Composition Evolution of Mo-Si-O Films Under Heat Treatment

Molybdenum disilicide (MoSi2) films were synthesized by heat treatment of a Si/Mo/Si and Mo/Si sample systems at different temperatures in air. The onset temperature of MoSi2 formation started from 350 celcius and continued to 900 celcius for both systems. Diffusion of Si into Mo in the Mo/Si system occurs at the same time and MoSi2 forms. MoO3 forms at 350 celcius and evaporates off the film surface at 500 celcius, leading to a mass loss of Mo in the Mo-Si-O system. An impervious SiOx layer is formed on the film surface at 600 celcius and higher, preventing further oxidation of the film and facilitating the formation of MoSi within an oxygen-free environment. The Si cover layer in the Si/Mo/Si system prevents the outside O in air diffusing into the film and the Mo evaporating off the film until 900 celcius. The thermally driven diffusion mechanism is discussed.