A review of some aspects of ternary metal-metal-Si and metal-B-Si systems

Abstract

The reactions in both metal-metal-Si (M-M-Si) and metal-boron-Si (M-Bi-Si) are discussed in terms of compound formation, solid solubility, and thermodynamical equilibrium. In M-M-Si systems, the formation of stable ternary compounds is accessible via two routes: the reaction of Si with an intermetallic compound or the reaction of a metal with a silicide. From a literature survey, it is apparent that only a minority of systems contain ternary phases with high heats of formation, a condition necessary to avoid phase separation into binary phases. For alloys or bilayers interactions with Si, intermetallic compound formation is rare, probably because of the identity of the moving species and the energetically more favorable M-Si bonding. Physical parameters affecting stability and solubility of silicides are the differences in metallic radii, electronegativity and number of valence electrons. For structures consisting of a thin silicide film on B-doped Si, we show that part of the stability predictions based on data obtained for M-B, B-Si, and M-Si couples could be misleading and are invalidated when compared to previously established phase diagrams.