Slow (low-rate) reactive deposition of a metal onto a Si substrate can result in direct formation of a metal disilicide, thereby skipping the metal-rich phases in the formation sequence. These observations have been explained thermodynamically by using the effective heat of formation model. As a result of this concentration-controlled phase selection, it is possible to form disilicides, such as CoSi2, NiSi2, or β-FeSi2 at much lower growth temperatures than possible in conventional solid-phase reaction of a metal layer deposited onto Si at room temperature (i.e., lower than the nucleation temperature). Moreover, epitaxial growth of CoSi2/Si(100), which is not possible by solid-phase reaction, becomes achievable when depositing Co atoms sufficiently slowly onto a heated Si substrate. © 1999 American Institute of Physics.