A thermo mechanical finite element modeling approach to solving stress induced passivation failures

Abstract

Multi-layered systems are susceptible to cracking and or delamination upon temperature cycling. Passivation integrity test (PIT) is widely leveraged to assess and qualify the mechanical integrity of the passivation films (oxide, nitride) deposited on metal conductor. Cracking/delamination in the passivation film over the metal line results in moisture diffusion and may lead to metal corrosion. Therefore, it is imperative to identify the key geometric and process parameters that significantly affect the passivation integrity and understand the physics-of-failure in order to have a reliable structure. This paper demonstrates the failure assessment and mitigation in passivation films for a leading technology node chip during PIT. A finite element (FE) stress-strain model of the test vehicle (TV) is built to provide fundamental understanding of the effect of the critical input design parameters including the Aluminum (Al) line layout, Al space, Al width, and the passivation thickness on the passivation stress level. The FE model is validated with the experimental pass/fail data and is further leveraged to mitigate the passivation cracking issue. The effect of Al plastic behavior on the interfacing passivation layer is highlighted to accurately predict and understand the failure mechanism.