In this work, we have demonstrated a simple approach to suppress interfacial layer (IL) formation for HfOx and HfOxNy gate dielectrics by sputtering HfOx and HfNx films, respectively, followed by further annealing. The material characteristicsof dielectric films were investigated by glacing incident angle X-ray diffraction (GIAXRD), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), and spectroscopic ellipsometry. Both HfOx and HfOxNy films show amorphous structures after annealing up to 700 oC; nevertheless, the HfOxNy film presents the superiority to prevent interfacial layer (IL) formation over the HfOx film. Formation of a self-doped nitrogen-contained IL in the HfOxNy dielectric stack is detected by XPS analysis. Furthermore, the HfOxNy dielectric layer presents higher refractive index (about 2.0) than that of HfOx (about 1.8) in the range of visible light, indicating its denser structure.