Growth of Si₃N₄ Thin Films on Si(111) Surface by RF-N₂ Plasma Nitriding

Ultra-thin Si3N4 films were grown on Si(111) surface by radio frequency (RF)-N2 plasma exposure at 900 °C with 1–1.2 sccm of a flux of atomic nitrogen. We discuss the effect of various conditions such as N2 flow rate, nitriding time and RF power on the optical, chemical, and structural properties of a nitrided Si3N4 layer. The optical properties, surface morphology and chemical composition are investigated by using ellipsometry, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Cross-sectional TEM images show that an RF power of 350 W induced some damage to the Si(111) surface. The thickness of nitrided Si3N4 was measured to be about 5–7 nm. XPS results shown that the binding energy of Si 2p3/2 located at 101.9 ± 0.1 eV is attributed to the Si–N bonds in the Si3N4 compound. Smooth Si3N4 ultra-thin films were obtained at a nitridation time close to 1 h with an RF power of 300 W, with a measured refractive index (n) nearly to 1.88 at 632 nm. The increase in refractive index with decreased RF-plasma power and nitrogen flow rate is probably attributed to the change in the stoichiometry of the film and less surface damage.