The improvement of the stability in the SiC/ Silicon-On-Insulator system by partial or complete replacement of the SiO2 by Si3N4 was studied by Transmission Electron Microscopy (TEM). The beneficial effects of the nitrogen implantation for the reduction of cavities, which are formed in the Si side at the SiC/Si interface during the epitaxial growth of 3C-SiC, are shown. The high dislocation density developed in the Si-overlayer during nitrogen implantation does not affect the quality of the 3C-SiC overgrown.