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Microstructure Evolution during Electric Current Induced Thermomechanical Fatigue of Interconnects



Robert Keller, Roy H. Geiss, Yi-Wen Cheng, David T. Read


We demonstrate the evolution of microstructure and deformation associated with the use of electrical methods for evaluating mechanical reliability of patterned interconnects on rigid substrates. Thermomechanical fatigue in aluminum and copper interconnects was induced by means of low frequency (100 Hz), high density (> 10 MA/cm2) alternating currents, which caused cyclic Joule heating and associated thermal expansion strains between the metal lines and oxidized silicon substrate. Such conditions caused cyclic temperature changes of approximately 100 K, corresponding to cyclic stress amplitudes approaching 200 MPa. The failure mechanism involved formation of localized plasticity, which caused topography changes on the free surfaces of the metal, leading to open circuit eventually taking place by melting at a region of severely reduced cross-sectional area. Both aluminum and copper responded to power cycling by deforming in a manner highly dependent upon variations in grain size and orientation. Isolated patches of damage appeared early within individual grains or clusters of grains, as determined by a quasi in situ scanning electron microscopy and automated electron backscatter diffraction measurement. With increased cycling, the extent of damage became more severe and widespread. We document some examples of the types of damage that mechanically confined interconnects exhibited when subjected to thousands of thermal cycles, including growth and re-orientation of grains in a systematic manner. We observed in the case of Al-1Si certain grains increasing by nearly an order of magnitude in size, and reorienting by greater than 30¿. The suitability of electrical methods for accelerated testing of mechanical reliability is also discussed.
Proceedings Title
Materials, Technology, and Reliability of Advanced Interconnects
Conference Dates
March 28-April 1, 2005
Conference Location
San Francisco, CA, USA
Conference Title
Mater. Res. Soc. Conf.


EBSD, electrical testing, interconnect reliability, thermomechanical cycling, thermomechanical fatigue, thin film fatigue


Keller, R. , Geiss, R. , Cheng, Y. and Read, D. (2005), Microstructure Evolution during Electric Current Induced Thermomechanical Fatigue of Interconnects, Materials, Technology, and Reliability of Advanced Interconnects, San Francisco, CA, USA, [online], (Accessed April 12, 2024)
Created March 31, 2005, Updated October 12, 2021