Fracture surfaces of a nanocrystallized Zr65Cu15Al10Pd10 metallic glass were observed on an atomic scale with field ion microscopy. Based on geometrical and phase characteristics of the fracture morphologies, it can be determined that a crack propagates along the interfaces between nanocrystals and the amorphous matrix in the alloy with optimized microstructures. Combining with macromechanical properties, it is proposed that the strengthening effect of nanocrystals in the Zr-based metallic glass arises from a strong interaction between nanocrystals and local shear bands during deformation processes of the glassy matrix.
Electroplated copper thin films have started to be applied to not only interconnections in printed wiring boards, but also thin film interconnections and TSV (Through Silicon Via) in semiconductor devices because of its low electric resistivity and high thermal conductivity. Thus, the electrical reliability of the electroplated copper interconnections was discussed experimentally.
The relationship between the electrical properties and crystallographic quality (crystallinity) of electroplated copper thin-film interconnections was investigated. The crystallinity of the grains and grain boundaries of the interconnections was evaluated on the basis of the image quality (IQ) value obtained by electron back-scatter diffraction (EBSD) analysis. The electrical properties of the interconnections vary significantly depending on their crystallinity. The crystallinity also changed drastically as functions of electroplating conditions and the annealing temperature after electroplating.
Although the electro migration (EM) resistance of the annealed interconnection is improved, the stress-induced migration (SM) is activated by a high residual tensile stress after annealing caused by the strong constraint of the shrinkage of the film during recrystallization. To improve its electrical reliability without heat treatment after the electroplating, the effects of the seed layer under the interconnections on the crystallinity of the electroplated film was investigated. As a result, the crystallinity was improved by changing the seed layer from Cu to Ru. In addition, the decrease in current density during electroplating also improves the crystallinity. Therefore, both introducing the Ru seed layer in addition to decreasing the current density during electroplating is effective for developing highly reliable copper interconnections.
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