A stress-induced diffusion model for failure of interconnects in microelectronic devices

Abstract

Voiding and open-circuit failures from cracking of interconnects in microelectronic devices are often observed during isothermal aging and thermal fatigue tests with or without electric current flow. Although the effects of many factors on the failure rate have been investigated experimentally, it is not yet known how to extrapolate the results of accelerated tests to normal operating conditions. Theoretical failure models for isothermal aging and thermal fatigue tests are constructed from diffusion theory and fracture mechanics in this paper. The results from many investigations can be incorporated into this model to explain many of the observed phenomena, for example, effects of the aging temperature, interconnect stress, linewidth, line thickness, passivation, interlayer dielectric stress, etc. Patterned Al-Cu interconnects were thermally cycled in air. It was found that the failure mechanisms of interconnects under isothermal aging and thermal fatigue are the same. Effects of hold time, frequency, and thermal fatigue temperatures on failure rate were studied both experimentally and theoretically. The predicted results according to the present failure model show excellent agreement with experiments.