| Cu-Cr metastable alloys are interesting both from a basic science viewpoint (i.e., alloy theory for elements with very limited mutual liquid and solid solubilities) and from a technological viewpoint (i.e., "stainless" copper for corrosion and thin film circuit fabrications). Single phase Cu-Cr metastable alloys have been successfully grown by bias rf sputtering. The effect of substrate bias and film composition on the early stages of film growth, on the film microstructure and morphology, and on the phase transformation process of the metastable films were studied using (S)TEM, SEM, AES, SIMS, ISS, WDX, X-ray diffraction, and resistivity measurements. The solid solubilities at room temperature were extended from less than 0.04 atomic percent to as much as 45 atomic percent. Cu-rich films were FCC and Cr-rich films were BCC. The lattice parameters of these films showed Vegard's law behaviour. Increase in substrate bias and in temperature caused preferential sputtering and evaporation of solute atoms, resulting in reduction of solubility and formation of two phases. The morphology and microstructures depended on film composition and very sensitively on substrate bias. Finally, a metastable phase map, a morphology model, and a growth rate model as functions of substrate bias and film composition were proposed. The map and the models could be used to predict how processing variables will affect the film's optical, electrical, mechanical and corrosive properties. |
