The semiconductor industry has exploited productivity improvements through aggressive feature size reduction for over four decades. While enormous effort has been expended in developing the optical lithography tools to print ever finer features, significant advances have also been required to measure the printed features. In this article we will discuss the current state of the art in the metrology for measuring critical dimensions of printed features for scanning electron microscopy and atomic force microscopy, and describe work at the National Institute of Standards and Technology advancing these tools as well as exploratory work on two new promising techniques, scatterfield microscopy and small angle X-ray scattering. Line width roughness critical dimension and overlay metrology and control are two of the most significant industry needs mentioned in the International Technology Roadmap for Semiconductors (2005). Published by Elsevier Masson SAS on behalf of Academic des sciences.
In the field of high current power conversion with high switching frequency, new topologies using parallel devices have been introduced, among which parallel multicell converters. An intrinsic feature of these converters is natural balancing of the currents flowing through the different switches. In the first section, an example will be used to demonstrate that this natural balancing property is related to the extra current harmonics induced by the current unbalance. However, for higher numbers of cells in parallel, the increased complexity does not allow predicting the transient behaviour of the system which makes design difficult. In the second section, a model based on the harmonic analysis is proposed to determine the balancing mechanisms; this model is then checked by simulation.
Nowadays, the development of power semiconductors has made that fuses used for their protection have to be improved. The high working frequency of IGBT leads to a modification of fuse characteristics. For high frequencies, it may occur a bad working due to an unequal current distribution between two fuses in parallel, or even between fuse's elements. The result is that fuse operates at below rated current. This unexpected operation can be attributed to proximity effects which are consequences of electromagnetic laws between close conductors. To prevent such a failure, their current rating must be reduced as a function of frequency and distance between the fuselink and other conductors (e.g. the return conductor).
The structure of ferroelectric domain walls in BaTiO3 has been investigated through two complementary approaches, a global ope by the fine analysis of X-ray diffraction patterns, the other essentially local via a quantitative image analysis method developed and applied to High Resolution Transmission Electron Microscopy images. These two original approaches converge towards a clear description of 90 degrees walls which are shown to be a 4-6 nm wide region where the crystallographic discontinuity is accommodated by irregular atomic displacements. The results given here demonstrate that the usual structural theoretical description of walls commonly accepted for energy calculations are far too simplistic. The two underlying methodologies which have been developed to carry out these approaches can possibly be applied to other ferroelectrics, but without any doubt to other systems where twins or coherent interfaces are expected.
Des changements importants de comportement sont observes sur des transducteurs de puissance utilisant des ceramiques de type PZT. Une meilleure caracterisation des materiaux piezoelectriques sous hauts niveaux s'avere alors necessaire. En effet, des phenomenes caracteristiques d'un comportement non lineaire tels que le decalage de la frequence de resonance avec hysteresis ou la generation d'harmoniques ont ete observes experimentalement. Ceci se traduit par des effets de saturation du niveau de deplacement de la face avant, une limitation des performances du systeme et un fonctionnement instable. Afin d'interpreter de tels comportements, une theorie non lineaire est proposee. Ce modele a ensuite ete applique a notre structure de transducteur. Une comparaison entre simulations et resultats experimentaux a permis de valider cette nouvelle approche. Les effets de saturation observes ont ete jusqu'a present toujours relies a la variation du coefficient d'amortissement, notre etude a permis de demontrer qu'une autre explication liee aux non linearites etait possible et permettait en meme temps d'expliquer d'autres phenomenes observes.
We prove that for localized states at extended defects the high-temperature sides of deep-level transient spectra can be written as a product of an amplitude function depending on the pulse length and a shape function depending on temperature. By this property localized states can be distinguished experimentally from bandlike states. Simulations of deep level transient spectra for localized and bandlike states using the same density of states function and parameter values illustrate the differences and show the failures of conventional analysis in both cases.
Des etudes precedentes ont montre l'interet de l'extraction, a l'aide de gaz carbonique dans l'etat supercritique, des additifs organiques de mise en forme de pieces ceramiques. Elles ont permis de developper un modele, etabli a partir des equations de diffusion, qui est en bon accord avec les resultats experimentaux. Les cinetiques experimentales d'extraction, par fluide supercritique, de paraffines a bas point de fusion utilisees comme liant pour des compositions d'injection sont maintenant etudiees. Une redistribution du liant a l'etat liquide au sein de la porosite de l'echantillon pendant le deliantage supercritique est mise en evidence. L'importance de ce mecanisme et son influence sur la validite du modele sont discutees.
Al-16 Si, Al-12.5 Si-1 Ni and Al-12.5 Si-1 Mg ribbons were prepared by melt spinning. Internal friction was measured in the forced flexural and torsional decay modes. Internal friction increases slowly with the increase in temperature up to a certain temperature, above which the rate of increase is higher. This behaviour is common-in all the three alloys, and is more pronounced in the torsional vibration mode than in the flexural vibration mode. The temperatures at which the internal friction shows a significant change in slope are 573, 518 and 554 K in the flexural mode and 456, 496 and 529 K in the torsional mode for Al-16 Si, Al-Si-Ni and Al-Si-Mg respectively. From the measurement of resonance frequency with temperature, Young's modulus was calculated. The room temperature values are 3.6, 2.1 and 1.4x10(10) N m(-2) for Al-16 Si, Al-Si-Ni and Al-Si-Mg respectively. These values are in fair agreement with the values deduced from the tensile tests. The variation of Young's modulus with temperature obeys the expression given by Andrews. The temperatures at which ln Y versus T(K) changes its value are about 100 degrees above 0.5 T-m on the average for the three alloys. A discussion on the relation between the behaviour of internal friction and Young's modulus with temperatures is given.
the method of collision cross section calculation 1.
Des couches epitaxiees de GaAs de type n (dopage au silicium, N D 10 17 cm -3 ) sont irradiees a 77 K avec des ions oxygene (0,163 GeV), krypton (5,15 GeV), xenon (5,73 GeV) et a 300 K avec des ions krypton (5,15 GeV). Les mesures d'effet Hall sont effectuees in situ, au fur et a mesure de l'accroissement de fluence. On observe une diminution de la concentration electronique et une degradation de la mobilite de Hall, respectivement dues au piegeage et a la diffusion des electrons sur les defauts ponctuels crees par l'irradiation. Dans de telles couches fortement dopees, les niveaux d'impuretes dopantes (donneurs peu profonds) sont engloutis dans une queue distordue de la bande de conduction. Un modele simple de conduction a deux bandes permet de simuler correctement les variations experimentales de la concentration de Hall a la fois en fonction de la temperature et de la fluence des ions. On simule egalement les variations de mobilite de Hall avec la fluence a 77 K car a cette temperature, la diffusion est principalement due aux impuretes et defauts ionises. A partir de ces simulations, il apparait que les niveaux E 1 et E 2 de la lacune d'arsenic correspondent vraisemblablement aux transitions simple accepteur (-/0) et simple donneur (0/+). Une estimation des taux de prospection de defauts est effectuee: la quantite totale de defauts detectes est egale a environ 50 % du nombre theorique de deplacements atomiques provoques par les collisions nucleaires, independamment du type d'ion incident et de la temperature. Bien que le pouvoir d'arret electronique S e soit environ 2000 fois plus grand que le pouvoir d'arret nucleaire S n , il semble que, dans la gamine exploree Se = 1-12 MeV/μm, l'excitation electronique induite par l'irradiation n'ait pas d'incidence sur la degradation des couches epitaxiees de GaAs de type n.
Durant cette derniere decennie le domaine des micro-techniques a connu un formidable essor et maintenant le dimensionnement des micro-systemes fait appel a de nombreuses disciplines scientifiques telles que l'electronique, les procedes d'obtention, l'optique, la mecanique... Celui-ci s'effectue le plus souvent de maniere globale et presente un caractere fortement interdisciplinaire. Dans ce contexte, la connaissance des proprietes mecaniques des materiaux utilises dans la conception des micro-systemes, fortement dependantes des procedes, est un aspect particulierement important. Dans cette logique, de nouveaux moyens experimentaux de caracterisation des materiaux en faibles dimensions ont ete realises et, parmi les differentes possibilites, on presente l'essai de flexion de micro-poutre encastree-encastree ou encastree-libre. La mesure des deplacements globaux est realisee simplement a l'aide d'une technique d'imagerie optique couplee a un traitement numerique d'images. Cette methode a ete validee sur des micro-poutres de silicium monocristallin et conduit a des mesures tres reproductibles. Une application sur des micro-poutres en nickel electro-depose et obtenues par technologie LIGA est egalement presentee. Les resultats experimentaux sont en bon accord avec ceux issus des calculs analytique et numerique, ce qui valide l'ensemble de l'experience.
We report on the structural characterization of epitaxial InSb films grown on InP substrates by atomic layer molecular beam epitaxy at relatively low temperatures (330 degrees C < T < 400 degrees C). Moreover, we study the effect of the introduction of an intermediate InSb/InP buffer layer grown by molecular beam epitaxy. The studies were carried out by TEM and HRTEM, to investigate the densities and nature of the defects and the accommodation mechanism between the two types of layers which have a large lattice mismatch (10.4%). Results show a high defect density at the interface vicinity whatever the growth method employed, with or without buffer layers, but better quality layers are obtained as growth proceeds. The prevailing type of defects are threading dislocations and stacking faults for both types of samples, but the introduction of the intermediate layers leads to the formation of two types of complex three-dimensional defects, consisting in crystal misorientations, that induce an anomalous growth of the InSb layer leading to different growth rates and the formation of pyramidal or truncated pyramidal hillocks on the surface. In this case scanning electron microscopy and Raman analysis were also performed to study the influence of the defects on surface morphology and confirm their structure. Moreover, anisotropy of the stacking fault distribution is noticed in this sample: the density for [1(1) over bar0$]-(111)A slip planes is higher than for the [110]-(111)B slip planes. Strain due to large lattice mismatch is relieved. in both types of samples by the generation of a pure edge-type misfit dislocation array.
In this article we study the mass tracer dispersion in organized flows. For this purpose we performed experiments in the flow arising from the Taylor-Couette hydrodynamic instability combined with axial flow. The tracer evolution is followed by means of optical measurements of the concentration. In this way transmission curves are obtained. We compare these curves with the solutions of the Gaussian models of mass diffusion and with phenomenological models including tracer trapping in the cells. This comparison gives us physical parameters related to the typical time and distances involved in the diffusive behaviour of tracers in the regions with recirculations and trapping.
We present a two dimensional simulation of the optical absorption of gold granular films, using a real space renormalization procedure. This numerical effective medium theory takes into account the actual morphology of the films. The results are compared both with experimental measurements and with other theoretical predictions asserting that the optical properties around the percolation threshold cannot be described by an effective dielectric function. Nevertheless, are obtain good agreement between the simulations and the experimental data, whatever the morphology and the concentration. It is concluded that the IR absorption can be attributed to the classical surface plasmon modes, generally situated in the visible spectral range for spheroidal inclusions, broadened here towards higher wavelengths due to the formation of fractal clusters of various sizes.
The thermal shock behavior and resistance of brittle materials are mostly investigated through the determination of a critical quenching temperature difference, Delta T-c. This technique, however, needs a large number of, almost, identical samples and is thus poorly adapted to products being in the stage of research and development. In order to overcome this difficulty, the indentation technique has been used in this work. The residual contact stresses, created during indentation, permit a stage of stable extension of the indentation cracks under the action of further stressing. The relative increase of radial crack length as a function of Vickers indentation load, c/c(0) vs. P, is taken as a criterion, or indicator, of relative thermal shock resistance, or of the severities of quenching conditions. This is validated, first in quenching materials whose empirical ranking is well established, and second in varying parameters of the Plot number. Finally, are two batches of a functional ceramic compared. The proposed criterion reflects the competition between the toughness of the quenched material, as an intrinsic property, and the thermal transient stresses, as a consequence of the physical properties of both the quenched sample and the quenching medium. Possibilities for extending the developed approach towards a more accurate description of quenching phenomena and stress states such as to refine theoretical models are discussed.
In order to predict the radial vibration of the stator core of a Doubly Salient Switched Reluctance Motor (D.S.S.R.M.), different causes of vibrations are considered. In this kind of machine, electromagnetic stress is found to be the most significant cause of vibrations. The local magnetic stress distribution, depending on magnetic field and finally on the phase current, is calculated in the case of an unsatured operation. This magnetic stress acts in two ways: a tangential force (torque) and a radial attractive force. This radial force excites the vibration modes of the stator, this vibration behaviour is measured in the aligned position and is identified as a transfert function. Finally several experiments show the good accuracy of this simple model. This model will be later used to study the effect of phase current and of static converter on vibration and acoustic noise emitted by the D.S.S.R.M.
Deep Level Transient Spectroscopy (DLTS) investigations of plastically deformed, n-type silicon have been performed. DLTS spectra revealed four lines usually found in deformed silicon but they were unusually dominated by a broadened level located at 0.40 eV from the conduction band edge. This trap resulted to be the most localized at the dislocations, while the other traps are probably related to point defects. The measured DLTS line widths have been simulated by the introduction of a broadening parameter delta, whose dependence on the dislocation density has been studied. Some hypotheses on the physical mechanisms responsible for the line broadening have been advanced. A tentative identification of the defects responsible for the deep levels observed has been performed.
In Parts I and II of this work we developed a model of oxygen O-18 tracer diffusion in a growing polycrystalline oxide film with parallel grain boundaries. In this paper we solve the basic equations of the model numerically using the Monte-Carlo approach. We introduce a new simulation technique that takes into account the finite-size effect, the film growth, the effect of the oxygen chemical potential gradient across the film, and other factors. We apply this technique for the simulation of the most important cases encountered in two-stage oxidation experiments. The oxygen tracer profiles obtained demonstrate good agreement with the previous theoretical analysis, the finite-difference solution of the problem, and exact analytical solutions when available. We discuss possible extensions of the simulation method to provide a more realistic description of the oxide growth.
Comparison of the characteristics of an electric are breakdown in vacuum between two silver or silver-nickel alloy electrodes prompted us to study the evolution of the breakdown voltage with electrode separation, with resistance value placed between the anode and the high voltage supply used for the breakdown, and with the effect of conditionning by heating in vacuum. The measurement of the commutation time and delay time, and the observations by a metallographic microscope of the electrodes surfaces after one breakdown, enabled us to evidence the origin of the electric are for each of the studied materials.
Mechanical alloying is a synthesis technique which is used to produce nanostructured powders. Nevertheless this high energy ball-milling process is not used only for refining of microstructure, but also for inducing chemical reactions between two powders or between powders and the atmosphere of grinding or for inducing chemical or phase transformations... Polymorphic transformations induced by ball-milling in SnO2, TiO2, Y2O3 and WO3 and the influence of the nature of milling media on these transformations are described as well as the formation mechanisms of nanocrystalline based zirconia alloys. The nanometric structure of so obtained powders is characterized by transmission electron microscopy and a hyperfine technique: the Mossbauer spectroscopy.
