Electromigration reliability of low capacitance air-gap interconnect structures

The electromigration lifetimes of aluminum lines with low capacitance air-gap structures is evaluated and compared to the case of traditional gapfill passivation. Electromigration lifetime of air-gap interconnect structures is determined to be significantly higher than that of the gapfill case. Failure analysis indicates that the elasticity of the airgap sidewall passivation reduces the line stress incurred during electromigration and increases the time necessary to reach the critical stress for void nucleation. Simulations support the experimental results. Capacitance measurements and simulations show the air-gap structures reduce capacitance by as much as 40%.