Improvement of the long-term reliability of TSV interconnections used in three-dimensional stacked modules

The long-term reliability of inerconnectons of threedimensional integrated modules was investigated from the view point of crystallographic quality of the interconnection. The dgradation process of the interconnections was dominated mainly by the diffusion of copper atoms along grain boundaries in a polycrystalline thin-film and the diffusion constant was found to vary drastically depending on the crystallinity of the copper interconnections. The crystallinity of the interconnections changed seriously as a strong function of the mismatch in the lattice constant between copper and the seed layer material used for electroplating of the copper interconnections. The crystallinity of the electroplated interconnections was evaluated quantitatively by using an electron back-scatter diffraction method. Both the quality of grains and grain boundaries in the copper interconnections varied drastically as a function of electroplating conditions and their thermal hystory after the electroplating. The most important factors for the long-term reliability was the initial quality of the interconnection just after the electroplating.