Volume 96, Issue 9

Both in situ microscopy experiments at embedded inlaid copper interconnect structures and numerical simulations based on a physical model provide information about electromigration-induced degradation mechanisms in on-chip interconnects. It is shown that the modification of the bonding strength of the weakest interface results in completely changed degradation and failure mechanisms. Transmission electron microscopy (TEM) images of standard Cu/SiN x interfaces are compared with strengthened interfaces, e. g., after applying an additional metal coating or a self-assembled monolayer (SAM) on top of the polished copper lines. The changed degradation mechanisms as observed with the in situ scanning electron microscopy (SEM) experiment and as predicted based on the numerical simulations are explained based on TEM images.

Electron spectroscopic methods as X-ray photoelectron spectrometry (XPS) and Auger electron spectrometry (AES) are well established in the field of thin-film and surface analysis. In the measured spectral information, always also chemical information on the sample is contained. It is discussed that often chemometrical methods are the only way to extract such (hidden) information from the measured data sets. We demonstrate for AES and XPS measurements, how factor analysis (FA) can help to derive chemical information at Ti-based material developed for body implants. An introduction to the methodology is given, and challenges and restrictions are discussed.

The application of radio frequency glow discharge optical emission spectroscopy for the investigation of the stability of different diffusion barriers for microelectronic applications against thermal diffusion of Cu is presented. Difficulties in the interpretation of the glow discharge results are overcome by performing an additional special experiment, where conductive and nonconductive parts are sputtered intentionally at the same time. As a consequence of the investigations, care must be taken, if glow discharge spectrometry is applied to samples with conductive and nonconductive components.

The structural prerequisites are investigated, which make star-shaped molecules suitable precursors for the formation of columnar liquid-crystalline phases. Electronic structure calculations on smaller mesogens show that not all conformers exhibit the atomistic structure, the stability against distortion, and additional dipole moments, which favour columnar stacking. For the presently studied compounds with short terminating alkyl chains, the calculations indicate that the steric factor becomes dominant with increasing star size. Thus, the optimised geometric structures were employed to generate a simplified mathematical model of the structures, which accounts only for the steric interaction in the larger stars. With the help of these diagrams, the most common conformers of star-shaped molecules can be derived in a systematic fashion.

Metal containing and metal free amorphous diamond-like carbon films were prepared by reactive magnetron sputter deposition using targets from transition metals or graphite and acetylene as reactive gas. Both types of coating materials are well known for their low friction coefficients. However, metal containing films exhibit clearly lower wear resistances and lower hardness values than metal free films. To study the differences between both materials, tungsten containing and metal free coatings were compared. The deposition experiments were carried out in an industrial scale d.c. magnetron sputter machine. Transmission electron microscopy, secondary ion mass spectroscopy, and Raman spectroscopy as well as hardness measurements and wear tests were performed to characterize and to compare composition, structure, mechanical, and tribological properties of both coating materials.

Local texture in hot extruded MgAl9Zn1 alloy has been studied using individual grain orientation measurement (BKD, “Automated EBSD”) in the SEM. In the shaft of a partial extrudate through a circular die orifice, a <0001> ring fiber texture has formed which continuously changes into a spiral fiber texture in the bottom neck. The flow tube of the internal back-end extrusion defect has a distinctly different texture whereby the (0002) lattice planes are preferentially aligned parallel to the radial and the extrusion directions. The formation of this texture is explained by basal glide, the pile-up of the hard billet mantle, and the inhomo-geneous metal flow during the extrusion process.

In this paper the microstructural development upon annealing of nanocrystalline Ni- and Co-based electrodeposits is described. New investigations on Ni, Ni – Fe, and Co–P are compared with previous results on Ni, Co, and Ni –P in terms of microstructural changes and stabilizing mechanisms. The conclusions are: pure nanocrystalline Ni and Co are stabilized by impurities in the grain boundaries. In the case of Co, also an allotropic phase transformation influences the occurrence of abnormal grain growth. Alloying and/or adding solutes is found to increase thermal stability. While in Ni-20 at.% Fe the ordering transformation is expected to be the reason for stabilization, in strongly segregating systems (Ni –P and Co–P) the stabilizing effect is the decrease in grain boundary energy due to solute segregation. After precipitation, Zener pinning still hinders grain boundary migration, but not sufficient to stabilize the nanocrystalline structure.

Heusler compounds are promising materials to be applied effectively as highly spin-polarized medium (or components) in spintronic devices. To prove their chances the microstructure, the phase formation, and the chemical homogeneity of sputtered thin films of Co 2 MnSi and Co 2 Cr 0.6 Fe 0.4 Al were studied by in-situ TEM observations as well as by analytical characterizations. The observed grain growth and phase formation in dependence on temperature agrees well with the results of measurements of the film resistivity. The chemical homogeneity varies and depends on the deposition process during thin film preparation, especially the incorporation of oxygen is an unwanted effect.

In contrast to vacuum-deposited Co/Cu multilayers the electrodeposited ones do not exhibit any oscillation behaviour in magnetic resistance properties as a function of the thickness of non-magnetic Cu layers. According to the magnetic investigations they show ferromagnetic and superparamagnetic character as a consequence of the lack of antiparallel coupling of neighbouring magnetic layers. Magnetic resistance observed on electrodeposited Co– Cu/Cu multilayers is believed to originate from the randomly antiparallel oriented magnetic domains. In the present paper the evolution of magnetic resistance properties is studied against the average Cu concentration of multilayers prepared under a Cu deposition potential of –0.25 and – 0.62 V, and the best magnetic resistance properties were found in the films with composition of 52% and 60% Cu, respectively. The average concentration was determined by electron microscopic and X-ray diffraction measurements.

Pearlite structures in eutectoid carbon steel seldom are perfectly lamellar. Structures in thermomechanically processed material in particular often consist of complex mixtures of lamellar, degenerated, and globular domains. In order to open the possibility of modelling structure –property relationships for such material, techniques have to be developed to quantitatively describe the morphology of its pearlite structure. The present article shows how EBSD and the Hough transform can give complementary information that can be further developed into a quantitative description of pearlitic structures.

The axial strains that develop during free-end torsion testing of copper wires have been modeled using the results of earlier measurements (L. S. Tóth, P. Szászvári, I. Kovács, J. J. Jonas: Mater. Sci. and Techn. 7 (1991) 458). In that work, the initial textures of the wires were changed by heat treatments. The as-received wires displayed shortening while the recrystallized ones lengthened during twisting at room temperature. In the simulations, the wire was divided into five cylindrical layers; in each layer, the texture development was simulated using the Taylor viscoplastic poly-crystal model up to large strains ( γ ≈ 5). The distribution of the hydrostatic stress was derived from the equilibrium equation of torsion. Using a suitable numerical scheme, the condition of zero axial force (free-end testing) was satisfied in an iterative way. Good agreements between the measurements and simulations have been obtained.

In discussing hardening characteristics in terms of crystalline lattice defects, in most cases the properties and kinetics of dislocations and their arrangement have been considered. However, during plastic deformation also vacancies and/or vacancy-type defects are produced in very high densities which are typically close to those of vacancies in thermal equilibrium at the melting point. This paper presents measurements of deformation-induced vacancies in deformed copper which have been achieved by combined evaluation of resistometry, calorimetry and X-ray diffraction. The density of vacancies during and after severe plastic deformation (SPD) deformation is found to be markedly higher than in cases of conventional deformation and/or coarse-grained material, which is attributed to the particular conditions of SPD, i. e., the enhanced hydrostatic pressure as well as the changes in the deformation path. The use of synchrotron radiation allows to apply the XPA method for in-situ deformation monitoring of intrinsic structural parameters. This also includes deformation-induced vacancies, evaluated by the diffuse background of Bragg peak profiles.

X-ray stress measurements can be done without the accurate knowledge of the unstressed lattice parameters, if the specimen’s surface can be assumed as stress-free and provided that the measured strains depend linearly on sin 2 ψ . This is usually done in the so-called sin 2 ψ method. An analytical formalism is proposed with which the same task can be performed even if the linear sin 2 ψ dependence is not given. Therefore, one is completely free in choosing and combining measurement parameters φ ; ψ , and ( hkl ). It can be used for single-crystalline, textured, texture-free, isotropic or anisotropic materials. Further advantages are an easy way for correct error calculus and a means to optimize the whole procedure for minimum errors in φ .

Nanoindentation experiments were performed before and after severe plastic deformation of W–Cu composites at room temperature, 200, and 400 °C. The strains were induced by high-pressure torsion (HPT). For the highest degrees of deformation, a particle size of 10 – 20 nanometer was achieved. The nanohardness of copper increased remarkably with increasing deformation, the hardness of tungsten was enhanced only slightly. A temperature of 400 °C during HPT significantly lowered the Cu hardness, probably recrystallisation during HPT had taken place, the hardness of tungsten, however, kept unaffected. With decreasing particle size, the influence of the adjacent material on the measured properties increased as well as the scatter of hardness and modulus. Proceeding to very small particle and grain sizes, the particles became smaller than the size of the indent. Thus, hardness and modulus values reflected some average over that of pure tungsten and copper.

The local deformation behaviour of powder metallurgy metal matrix composites (MMCs) with two different SiC particle sizes and aging conditions are investigated and compared to the behaviour of the un-reinforced matrix. In situ tensile loading experiments are carried out in a scanning electron microscope. Images taken at different deformation stages are analysed by a system for local deformation measurement. It is found that even the pure matrix material deforms inhomogeneously, showing a shear-band pattern which is independent of the loading stage. The MMCs with coarse reinforcements deform mainly due to shear bands which are induced by fractured particles. The MMCs with small particles exhibit a shear-band pattern which is controlled by the particle arrangement. The fracture of small particles does not induce far-reaching shear bands and, therefore, these materials have a higher strength and ductility.

A new methodology is presented that allows the quantification of experimental X-ray elastic constants of polycrystalline thin films without use of special diffractometer attachments. The approach is based on the combination of sin 2 ψ and curvature methods. The elastic strains in the polycrystalline films are characterized by the measurement of lattice spacings at different sample tilt angles, while the macroscopic stress in the film is calculated from the substrate curvature applying the Stoney formula. The radius of the curvature is determined from a sequence of rocking curves measured at different sample positions. The method is demonstrated on Al thin films deposited on Si(100) substrates. The X-ray diffraction measurements were performed at the synchrotron source BESSY in Berlin.

Understanding the precipitation reactions is of vital importance for the development of advanced steels. A comprehensive characterization of all phases, however, is still demanding in these complex materials. Transmission electron microscopy is widely used, but the prevailing ferromagnetism makes the analysis of small precipitates difficult. Furthermore, the investigated specimen volume is small, making statistically relevant findings time-consuming. Therefore, in our study, transmission electron microscopy measurements are complemented by small-angle neutron scattering and atom-probe field ion microscopy. These methods were used to characterize the precipitates in a model steel which hardens by secondary hardening carbides and an intermetallic NiAl-based phase. Assets and drawbacks of each method are discussed and it will be shown that an appropriate combination of the differently obtained findings leads to a detailed description of the precipitation behavior.

Al-free Mg–Zn alloys with alternative alloying elements were investigated in order to form Mg–Zn-based alloys with improved thermal stability. Based on thermodynamic calculations, Zn and Sn additives are expected to form stable intermetallic phases with Mg and cause precipitation hardening. An Mg alloy containing 4.5 wt.% Zn and 3.8 wt.% Sn was examined in detail and subsequently alloyed with Ca and Si, in order to promote additional precipitation. The as-cast microstructure and its stability during exposure to elevated temperatures were investigated. Precipitation hardening was investigated in the temperature range of 175 – 250 °C by Vickers hardness measurements and analysis of the microstructure evolution, using X-ray diffraction and electron microscopy techniques. During aging at 175 °C for 1 to 96 h, two hardness maxima were observed: the first after 2 h, and the second after 16 h. The occurrence of two hardness peaks can be related to a precipitation sequence. Firstly, MgZn 2 precipitates form, and secondly Mg 2 Sn. The results indicate that the precipitation mechanism is most likely diffusion-controlled. The precipitates are uniformly distributed in the Mg matrix with two morphologies: needle- and plate-like shapes. The addition of Si and Ca did not result in the expected effect on the precipitation behavior.