High quality pseudomorphic Si1-yCy and Si1-x-yGexCy layers were grown on (100) Si between 530 and 650 degrees C by rapid thermal chemical vapor deposition in the SiH4/GeH4/SiH3CH3/H-2 system. These layers contained up to 30 at. % Ge and up to 2.2 at. % C. Strain engineering was achieved. The strain could be tailored continuously from compressive (up to 2.2% in Si1-xGex) to tensile (up to -0.8% in Si1-yCy and -0.35% in Si1-x-yGexCy). The relationship between the process parameters and the physical properties of the layers was investigated. A process window for growing high quality layers was defined in terms of the partial pressures of SiH4 and SiH3CH3. It was found to be independent of Ge content, growth temperature, and growth rate. No carbon contamination was observed. No interference between Ge and C incorporation was observed. A model for the incorporation of substitutional C in the films which is based on the chemical reaction of SiH4 and SiH3CH3 on the surface is proposed.