| dc.description.abstract | In recent years, three-dimension integration technology has been widely discussed in regard to the packaging industry. Because of its many advantages such as reductions in power and device size, an increase in efficiency, and the miniaturization of electronic devices, the reliability of bonding in packaging is becoming gradually more evident. Wafer-level bonding is a key aspect of three-dimension integrated circuits, and Cu-Cu thermocompression bonding has become main stream because of its low cost and simple processes. In this study, a simple co-sputter technology was used to add Ti into Cu to deposit Cu(Ti) films. First, the characteristics of a single Cu(Ti) film after annealing at 400 oC were investigated. We obtained samples with various Ti concentrations, and through in-depth profile analysis we determined that the samples exhibited different levels of phase separation. The results showed that the Cu(Ti) alloy films with 15% Ti contained approximately 150 nm of pure Cu near their sample surfaces.
Evidence for phase separation was obtained from a cross section of high-resolution transmission electron microscopy images, line-scan images, and mapping images. Moreover, the morphology of the sample plane view was observed through electron probe microanalysis images and mapping. In the experiment, the crystal characteristics and sheet resistance were detected through grazing incidence X-ray diffraction and a four-point probe. Theoretically, the calculation of the diffusivity of Ti in Cu is one order of magnitude smaller than that of Cu in Cu. Both calculations prove thermodynamically and kinetically that Ti is a dominant diffusing species that is segregated near SiO2, whereas Cu atoms are pushed toward the surface. In this study, the films were bonded through thermocompression. A Cu(Ti) film containing 15 at% Ti with a bonding time of 60 min at 400 oC exhibited the highest bonding strength with no void caused by phase separation. The relationships between bonding strength and the samples with various Ti concentrations were measured over different bonding times through shear testing.
Finally, the evolution of phase separation and bonding were proposed. From the results, we know that phase separation of Cu and Ti in co-sputtered Cu(Ti) films provides a innovative method for forming high-quality Cu bonds.
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