Comparison of the Three Classes (Rare Earth, Refractory and Near-Noble) of Silicide Contacts

It is well established that near-noble metals and refractory metals form two distinct classes of silicide contacts with silicon. Rare earth metals have been studied in the same manner and found to form a new class that is very distinct from the other two in terms of properties and characteristics. Some of these characteristics are the formation of a disilicide phase, as an apparently first and last phase, at a surprisingly low temperature (250–400°C). Marker motion study using implanted krypton and argon showed silicon to be the dominant diffusing species for ErSi2. The Schottky barrier height to n-Si is 0.40 ± 0.04 eV and to p-Si is 0.70 ± 0.04 eV for all six of the metals studied. The surface morphology after reaction indicates the formation of a tensile stress by the silicide reaction. Oxidation of the rare earth metals is a severe problem although a variety of passivation schemes have been shown to work.