Adhesion of copper films on silicon is investigated by microindentation measurements. Load-displacement tests with loads in the range of 1-1000 mN are performed on immersion plating copper films deposited on Si(100) from fluoride containing solutions, with or without adhesion-promoting additives. The results are analyzed with the aid of a composite hardness model for soft films on hard substrates. The composite Vickers microhardness is influenced by the adhesion of the copper film to the substrate: stronger adhesion corresponds to higher composite hardness and more extended deformation zone at the film/substrate interface. Thus, microhardness measurements provide a useful way to quantify the effect of solution additives (such as ascorbic acid or sodium sulfite) and heat treatment on copper film adhesion, and to rank additives accordingly. (C) 2003 Elsevier Science B.V. All rights reserved.