Iron silicide thin films were deposited on Si (1 1 1) substrates at 750degreesC and 800degreesC by metal organic chemical vapor deposition (MOCVD). SiH4 and iron-pentacarbonyl [Fe(CO)(5)] were employed as Si and Fe sources, respectively. The composition and the constituent phase of the film were investigated. Based on these results, formation mechanism of the film was discussed. The constituent phase against the film composition was in good agreement with that of the phase-diagram in Fe-Si system. There was no wide range of nonstoichiometry of beta iron silicide (beta-FeSi2). A diffusion of Si from the substrate was dramatically increased when the deposition temperature increased from 750degreesC to 800degreesC. This diffusion leads to the relatively large single-phase region of beta-FeSi2 against the input gas concentration ratio of Si to Fe sources. (C) 2002 Elsevier Science B.V. All rights reserved.