Epitaxial growth of Si on Si(100) wafers was carried out at 700 degrees C in an Ar microwave electron cyclotron resonance plasma chemical vapor deposition system. Both plasma exposure prior to growth and epitaxial growth were monitored by real-time single-wavelength ellipsometry, first to determine an optimum end point for Ar plasma cleaning which would favor quality epitaxial growth, and second to follow the growth of the epitaxial film. Spectroscopic ellipsometry combined with cross-sectional transmission electron microscopy and atomic force microscopy were used to characterize the epitaxial films, the epitaxial film/substrate interface, and the surface morphology. Secondary-ion mass spectroscopy was used to evaluate the contamination levels st the film/substrate interface. Epitaxial films were successfully grown on both, smooth and rough (20-30 nm roughness layer) Si substrates. For both cases the top surface of the epitaxial film was smooth, but the interfaces were different.