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

Abstract

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.