Evaluation Method of Delamination Strength at Interface Edge of Thin Films in Conductor of Advanced LSI

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Copper thin film is used for the conductor in advanced large-scale-integrated-circuits (LSI) in order to reduce electric resistance and to prevent fracture due to atom migration. A barrier layer is usually placed between the substrate and the film to prevent diffusion of copper atoms. The poor adhesiveness between them, however, sometimes causes interface fracture from the interface edge due to the free-edge effect. Although it is necessary to elucidate the mechanics of the delamination strength at the interface edge, no proper evaluation method has been proposed so far. In this study, an experimental method for the crack initiation is investigated based on the fracture mechanics concept. Especially, the focus is put on the stress singularity near the interface edge. In the experiment, the metal film is sandwiched by rigid substrate and beam so that the plastic deformation of film is constraint. Delamination tests are carried out by means of a loading apparatus, which is a modified Vickers hardness test machine. The experiments, the BEM (Boundary Element Method) analysis and MD (Molecular Dynamics) simulation reveal that the delamination criterion is successfully evaluated by the proposed method. The critical magnitude of the stress intensity factor, which governs the stress field near the edge, is examined for several film/substrate interfaces. Moreover, the crack initiation is governed not only by the external mechanical loading but also by the internal stress introduced in the fabrication process of the film, on the delamination. The experimental investigation shows that the superposition of both influence controls the crack initiation.