The effects of Si addition and of deposition temperature on the precipitation processes of Al2Cu (theta) 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 degrees C, in the three-phase, Al(alpha)-Al2Cu-Si region resulted in formation of fine, uniformly distributed spherical theta-phase particles due to the coprecipitation of the theta and Si phase particles during deposition. For deposition in the two-phase, Al(alpha)-Si region (435 degrees C), fine theta-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 theta-phase precipitates, since extensive Cu segregation can be reduced by coprecipitation at 305 degrees C and the Al matrix supersaturated with Si reduced galvanic action with respect to the theta-phase precipitate. (c) 2005 Springer Science + Business Media, Inc.