphization stage. In this article, we discuss the relation between boron anomalous diffusion and end-of-range defects. Modeling of the behavior of these defects upon annealing allows one to understand why and how they affect dopant diffusion. This is possible through the development of the Ostwald ripening theory applied to extrinsic dislocation loops. This theory is shown to give access to the variations of the mean supersaturation of Si self-interstitial atoms between the loops and also to be responsible for anomalous diffusion. This initial supersaturation is, before annealing, at least five decades larger than the equi...

Kinetic aspects of the growth of hydrogen induced platelets in SiC

Annealing of heavily hydrogen-implanted silicon carbide (SiC) leads to the formation of one specific type of defect: hydrogen induced platelets. These defects may be regarded as two-dimensional precipitates of H atoms stored in a stable configuration. In this article, we have studied the growth kinetics of these platelets upon annealing in the 800–1000 °C range by transmission electron microscopy. We show that the growth of these defects proceeds through the exchange of H atoms with the result that larger ones grow at the expense of the smaller ones during annealing. This process can be described in terms of a conservative Ostwald ripening mechanism. The activation energy for this growth is found to be about 3.4 eV, a value similar to that observed for the “effective” diffusion of H in heavily H-implanted SiC.

TEM studies of the defects introduced by ion implantation in SiC

Abstract We have undertaken a systematic study of the defects formed by ion implantation in SiC for a large variety of experimental conditions. B, N, Al and Ne ions were implanted into 6H–SiC at room temperature RT and at 650°C. Multiple energy implants were carried out in order to obtain “flat” dopant profiles. The samples were annealed from 1100°C to 1750°C for various duration times. Transmission Electron Microscopy (TEM) analysis was carried out on cross-sectional samples using weak beam dark field imaging conditions. All these defects are of interstitial type (clusters or loops). A statistical analysis of digital images was performed to extract the depth-distributions of the defects. The depth-distributions were compared with Monte-Carlo simulations of the ion implantation process. It is shown that when implanted at RT, the defect distributions follow the “damage” profiles i.e., defects appear in regions where atomic displacements occur in the target. In contrast, the defects found after implantation at 650°C always mirror the “range” profile before and after annealing. We show that there is a concentration threshold under which no defect appear. These results are discussed in terms of point defect annihilation, clustering and dopant activation in SiC.

Characterization of extended defects in SiGe alloys formed by high dose Ge+ implantation into Si

The synthesis of SiGe/Si heterostructures by Ge+ ion implantation is reported. 400 keV Ge+ ions were implanted at doses ranging from 3 × 1016 to 10 × 1016 ions/cm2 into (001) Si wafers, followed by Si+ amorphisation and low temperature Solid Phase Epitaxial Regrowth (SPER). TEM investigations show that strained alloys can be fabricated if the elastic strain energy (Eel) of the SiGe layer does not exceed a critical value (E′el) of about 300 mJ/m2, which is independent of the implantation energy. Our analysis also suggests that “hairpin” dislocations are formed as strain relieving defects in relaxed structures. A “strain relaxation” model is proposed to explain their formation.

Structural and technological properties of heavily in situ phosphorus-doped low pressure chemically vapour deposited silicon films

Abstract Films of 100–200 nm thickness doped with 10 21 P cm −3 were isothermally deposited at temperatures ranging from 520 to 620°C from an SiH 4 -PH 3 -H 2 gas mixture. The structure (as deduced from transmission electron microscopy observations of sample plane views and cross-sections) and electronic properties (ultraviolet reflectance, resistivity, wet etching and oxidation rate) of the films showed specific features which are associated with nucleation and crystal growth mechanisms occurring at the gas-film interface during the deposition of the films.

Material and electronic properties of boron-doped silicon films deposited from SiH4BCl3N2 mixtures in an industrial low pressure chemical vapour deposition furnace

Abstract Heavily boron-doped polycrystalline silicon (p-Si) films were deposited in the 520–605°C temperature range using an industrial low pressure chemical vapour deposition (LPCVD) reactor equipped with gas injectors. The simulation of the film deposition rates and the theoretical calculations of the distribution of gaseous species along the reactor load showed that, in all the cases studied, the wafer position in the process load had only a small effect on the local deposition parameters for the films. From characterization by transmission electron microscopy of plane view and cross-section, reflection high energy electron diffraction patterns and Raman spectroscopy, the polycrystalline character of the boron-doped silicon films appears to result from heterogeneous crystal nucleation and growth occurring at the gas-film interface during deposition at temperatures Td≤520°C. The increase in the number of crystalline Si(c-Si) nuclei is responsible for the smaller grain size of the silicon films deposited at Td≥560°C. Correlations between deposition parameters and surface roughness, polarization properties at 405 nm and electrical resistivity of the films were established. Comparisons with the microstructure and properties of undoped and in situ phosphorus-doped LPCVD silicon films were also carried out.