Effect of Sputter Deposition on the Adhesion and Failure Behavior between Cu Film and Glassy Calcium Aluminosilicate: A Molecular Dynamics Study

Understanding the physical vapor deposition (PVD) process of metallic coatings on an inorganic substrate is essential for the packaging and semiconductor industry. In this work, we investigate a Copper (Cu) film deposition on a glassy Calcium Aluminosilicate (CAS) by PVD and its dependence on the incident energy. Molecular dynamics simulation is adopted to mimic the deposition process, and pure Cu film is grown on top of CAS surface forming intermixing region (IR) of Cu oxide. In the initial stage of deposition, incident Cu atoms are diffused into CAS bulk and aggregated at the surface which leads to the formation of IR. When the high incident energy, 2 eV, is applied, 20% more Cu atoms are observed at the interface compared to the low incident energy, 0.2 eV, due to enhanced lateral diffusion. As the Cu film grows, the amorphous thin Cu layer of 1 nm is temporarily formed on top of CAS, and crystallization with face-centered cubic from amorphous structure follows regardless of incident energy, and surface roughness is observed to be low for high incident energy cases. Deformation and failure behavior of Cu-CAS bilayer by pulling is investigated by steered molecular dynamics technique. The adhesive failure mode is observed, which implies the bilayer experiences a failure at the interface, and a 7% higher adhesion force is predicted for the high incident energy case. To find an origin of adhesion enhancement, the distribution of Cu atoms on the fractured CAS surface is analyzed, and it turns out that 6.3% more Cu atoms remain on the surface, which can be regarded as a source for the high adhesion force. Our findings hopefully give the insight to understand deposition and failure mechanisms between heterogeneous materials and are also helping to further improve Cu adhesion in sputter experiments.

Cross sections for electron-impact ionization of water molecules

Theoretical triple differential cross sections for the electron-impact ionization of water molecules at high incident energy are presented. The results are derived using an analytical expression for the transition amplitude in the framework of the one Coulomb wave model. For accurate comparison with experiments, an average of the cross sections on the random orientations of the target has been used. The comparison of our results with the available experimental measurements shows that our formalism is able to describe the water molecule ionization process with good precision. The present approach can be used to describe the ionization of other molecular targets with chemical form XHn by other charged particles.

Backscattered Electron Imaging in the Scanning Electron Microscope: the Use of Either: (a) High Incident Energy or (b) an Array Detector

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

Atomistic Mechanism of Ion Beam Deposition Induced Curvature Formation in Thin-Films

Molecular dynamics (MD) simulations are performed to study the stress generation mechanisms in cantilever graphene sheets impacted by energetic carbon neutrals. The carbon-carbon interactions are described by the Tersoff-Brenner potential [1]. The MD simulations show that the free-end deflection of the graphene sheets is strongly dependent on the kinetic energy of the incident ions. At low incident energy (<<10eV), the free end bends towards to the side on which ions are deposited (upward deflection); at high incident energy, the free end bends away from the side on which the ions are deposited (downward deflection). The downward deflection reaches its maximum at around 50 eV, beyond which the downward deflection decreases with increasing incident energies. In addition, the evolution of the free-end deflection in terms of the number of deposited atoms is also dependent on the kinetic energy of the incident ions. These numerical observations suggest that intrinsic stress of different levels in the graphene sheets is generated. A close examination of the microstructures of the grown films indicates that the generated stress can be attributed to a competing mechanism of the production and annihilation of vacancy-like and interstitial-like defects in the films.

INFLUENCE OF ION BOMBARDMENT ON CRITICAL LOAD OF CrN FILM DEPOSITED ONTO ALUMINUM ALLOY BY ARC ION PLATING METHOD

To improve the adhesive strength between the film and substrate, ion bombardment is frequently performed before the deposition of thin film coatings. In this study scratch tests were carried out on aluminum alloy protected with CrN film coated by arc ion plating method. In order to investigate the influence of ion bombardment conditions on the adhesive strength between the aluminum alloy substrate and the CrN coating, the ion bombardment process was performed before CrN coating under several different bias voltages. The properties near the interface were analyzed using SIMS. As a result, the ion bombardment process had an optimum condition and excessive bias voltage reduced the critical load. A Cr rich layer forms near the substrate surface by implantation of Cr ions due to the high incident energy ions. The Cr rich layer is shallow for the high critical load sample, while the low critical load sample has a deep Cr rich layer. It appears that the adhesion strength between the substrate and the film will depend on the depth or intensity of this Cr rich layer.