Influence of silicon concentration and layering of molybdenum silicide on the reliability of Al–Si–Cu interconnections

The influence of Si concentration on the stress induced migration resistance and the electrical resistivity change from silicon precipitates of Al–Si–Cu and Al–Si–Cu/MoSi2 interconnections was investigated. Electromigration of Al–Si–Cu/MoSi2 was examined as a function of MoSi2 thickness. A 1.5 wt. % Si concentration in aluminum alloy prevented grain growth and improved the stress induced migration resistance of the interconnections. However, this amount of Si addition caused resistance increases, because Si precipitates grew to the point that they were the same size as the interconnection linewidth. Layering of the Al–Si–Cu alloy containing 0.7 wt. % Si with MoSi2 improved the stress induced migration resistance of aluminum interconnections and prevented the resistance increases. Furthermore, increasing MoSi2 thickness improved electromigration resistance of layered interconnections. For MoSi2 thickness of >30 nm, electromigration resistance was better than that of single layer Al–Si–Cu interconnections.