Effect of Si addition on the precipitation of Al2Cu-phase in Al-Cu-Si thin films

The effects of Si addition and of deposition temperature on the precipitation processes of Al2Cu (θ) and Si particles in Al-Cu-Si alloy films were studied with in-situ hot stage transmission electron microscopy (TEM). Deposition of an Al-1.5Cu-1.5Si (wt%) film at 305◦C, in the three-phase, Al(α)-Al2Cu-Si region resulted in formation of fine, uniformly distributed spherical θ-phase particles due to the coprecipitation of the θ and Si phase particles during deposition. For deposition in the two-phase, Al(α)-Si region (435◦C), fine θ-phase particles precipitated during wafer cooldown, while coarse Si nodules formed at the sublayer interface during deposition. In-situ heat treatment of the film revealed that excess Si existed in a supersaturated Al matrix. Si addition decreased film susceptibility to corrosion induced by the θ-phase precipitates, since extensive Cu segregation can be reduced by coprecipitation at 305◦C and the Al matrix supersaturated with Si reduced galvanic action with respect to the θ-phase precipitate. C 2005 Springer Science + Business Media, Inc.