Semiconductor interlevel shorts caused by hillock formation inAl-Cu metallization

摘要

A failure mode in AlCu and AlCuSi metallization in whichinterlevel metal short-circuiting occurs between two or more levels ofmetal is described. Shorts are caused by theta-phase (Al₂Cu)hillocks that nucleate and grow during high-temperature vacuum heattreatment and processing. Hillock growth occurs at high-energy sitessuch as silicon precipitates and grain boundary nodal points. The growthof Al₂Cu hillocks depends on heat treatment/processingtemperature and aluminum film purity. Methods used to limit theta-phasehillock formation and growth concentrate on the grain-boundary diffusionand nucleation mechanisms involved. Decreasing heat treatment/processingtemperature slows the atomic diffusion required for hillock growth andreduces, but does not prevent, theta-phase formation. Deposition of ahard coating as a cap on the layered structure of an aluminium-basedmetallization mechanically suppresses hillock formation. A layer of purealuminum deposited beneath the aluminum-copper layer acts as a sink forcopper and delays hillock formation