Effects of underlayer dielectric on the thermal characteristics and electromigration resistance of copper interconnect

Abstract

The effects of underlayer dielectric on the thermal characteristics and electromigration resistance of copper interconnects are investigated. It is shown that the thermal impedance of metal lines on polyimide is about three times that of metal lines on plasma-enhanced chemical vapor deposition of tetraethylorthosilicate (PETEOS) oxide. The open-circuit failure occurs after 75 s stressing at a current density of 1.4 x 10(7) A/cm(2) for polyimide underlayer specimens due to the high joule heating effect which causes the extreme temperature rise at, interconnects. Hence, decomposition of polyimide occurred which further accelerated the breakdown of interconnects. The thermal impedance is one of the major factors causing the electrical resistance to change during the electromigration (EM) test. The activation energies for electromigration of Cu are 0.87 eV for SiO2/Cu/PI2610 and 0.65 eV for SiO2/Cu/SiO2. After 500 thermal cycles, both the mean time-to-failure (MTF) and activation energy E-a decrease for EM, and lognormal standard deviation increases. At 225degreesC, the MTF of SiO2/Cu/PI2610 is about two times longer than that of SiO2/Cu/SiO2.