A novel via failure mechanism in an Al-Cu/Ti double level metal system

An open-circuit failure mechanism for metal-to-metal via contacts in an Al-Cu/Ti metallization system during high-temperature stressing was studied. The test chips used were fully functional state-of-the-art nonvolatile memory devices fabricated on a submicron double-poly/double-metal technology. The upper metal layer (metal 2) was a 0.9 mu m-thick film of Al-0.5% Cu on a 0.1 mu m-thick Ti barrier layer, and the lower metal layer (metal 1) was 0.40 mu m-thick Al-0.5% cu film on a 0.12 mu m-thick TiN barrier layer. The temperature effect on void formation was investigated and the activation energy of open via contacts was determined. The failure mechanism can be explained by a reaction of the titanium barrier layer in metal 2 with the aluminum film in metal 1 rather than the well-known stress-induced voiding mechanism.<>