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•Silicon-to-sapphire wafer bonding through an innovative method and characterized by high-resolution XRD and X-ray micro-CT.•The innovative silicon-to-sapphire wafer bonding proved ...effective and strong opening the floor to a remarkable advancing in packaging design.•X-ray micro computed tomography revealed powerful for quantifying 3D-volume defects in mm-thick structures and assess the bonding process effectiveness.•A comprehensive understanding of the degradation mechanisms acting at the micron/nano-scale is only accessible by a conjoint X-ray-based approach.•The approach demonstrated applies to the quantitative analysis of the status of materials involved into each partially destructive microfabrication process.
Devices such as sensors, actuators, or micro-electromechanical systems (MEMS) are obtained by a variety of microfabrication processes. Many of these processes influence the material systems by the introduction of strain and defects, which may affect the final device's performance and reliability. Indeed, controlling materials' status during the microfabrication is fundamental for the process optimization itself and for guaranteeing the highest devices performances during their lifetime. In this work, a conjoint analytical approach between high-resolution X-ray diffraction (HRXRD) and X-ray micro-computed tomography (CT) evaluates an innovative silicon-to-sapphire wafer bonding process. Large cracks 30–60 µm-thick were identified in both crystals by micro-CT and related to the interfacial high-stress release. In parallel, a multi-domain microstructure associated with strain and tilt affect the silicon crystallinity due to smaller cracks and defects which originate at the bonding interface and travel to the outer part of the crystal. The effectiveness of the bonding is also assessed by our approach and further enforced by means of SEM observation of the sample cross-section. Here, a unique approach by combining X-ray micro CT with HRXRD for a holistic evaluation of silicon-to-sapphire wafer-bonding processes and correlate the micrometer scale and volumetric defect detection (voids and cracks) with atomic-level strain and defect analysis is presented.
Transitions from the liquid to the solid state of matter are omnipresent. They form a crucial step in the industrial solidification of metallic alloy melts and are greatly influenced by the ...thermophysical properties of the melt. Knowledge of the thermophysical properties of liquid metallic alloys is necessary in order to gain a tight control over the solidification pathway, and over the obtained material structure of the solid. Measurements of thermophysical properties on ground are often difficult, or even impossible, since liquids are strongly influenced by earth's gravity. Another problem is the reactivity of melts with container materials, especially at high temperature. Finally, deep undercooling, necessary to understand nucleus formation and equilibrium as well as non-equilibrium solidification, can only be achieved in a containerless environment. Containerless experiments in microgravity allow precise benchmark measurements of thermophysical properties. The electromagnetic levitator ISS-EML on the International Space Station (ISS) offers perfect conditions for such experiments. This way, data for process simulations is obtained, and a deeper understanding of nucleation, crystal growth, microstructural evolution, and other details of the transformation from liquid to solid can be gained. Here, we address the scientific questions in detail, show highlights of recent achievements, and give an outlook on future work.
Cathodic arc evaporation was applied to form a layer stack on a Ni-based superalloy single crystalline substrate in a single in-situ vacuum deposition process. The initial layer was deposited using a ...target with the same nominal composition as the superalloy substrate. Subsequently, a second layer was deposited using a target with a composition of 70 at.% Al and 30 at.% Cr, and the deposition was conducted in flowing oxygen to form Al-Cr-O. The thermal stability of the layer stack was investigated by means of a heat treatment at 1100 °C in air. The substrate-like coating recrystallized at elevated temperature and showed epitaxial growth on the superalloy single crystal, according to transmission Kikuchi diffraction measurements. A thin layer of pure α-alumina formed on top of the substrate-like coating and a compact Al-Cr-O phase with corundum structure developed towards the top of the coating. Microstructural and chemical analyses of the coating architectures in the as-deposited and annealed states were performed by means of transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and Rutherford backscattering spectrometry, and utilized to explain the recrystallization and diffusion processes in the layer stack.
•Synthesis of Al-Cr-O on a single-crystalline Ni-based superalloy•Formation of α-alumina on top of the superalloy•Control of Ni diffusion due to a limited reservoir of elements in the layer stack•Epitaxial growth at the interface between superalloy substrate and coating
Thin coatings were synthesized by cathodic arc evaporation of powder metallurgically fabricated Al-Ni targets with the chemical compositions of Al75Ni25, Al67Ni33 and Al52Ni48 atomic percent. The ...coatings were produced both either from pure metallic vapour or in reactive oxygen atmosphere. Phase transformations and chemical composition at the target surface were investigated by X-ray diffraction (XRD) and by energy-dispersive X-ray spectroscopy (EDS) techniques and compared with the phases composition obtained in the coating. The deposition in non-reactive mode produces intermetallic coatings containing different Ni aluminides. The formation of the aluminides can be controlled by the target composition and is by trend predictable from the Al-Ni phase diagram. The coatings produced in reactive mode are composed of both Al3Ni and Al3Ni2 with the additional formation of AlNi and Al2NiO4 in all the coatings. The coatings composed of intermetallics show high indentation hardness in the range of 10 GPA while the coatings composed of both oxides and intermetallics demonstrate exceptional high hardness of about 30GPa. All coatings have been annealed in ambient air up to 1200°C and were investigated by in-situ XRD analysis in order to follow in detail their oxidation process. For all coatings, the formation of α-Al2O3 and Al2NiO4 could be observed after annealing forming a thin high temperature stable protective layer for remaining AlNi. The coatings deposited in reactive atmosphere contain additional NiO, independently of their original composition.
High temperature annealing of an Al-Ni-O coating synthesized by reactive cathodic arc evaporation. Display omitted
•Cathodic arc evaporation of Al-Ni is demonstrated for different target compositions.•Target surface versus coating compositions are given for reactive and non-reactive modes.•We show that both oxide and Al-Ni intermetallics can be formed in a single process.•The progressive oxide scaling during annealing of Al-Ni and Al-Ni-O coatings is discussed.
A novel cathodic arc evaporation process operated in pure oxygen forms corundum‐type micro‐crystalline structures at temperatures below 600°C. Thermally stable crystalline solid solutions of ...corundum‐type (Al1–xCrx)2Oy have been prepared with this method for x ≥ 0.3 at non‐equilibrium conditions. The stability in (Al,Cr)2O3 phases can be explained by their degree of crystallinity and ordering within the structure. The applied processing method results in highly crystalline coatings of pure α‐(Al1–xCrx)2Oy. With increasing fabrication temperature (maximum 600°), more stable phases are obtained showing no metal site splitting in the atomic structure.
Al–Hf and Al–Hf–O coatings were synthesized by cathodic arc evaporation utilizing composite targets with composition of Al75Hf25. The reaction at the target surface and the composition of the film ...were analyzed by energy-dispersive X-ray spectroscopy (EDX), Rutherford backscattering spectrometry (RBS) and X-ray diffraction (XRD) techniques. The Al–Hf coatings deviate distinctively from target composition showing a deficiency in Al. XRD phase analysis shows the synthesis of Al3Hf intermetallic compound for the Al–Hf coatings while the oxide coatings indicate an amorphous matrix and monoclinic HfO2. The coatings were annealed in ambient air up to 1290°C to study the oxidation process. In-situ XRD analysis of the coatings was performed during annealing. The intermetallic phase undergoes phase transformations at temperatures between 700°C and 1100°C, with the formation of a metastable face-centered cubic (fcc) HfO2 simultaneously with the monoclinic polymorph. After this transition period, the cubic phase disappears and the coating stabilizes with two oxide phases: corundum (α-Al2O3) and monoclinic HfO2 (m-HfO2). Applying the same treatments to the Al–Hf–O coatings results in a similar evolution with an improvement of crystallinity for the monoclinic HfO2 phase and the crystallization of the fcc HfO2 starting at about 860°C. This phase disappears above 1200°C, where the coating stabilizes with corundum and m-HfO2 phases. The formation of the metastable fcc HfO2 phase is discussed and associated with a deficiency in oxygen during the oxidation process.
•Synthesis of Al–Hf and Al–Hf–O by cathodic arc evaporation•Analysis of the phase evolution in these materials during annealing in ambient air•Investigation of the transient cubic HfO2 phase during annealing•Comparison of the oxidation process of the Al–Hf intermetallic coating with the related Al–Hf–O coating
Superalloy targets were produced from Ni-(Al-C-Co-Cr-Mo-Ta-Ti-W) powders by spark plasma sintering technology. The crystalline structure of the as-produced targets was investigated by XRD analysis ...and compared with the evolution of phases resulting from the operation of the cathodic arc at the target (cathode) surface. Coatings were synthesized at superalloy substrates utilizing these superalloy targets in non-reactive and reactive evaporation processes. Synthesized coatings and target surfaces were compared with respect to chemical composition and crystal structure. The interface between coating and superalloy substrates was investigated by TEM. As an example, a complete layer stack was synthesized by cathodic arc evaporation starting from the superalloy substrate - superalloy coating interface to a fully oxidized superalloy coating showing epitaxial growth in the interface to the superalloy substrate.
•Superalloy substrate-identical targets were fabricated and utilized in non-reactive and reactive cathodic arc deposition•The chemical composition and structure of the targets were also found in the synthesized superalloy coating•In-situ processing is demonstrated for the whole bond coat•Epitaxial growth was achieved in the interface between superalloy coating and superalloy substrate
The evolution of the composition of tungsten carbide and silicon surfaces initiated by the bombardment with Zr and Cr ions has been investigated as a function of the substrate bias voltage. Surface ...composition profiles were measured by Rutherford backscattering and have been compared with the results obtained by the TRIDYN simulation program. It is found that the general dependence of film thickness on substrate bias is satisfactorily reproduced by this model. Deviations between experiment and simulation are attributed to possible partial oxidation of the surface or uncertainties in the charge state distribution of metal ions. The results confirm that TRIDYN facilitates the predictability of the nucleation of metallic vapor at substrate surfaces.
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