Elimination of stress-induced voids on AlCu multilevel interconnect lines

Abstract

Multilevel metal (MLM) structures utilizing four layers of large grain size Al 1.5% Cu metallization have displayed `in process' stress voiding in metal layers two through four upon completion of final passivation and anneal. Changing the deposited dielectric stress from 2E8 dynes/cm2 to a slightly more compressive 1.25E9 dynes/cm2 eliminated the formation of `in process' stress voids. However, thermal stressing at 200 degree(s)C still produced stress voiding in metal layers two and three. The addition of a 125 angstrom TiW cap to the second, third, and fourth metal layer was shown to eliminate both `in process' stress voids and long term 200 degree(s)C thermal stress induced metal line voids on all material with standard dielectric thicknesses. The results comparing various dielectric stress levels and metal structures with and without a TiW cap are reported here.