HfO2 films were grown on SiO2/4H-SiC and SiON/4H-SiC layers by deposition of metallic Hf in an electron beam evaporation system followed by thermal oxidation. X-ray photoelectron spectroscopy confirmed the formation of stoichiometric HfO2 films. There is no evidence of formation of hafnium silicide or carbon pileup at the surface as well as at the interfacial layer. Electrical measurements show the presence of fewer trapped charges in the HfO2/SiON gate dielectric stack compared to HfO2/SiO2 stack with a comparable interface state density. The HfO2/SiON stack layer improves leakage current characteristics with a higher breakdown field and has smaller flatband voltage shift under electrical stress, indicating improved reliability.