In this work a comparison between atmospheric pressure (AP) and low pressure (LP) carbonization as the first step in the growth process of 3C-SiC on Si substrates is presented. Three different Si substrate orientations have been studied and compared. Characterization analysis has been performed by Atomic Force Microscopy (AFM), X-ray Diffraction Spectroscopy (XRD) and Transmission Electron Microscopy (TEM). XRD and AFM analysis show a lower roughness and a better quality for LPCVD carbonized samples. Substrate orientation plays an important role both in the generation as well as in the effect of such defects in the subsequent growth process, leading to a rougher SiC surface for growth on (110) Si while micro-twin effects are limited for growth on (111) Si, resulting in an extremely flat film.