The effect of surface preparation on the growth of epitaxial Si films by plasma enhanced chemical vapor deposition was investigated. The surface preparations considered were an ex situ ozone scrub and an in situ Ar/H-2-plasma clean. Both methods were found to be effective at removing carbon contamination from the substrate surface which is, critical for epitaxial growth. The thin-film quality was. determined by Rutherford backscatter spectrometry, high-resolution x-ray diffraction, and transmission electron microscopy. To gain insight into mechanisms controlling the in situ cleaning process, hydrogen was replaced by deuterium in the plasma clean prior to film growth. The film/substrate interface was then analyzed by secondary ion mass spectrometry. Surprisingly, the plasma clean had little influence on the interfacial hydrogen concentration established by the previous hydrofluoric acid dip. It was found that hydrogen remains bound to C and O contaminants at the interface caused by the initial growth surface, and that neither an ex situ process containing an ozone scrub nor an. in situ process containing a hydrogen-plasma clean could completely remove them. (C) 2003 American Vacuum Society.