Carbon nitride thin films prepared by radio-frequency magnetron sputtering combined with a nitrogen radical beam source

Carbon nitride (CNx) thin films were prepared by radio-frequency magnetron sputtering combined with a nitrogen radical beam source. X-ray photoelectron spectroscopy, Raman spectroscopy, and grazing-incidence x-ray reflectivity have been used to analyze the chemical composition and structure of the CNx films. An atomic force microscope equipped with a diamond tip was employed to measure the hardness of the films. The nitrogen concentration, composition, hardness, density, and surface roughness varied with the operating power and gas flow applied to the sputtering target and radical gun in the sample preparation. CNx films were fabricated with a maximum nitrogen concentration of ∼62 at. % on the surface and ∼44 at. % after Ar⁺ sputtering, as well as a maximum hardness of ∼33.7 GPa. Compared with N₂⁺ and N₂, excited molecular and atomic nitrogen were more active in the formation of carbon nitrides. With the combination of magnetron sputtering, the radical beam source enables an obvious increase in the nitrogen concentration but only a slight increase in the film hardness. A relationship between the Raman spectra and hardness was found: CNx films with a higher G peak frequency and lower I_D/I_G have higher hardness. Our results also suggested that a higher concentration of the sp³ phase produces a harder CNx film. © 2003 American Institute of Physics.