Radioactive 31Si marker studies of metal silicide formation—computer simulation

Abstract

The results obtained from radioactive 31Si (half-life, 2.62 h) marker studies of silicide formation are often difficult to interpret, owing to spreading of the activity in the silicide. In an attempt to interpret such complex activity profiles a computer programme, simulating various diffusion mechanisms, was written. A numerical approach was used whereby silicide growth occurs in small increments and the concentration of radioactive silicon in each newly formed increment is determined by exchange between atoms in the silicon flux passing through the already formed silicide and silicon atoms in the silicide itself. Pure interstitial or grain boundary diffusion of silicon implies a percentage exchange of silicon of 0%, whereas 100% exchange describes “pure” substitutional (vacancy) silicon diffusion. Percentage exchanges between these two values lead to activity profiles which are spread out to a larger or lesser degree throughout the silicide. The calculations also take into consideration metal diffusion. The computer simulation results based on the above-mentioned model helped us to interpret the diffusion mechanisms involved during Ni 2Si and Pd 2Si formation, where complicated 31Si activity profiles are obtained. Not only can information be obtained regarding the diffusion species and its mechanism of diffusion, but an estimate can also be made of the relative contribution of each diffusion mechanism towards silicide formation.