To understand a void formation mechanism in electroplated Cu interconnects used for Si-ULSI (ultra-large scale integrated) devices, microstructures of Cu films which were prepared by the electroplating technique using plating baths with or without organic additives were investigated by transmission electron microscopy (TEM). In the as-deposited samples, a high density of micro-voids were observed at the interface between a seed Cu layer and the electroplated Cu film which was prepared in the plating bath with organic additives. Growth of the micro-voids was observed in the samples annealed at elevated temperatures in an atmosphere containing hydrogen, whereas no void growth was observed in the samples annealed in Ar atmosphere. No void formation was observed in the Cu films which were prepared in the plating bath without organic additives. The present results suggested that the void formation in the electroplated Cu films was induced by existence of impurities such as organic additives or oxygen in the Cu films, and that the void growth was strongly enhanced by annealing in hydrogen.
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