Bilayer Passivation Film for Cu Interconnects on Si Interconnect Fabric

The Silicon Interconnect Fabric (Si-IF) is a heterogenous integration platform where heterogeneous bare dies are bonded to a Si substrate at fine die-to-wafer interconnect pitches (2-10 μm), Since Cu-Cu thermo compression bonding (TCB) is needed to enable fine die-to-wafer interconnect pitches, there arises a need for a novel low thermal-budget passivation thin film to protect the bonded Cu interconnect pillars against moisture ingress to prevent Cu oxidation. In this paper, we present a novel low-thermal budget (130 °C) bilayer thin film made of SiN_x/Parylene C, which is used for passivation of the Si-IF. Parylene C adhesion to SiN_x was optimized using an adhesion promoter under various annealing conditions. Adhesion of Parylene C to SiN_x was then tested using the ASTM D3359 standard. Adhesion of Parylene C to SiN_x substrate was evaluated after subjecting the bilayer to “85/85” Steady-State Humidity Life Test standard”. The tape test was performed on a passivated sample every 24 hours during humidity testing up to 144 hours. Results show that adhesion remains constant throughout test duration. “85/85” test was also used to study moisture ingress induced failure mechanisms in a period of 168 hours. X-Ray Diffraction (XRD) was utilized to detect oxidation in the blanket Cu samples passivated with bilayer thin film. XRD scans showed no signs of oxidation in the samples up to 168 hours of testing. In addition, Cu interconnects of various widths (10-100 μm) were passivated and tested for electrical resistance change after similar stress time. Change in average resistance was less than 3% after testing for 168 hours.