We have studied the deposition of Si1-x-yGexCy epitaxial films using ultrahigh vacuum chemical vapor deposition at temperatures from 475 to 600 degrees C. The growth rate is found to decrease substantially with the addition of methylsilane. Incorporation of C, as measured by secondary ion mass spectroscopy (SIMS), is found to increase linearly with flow for low C concentration (similar to 2%) but the dependence becomes sublinear at higher CH3SiH3 flow rates. The substitutional incorporation of C, determined using X-ray diffraction is found to increase with decreasing temperature. For the films studied here we find substitutional incorporation up to 1.8% in Si1-yCy films This is for a total incorporation of 2.5%, as measured by SIMS. Complete substitutional incorporation of C is obtained for up to 1.2%. For Si1-x-yGexCy films, we find that the amount of substitutional C that can be incorporated decreases with increasing temperature. At 550 degrees C we find a maximum of 0.7% C can be incorporated substitutionally, whereas at 475 degrees C we are able to incorporate higher concentrations, similar to that for Si1-yCy layers. Morphology studies also indicate that lower growth temperatures are preferable in the growth of Si1-yCy films.