Abstract: In order to study the failure of IC devices induced by the stress in VLSI metal interconnect, In-situ observation of the stress changes of VLSI Al interconnect was studied under the electromigration and thermal conditions by using a synchrotron radiation x-ray diffraction technique. The tensile stress in deposited Al interconnects was measured in the room temperature. During the annealing process, the tensile stress gradually decreased and then conversed into the compress stress at the temperatures between 300 ℃ and 350 ℃. During the electronmigration tests in the range of 3×10⁵ A/cm² and 4×10⁶ A/cm² for 275 min, the tensile stress at the anode of Al interconnects changed into the compress stress, which then increased with the increasing of current density. Furthermore, the electronmigration failure characteristic and the stress relax of Al interconnects was observed by using the SEM.