Polyimides have been considered the most promising organic polymers for use as an inner-layer dielectric or over-metal passivation layer on ICs. These polymers have certain processing advantages over traditional inorganic dielectrics such as SiO2 or Si3N4. However, polyimide (PI) must meet the stringent standards that inorganic materials have met, including good adhesion to the substrate and resistance to diffusion of water. Failure to meet these standards may result in increased aluminum corrosion rate and consequent degraded reliability.
In this study, the corrosion rate of sputtered aluminum test patterns passivated with either PI or plasma-deposited silicon nitride (SiN) was measured at 85°C and 85% relative humidity (RH). The objectives of this work were to: (1) assess the failure rates of biased aluminum interconnection with PI or SiN passivation; (2) determine the failure mechanisms in each case; and (3), as a result, evaluate the suitability of PI passivation for high voltage ICs in non-hermetic packages. In this report, the test device fabrication and evaluation procedures are first described. Then the results are presented, including both the failure rate measurements and the failure analyses. Finally, the results are compared and discussed.