Electrical Methods for Mechanical Characterization of Interconnect Thin Films

We describe the use of electrical methods for evaluating mechanical reliability and properties of patterned copper and aluminum interconnects on silicon substrates. The approach makes use of controlled Joule heating, which causes thermal strains in the materials system due to differences in thermal expansion between the metal and constraining substrate and passivation. Our efforts concentrate on understanding damage formation in the interconnects and on the development of meaningful test methods. We make use of alternating currents in a frequency range (100 Hz to 10 kHz) that does not lead to electromigration but instead causes extensive thermal fatigue damage and failure in the metal interconnects.