The present disclosure generally relate to methods of processing a substrate in an epitaxy chamber. The method includes exposing a substrate having one or more fins to a group IV-containing precursor and a surfactant containing antimony to form an epitaxial film over sidewalls of the one or more fin structures, wherein the surfactant containing antimony is introduced into the epitaxy chamber before epitaxial growth of the epitaxial film, and a molar ratio of the surfactant containing antimony to the group IV-containing precursor is about 0.0001 to about 10.