We present process optimization for rapid homoepitaxial growth of thick 4H-SiC films on 4 degrees off-cut substrates via hydrogen chloride chemical vapor deposition (HCVD). The gas used is a mixture of HCl additive, SiH4, C2H4 and H-2. After characterization of the 4H-SiC films using Nomarski, AFM, Raman and XRD, we investigate the effect of HCl additive, Cl/Si ratio, on the quality of the epitaxial film and the growth rate. With the optimized chlorine based method HCVD, the 4H-SiC epitaxial growth rate was up to 52 mu m/h in a home-made vertical hot-wall HCVD system. At a steady growth rate of 46 mu m/h, a 4H-SiC epitaxial film with a thickness of 100 mu m was obtained. The epitaxial films were of homogeneous 4H polytype, with a maximum root mean square roughness (RMS) of 1.3nm.