Adhesion studies of Ta/low-k (black diamond) interface using thermocompressive wafer bonding and four-point bend

The four-point bend test is used to quantitatively determine the adhesion energy of the Ta/low-k (Black Diamond) interface, a technologically important interface found in a Cu/low-k dual-damascene interconnection system. The samples containing the interface of interest were prepared by 200 mm wafer-level Cu thermocompression bonding. By bonding the Cu wafers at 300°C for 30 min at 10 kN without any prior prebond surface clean helps to form a moderately weaker Cu-to-Cu bonding interface, which deflects the vertical precrack to the direction parallel to the interface of interest. The crack then seeks out a new weak path for further growth, and this mode mixity ensures that it kinks downward to the multilayer containing the Ta/low-k interface. Focused-ion beam scanning electron microscopy, cross-sectional scanning electron microscopy, and Auger analysis are used to evaluate the failure interfaces.