High-temperature and electrochemical oxidation of transition metal silicides

High-temperature and electrochemical oxidation of transition metal silicides, which are widely used in microelectronics as ohmic contacts and protective coatings for high-temperature alloys, are discussed in this review. The process of oxide film formation during annealing or anodizing is extremely important for both applications of silicides. It is discussed for three disilicides: MoSi2, WSi2, and TiSi2. It has been shown that different types of oxide films may form on the disilicide surface depending on the thermodynamic (formation enthalpies of silicides and associated oxides) and kinetic (diffusion coefficients of silicon in silicide and oxygen diffusivity in oxide) factors: onephase (MoSi2), mixed (WSi2), and multilayer (TiSi2) films. The "silicide pest" phenomenon is discussed in terms of thermodynamic, kinetic, and structural factors influencing the pesting. Analysis of electrochemical oxidation mechanisms for silicides in various electrolyte media reveals numerous similarities between anodic and high-temperature oxidation mechanisms. It is shown that slow silicon transport during anodic treatment at room temperature leads to the formation of multiphase mixed oxide films under electrochemical polarization.