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Abstract

We have studied the matrix effects in Si1-xGex structures under O2+ and Cs+ bombardments. Matrix effects are practically suppressed with Cs2Ge+ secondary ions, for Ge concentrations between 0 and 100 at. %. A procedure for the accurate quantification of the Ge concentration in Si1-xGex alloys using Cs2Ge+ and CsGe+ clusters has been proposed. For structures in which the Ge content is constant over several hundreds of nanometers, both methods provide very similar results, with an excellent agreement between the Ge concentrations measured by secondary ions mass spectrometry and x-ray diffraction. However, for continuously varying Ge concentration profiles, the nonlinear response of the CsGe+ normalized intensity and the persistence of strong matrix effects for CsSi+ ions lead to differences between the Ge concentration profiles measured with the CsGe+ method compared to the Cs2Ge+ one. The latter is therefore the only reliable method for the study of Ge indiffusion into Si from a pure Ge layer grown by chemical vapor deposition. An application of this method to the analysis of Ge indiffusion in Si at 900 °C is also reported.

Abstract

Millisecond annealing as an equipment technology provides ultra-sharp temperature peaks which favours dopant activation but nearly eliminates dopant diffusion to form extremely shallow highly electrically-activated junctions. On arsenic beamline implanted wafers the formation of ultra-shallow junctions at peak temperatures ranging from 1275degC to 1325degC was investigated. The thermal stability of these junctions was evaluated by subsequent thermal anneals ranging from 250 degC to 1050 degC with times ranging from seconds up to several hundred seconds. From these data the deactivation/reactivation mechanism for subsequent annealing can be quantified. Furthermore, the combination of spike and flash annealing is investigated to achieve a desired level of dopant diffusion and activation. For arsenic by far the lowest sheet resistance number is achieved by this annealing strategy. Finally, the arsenic profiles are compared to predictive simulation results which address the diffusion and activation at extrinsic concentrations.

Résumé

Nous présentons une technique de réalisation d'un oxyde enterré localisé. Il s'agit d'un procédé, appliqué en surface, basé sur la photolithographie, la gravure sèche par plasma et l'oxydation thermique humide. Cette méthode permet d'oxyder localement une couche enterrée riche en Aluminium per un processus vertical. Contrairement à l'oxydation latérale habituelle elle permet la réalisation de différentes formes des zones oxidées et ouvre l'accès à des dimensions de diaphragmes d'oxyde plus petites et mieux controlées.

Abstract

Different shallow n-type and p-type dopants were annealed with spike, flash, and a combination of spike+flash or vice versa to find the optimum annealing condition for both activation and diffusion. The implant conditions investigated during this study were 74Ge+ with 11B+ as well as 11B+, 49BF2+, and 75As+. The wafers were characterized regarding sheet resistance, junction depth, and chemical dose. An electrically active dose was derived from the Hall-effect measurement. Transmission electron microscopy analysis for the characterization of defects was done on selected samples. Boron implanted into crystalline as well as preamorphized silicon shows a similarly low sheet resistance which is independent of whether they are annealed with spike+flash, flash, or flash+spike. For arsenic by far the lowest sheet resistance is seen with a combination of spike+flash anneal. The main advantage when using a spike+flash anneal combination is that similar sheet resistance values for arsenic and boron implant can be achieved with the same anneal sequence.

Abstract

Experimental data obtained in bulk and silicon on insulator (SOI) structures by transmission electron microscopy (TEM) are reported showing that the density of extended defects in SOI structures is reduced in comparison with bulk silicon. Additional data obtained on strained SOI structures show that a less pronounced reduction is observed in these structures. It will also be shown that simulations based on an already existing model and taking into account the effect of the Si/BOX interface acting as a sink for interstitials are not able to explain the experimentally observed defect density reduction in unstrained SOI.

Abstract

We present here preliminary results on boron diffusion in presence of pre-formed voids of different characteristics. The voids were fabricated by helium implantation followed by annealing allowing the desorption of He prior to boron implantation. We show that under such conditions boron diffusion is always largely reduced and can even be suppressed in some cases. Boron diffusion suppression can be observed in samples not containing nanovoids in the boron-rich region. It is suggested that direct trapping of Si(int)s by the voids is not the mechanism responsible for the reduction of boron diffusion in such layers. Alternatively, our experimental results suggest that this reduction of diffusivity is more probably due to the competition between two Ostwald ripening phenomena taking place at the same time: in the boron-rich region, the competitive growth of extrinsic defects at the origin of TED and, in the void region, the Ostwald ripening of the voids which involves large supersaturations of Vs.

Mots-Clés / Keywords

Abstract

The thermal evolution of large boron-interstitials clusters (BICs) in crystalline Si has been studied by transmission electron microscopy (TEM). After ion implantation (20 keV and 1×1014 Si/cm2) and annealing (815 °C and 5 min), large clusters (68 nm) have been observed in correspondence of a narrow, highly doped Si:B layer (2×1020 B/cm3). Under prolonged annealing, such clusters dissolve, progressively shrinking their mean size below the TEM detection limit. The time evolution of such a BIC shrinking is fully compatible with the slow path dissolution kinetics recently published. These data suggest the identification of the slow dissolving BICs with the large observed clusters.

Abstract

We studied the influence of energy and fluence of a F+ implantation on the end-of-range (EOR) defects and on B activation in Ge+-preamorphized Si. After F+ co-implantation at either 10 or 22 keV, B transient-enhanced diffusion as well as B electrical deactivation are both reduced. In contrast, 10 keV F+ implantation does not affect the EOR evolution, while defects are stabilized after 22 keV F+ implantation. Our results, therefore, show that the beneficial effects related to F+ co-implantation cannot be explained in terms of a stabilization of the EOR defects.