The Failure of Thin Alluminum Current-Carrying Strips on Oxidized Silicon

A new mode of metal failures is described - electrical opens in Al strips on SiO2 - resulting from the passage of direct current at high current density. The lifetime of aluminum strips was found to depend not only on the magnitude of the applied current, but also on its direction. At lower current levels (longer lifetimes), a much longer lifetime was seen when alternating current was employed (60 cycles/sec) than for direct current. This effect, toether with the fact that aluminum films carrying direct currents have a blistered appearance suggests that an electrochemical or electromigration mechanism is involved in the disruption of the aluminum strips. While opens are very rarely seen at "normal" current densities of 105 a/cm2, the failure mode is accelerated at high current densities (106 a/cm2) and elevated temperatures (200°c). The distruption of the aluminum films does not originate from diffusion of the aluminum into silicon (emitted or base region) or addition, the gold ball bonds can act as sinks for the thin aluminum films surrounding them, and, hence, cause a certain enhancement of failures.