Impact of temperature cycling on copper interconnect

Temperature cycling is widely used as a qualification test in the microelectronic industry. This paper investigates an intriguing failure mode observed in such a test. FIB cross-section of test structure and SEM observation were performed for in-situ morphology analysis before and after temperature cycling. It was found that copper films surface morphology damaged substantially. Extrusions and voids were found in these films. Then, a two-dimensional finite element analysis was used to analyze the stress distribution in the test structure, taking into account the thermo-mechanical confinement effect after temperature cycling. Finally, the concept of ratcheting was used to explain fatigue phenomenon of Cu line structures.