Atomic Layer Deposited Al2O3 Encapsulation for the Silicon Interconnect Fabric

In this paper, we have investigated the effectiveness of atomic layer deposition (ALD) of Al
₂
O
₃
as a passivation for wafer scale integration on the silicon interconnect fabric (Si-IF). Due to high conformality and quality of ALD thin films, this deposition technique is gaining more applications in microelectronics fabrication. Humidity testing was utilized to evaluate barrier properties of Al
₂
O
₃
for different thicknesses (10 to 17 nm). XRD analysis was used to identify oxide formation in blanket copper samples passivated with Al
₂
O
₃
. We have concluded that thin films with thicknesses above 10 nm can efficiently protect Cu from oxidation under standard humidity exposure conditions. To study the conformality of the film on bonded samples, focused ion beam (FIB) and SEM imaging were performed. Thickness of the film remained constant from the top surface of the bonded die all the way down to the interface of the die and substrate. To further analyze the robustness of Al
₂
O
₃
films in protecting Cu interconnects from oxidation, bonded and passivated samples were exposed to humidity testing for 216 hours and the variation in electrical resistance of the samples before and after the testing was less than 5%.Finite element analysis was utilized to study residual thermal stresses in samples with and without passivation as well as the effect of the passivation material on residual stresses. Adding passivation layer increases compressive residual stresses within Cu pillar. However, in case of the bilayer passivation (Parylene C/SiN
_x
); high tensile residual stress at the interface of the two thin films may adversely affect the barrier properties.