Si/Si0.97C0.03 superlattices grown on Si(001) substrates by Sb surfactant assisted molecular beam epitaxy are characterized by in situ reflection high energy electron diffraction (RHEED), atomic force microscopy, transmission electron microscopy (TEM), and high resolution x-ray diffraction. The RHEED shows that, in the absence of Sb, the growth front roughens during Si0.97C0.03 growth and smooths during subsequent Si growth. In contrast, when Sb is present, the growth front remains smooth throughout the growth. This observation is confirmed by cross-sectional TEM, which reveals that for samples grown without the use of Sb, the Si/Si0.97C0.03 interfaces (Si0.97C0.03 on Si) are much more abrupt than the Si0.97C0.03/Si interfaces. In the case of Sb assisted growth, there is no observable difference in abruptness between the two types of interfaces. Atomic force microscopy micrographs of the Si0.97C0.03 surface reveal features that could be the source of the roughness observed by RHEED and TEM.