Electromigration in aluminum/silicon/copper metallization due to the presence of a thin oxide layer

The effect of a thin layer of SiO₂ (50 nm) on the electromigration behavior of Al/ 0.8wt.%Si/0.5wt.%Cu metallization, passivated by spin-on-glass, phosphorus silicate glass and silicon nitride as part of the complementary metal oxide semiconductor technology fabrication process was studied. It is found that voids were formed along the edge of the metallization line as opposed to formation at triple point of grain boundaries. At the same stress current of 1 × 10⁶ A/cm², thicker metallization layer (600 nm) showed an improvement in median time to failure (MTF) (1.4 times) with smaller void size (0.2 to 0.4 μm) over one without an underlying oxide, whereas if the metallization thickness is thin (300 nm), the MTF is degraded (0.6 times) with larger void size formed (0.3 to 1.0 μm).