Joris Proost

Microtexture and electromigration-induced drift in electroplated damascene Cu

In this work, the electromigration (EM) performance of electroplated damascene Cu is investigated by drift experiments on Blech-type test structures in both polycrystalline and bamboo microstructures. For the first, microtexture data were obtained from electron backscatter diffraction as well. While both bonding areas and 10 μm wide lines were found to have a predominantly random grain orientation, the drift studies indicated the importance of strongly segregating impurities in controlling Cu grain-boundary EM. For the bamboo lines, the impact of different barrier layers has been investigated, comparing Ta, TaN, and TiN. Drift was shown to proceed in all cases at the metallic Cu barrier interface, but faster for the Ta as compared to the TaN and TiN barriers. Cu drift data were finally compared to available literature results and to our previous drift studies on Al(Cu).

Current Understanding of Ti Anodisation : Functional, Morphological, Chemical and Mechanical Aspects

This paper provides an overview of the current understanding of the Ti anodisation process. As compared to other valve-metals, Ti exhibits several significant differences regarding its anodisation behaviour, the most important one being the marked semiconducting character of its anodic oxide. In the first part of this paper, a general introduction to anodisation processes is given and theoretical models describing the growth kinetics, breakdown and internal stress development in anodic oxide films are presented. In the second part, the peculiarities of Ti regarding the anodisation behaviour are discussed extensively. In particular, the influence of the main experimental parameters (metal substrate, electrolyte and growth rate) on both the anodisation process and the functional, morphological, chemical and mechanical characteristics of the anodic films is reviewed.

Simulation of the effect of viscosity on jet penetration into a single cavitating bubble

The dynamics of a cavitating bubble in a viscous liquid near a solid surface is numerically calculated. In the model, the two dimensional axisymmetric Navier-Stokes equations are solved for both the compressible gas phase and the incompressible liquid phase on a fixed Cartesian grid. The bubble-liquid interface is tracked by the Volume Of Fluid method. Our numerical model, which explicitly takes into account the liquid viscosity, is first validated against available experimental data from the literature on single laser-induced bubble collapse near a solid surface. Next, the time evolution of the jet front velocity of penetrating jets has been calculated for different values of the viscosity as a function of the so-called stand-off parameter gamma, the latter being characteristic of the distance separating the initial bubble center from the solid surface. Finally, from these data, the maximum jet front velocity has been calculated. Good agreement was obtained with experimental data. Our numerical calculations further predict a maximum in the evolution of the maximum jet front velocity as a function of gamma, the magnitude and position of which decrease with increasing liquid viscosity. Before the maximum, increasing the viscosity gives rise to a strongly diverging maximum jet front velocity with decreasing gamma

On the use of a multiple beam optical sensor for in situ curvature monitoring in liquids

Several methods have been developed since the early 1900 to extract thin film stresses from the curvature of the substrate to which it is attached. One robust method particularly suitable for in situ curvature monitoring is the multiple beam optical sensor, which consists in measuring the change in relative spacings between parallel laser beams reflecting off the curved substrate. Although the technique is already well established for curvature monitoring in low pressure, gaseous environments, its use in liquid media has not yet received similar attention. Moreover, in the majority of the published work so far, spot spacings have been assumed to depend linearly on curvature. In this paper, it is first shown that this assumption may induce significant errors, particularly at large curvature. A more accurate set of equations is proposed. Next, the relationship between spot spacings and curvature is established when the substrate of interest is in a liquid, and a constitutive formula is proposed in that case as well. Finally, some practical aspects of the multiple beam technique for performing curvature measurements in a liquid are discussed. Various factors disturbing the measurement resolution are identified, with a specific interest for thin film anodizing, and a cell design is proposed to minimize their effect.

In situ detection of porosity initiation during aluminum thin film anodizing

High-resolution curvature measurements have been performed in situ during aluminum thin film anodizing in sulfuric acid. A well-defined transition in the rate of internal stress-induced curvature change is shown to allow for the accurate, real-time detection of porosity initiation. The validity of this in situ diagnostic tool was confirmed by a quantitative analysis of the spectral density distributions of the anodized surfaces. These were obtained by analyzing ex situ atomic force microscopy images of surfaces anodized for different times, and allowed to correlate the in situ detected transition in the rate of curvature change with the appearance of porosity.

An in situ study of the hydriding kinetics of Pd thin films

The hydriding kinetics of Pd thin films has been investigated in detail. The in situ experimental technique used in this work consists of a high resolution curvature measurement setup, which continuously monitors the reflections of multiple laser beams reflecting off a cantilevered sample. After mounting the sample inside a vacuum chamber, a H-containing gas mixture is introduced to instantaneously generate a given hydrogen partial pressure (p(H(2))) inside the chamber. The resulting interaction of hydrogen with the Pd layer then leads to a volume expansion of the thin film system. This induces in turn changes in the sample curvature as a result of internal stresses developing in the Pd film during a hydriding cycle. Based on such in situ curvature data, three different kinetic regimes have been resolved. The first two exhibited a linear increase of the internal stress in the compressive direction with time. A systematic study of the p(H(2))-dependency of the two constant slopes was performed, based on newly derived constitutive kinetic equations. This resulted in the identification of the first linear regime to be limited by absorption and the second one by adsorption. After adsorption equilibrium is reached at the end of the second regime, a third, non-linear kinetic regime, limited by absorption, was found to precede the final hydriding equilibrium. This switch back to absorption-limited kinetics likely occurs due to a coverage dependent change in the adsorption enthalpy of the surface hydrogen. Furthermore, from our in situ experimental data, relevant kinetic and thermodynamic hydriding parameters have been derived. As a result, this study was able to provide a self-consistent quantitative interpretation of the entire Pd room temperature hydriding cycle in the alpha-phase domain.

Glasses and bioglasses : synthesis and coatings

Abstract In this paper a production technique is described for the application of glass coatings on diverse substrates, more particularly bioglass coatings on titanium. The glass is synthesized from base chemicals in a plasma torch and is applied as a coating in the same operation. In this way well-adhering coatings with controlled composition and amorphicity are obtained. Adhesion strengths above 40 MPa are easily obtained.

High resolution transmission electron microscopy characterization of fcc → 9R transformation in nanocrystalline palladium films due to hydriding

Sputtered nanocrystalline palladium thin films with nanoscale growth twins have been subjected to hydriding cycles. The evolution of the twin boundaries has been investigated using high resolution transmission electron microscopy. Surprisingly, the ∑3{112} incoherent twin boundaries dissociate after hydriding into two phase boundaries bounding a 9R phase. This phase which corresponds to single stacking faults located every three {111} planes in the fcc Pd structure was not expected because of the high stacking fault energy of Pd. This observation is connected to the influence of the Hydrogen on the stacking fault energy of palladium and the high compressive stresses building up during hydriding.

On the relation between growth instabilities and internal stress evolution during galvanostatic Ti thin film anodization

Sputtered Ti thin-film electrodes have been anodized, both continuously and in an interrupted way, under galvanostatic conditions in 1.0 M H2SO4 up to forming voltages in the range of 5-40 V. The internal stresses developing in the anodic oxide film have been followed in situ during anodizing using a high-resolution curvature measurement technique. The observed stress evolution is discussed in relation to the oxygen evolution reaction and other growth instabilities previously reported in the literature. The onset of the oxygen evolution reaction, which significantly reduces the growth efficiency, is observed to induce very large compressive stresses. The latter are likely to result from oxygen evolution inside the oxide film. At some stage during film growth, the growth efficiency is observed to return to its initial high value, and the instantaneous stress in the film changes from compressive to tensile. A tentative explanation is proposed for the observed phenomena, taking into account the kinetics of the oxygen evolution reaction inside the film

Stress Relaxation in Al–Cu and Al–Si–Cu Thin Films

Substrate curvature measurements were used to study stress changes during thermal cycling and isothermal tensile stress relaxation in 800 nm Al–0.5 wt% Cu and Al–1 wt% Si–0.5 wt% Cu films. For both compositions dislocation glide can describe the relaxation data well for temperatures up to 120 °C for Al–Si–Cu and up to 100 °C for Al–Cu. The average activation energy for Al–Si–Cu and Al–Cu is 1.7 ± 0.2 eV and 3.0 ± 0.3 eV, respectively. The athermal flow stress is the same for both and equal to 600 ± 200 MPa. This result is consistent with the obstacles for glide being Al2Cu precipitates, which, in the case of Al–Si–Cu, are fine and can be cut by the dislocations, and, in the case of Al–Cu, are strong and provide Orowan strengthening. Also, the stress changes during thermal cycling in the Al–Cu films are different from those in the Al–Si–Cu films. For Al–Cu films, the room temperature stress decreases after each thermal cycle, while for Al–Si–Cu stress changes during thermal cycling are stable from the second cycle on. These observations are supported by thorough transmission electron microscopy (TEM) studies.