Epitaxial Al and Cu films grown on CaF2/Si(111)

Abstract

AbstractThe ability to grow single-crystalline Al and Cu films is of significance for several areas of materials research, such as the resistivity size effect in thin metal films, electromigration failure of interconnects, and magneto-resistance studies. Here, we explore the microstructure and resistivity of thin Al and Cu films grown on CaF2/Si(111). A three-step technique of CaF2 growth is described that permits deposition under imperfect vacuum conditions and promotes smoothness of subsequent thin metal films. Reflection high-energy electron diffraction shows that epitaxial Al(111) is obtained directly on CaF2, while epitaxial Cu(111) is obtained only by growing on a 1 nm thick Al seed layer pre-deposited on CaF2. Transmission electron microscopy reveals that 75 nm thick Al films have 150 nm wide sub-grains misoriented by less than 1 degree. For 75 nm thick Cu, the grains are only 30 nm wide and are misoriented by as much as 10 degrees. Room temperature resistivity measurements of the 10-300 nm thick Al films agree with the Fuchs-Sondheimer model in which conduction electrons scatter totally diffusely at the film interfaces. For 50-1000 nm thick Cu films, the resistivity size effect is substantially greater than the prediction of this model, which may be explained in terms of grain boundary scattering.