The effect of residual tensile stress on electromigration lifetime of metal lines passivated by various oxides

Residual stress of metal interconnects passivated by four different oxides was precisely measured by X-ray diffraction method, and the effect of this stress on electromigration (EM) lifetime of the Al-Cu lines was investigated. The EM lifetime was not a monotonous function of the residual stress; instead, it increased with the stress at low stress region, but decreased at the higher stress region. The stress of 200-250 MPa, which is the mid-value between compressive and tensile yield strength of the Al-Cu lines, provided the maximum EM lifetime. This result gives an experimental support to a theoretical calculation on the stress evolution due to EM and a guideline to maximize the EM lifetime for applications.