Growth of si₃ n₄ thin films on si(111) surface by rf-n₂ plasma nitriding

Ultra-thin Si₃ N₄ 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 Si₃ N₄ 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 Si₃ N₄ was measured to be about 5–7 nm. XPS results shown that the binding energy of Si 2p_3/2 located at 101.9 ± 0.1 eV is attributed to the Si–N bonds in the Si₃ N₄ compound. Smooth Si₃ N₄ 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.