Interfacial adhesion study for copper/SiLK 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/SiLK 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 adhesion data were obtained for samples containing SiLK in various configurations with Si₃N₄ , SiO₂, Ta and TaN. In the second part, these data are compared to the crack driving force for a flip-chip structure containing a small interfacial delamination in the vicinity of the Cu/Low-k interconnect structure, determined previously via phase-shifting moire interferometry (PSMI) and finite element analysis (FEA). In this study, the model was used to examine the effect of geometry and material properties on the deformation state, mode-mixity and crack driving force for a thermal load, ΔT=-143°C. Results show that the deposition of Ta, TaN and Si₃N₄ onto SiLK weakened the underlying SiLK/Si₃N₄ interface by 30-50%. The weakest interface tested was formed by the deposition of SiO₂ onto SiLK. However, the adhesion of all tested SiLK interfaces was 100-1000% greater than the crack driving force. From FEA it is shown that the crack driving force and mode-mixity are relatively insensitive to package geometry and most sensitive to the properties of the printed circuit board (PCB). In terms of PCB properties, the combination of low CTE and high modulus was found to provide the optimal combination of driving force and mode-mixity