Comparison of refractory metal and silicide capping effects on aluminum metallizations

The effects of various refractory metal and silicide capping layers on aluminum metallizations are investigated. Ti-Al, Mo-Al, Ta-Al, WSi₂-Al, and MoSi₂-Al layered structures are compared in terms of electromigration and stress-induced voiding. The authors have found that the Ti-Al layered structure can suppress stress-induced void formation in underlying Al conductors. The effect of the Ti-Al layered structure on the suppression of stress-induced voiding can be attributed to the formation of the intermetallic compound Al₃Ti, which prevents plastic deformation of the film. Electromigration results indicate that the capping layers of refractory metals and silicides such as Ti, W, WSi₂, and MoSi₂ improve the mean time to failure by 4-10 times compared with Al without capping