Joule Expansion Imaging Techniques on Microlectronic Devices

We have studied the electrically induced off-plane surface displacement on two microelectronic devices using Scanning Joule Expansion Microscopy (SJEM). We present the experimental method and surface displacement results. We show that they can be successfully compared with surface displacement images obtained using an optical interferometry method. We also present thermal images using Scanning Thermal Microscopy (SThM) technique to underline that SJEM is more adapted to higher frequency measurements, which should improve the spatial resolution.Comment: Submitted on behalf of TIMA Editions (http://irevues.inist.fr/tima-editions

Precise control of thermal conductivity at the nanoscale through individual phonon-scattering barriers

International audienceThe ability to precisely control the thermal conductivity (κ) of a material is fundamental in the development of on-chip heat management or energy conversion applications. Nanostructuring permits a marked reduction of κ of single-crystalline materials, as recently demonstrated for silicon nanowires. However, silicon-based nanostructured materials with extremely low κ are not limited to nanowires. By engineering a set of individual phonon-scattering nanodot barriers we have accurately tailored the thermal conductivity of a single-crystalline SiGe material in spatially defined regions as short as ∼15 nm. Single-barrier thermal resistances between 2 and 4×10−9 m2 K W−1 were attained, resulting in a room-temperature κ down to about 0.9 W m−1 K−1, in multilayered structures with as little as five barriers. Such low thermal conductivity is compatible with a totally diffuse mismatch model for the barriers, and it is well below the amorphous limit. The results are in agreement with atomistic Green’s function simulations

Développement de bancs d'acoustique picoseconde pour la caractérisation sans contact par impulsions laser ultracourtes de couches micrométriques et sub-micrométriques de composants microélectroniques

Le travail présenté dans ce mémoire porte sur le développement de deux bancs laser impulsionnel dédiés à l'étude de films minces par des techniques d'acoustique picoseconde. Deux dispositifs pompe-sonde utilisant un laser femtoseconde et picoseconde ont été mis au point, la détection pouvant être réflectométrique et interférométrique. Elle permet de mesurer simultanément les variations d'amplitude et de phase du changement relatif de réflectivité induit par le champ acoustique excité par l'impulsion pompe, et ce, de manière non destructive. La conception, construction et mise au point d'un oscillateur laser femtoseconde Ti:Saphir ont été les premières étapes du développement des bancs. Dans le premier banc d'expériences, la source produit des impulsions laser d'une durée inférieure à 100 fs et dont le taux de répétition est de l'ordre de plusieurs dizaines de mégahertz. De plus, l'énergie par impulsion est de quelques nanojoules à une longueur d'onde proche de 800 nm. Ces caractéristiques sont conformes au cahier des charges des bancs d'expériences. Cet oscillateur femtoseconde et un laser commercial impulsionnel de 12 ps ont chacun été intégrés dans les deux bancs de mesures pompe-sonde résolus en temps. Les variations des caractéristiques optiques de l'échantillon sont mesurées par deux systèmes optiques réflectométrique et interférométrique. Les systèmes optiques de génération et de détection des phénomènes acoustiques mis en place lors du travail de thèse ont été validés par plusieurs séries d'expériences avec des échantillons types de la microélectronique. Ils permettent d'illustrer le champ d'applications de l'acoustique picoseconde. Après avoir caractérisé une couche métallique sur substrat semi-conducteur (vitesse du son, épaisseur), nous avons appliqué la technique d'acoustique picoseconde à des semi-conducteurs semi-transparents et, en particulier, mis en évidence des oscillations Brillouin les caractérisant. Finalement, les différents effets analysés précédemment ont permis l'interprétation de la réponse acoustique d'une structure multicouches d'un composant microélectronique.In this work, I present the development of two experimental methods using laser pulses for thin film metrology by picosecond acoustic technique. The pump-probe set-ups use a femtosecond and picosecond laser while detection is either reflectometric or interferometric. Both methods make it possible to measure simultaneously the amplitude and phase variations reflectivity induced by the acoustic field excited by the laser pump pulse. It's a nondestructive way of measurement. The first step of our work was the design, construction and development of a femtoseconde oscillator Ti:Saphir were the first step. In one set-up, the oscillator produces lower 100 fs laser pulses and a repetition rate is near several tens megahertz. Moreover, the energy pulse is some nanojoules with a wavelength around 800 nm. These characteristics meet with the requirements for acoustic characterisation. This femtosecond oscillator and a commercial 12 ps laser were implemented in two pump-probe set-ups. In both instruments, the sample characteristics are measured by two optical systems, one reflectometric and one interferometric. The optical generation and detection of acoustic waves has been validated in this work by several experiments using representative microelectronic samples. They illustrate the application fields of picosecond acoustic technique. After characterisation of a metal layer on semiconductor substrate (acoustic velocity, thickness), we have studied phenomena in semi-transparent semiconductors, like Brillouin oscillations. Finally, we have succeeded in the analysis and interpretation of the acoustic response of a multi-layer microelectronic component structure.BORDEAUX1-BU Sciences-Talence (335222101) / SudocSudocFranceF

Scanning thermal microscopy of individual silicon nanowires

Thermal imaging of individual silicon nanowires (Si NWs) is carried out by a scanning thermal microscopy (SThM) technique. The vertically aligned 1.7 (micro)m long Si NWs are fabricated combining nanosphere lithography and metal-induced wet chemical etching. A thermal model for the SThM probe is then presented with two steps: a model out of contact which enables a calibration of the probe, and a model in contact to extract thermal parameters from the sample under study. Using this model and the experimental thermal images, we finally determine a mean value of the tip-to-sample thermal contact resistance and a mean value of the Si NWs thermal conductivity. No significant thermal conductivity reduction in comparison with bulk Si is observed for Si NWs with diameters ranging from 200 to 380 nm. However, the technique presented here is currently the only one available to perform thermal measurements simultaneously on an assembly of individual one-dimensional nanostructures. It enables to save time and to make a statistical processing of the thermal data in order to deduce a reliable mean thermal conductivity, even when the tip-to-sample thermal contact resistance cannot be considered neither negligible in comparison with the Si NW intrinsic thermal resistance nor constant from one Si NW to another

Sur l'évolution néotectonique du Maroc septentrional

In Morocco, the Rif and its southern and eastern borders has been submitted, after the miocene paroxysmal compression, to neotectonic deformations from the Tortonian till the present time. We distinguish successively : - one period principally extensive (Tortonian -Pliocene) corresponding to the individualisation and the working of the "post-nappe" basins ; - one compressive period towards the Pliocene-Quaternary boundary with, sometimes, pluri-kilometrical folded structures ; - one probably distensive quaternary period. During this time, there is maintenance or individualisation of subsidence areas and concomitant surrection of relieves.Au Maroc, le Rif et ses bordures méridionales et orientales ont été soumis, après le serrage paroxysmal miocène, à des déformations néotectoniques s'étageant depuis le Tortonien jusqu'à l'actuel. On distingue ainsi : - une période à dominante distensive (Tortonien à Pliocène) correspondant à l'individualisation et au fonctionnement des bassins "post-nappes" ; - une période compressive vers la limite Pliocène-Quaternaire responsable, parfois, de structures plicatives pluri-kilométri-ques ; - une période probablement distensive quaternaire au cours de laquelle il y a maintien ou individualisation d'aires de subsidence et surrection concomitante de reliefs.Rampnoux Jean Paul, Angelier Jean, Colletta Bernard, Fudral Serge, Guillemin Michel, Pierre Guillaume. Sur l'évolution néotectonique du Maroc septentrional. In: Géologie Méditerranéenne. Tome 6, numéro 4, 1979. Tectonique. pp. 439-464

Effect of the laser pulse duration on picosecond ultrasonic signals

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Si and SiGe Nanowires: Fabrication Process and Thermal Conductivity Measurement by 3ω-Scanning Thermal Microscopy

We have grown various samples of Si and SiGe nanowires (NWs), either by a classical vapor?liquid?solid (VLS) process or by chemical etching, to measure their thermal conductivity and thus evaluate their efficiency for thermoelectrics applications. To do so, we have chosen a 3ω-Scanning Thermal Microscopy (SThM) imaging technique which is until now the only method able to perform topographical and thermal measurements simultaneously on an assembly of individual NWs, leading to a statistical value of their thermal conductivity. A size effect is clearly observed on Si NWs: 50 nm diameter NWs offer a reduced thermal conductivity in comparison with 200 nm diameter or even larger NWs. On the contrary, the thermal conductivity of SiGe NWs is widely reduced in comparison with the SiGe bulk value, even for large diameters, bigger than Si NWs ones. We discuss our results, comparing them with thermal conductivity values from the literature obtained by other measurement methods or models.Etude de l'amplification de la Conduction Thermique dans des Réseaux de Nanoparticule

Laser scanning thermoreflectance imaging system using galvanometric mirrors for temperature measurements of microelectronic devices

We present a thermoreflectance imaging system using a focused laser sweeping the device under test with a scanner made of galvanometric mirrors. We first show that the spatial resolution of this setup is submicrometric, which makes it adapted to microelectronic thermal measurements. Then, we studied qualitative temperature variations on two dissipative structures constituted of thin (0.35μm) dissipative resistors, the distance between two resistors being equal to 0.8 or 10μm. This technique combines sensitivity and speed: it is faster than a point classical thermoreflectance technique and, in addition, more sensitive than a charge-coupled device thermoreflectance imaging technique