SILICON OXYNITRIDE FILMS DEPOSITED BY MERCURY PHOTOSENSITIZATION CHEMICAL-VAPOR-DEPOSITION

Silicon oxynitride films have been deposited by the process of mercury-sensitized photochemical vapour deposition using a gaseous mixture of SiH4 (2% in argon), NH3 and N2O under 253.7 nm UV light irradiation. Films of different compositions were deposited by changing the N2O:(N2O + NH3) flow rate ratio while keeping N2O + NH3 and SiH4 flow rates constant. The physical, chemical and optical properties were found to depend strongly on N2O content in the gas mixture. The refractive index varied from 1.90 to 1.49, the dielectric constant varied from 6.7 to 4.5 and the optical band gap increased from 4.8 to 5.7 eV as the flow rate ratio N2O:(N2O + NH3) was varied from 0 to 0.25. Also, the Si-N bond shifts to higher frequency owing to incorporation of oxygen as the electronegativity of the oxygen atom is greater than that of the nitrogen atom.