Reliability Model for Polyimide–Metal Interconnect Shorts in GaAs ASICs

A physical reliability model has been developed to calculate the time to failure of polyimide–metal multilevel interconnected GaAs components due to the shorts between interconnect metallizations through a polyimide interlayer. The failure mechanism for the shorts between neighboring metals through the polyimide is described as a stress‐assisted diffusion process along a polyimide microcrack due to the combination of process defect and high thermal stress concentration. The finite element method has been used to determine the temperature increase during operation and the resulting thermal stress due to the difference in coefficients of thermal expansion (CTEs) of the materials used in the multilevel metallization GaAs module of devices. Numerical methods have been used to solve the partial differential diffusion equations with stress gradients in order to obtain the time to failure of the devices. The time to failure for the shorts between metal level 4 and metal 2 at 123 °C operating temperature was calculated to be 20 h for the conditions analyzed. The activation energy for the failure of the shorts between two level metals was calculated to be 0.48 eV. Copyright © 2004 John Wiley & Sons, Ltd.