Deposition mechanisms and properties of oxygenated carbon nitride films from rf discharges of acetylene, nitrogen, oxygen and argon mixtures

• Published in: Journal of non-crystalline solids Vol. 262; no. 1; pp. 216 - 227
• Main Authors: Wang, Jianjun, Durrant, Steven F., de Moraes, Mário A.B.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.02.2000; Elsevier
• Subjects: Chemical vapor deposition (including plasma-enhanced cvd, mocvd, etc.); Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity); Optical constants: refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of bulk materials and thin films; Optical properties of specific thin films; Optical properties of specific thin films, surfaces, and low-dimensional structures; Physics; T200; 78.66; 81.15.A; 52.75.R; 77.84.B; N180; Inorganic compounds; Refractive index; Ethylene propylene rubber; Spin density; Infrared spectra; Experimental study; Fabrication property relation; Film growth; Dangling bonds; Energy gap; Reflection spectrum; Ultraviolet visible spectrum; Carbon nitrides; PECVD; Absorption spectra
• ISSN: 0022-3093; 1873-4812
• DOI: 10.1016/S0022-3093(99)00663-8

Oxygen-containing carbon nitride films were deposited in rf discharges of C 2H 2, N 2, O 2 and Ar mixtures. Actinometric optical emission spectroscopy was used to determine relative concentrations of the species H, O, CH, CN and CO in the discharge as a function of the proportion of oxygen in the feed, using Ar as an actinometer. The Ar emission intensity decreases as the proportion of O 2 in the feed increases, indicating that O 2 has a `cooling effect' on the discharge. The variations in the concentrations of CH and CN species, two possible precursors of film formation, showed different behaviors. The concentration of CH increases monotonically as the proportion of O 2 in the feed is increased, but the concentration of CN shows a maximum at an oxygen to acetylene ratio of about 0.15, which coincides with the maximum film deposition rate. This strongly suggests that the CN species is the main precursor of film formation. Infrared reflection spectroscopy revealed the presence of CN, CH, NH and CO functionalities in the deposited films. The presence of such species and their relationship to deposition via gas-phase and surface reactions are outlined. The optical properties of the films were investigated using transmission and reflection ultraviolet–visible spectroscopy. At increasing proportions of oxygen in the gas feed, the refractive index decreases while the optical gap increases. Free radicals were investigated using electron paramagnetic resonance. Unpaired spin concentrations of the order of 10 20 cm −3 were measured in the films a short time after deposition. These large spin concentrations are common in films prepared by plasma-enhanced chemical-vapor deposition (PECVD) but decrease at relatively high rates with time. Possible mechanisms accounting for the high spin concentrations and for the disappearance of the free radicals are discussed.