We have performed the two-step epitaxial growth of CoSi2 on Si(100) surfaces with Al interlayers. Microstructures of the surface and the interface during the growth have been investigated by scanning tunneling microscopy and transmission electron microscopy (TEM). At the first-step growth, the introduction of an 1-monolayer (ML)-thick Al interlayer prior to a 3-ML-thick Co layer deposition on the Si clean surface results in the formation of two dimensional islands of epitaxial CoSi2 with higher coverage, compared to the case without the Al interlayer. Cross-sectional TEM observations revealed atomically-flat CoSi2-Si interfaces. At the second step, CoSi2 is epitaxially grown on these islands that acts as a template layer. In-depth growth of CoSi2 domains is also observed to occur forming {111} facets at the CoSi2-Si interfaces. Effects of the Al interlayer on the growth morphology of epitaxial CoSi2 are discussed. (C) 2003 Elsevier Science B.V. All rights reserved.