Magnesium silicide thin film formation by reactive diffusion

Abstract

An industrial Rapid Thermal Processing has been used to grow nano-scale magnesium silicide (Mg2Si) thin films for thermoelectric applications, using reactive diffusion in vacuum. This formation is compared to that obtained by treatment in conventional high-vacuum furnace. Reaction between Mg and Si substrate occurs approximately at 200°C and its rate depends on the temperature and the heating rate of annealing, while the treatment duration determines the completeness of the reaction. These observations confirm the diffusion governed process of Mg silicidation. Two simultaneous processes occur in the films: Mg desorption from the surface and silicide formation at the Si/Mg interface. Applying the annealing temperature of 350°C is likely the sufficient condition to complete the reaction. The obtained films have shown stability regarding decomposition until the temperature of 450°C. However, in the presence of oxygen-contaminated atmosphere the Mg2Si tends to decompose at lower temperatures starting from circa 300°C and dissociated magnesium oxidizes. The rapid thermal annealing of Mg/Si layers allows to decrease the duration of silicide formation, while the risk of decomposition of Mg2Si film and surface oxidation due to high heating rate and presence of oxygen is increased. The optimum parameters for nano-scale Mg2Si thin films preparation have been proposed.