The deposited Si/Fe ratio has been found to have a significant influence on crystalline growth of β-FeSi2 film on Si substrate. Stoichiometry is always satisfied by interdiffusion of Si, under both Si-lean and Si-rich conditions. However, Si diffusion from the substrate into the deposited layer, which compensates for deficient Si, induces an undulated interface, as well as Fe and Si vacancies. On the other hand, excess Si is driven to the β-FeSi2/Si interface, which results in a lamellar structure with a large number of small grains. Fe and Si vacancies are significantly reduced by excess Si. These results suggest that precise control of the Si/Fe ratio is essential for good crystallinity and fewer vacancies.