Interfacial adhesion study for low-k interconnects in flip-chip packages

This paper presents the results of a two-part study to determine the fracture toughness of relevant interfaces within Cu/Low-k interconnect structures and relate those data to the actual driving force for interfacial crack propagation within a flip-chip structure. In the first part, critical and time-dependent subcritical adhesion data were obtained for BCB/Si₃N₄, BCB/Ta and BCB/TaN interfaces. In the second part, phase-shifting moire interferometry was used to measure the deformation state and crack driving force for a flip-chip structure containing a small interfacial delamination. Finite element analysis was used to verify the moire data and then extend the study to examine the effect of low-k on the deformation state, mode-mixity and crack driving force. The results of both parts were combined to assess the severity of an existing interfacial delamination with regard to loss of package integrity. Results show that the crack driving force exceeds the critical fracture toughness of Ta/BCB and TaN/BCB interfaces and is sufficient to cause subcritical crack growth along Si₃N₄/BCB interfaces